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1.  FcgammaR expression on macrophages is related to severity and chronicity of synovial inflammation and cartilage destruction during experimental immune-complex-mediated arthritis (ICA) 
Arthritis Research  2000;2(6):489-503.
We investigated the role of Fcγ receptors (FcγRs) on synovial macrophages in immune-complex-mediated arthritis (ICA). ICA elicited in knee joints of C57BL/6 mice caused a short-lasting, florid inflammation and reversible loss of proteoglycans (PGs), moderate chondrocyte death, and minor erosion of the cartilage. In contrast, when ICA was induced in knee joints of Fc receptor (FcR) γ-chain-/- C57BL/6 mice, which lack functional FcγRI and RIII, inflammation and cartilage destruction were prevented. When ICA was elicited in DBA/1 mice, a very severe, chronic inflammation was observed, and significantly more chondrocyte death and cartilage erosion than in arthritic C57BL/6 mice. The synovial lining and peritoneal macrophages of naïve DBA/1 mice expressed a significantly higher level of FcγRs than was seen in C57BL/6 mice. Moreover, elevated and prolonged expression of IL-1 was found after stimulation of these cells with immune complexes. Zymosan or streptococcal cell walls caused comparable inflammation and only mild cartilage destruction in all strains. We conclude that FcγR expression on synovial macrophages may be related to the severity of synovial inflammation and cartilage destruction during ICA.
Introduction:
Fcγ receptors (FcγRs) present on cells of the haematopoietic lineage communicate with IgG-containing immune complexes that are abundant in the synovial tissue of patients with rheumatoid arthritis (RA). In mice, three classes of FcγR (RI, RII, and RIII) have been described. Binding of these receptors leads to either activation (FcγRI and RIII) or deactivation (FcγRII) of intracellular transduction pathways. Together, the expression of activating and inhibitory receptors is thought to drive immune-complex-mediated diseases.
Earlier studies in our laboratory showed that macrophages of the synovial lining are of utmost importance in the onset and propagation of immune-complex-driven arthritic diseases. Selective depletion of macrophages in the joint downregulated both inflammation and cartilage destruction. As all three classes of FcγR are expressed on synovial macrophages, these cells are among the first that come in contact with immune complexes deposited in the joint. Recently, we observed that when immune complexes were injected into the knee joints of mice, strains susceptible to collagen-type-II arthritis (DBA/1, B10.RIII) developed more severe arthritis than nonsusceptible strains did, or even developed chronic arthritis. One reason why these strains are more susceptible might be their higher levels of FcγRs on macrophage membranes. To test this hypothesis, we investigated the role of FcγRs in inflammation and cartilage damage during immune-complex-mediated arthritis (ICA). First, we studied arthritis and subsequent cartilage damage in mice lacking functional FcγRI and RIII (FcR γ-chain-/- mice). Next, DBA/1 mice, which are prone to develop collagen-type-II arthritis (`collagen-induced arthritis'; CIA) and are hypersensitive to immune complexes, were compared with control C57BL/6 mice as regards cartilage damage and the expression and function of FcγRs on their macrophages.
Aims:
To examine whether FcγR expression on macrophages is related to severity of synovial inflammation and cartilage destruction during immune-complex-mediated joint inflammation.
Methods:
ICA was induced in three strains of mice (FcR γ-chain-/-, C57BL/6, and DBA/1, which have, respectively, no functional FcγRI and RIII, intermediate basal expression of FcγRs, and high basal expression of FcγRs) by passive immunisation using rabbit anti-lysozyme antibodies, followed by poly-L-lysine lysozyme injection into the right knee joint 1 day later. In other experiments, streptococcal-cell-wall (SCW)- or zymosan-induced arthritis was induced by injecting SCW (25 μg) or zymosan (180 μg) directly into the knee joint. At several time points after arthritis induction, knee joints were dissected and studied either histologically (using haematoxylin/eosin or safranin O staining) or immuno-histochemically. The arthritis severity and the cartilage damage were scored separately on an arbitrary scale of 0-3.
FcγRs were immunohistochemically detected using the monoclonal antibody 2.4G2, which detects both FcγRII and RIII. Deposition of IgG and C3c in the arthritic joint tissue was also detected immunohistochemically. Expression of FcγRs by murine peritoneal macrophages was measured using a fluorescence-activated cell sorter (FACS).
Peritoneal macrophages were stimulated using heat-aggregated gamma globulins (HAGGs), and production of IL-1 was measured using a bioassay. To assess the levels of IL-1 and its receptor antagonist (IL-1Ra) during arthritis, tissue was dissected and washed in RPMI medium. Washouts were tested for levels of IL-1 and IL-1Ra using radioimmunoassay and enzyme-linked immunosorbent assay. mRNA was isolated from the tissue, and levels of macrophage inflammatory protein (MIP)-2, monocyte chemoattractant protein (MCP)-1, IL-1, and IL-1Ra were determined using semiquantitative reverse-transcription polymerase chain reaction (RT-PCR).
Results:
ICA induced in knee joints of C57BL/6 mice caused a florid inflammation at day 3 after induction. To investigate whether this arthritis was FcγR-mediated, ICA was induced in FcR γ-chain-/- mice, which lack functional FcγRI and RIII. At day3, virtually no inflammatory cells were found in their knee joints. Levels of mRNA of IL-1, IL-1Ra, MCP-1, and MIP-2, which are involved in the onset of this arthritis, were significantly lower in FcR γ-chain-/- mice than in control C57BL/6 mice. Levels of IL-1 protein were also measured. At 6 h after ICA induction, FcR γ-chain-/- mice and control C57BL/6 mice showed similar IL-1 production as measured by protein level. By 24 h after induction, however, IL-1 production in the FcR γ-chain-/- mice was below the detection limit, whereas the controls were still producing a significant amount. To investigate whether the difference in reaction to immune complexes between the DBA/1 and C57BL/6 mice might be due to variable expression of FcγRs in the knee joint, expression in situ of FcγRs in naïve knee joints of these mice was determined. The monoclonal antibody 2.4G2, which detects both FcγRII and RIII, stained macrophages from the synovial lining of DBA/1 mice more intensely than those from C57BL/6 mice. This finding suggests a higher constitutive expression of FcγRs by macrophages of the autoimmune-prone DBA/1 mice. To quantify the difference in FcγR expression on macrophages of the two strains, we determined the occurrence of FcγRs on peritoneal macrophages by FACS analysis. The levels of FcγR expressed by macrophages were twice as high in the DBA/1 mice as in the C57BL/6 mice (mean fluorescence, respectively, 440 ± 50 and 240 ± 30 intensity per cell). When peritoneal macrophages of both strains were stimulated with immune complexes (HAGGs), we found that the difference in basal FcγR expression was functional. The stimulated macrophages from DBA/1 mice had significantly higher IL-1α levels (120 and 135 pg/ml at 24 and 48 h, respectively) than cells from C57BL/6 mice (45 and 50 pg/ml, respectively).
When arthritis was induced using other arthritogenic triggers than immune complexes (zymosan, SCW), all the mouse strains tested (DBA/1, FcR γ-chain-/-, and C57BL/6) showed similar inflammation, indicating that the differences described above are found only when immune complexes are used to elicit arthritis.
We next compared articular cartilage damage in arthritic joints of the three mouse strains FcR γ-chain-/-, C57BL/6 (intermediate basal expression of FcγRs), and DBA/1 (high basal expression of FcγRs). Three indicators of cartilage damage were investigated: depletion of PGs, chondrocyte death, and erosion of the cartilage matrix. At day 3 after induction of ICA, there was no PG depletion in FcR γ-chain-/- mice, whereas PG depletion in the matrix of the C57BL/6 mice was marked and that in the arthritic DBA/1 mice was even greater. PG depletion was still massive at days 7 and 14 in the DBA/1 mice, whereas by day 14 the PG content was almost completely restored in knee joints of the C57BL/6 mice. Chondrocyte death and erosion of cartilage matrix, two indicators of more severe cartilage destruction, were significantly higher in the DBA/1 than in the C57BL/6 mice, while both indicators were completely absent in the FcR γ-chain-/- mice. Again, when arthritis was induced using other triggers (SCW, zymosan), all strains showed similar PG depletion and no chondrocyte death or matrix erosion. These findings underline the important role of immune complexes and FcγRs in irreversible cartilage damage.
Discussion:
Our findings indicate that inflammation and subsequent cartilage damage caused by immune complexes may be related to the occurrence of FcγRs on macrophages. The absence of functional FcγRI and RIII prevented inflammation and cartilage destruction after induction of ICA, whereas high basal expression of FcγRs on resident joint macrophages of similarly treated mice susceptible to autoimmune arthritis was correlated with markedly more synovial inflammation and cartilage destruction. The difference in joint inflammation between the three strains was not due to different susceptibilities to inflammation per se, since intra-articular injection of zymosan or SCW caused comparable inflammation. Although extensive inflammatory cell mass was found in the synovium of all strains after intra-articular injection of zymosan, no irreversible cartilage damage (chondrocyte death or matrix erosion) was found. ICA induced in C57BL/6 and DBA/1 mice did cause irreversible cartilage damage at later time points, indicating that immune complexes and FcγRs play an important role in inducing irreversible cartilage damage. Macrophages communicate with immune complexes via Fcγ receptors. Absence of functional activating receptors completely abrogates the synovial inflammation, as was shown after ICA induction in FcR γ-chain-/- mice. However, the γ-chain is essential not only in FcγRI and RIII but also for FcεRI (found on mast cells) and the T cell receptor (TcR)-CD3 (Tcells) complex of γδT cells. However, T, B, or mast cells do not play a role in this arthritis that is induced by passive immunisation. Furthermore, this effect was not caused by a difference in clearance of IgG or complement deposition in the tissue. In this study, DBA/1 mice, which are susceptible to collagen-induced autoimmune arthritis and in a recent study have been shown to react hypersensitively to immune complexes, are shown to express higher levels of FcγRs on both synovial and peritoneal macrophages. Because antibodies directed against the different subclasses of FcγR are not available, no distinction could be made between FcγRII and RIII. Genetic differences in DBA/1 mice in genes coding for or regulating FcγRs may be responsible for altered FcγR expression. If so, these mouse strains would have a heightened risk for immune-complex-mediated diseases.
To provide conclusive evidence for the roles of the various classes of FcγR during ICA, experiments are needed in which FcγRs are blocked with specific antibodies, or in which knockout mice lacking one specific class of FcγR are used. The only available specific antibody to FcγR (2.4G2) has a stimulatory effect on cells once bound to the receptor, and therefore cannot be used in blocking experiments. Experiments using specific knockout mice are now being done in our laboratory.
Macrophages are the dominant type of cell present in chronic inflammation during RA and their number has been shown to correlate well with severe cartilage destruction. Apart from that, in humans, these synovial tissue macrophages express activating FcRs, mainly FcγIIIa, which may lead to activation of these macrophages by IgG-containing immune complexes. The expression of FcRs on the surface of these cells may have important implications for joint inflammation and severe cartilage destruction and therefore FCRs may constitute a new target for therapeutic intervention.
PMCID: PMC17821  PMID: 11056679
autoimmunity; cytokines; Fc receptors; inflammation; macrophages
2.  Acute-phase serum amyloid A production by rheumatoid arthritis synovial tissue 
Arthritis Research  2000;2(2):142-144.
Acute-phase serum amyloid A (A-SAA) is a major component of the acute-phase response. A sustained acute-phase response in rheumatoid arthritis (RA) is associated with increased joint damage. A-SAA mRNA expression was confirmed in all samples obtained from patients with RA, but not in normal synovium. A-SAA mRNA expression was also demonstrated in cultured RA synoviocytes. A-SAA protein was identified in the supernatants of primary synoviocyte cultures, and its expression colocalized with sites of macrophage accumulation and with some vascular endothelial cells. It is concluded that A-SAA is produced by inflamed RA synovial tissue. The known association between the acute-phase response and progressive joint damage may be the direct result of synovial A-SAA-induced effects on cartilage degradation.
Introduction:
Serum amyloid A (SAA) is the circulating precursor of amyloid A protein, the fibrillar component of amyloid deposits. In humans, four SAA genes have been described. Two genes (SAA1 and SAA2) encode A-SAA and are coordinately induced in response to inflammation. SAA1 and SAA2 are 95% homologous in both coding and noncoding regions. SAA3 is a pseudogene. SAA4 encodes constitutive SAA and is minimally inducible. A-SAA increases dramatically during acute inflammation and may reach levels that are 1000-fold greater than normal. A-SAA is mainly synthesized in the liver, but extrahepatic production has been demonstrated in many species, including humans. A-SAA mRNA is expressed in RA synoviocytes and in monocyte/macrophage cell lines such as THP-1 cells, in endothelial cells and in smooth muscle cells of atherosclerotic lesions. A-SAA has also been localized to a wide range of histologically normal tissues, including breast, stomach, intestine, pancreas, kidney, lung, tonsil, thyroid, pituitary, placenta, skin and brain.
Aims:
To identify the cell types that produce A-SAA mRNA and protein, and their location in RA synovium.
Materials and methods:
Rheumatoid synovial tissue was obtained from eight patients undergoing arthroscopic biopsy and at joint replacement surgery. Total RNA was analyzed by reverse transcription (RT) polymerase chain reaction (PCR) for A-SAA mRNA. PCR products generated were confirmed by Southern blot analysis using human A-SAA cDNA. Localization of A-SAA production was examined by immunohistochemistry using a rabbit antihuman A-SAA polyclonal antibody. PrimaryRA synoviocytes were cultured to examine endogenous A-SAA mRNA expression and protein production.
Results:
A-SAA mRNA expression was detected using RT-PCR in all eight synovial tissue samples studied. Figure 1 demonstrates RT-PCR products generated using synovial tissue from three representative RA patients. Analysis of RA synovial tissue revealed differences in A-SAA mRNA levels between individual RA patients.
In order to identify the cells that expressed A-SAA mRNA in RA synovial tissue, we analyzed primary human synoviocytes (n = 2). RT-PCR analysis revealed A-SAA mRNA expression in primary RA synoviocytes (n = 2; Fig. 2). The endogenous A-SAA mRNA levels detected in individual primary RA synoviocytes varied between patients. These findings are consistent with A-SAA expression in RA synovial tissue (Fig. 1). Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) levels were relatively similar in the RA synoviocytes examined (Fig. 2). A-SAA protein in the supernatants of primary synoviocyte cultures from four RA patients was measured using ELISA. Mean values of a control and four RA samples were 77.85, 162.5, 249.8, 321.5 and 339.04 μg/l A-SAA, respectively, confirming the production of A-SAA protein by the primary RA synoviocytes. Immunohistochemical analysis was performed to localize sites of A-SAA production in RA synovial tissue. Positive staining was present in both the lining and sublining layers of all eight RA tissues examined (Fig. 3a). Staining was intense and most prominent in the cells closest to the surface of the synovial lining layer. Positively stained cells were evident in the perivascular areas of the sublining layer. In serial sections stained with anti-CD68 monoclonal antibody, positive staining of macrophages appeared to colocalize with A-SAA-positive cells (Fig. 3b). Immunohistochemical studies of cultured primary RA synoviocytes confirmed specific cytoplasmic A-SAA expression in these cells. The specificity of the staining was confirmed by the absence of staining found on serial sections and synoviocyte cells treated with IgG (Fig. 3c).
Discussion:
This study demonstrates that A-SAA mRNA is expressed in several cell populations infiltrating RA synovial tissue. A-SAA mRNA expression was observed in all eight unseparated RA tissue samples studied. A-SAA mRNA expression and protein production was demonstrated in primary cultures of purified RA synoviocytes. Using immunohistochemical techniques, A-SAA protein appeared to colocalize with both lining layer and sublining layer synoviocytes, macrophages and some endothelial cells. The detection of A-SAA protein in culture media supernatants harvested from unstimulated synoviocytes confirms endogenous A-SAA production, and is consistent with A-SAA mRNA expression and translation by the same cells. Moreover, the demonstration of A-SAA protein in RA synovial tissue, RA cultured synoviocytes, macrophages and endothelial cells is consistent with previous studies that demonstrated A-SAA production by a variety of human cell populations.
The RA synovial lining layer is composed of activated macrophages and fibroblast-like synoviocytes. The macrophage is the predominant cell type and it has been shown to accumulate preferentially in the surface of the lining layer and in the perivascular areas of the sublining layer. Nevertheless, our observations strongly suggest that A-SAA is produced not only by synoviocytes, but also by synovial tissue macrophage populations. Local A-SAA protein production by vascular endothelial cells was detected in some, but not all, of the tissues examined. The reason for the variability in vascular A-SAA staining is unknown, but may be due to differences in endothelial cell activation, events related to angiogenesis or the intensity of local inflammation.
The value of measuring serum A-SAA levels as a reliable surrogate marker of inflammation has been demonstrated for several diseases including RA, juvenile chronic arthritis, psoriatic arthropathy, ankylosing spondylitis, Behçet's disease, reactive arthritis and Crohn's disease. It has been suggested that serum A-SAA levels may represent the most sensitive measurement of the acute-phase reaction. In RA, A-SAA levels provide the strongest correlations with clinical measurements of disease activity, and changes in serum levels best reflect the clinical course.
A number of biologic activities have been described for A-SAA, including several that are relevant to the understanding of inflammatory and tissue-degrading mechanisms in human arthritis. A-SAA induces migration, adhesion and tissue infiltration of circulating monocytes and polymorphonuclear leukocytes. In addition, human A-SAA can induce interleukin-1β, interleukin-1 receptor antagonist and soluble type II tumour necrosis factor receptor production by a monocyte cell line. Moreover, A-SAA can stimulate the production of cartilage-degrading proteases by both human and rabbit synoviocytes. The effects of A-SAA on protease production are interesting, because in RA a sustained acute-phase reaction has been strongly associated with progressive joint damage. The known association between the acute-phase response and progressive joint damage may be the direct result of synovial A-SAA-induced effects on cartilage degradation.
Conclusion:
In contrast to noninflamed synovium, A-SAA mRNA expression was identified in all RA tissues examined. A-SAA appeared to be produced by synovial tissue synoviocytes, macrophages and endothelial cells. The observation of A-SAA mRNA expression in cultured RA synoviocytes and human RA synovial tissue confirms and extends recently published findings that demonstrated A-SAA mRNA expression in stimulated RA synoviocytes, but not in unstimulated RA synoviocytes.
PMCID: PMC17807  PMID: 11062604
acute-phase response; rheumatoid arthritis; serum amyloid A; synovial tissue
3.  Monoarticular antigen-induced arthritis leads to pronounced bilateral upregulation of the expression of neurokinin 1 and bradykinin 2 receptors in dorsal root ganglion neurons of rats 
Arthritis Research  2000;2(5):424-427.
This study describes the upregulation of neurokinin 1 and bradykinin 2 receptors in dorsal root ganglion (DRG) neurons in the course of antigen-induced arthritis (AIA) in the rat knee. In the acute phase of AIA, which was characterized by pronounced hyperalgesia, there was a substantial bilateral increase in the proportion of lumbar DRG neurons that express neurokinin 1 receptors (activated by substance P) and bradykinin 2 receptors. In the chronic phase the upregulation of bradykinin 2 receptors persisted on the side of inflammation. The increase in the receptor expression is relevant for the generation of acute and chronic inflammatory pain.
Introduction:
Ongoing pain and hyperalgesia (enhanced pain response to stimulation of the tissue) are major symptoms of arthritis. Arthritic pain results from the activation and sensitization of primary afferent nociceptive nerve fibres ('pain fibres') supplying the tissue (peripheral sensitization) and from the activation and sensitization of nociceptive neurons in the central nervous system (central sensitization). After sensitization, nociceptive neurons respond more strongly to mechanical and thermal stimulation of the tissue, and their activation threshold is lowered. The activation and sensitization of primary afferent fibres results from the action of inflammatory mediators such as bradykinin (BK), prostaglandins and others on membrane receptors located on these neurons. BK is a potent pain-producing substance that is contained in inflammatory exudates. Up to 50% of the primary afferent nerve fibres have receptors for BK. When primary afferent nerve fibres are activated they can release neuropeptides such as substance P (SP) and calcitonin gene-related peptide from their sensory endings in the tissue. SP contributes to the inflammatory changes in the innervated tissue (neurogenic inflammation), and it might also support the sensitization of nociceptive nerve fibres by binding to neurokinin 1 (NK1) receptors. NK1 receptors are normally expressed on a small proportion of the primary afferent nerve fibres.
Aims:
Because the expression of receptors on the primary afferent neurons is essential for the pain-producing action of inflammatory mediators and neuropeptides, we investigated in the present study whether the expression of BK and NK1 receptors on primary afferent neurons is altered during the acute and chronic phases of an antigen-induced arthritis (AIA). AIA resembles in many aspects the inflammatory process of human rheumatoid arthritis. Because peptide receptors are expressed not only in the terminals of the primary afferent units but also in the cell bodies, we removed dorsal root ganglia (DRGs) of both sides from control rats and from rats with the acute or chronic phase of AIA and determined, after short-term culture of the neurons, the proportion of DRG neurons that expressed the receptors in the different phases of AIA. We also characterized the inflammatory process and the nociceptive behaviour of the rats in the course of AIA.
Materials and methods:
In 33 female Lewis rats 10 weeks old, AIA was induced in the right knee joint. First the rats were immunized in two steps with methylated bovine serum albumin (m-BSA) emulsified with Freund's complete adjuvant, and heat-inactivated Bordetella pertussis. After immunization, m-BSA was injected into the right knee joint cavity to induce arthritis. The joint swelling was measured at regular intervals. Nociceptive (pain) responses to mechanical stimulation of the injected and the contralateral knee were monitored in the course of AIA. Groups of rats were killed at different time points after the induction of AIA, and inflammation and destruction in the knee joint were graded by histological examination. The DRGs of both sides were dissected from segments L1–L5 and C1–C7 from arthritic rats, from eight immunized rats without arthritis and from ten normal control rats. Excised DRGs were dissociated into single cells which were cultured for 18 h.
The expression of the receptors was determined by assessment of the binding of SP-gold or BK-gold to the cultured neurons. For this purpose the cells were slightly fixed. Binding of SP-gold or BK-gold was detected by using enhancement with silver and subsequent densitometric analysis of the relative grey values of the neurons. Displacement controls were performed with SP, the specific NK1 receptor agonist [Sar9, Met(O2)11]-SP, BK, the specific BK 1 (B1) receptor agonist D-Arg (Hyp3-Thi5,8-D-Phe7)-BK and the specific BK 2 (B2) receptor agonist (Des-Arg10)-Lys-BK.
Results:
The inflammatory process in the injected right knee joint started on the first day after induction of AIA and persisted throughout the observation period of 84 days (Fig. 1). The initial phase of AIA was characterized by strong joint swelling and a predominantly granulocytic infiltration of the synovial membrane and the joint cavity (acute inflammatory changes). In the later phases of AIA (10–84 days after induction of AIA) the joint showed persistent swelling, and signs of chronic arthritic alterations such as infiltration of mononuclear leucocytes, hyperplasia of synovial lining layer (pannus formation) and erosions of cartilage and bone were predominant. The contralateral knee joints appeared normal at all time points. Destruction was observed only in the injected knee but some proteoglycan loss was also noted in the non-injected, contralateral knee. In the acute and initial chronic phases of AIA (1–29 days) the rats showed mechanical hyperalgesia in the inflamed knee (limping, withdrawal response to gentle pressure onto the knee). In the acute phase (up to 9 days) a pain response was also seen when gentle pressure was applied to the contralateral knee.
Figure 2 displays the changes in the receptor expression in the DRG neurons during AIA. The expression of SP–gold-binding sites in lumbar DRG neurons (Fig. 2a) was substantially increased in the acute phase of arthritis. In untreated control rats (n = 5), 7.7 ± 3.8% of the DRG neurons from the right side and 10.0 ± 1.7% of the DRG neurons from the left side showed labelling with SP–gold. The proportion of SP–gold-labelled neurons in immunized animals without knee injection (n = 3) was similar. By contrast, at days 1 (n = 2 rats) and 3 (n = 5 rats) of AIA in the right knee, approximately 50% of the DRG neurons exhibited labelling with SP–gold, and this was seen both on the side of the injected knee and on the opposite side. At day 10 of AIA (n = 3 rats), 26.3 ± 6.1% of the ipsilateral DRG neurons but only 15.7 ± 0.6% of the contralateral neurons exhibited binding of SP–gold. At days 21 (n = 5 rats), 42 (n = 3 rats) and 84 (n = 5 rats) of AIA, the proportion of SP–gold-positive neurons had returned to the control values, although the arthritis, now with signs of chronic inflammation, was still present. Compared with the DRG neurons of the untreated control rats, the increase in the proportion of labelled neurons was significant on both sides in the acute phase (days 1 and 3) and the intermediate phase (day 10) of AIA (Mann–Whitney U-test). The size distribution of the neurons was similar in the DRG neurons of all experimental groups. Under all conditions and at all time points, SP–gold binding was found mainly in small and medium-sized (less than 700 μm2) neurons. In the cervical DRGs the expression of NK1 receptors did not change in the course of AIA. The binding of SP–gold to the neurons was suppressed by the coadministration of the specific NK1 receptor agonist [Sar9, Met(O2)11]–SP in three experiments, showing that SP–gold was bound to NK1 receptors.
The expression of BK–gold-binding sites in the lumbar DRG neurons showed also changes in the course of AIA, but the pattern was different (Fig. 2b). In untreated control rats (n = 5), 42.3 ± 3.1% of the DRG neurons of the right side and 39.6 ± 2.6% of the DRG neurons of the left side showed binding of BK–gold. At days 1 (n = 2 rats) and 3 (n = 5 rats) of AIA, approximately 80% of the DRG neurons on the side of the knee injection (ipsilateral) and approximately 70% on the opposite side were labelled. In comparison with the untreated control group, the increase in the proportion of labelled neurons was significant on both sides. The proportion of labelled neurons in the ipsilateral DRGs remained significantly increased in both the intermediate phase (day 10, n = 3 rats) and chronic phase (days 21, n = 5 rats, and 42, n = 3 rats) of inflammation. At 84 days after the induction of AIA (n = 5 rats), 51.0 ± 12.7% of the neurons showed an expression of BK–gold-binding sites and this was close to the prearthritic values. However, in the contralateral DRG of the same animals the proportion of BK–gold-labelled neurons declined in the intermediate phase (day 10) and chronic phase (days 21–84) of AIA and was not significantly different from the control value. Thus the increase in BK–gold-labelled neurons was persistent on the side where the inflammation had been induced, and transient on the opposite side. The size distribution of the DRG neurons of the different experimental groups was similar. In the cervical DRGs the expression of BK receptors did not change in the course of AIA. In another series of experiments, we determined the subtype(s) of BK receptor(s) that were expressed in DRGs L1–L5 in different experimental groups. In neither untreated control animals (n = 5) nor immunized rats without knee injection (n = 5) nor in rats at 3 days (n = 5) and 42 days (n = 5) of AIA was the binding of BK–gold decreased by the coadministration of BK–gold and the B1 agonist. By contrast, in these experimental groups the binding of BK–gold was suppressed by the coadministration of the B2 agonist. These results show that B2 receptors, but not B1 receptors, were expressed in both normal animals and in animals with AIA.
Discussion:
These results show that in AIA in the rat the expression of SP-binding and BK-binding sites in the perikarya of DRGs L1–L5 is markedly upregulated in the course of knee inflammation. Although the inflammation was induced on one side only, the initial changes in the binding sites were found in the lumbar DRGs of both sides. No upregulation of SP-binding or BK-binding sites was observed in the cervical DRGs. The expression of SP-binding sites was upregulated only in the first days of AIA, that is, in the acute phase, in which the pain responses to mechanical stimulation were most pronounced. By contrast, the upregulation of BK-binding sites on the side of AIA persisted for up to 42 days, that is, in the acute and chronic phase of AIA. Only the B2 receptor, not the B1 receptor, was upregulated. The coincidence of the enhanced expression of NK1 and BK receptors on sensory neurons and the pain behaviour suggests that the upregulation of these receptors is relevant for the generation and maintenance of arthritic pain.
In the acute phase of AIA, approximately 50% of the lumbar DRG neurons showed an expression of SP-binding sites. Because peptide receptors are transported to the periphery, the marked upregulation of SP-binding receptors probably leads to an enhanced density of receptors in the sensory endings of the primary afferent units. This will permit SP to sensitize more neurons under inflammatory conditions than under normal conditions. However, the expression of NK1 receptors was upregulated only in the acute phase of inflammation, suggesting that SP and NK1 receptors are less important for the generation of hyperalgesia in the chronic phase of AIA.
Because BK is one of the most potent algesic compounds, the functional consequence of the upregulation of BK receptors is likely to be of immediate importance for the generation and maintenance of inflammatory pain. The persistence of the upregulation of BK receptors on the side of inflammation suggests that BK receptors should be an interesting target for pain treatment in the acute and chronic phases. Only B2 receptors were identified in normal animals and in rats with AIA. This is surprising because previous pharmacological studies have provided evidence that, during inflammation, B1 receptors can be newly expressed.
Receptor upregulation in the acute phase of AIA was bilateral and almost symmetrical. However, hyperalgesia was much more pronounced on the inflamed side. It is most likely that receptors on the contralateral side were not readily activated because in the absence of gross inflammation the local concentration of the ligands BK and SP was probably quite low. We hypothesize that the bilateral changes in receptor expression are generated at least in part by mechanisms involving the nervous system. Symmetrical segmental changes can be produced only by the symmetrical innervation, involving either the sympathetic nervous system or the primary afferent fibres. Under inflammatory conditions, primary afferent fibres can be antidromically activated bilaterally in the entry zone of afferent fibres in the spinal cord, and it was proposed that this antidromic activation might release neuropeptides and thus contribute to neurogenic inflammation. Because both sympathetic efferent fibres and primary afferent nerve fibres can aggravate inflammatory symptoms, it is also conceivable that they are involved in the regulation of receptor expression in primary afferent neurons. A neurogenic mechanism might also have been responsible for the bilateral degradation of articular cartilage in the present study.
PMCID: PMC17819  PMID: 11056677
antigen-induced arthritis; bradykinin receptor; dorsal root ganglion neurons; neurokinin 1 receptor; pain
4.  Specificity of T cells in synovial fluid: high frequencies of CD8+ T cells that are specific for certain viral epitopes 
Arthritis Research  2000;2(2):154-164.
CD8+ T cells dominate the lymphocyte population in synovial fluid in chronic inflammatory arthritis. It is known that these CD8+ T cells are often clonally or oligoclonally expanded, but their specificity and their relevance to the pathogenesis of joint disease has remained unclear. We found that as many as 15.5% of synovial CD8+ T cells may be specific for a single epitope from an Epstein-Barr virus lytic cycle protein. The virus-specific T cells within the joint showed increased expression of markers of activation and differentiation compared with those in the periphery, and retained their functional capacity to secrete proinflammatory cytokines on stimulation. These activated, virus-specific CD8+ T cells could therefore interact with synoviocytes, either by cell-cell contact or by a cytokine network, and play a 'bystander' role in the maintenance of inflammation in patients with arthritis.
Introduction:
Epstein-Barr virus (EBV) is transmitted orally, replicates in the oropharynx and establishes life-long latency in human B lymphocytes. T-cell responses to latent and lytic/replicative cycle proteins are readily detectable in peripheral blood from healthy EBV-seropositive individuals. EBV has also been detected within synovial tissue, and T-cell responses to EBV lytic proteins have been reported in synovial fluid from a patient with rheumatoid arthritis (RA). This raises the question regarding whether T cells specific for certain viruses might be present at high frequencies within synovial fluid and whether such T cells might be activated or able to secrete cytokines. If so, they might play a 'bystander' role in the pathogenesis of inflammatory joint disease.
Objectives:
To quantify and characterize T cells that are specific for epitopes from EBV, cytomegalovirus (CMV) and influenza in peripheral blood and synovial fluid from patients with arthritis.
Methods:
Peripheral blood mononuclear cells (PBMCs) and synovial fluid mononuclear cells (SFMCs) were obtained from patients with inflammatory arthritis (including those with RA, osteoarthritis, psoriatic arthritis and reactive arthritis). Samples from human leucocyte antigen (HLA)-A2-positive donors were stained with fluorescent-labelled tetramers of HLA-A2 complexed with the GLCTLVAML peptide epitope from the EBV lytic cycle protein BMLF1, the GILGFVFTL peptide epitope from the influenza A matrix protein, or the NLVPMVATV epitope from the CMV pp65 protein. Samples from HLA-B8-positive donors were stained with fluorescent-labelled tetramers of HLA-B8 complexed with the RAKFKQLL peptide epitope from the EBV lytic protein BZLF1 or the FLRGRAYGL peptide epitope from the EBV latent protein EBNA3A. All samples were costained with an antibody specific for CD8. CD4+ T cells were not analyzed. Selected samples were costained with antibodies specific for cell-surface glycoproteins, in order to determine the phenotype of the T cells within the joint and the periphery. Functional assays to detect release of IFN-γ or tumour necrosis factor (TNF)-α were also performed on some samples.
Results:
The first group of 15 patients included 10 patients with RA, one patient with reactive arthritis, one patient with psoriatic arthritis and three patients with osteoarthritis. Of these, 11 were HLA-A2 positive and five were HLA-B8 positive. We used HLA-peptide tetrameric complexes to analyze the frequency of EBV-specific T cells in PBMCs and SFMCs (Figs 1 and 2). Clear enrichment of CD8+ T cells specific for epitopes from the EBV lytic cycle proteins was seen within synovial fluid from almost all donors studied, including patients with psoriatic arthritis and osteoarthritis and those with RA. In donor RhA6, 9.5% of CD8+ SFMCs were specific for the HLA-A2 restricted GLCTLVAML epitope, compared with 0.5% of CD8+ PBMCs. Likewise in a donor with osteoarthritis (NR4), 15.5% of CD8+ SFMCs were specific for the HLA-B8-restricted RAKFKQLL epitope, compared with 0.4% of CD8+ PBMCs. In contrast, we did not find enrichment of T cells specific for the HLA-B8-restricted FLRGRAYGL epitope (from the latent protein EBNA3A) within SFMCs compared with PBMCs in any donors. In selected individuals we performed ELISpot assays to detect IFN-γ secreted by SFMCs and PBMCs after a short incubation in vitro with peptide epitopes from EBV lytic proteins. These assays confirmed enrichment of T cells specific for epitopes from EBV lytic proteins within synovial fluid and showed that subpopulations of these cells were able to secrete proinflammatory cytokines after short-term stimulation.
We used a HLA-A2/GILGFVFTL tetramer to stain PBMCs and SFMCs from six HLA-A2-positive patients. The proportion of T cells specific for this influenza epitope was low (<0.2%) in all donors studied, and we did not find any enrichment within SFMCs.
We had access to SFMCs only from a second group of four HLA-A2-positive patients with RA. A tetramer of HLA-A2 complexed to the NLVPMVATV epitope from the CMV pp65 protein reacted with subpopulations of CD8+ SFMCs in all four donors, with frequencies of 0.2, 0.5, 2.3 and 13.9%. SFMCs from all four donors secreted TNF after short-term incubation with COS cells transfected with HLA-A2 and pp65 complementary DNA. We analyzed the phenotype of virus-specific cells within PBMCs and SFMCs in three donors. The SFMC virus-specific T cells were more highly activated than those in PBMCs, as evidenced by expression of high levels of CD69 and HLA-DR. A greater proportion of SFMCs were CD38+, CD62L low, CD45RO bright, CD45RA dim, CD57+ and CD28- when compared with PBMCs.
Discussion:
This work shows that T cells specific for certain epitopes from viral proteins are present at very high frequencies (up to 15.5% of CD8+ T cells) within SFMCs taken from patients with inflammatory joint disease. This enrichment does not reflect a generalized enrichment for the 'memory pool' of T cells; we did not find enrichment of T cells specific for the GILGFVFTL epitope from influenza A or for the FLRGRAYGL epitope from the EBV latent protein EBNA3A, whereas we found clear enrichment of T cells specific for the GLCTLVAML epitope from the EBV lytic protein BMLF1 and for the RAKFKQLL epitope from the EBV lytic protein BZLF1.
The enrichment might reflect preferential recruitment of subpopulations of virus-specific T cells, perhaps based on expression of selectins, chemokine receptors or integrins. Alternatively, T cells specific for certain viral epitopes may be stimulated to proliferate within the joint, by viral antigens themselves or by cross-reactive self-antigens. Finally, it is theoretically possible that subpopulations of T cells within the joint are preferentially protected from apoptotic cell death. Whatever the explanation, the virus-specific T cells are present at high frequency, are activated and are able to secrete proinflammatory cytokines. They could potentially interact with synoviocytes and contribute to the maintenance of inflammation within joints in many different forms of inflammatory arthritis.
PMCID: PMC17809  PMID: 11062606
CD8+ T cell; Epstein-Barr virus lytic cycle; human leucocyte antigen peptide tetrameric complex; rheumatoid arthritis; viral immunity
5.  Mast cell activation and its relation to proinflammatory cytokine production in the rheumatoid lesion 
Arthritis Research  1999;2(1):65-74.
Mast cell (MC) activation in the rheumatoid lesion provides numerous mediators that contribute to inflammatory and degradative processes, especially at sites of cartilage erosion. MC activation in rheumatoid synovial tissue has often been associated with tumour necrosis factor (TNF)-α and interleukin (IL)-1β production by adjacent cell types. By contrast, our in situ and in vitro studies have shown that the production of IL-15 was independent of MC activation, and was not related to TNF-α and IL-1β expression. Primary cultures of dissociated rheumatoid synovial cells produced all three proinflammatory cytokines, with production of IL-1β exceeding that of TNF-α, which in turn exceeded that of IL-15. In vitro cultures of synovial macrophages, synovial fibroblasts and articular chondrocytes all produced detectable amounts of free IL-15, macrophages being the most effective.
Introduction:
Increased numbers of mast cells (MCs) are found in the synovial tissues and fluids of patients with rheumatoid arthritis (RA), and at sites of cartilage erosion. MC activation has been reported for a significant proportion of rheumatoid specimens. Because the MC contains potent mediators, including histamine, heparin, proteinases, leukotrienes and multifunctional cytokines, its potential contributions to the processes of inflammation and matrix degradation have recently become evident.
Proinflammatory cytokines are important mediators of inflammation, immunity, proteolysis, cell recruitment and proliferation. Tumour necrosis factor (TNF) reportedly plays a pivotal role in the pathogenesis of RA, especially its ability to regulate interleukin (IL)-1β expression, this being important for the induction of prostanoid and matrix metalloproteinase production by synovial fibroblasts and chondrocytes. IL-15 has been assigned numerous biological effects and has been implicated as an important factor in TNF-α expression by monocyte/macrophages. Some in vitro studies have placed IL-15 upstream from TNF-α in the cytokine cascade, suggesting an interdependence between TNF, IL-1 and IL-15 for the promotion of proinflammatory cytokine expression in the rheumatoid joint.
Aims:
To examine the in situ relationships of TNF-α, IL-1β and IL-15 in relation to MC activation in rheumatoid tissues by use of immunolocalization techniques; and to compare quantitatively the proinflammatory cytokine production by specific cell cultures and rheumatoid synovial explants with and without exposure to a MC secretagogue.
Materials and methods:
Samples of rheumatoid synovial tissue and cartilage–pannus junction were obtained from patients (n = 15) with classic late-stage RA. Tissue sections were immunostained for MC (tryptase) and the proinflammatory cytokines IL-1, TNF-α and IL-15. Rheumatoid synovial tissue explants were cultured in Dulbecco's modified Eagles medium (DMEM) containing either the MC secretagogue rabbit antihuman immunoglobulin (Ig)E, or control rabbit IgG. Primary rheumatoid synovial cell cultures, human articular chondrocytes, synovial fibroblasts and synovial macrophages were prepared as described in the full article. Conditioned culture media from these cultures were collected and assayed for IL-1β, TNF-α and IL-15 using enzyme-linked immunosorbent assay methodology.
Results:
Immunohistological studies of rheumatoid synovial tissues have demonstrated local concentrations of MCs in most specimens of the rheumatoid lesion. Sites of MC activation were associated with localized oedema, and TNF-α, IL-1α and IL-1β production by a proportion of mononuclear inflammatory cells. By contrast, no evidence was found for IL-15 production in tissue sites containing either intact or activated MCs, and IL-15 expression, when observed, bore no relation to tissue sites where TNF-α and IL-1β were evident. The immunodetection of IL-15 was restricted to microfocal sites and was not typical of most junctional specimens, but was associated with a proportion of articular chondrocytes in a minority of junctional specimens.
MC activation within synovial explant cultures was induced by the addition of polyclonal antibody to human IgE. MC activation significantly reduced the levels of TNF-α and IL1β released into the medium, this representing approximately 33% of control values. By contrast, MC activation had little effect on the levels of IL-15 released into the culture medium, the average value being very low in relation to the release of TNF-α and IL-1β . Thus, induced MC activation brings about changes in the amounts of released tryptase, TNF-α and IL-1β , but not of IL-15.
Four preparations of primary rheumatoid synovial cell cultures produced more IL-1β than TNF-α, with only modest values for IL-15 production, indicating that all three cytokines are produced and released as free ligands by these cultures. Of specific cell types that produced IL-15 in vitro, macrophages produced more than fibroblasts, which in turn produced more than chondrocytes. This demonstrates that all three cell types have the potential to produce IL-15 in situ.
Discussion:
The biological consequences of MC activation in vivo are extremely complex, and in all probability relate to the release of various combinations of soluble and granular factors, as well as to the expression of appropriate receptors by neighbouring cells. The subsequent synthesis and release of cytokines such as TNF-α and IL-1 may well follow at specific stages after activation, or may be an induced cytokine response by adjacent macrophagic or fibroblastic cells. However, because no IL-15 was detectable either in or around activated or intact MCs, and the induced MC activation explant study showed no change in IL-15 production, it seems unlikely that the expression of this cytokine is regulated by MCs. The immunohistochemistry (IHC) demonstration of IL-15 at sites of cartilage erosion, and especially by some chondrocytes of articular cartilage, showed no spatial relationship with either T cells or neutrophils, and suggests other functional properties in these locations. The lack of evidence for an in situ association of IL-15 with TNF and IL-1 does not support a role for IL-15 in a proinflammatory cytokine 'cascade', as proposed by other in vitro experiments. We believe that sufficient evidence is available, however, to suggest that MC activation makes a significant contribution to the pathophysiological processes of the rheumatoid lesion.
PMCID: PMC17805  PMID: 11219391
interleukin-15; interleukin-1β; mast cells; rheumatoid arthritis; tumour necrosis factor-α
6.  Apoptosis and p53 expression in rat adjuvant arthritis 
Arthritis Research  2000;2(3):229-235.
The kinetics of apoptosis and the apoptosis-regulating gene p53 in adjuvant arthritis (AA) were investigated to assess the value of the AA rat model for testing apoptosis-inducing therapies. Very few terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP) nick end-labeling (TUNEL)-positive cells were detected during the early phases of AA, but on day 23 (chronic arthritis) the percentage of TUNEL-positive cells was significantly increased. Expression of p53 in synovial tissue gradually increased from days 5-23, which was markedly higher than p53 levels in rheumatoid arthritis (RA) synovium. Significant apoptosis only occurs late in rat AA and is concordant with marked p53 overexpression, making it useful model for testing proapoptotic therapies, but rat AA is not the best model for p53 gene therapy because dramatic p53 overexpression occurs in the latter stages of the disease.
Introduction:
RA is a chronic inflammatory disorder that is characterized by inflammation and proliferation of synovial tissue. The amount of DNA fragmentation is significantly increased in rheumatoid synovium. Only low numbers of apoptotic cells are present in rheumatoid synovial tissue, however. The proportion of cells with DNA strand breaks is so great that this disparity suggests impaired apoptosis. Therefore, the development of novel therapeutic strategies that are aimed at inducing apoptosis in rheumatoid synovial tissue is an attractive goal.
Although animal models for arthritis only approximate RA, they provide a useful test system for the evaluation of apoptosis-inducing therapies. AA in rats is among the most commonly used animal models for RA. For the interpretation of such studies, it is essential to characterize the extent to which apoptosis occurs during the natural course of the disease. Therefore, we evaluated the number of apoptotic cells and the expression of p53 in various phases of AA.
Materials and methods:
In order to generate the AA rat model, Lewis rats were immunized with Mycobacterium tuberculosis in mineral oil on day 0. Paw swelling usually started around day 10. For the temporal analysis rats were sacrificed on days 0, 5 (prearthritis), 11 (onset of arthritis), 17 (accelerating arthritis), or 23 (chronic arthritis).
For the detection of apoptotic cells, the hind paws were harvested on days 0(n=6),5 (n=6), 11 (n=6), 17 (n=6), or 23 (n=4). The right ankle joints were fixed in formalin, decalcified in ethylenediaminetetra-acetic acid, embedded in paraffin, and sectioned. The TUNEL method was applied. The percentage of TUNEL-positive cells of the total inflammatory cell infiltrate was noted.
For Western blot analysis, hind paws were harvested on days 0 (n=2), 5 (n=3), 11 (n=4), 17 (n=4), or 23 (n=4). In addition, hind paws of normal rats (n=2) were studied. The right ankle joints were snap frozen and pulverized. Synovial tissue was also obtained by arthroscopy of three patients with longstanding (>5 years) RA. After protein extraction in lysis buffer, equal amounts of protein samples from lysates were pooled and examined by Western bolt analysis using anti-p53 monoclonal antibody D07, which recognizes wild-type and mutant p53 from rodents and humans.
For immunohistochemical analysis, six rats were sacrificed on day 23 after immunization and synovial tissue of the right ankle joints was snap frozen and evaluated by immunohistochemistry using anti-p53-pan. The sections were evaluated semi-quantitatively using a 0-4 scale.
The kruskal-Wallis test for several group means was used to compare the percentage of TUNEL-positive cells at different time points.
Results:
The percentages of TUNEL-positive cells were strongly dependent on the stage of the disease. Very few TUNEL-positive cells were detected in normal rats or in the early phases of AA; the number of TUNEL-positive cells was 1% or less of the total cell infiltrate, including neutrophils, from days 0-17 (Table 1). On day 23, however, the percentage of TUNEL-positive cells was significantly increased [15.8±5.1% (mean ± standard error of the mean); P=0.01]. TUNEL-positive cells were observed in the intimal lining layer and synovial sublining of the invasive front, as well as in the articular cartilage (Fig. 1).
Subsequently, we examined expression of the tumor suppressor gene p53, because this is a key regulator of apoptosis. Expression of p53 in pooled rat AA joint extracts gradually increased from day 0 (6 arbitrary units) to day 23 (173 arbitrary units), which was markedly higher than p53 levels in RA synovium (32 arbitrary units; Table 1). Overexpression of p53 protein on day 23 was confirmed by immunohistochemistry in a separate experiment in six rats with AA. Overexpression of p53 was observed in the intimal lining layer and synovial sublining in all rats on day 23. In all cases a semiquantitative score of 4 was assigned, indicating that 51% or more of the cells were positive, whereas control sections were negative.
Discussion:
The results presented here reveal that the number of TUNEL-positive cells remained very low until chronic arthritis developed. This indicates that, although there was sufficient DNA damage to cause an increment in p53 expression in the early phases, DNA strand breaks that can be detected by TUNEL assays only occurred in chronic AA. The observation that TUNEL-positive cells were nearly absent in early AA clearly indicates that only very few cells were undergoing programmed cell death. This is an important observation, which makes it possible to study the effects of apoptosis-inducing therapies in situ in early and accelerating AA. An effective therapy would obviously increase the number of TUNEL-positive cells.
There is already some overexpression of p53 in the preclinical phase and during the onset of the arthritis, with an additional increment in p53 expression during accelerating and chronic arthritis. Presumably, this is wild-type p53, because the disease duration is likely too short to allow for the development of p53 mutations. Transcription of p53 is probably increased in response to the toxic environment of the inflamed joint. The increased expression of p53 in the joints of rats with chronic AA was even greater than that observed in synovial tissue of RA patients with long-standing disease.
Overexpression of p53 and increased numbers of apoptotic cells did not occur simultaneously in this model; rather p53 overexpression preceded increased apoptosis. Activation of p53 leads to induction of cell growth arrest, allowing time for DNA repair. It appears that DNA damage is only extensive enough to induce apoptosis in the latter stages of AA. Factors other than p53 may also play an important role in the actual induction of apoptosis
Taken together, significant apoptosis only occurs late in AA and it follows marked p53 overexpression, making it a useful model for testing proapoptotic therapies. AA is not the best model for p53 gene therapy, however, because dramatic p53 overexpression occurs in the latter stages of the disease.
PMCID: PMC17810  PMID: 11056668
adjuvant arthritis; apoptosis; p53; rheumatoid arthritis
7.  Activation pathways of synovial T lymphocytes. Expression and function of the UM4D4/CDw60 antigen. 
Journal of Clinical Investigation  1990;86(4):1124-1136.
Accumulating evidence implicates a central role for synovial T cells in the pathogenesis of rheumatoid arthritis, but the activation pathways that drive proliferation and effector function of these cells are not known. We have recently generated a novel monoclonal antibody against a rheumatoid synovial T cell line that recognizes an antigen termed UM4D4 (CDw60). This antigen is expressed on a minority of peripheral blood T cells, and represents the surface component of a distinct pathway of human T cell activation. The current studies were performed to examine the expression and function of UM4D4 on T cells obtained from synovial fluid and synovial membranes of patients with rheumatoid arthritis and other forms of inflammatory joint disease. The UM4D4 antigen is expressed at high surface density on about three-fourths of synovial fluid T cells and on a small subset of synovial fluid natural killer cells; in synovial tissue it is present on more than 90% of T cells in lymphoid aggregates, and on approximately 50% of T cells in stromal infiltrates In addition, UM4D4 is expressed in synovial tissue on a previously undescribed population of HLA-DR/DP-negative non-T cells with a dendritic morphology. Anti-UM4D4 was co-mitogenic for both RA and non-RA synovial fluid mononuclear cells, and induced IL-2 receptor expression. The UM4D4/CDw60 antigen may represent a functional activation pathway for synovial compartment T cells, which could play an important role in the pathogenesis of inflammatory arthritis.
Images
PMCID: PMC296841  PMID: 2212003
8.  The effects of 1α,25-dihydroxyvitamin D3 on matrix metalloproteinase and prostaglandin E2 production by cells of the rheumatoid lesion 
Arthritis Research  1999;1(1):63-70.
The biologically active metabolite of vitamin D3, 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3], acts through vitamin D receptors, which were found in rheumatoid tissues in the present study. IL-1β-activated rheumatoid synovial fibroblasts and human articular chondrocytes were shown to respond differently to exposure to 1α,25(OH)2D3, which has different effects on the regulatory pathways of specific matrix metalloproteinases and prostaglandin E2.
Introduction:
1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3], the biologically active metabolite of vitamin D3, acts through an intracellular vitamin D receptor (VDR) and has several immunostimulatory effects. Animal studies have shown that production of some matrix metalloproteinases (MMPs) may be upregulated in rat chondrocytes by administration of 1α,25(OH)2D3; and cell cultures have suggested that 1α,25(OH)2D3 may affect chondrocytic function. Discoordinate regulation by vitamin D of MMP-1 and MMP-9 in human mononuclear phagocytes has also been reported. These data suggest that vitamin D may regulate MMP expression in tissues where VDRs are expressed. Production of 1α,25(OH)2D3 within synovial fluids of arthritic joints has been shown and VDRs have been found in rheumatoid synovial tissues and at sites of cartilage erosion. The physiological function of 1α,25(OH)2D3 at these sites remains obscure. MMPs play a major role in cartilage breakdown in the rheumatoid joint and are produced locally by several cell types under strict control by regulatory factors. As 1α,25(OH)2D3 modulates the production of specific MMPs and is produced within the rheumatoid joint, the present study investigates its effects on MMP and prostaglandin E2 (PGE2) production in two cell types known to express chondrolytic enzymes.
Aims:
To investigate VDR expression in rheumatoid tissues and to examine the effects of 1α,25-dihydroxyvitamin D3 on cultured rheumatoid synovial fibroblasts (RSFs) and human articular chondrocytes (HACs) with respect to MMP and PGE2 production.
Methods:
Rheumatoid synovial tissues were obtained from arthroplasty procedures on patients with late-stage rheumatoid arthritis; normal articular cartilage was obtained from lower limb amputations. Samples were embedded in paraffin, and examined for presence of VDRs by immunolocalisation using a biotinylated antibody and alkaline-phosphatase-conjugated avidin-biotin complex system. Cultured synovial fibroblasts and chondrocytes were treated with either 1α,25(OH)2D3, or interleukin (IL)-1β or both. Conditioned medium was assayed for MMP and PGE2 by enzyme-linked immunosorbent assay (ELISA), and the results were normalised relative to control values.
Results:
The rheumatoid synovial tissue specimens (n = 18) immunostained for VDRs showed positive staining but at variable distributions and in no observable pattern. VDR-positive cells were also observed in association with some cartilage-pannus junctions (the rheumatoid lesion). MMP production by RSFs in monolayer culture was not affected by treatment with 1α,25(OH)2D3 alone, but when added simultaneously with IL-1β the stimulation by IL-1β was reduced from expected levels by up to 50%. In contrast, 1α,25(OH)2D3 had a slight stimulatory effect on basal production of MMPs 1 and 3 by monolayer cultures of HACs, but stimulation of MMP-1 by IL-1β was not affected by the simultaneous addition of 1α,25(OH)2D3 whilst MMP-3 production was enhanced (Table 1). The production of PGE2 by RSFs was unaffected by 1α,25(OH)2D3 addition, but when added concomitantly with IL-1β the expected IL-1 β-stimulated increase was reduced to almost basal levels. In contrast, IL-1β stimulation of PGE2 in HACs was not affected by the simultaneous addition of 1α,25(OH)2D3 (Table 2). Pretreatment of RSFs with 1α,25(OH)2D3 for 1 h made no significant difference to IL-1β-induced stimulation of PGE2, but incubation for 16 h suppressed the expected increase in PGE2 to control values. This effect was also noted when 1α,25(OH)2D3 was removed after the 16h and the IL-1 added alone. Thus it appears that 1α,25(OH)2D3 does not interfere with the IL-1β receptor, but reduces the capacity of RSFs to elaborate PGE2 after IL-1β induction.
Discussion:
Cells within the rheumatoid lesion which expressed VDR were fibroblasts, macrophages, lymphocytes and endothelial cells. These cells are thought to be involved in the degradative processes associated with rheumatoid arthritis (RA), thus providing evidence of a functional role of 1α,25(OH)2D3 in RA. MMPs may play important roles in the chondrolytic processes of the rheumatoid lesion and are known to be produced by both fibroblasts and chondrocytes. The 1α,25(OH)2D3 had little effect on basal MMP production by RSFs, although more pronounced differences were noted when IL-1β-stimulated cells were treated with 1α,25(OH)2D3, with the RSF and HAC showing quite disparate responses. These opposite effects may be relevant to the processes of joint destruction, especially cartilage loss, as the ability of 1α,25(OH)2D3 to potentiate MMP-1 and MMP-3 expression by 'activated' chondrocytes might facilitate intrinsic cartilage chondrolysis in vivo. By contrast, the MMP-suppressive effects observed for 1α,25(OH)2D3 treatment of 'activated' synovial fibroblasts might reduce extrinsic chondrolysis and also matrix degradation within the synovial tissue. Prostaglandins have a role in the immune response and inflammatory processes associated with RA. The 1α,25(OH)2D3 had little effect on basal PGE2 production by RSF, but the enhanced PGE2 production observed following IL-1β stimulation of these cells was markedly suppressed by the concomitant addition of 1α,25(OH)2D3. As with MMP production, there are disparate effects of 1α,25(OH)2D3 on IL-1β stimulated PGE2 production by the two cell types; 1α,25(OH)2D3 added concomitantly with IL-1β had no effect on PGE2 production by HACs. In summary, the presence of VDRs in the rheumatoid lesion demonstrates that 1α,25(OH)2D3 may have a functional role in the joint disease process. 1α,25(OH)2D3 does not appear to directly affect MMP or PGE2 production but does modulate cytokine-induced production.
Comparative effects of 1 α,25-dihydroxyvitamin D3 (1 α,25D3) on interleukin (IL)-1-stimulated matrix metalloproteinase (MMP)-1 and MMP-3 production by rheumatoid synovial fibroblasts and human articular chondrocytes in vivo
Data given are normalized relative to control values and are expressed ± SEM for three cultures of each cell type.
Comparative effects of 1α,25-dihydroxyvitamin D3 (1α,25D3) on Interleukin (IL)-1-stimulated prostaglandin E2 production by rheumatoid synovial fibroblasts and human articular chondrocyte in vivo
Data given are normalized relative to control values and are expressed ± SEM for three cultures of each cell type.
PMCID: PMC17774  PMID: 11056661
1α,25-dihydroxyvitamin D3; matrix metalloproteinase; prostaglandin E2; rheumatoid arthritis
9.  Cytokine, activation marker, and chemokine receptor expression by individual CD4+ memory T cells in rheumatoid arthritis synovium 
Arthritis Research  2000;2(5):415-423.
IL-10, IL-13, IFN-γ, tumor necrosis factor (TNF)-α, LT-α, CD154, and TNF-related activation-induced cytokine (TRANCE) were expressed by 2-20% of rheumatoid arthritis (RA) synovial tissue CD4+ memory T cells, whereas CD4+ cells that produced IL-2, IL-4, or IL-6 were not detected. Expression of none of these molecules by individual CD4+ cells correlated with the exception of TRANCE and IL-10, and TRANCE and TNF-α . A correlation between expression of IL-10 and CCR7, LT-α and CCR6, IFN-γ and CCR5, and TRANCE and CXCR4 was also detected.
Introduction:
In RA large numbers of CD4+ memory T cells infiltrate the inflamed synovium [1,2,3]. The accumulated CD4+ memory T cells in the RA synovium appear to be activated, because they express cytokines and activation markers [4,5,6,7,8]. Expressed cytokines and activation markers should play important roles in the pathogenesis of RA. However, the frequency of cytokine expression by RA synovial CD4+ T cells has not been analyzed accurately. Recently, the roles of chemokine and chemokine receptor interactions in T-cell migration have been intensively examined. Interactions of chemokine and chemokine receptors might therefore be important in the accumulation of the CD4+ T cells in the RA synovium. Accordingly, correlation of cytokine and chemokine receptor expression might be important in delineating the function and potential means of accumulation of individual CD4+ memory T cells in the RA synovium.
In the present study we analyzed cytokine (IL-2, IL-4, IL-6, IL-10, IL-13, IFN-γ , TNF-α , and LT-α ), activation marker (CD154 [CD40 ligand] and TRANCE - also called receptor activator of nuclear factor κ B ligand [RANKL] or osteoclast differentiation factor [ODF]), and chemokine receptor expression by individual CD4+ memory T cells isolated from rheumatoid synovium and blood. To achieve this we employed a single-cell reverse transcription (RT) polymerase chain reaction (PCR) technique. This technique made it possible to correlate mRNAs expressed by individual CD4+ memory T cells in the synovium and blood.
Materials and method:
Synovial tissues from three RA patients and peripheral blood mononuclear cells from two RA patients and a normal donor were analyzed.
Cytokine (IL-2, IL-4, IL-6, IL-10, IL-13, IFN-γ, TNF-α, and LT-α ) and activation marker (CD154 and TRANCE) expression by individual CD4+CD45RO+ T cells from RA synovium or blood were analyzed using a single-cell RT-PCR. In brief, single CD4+CD45RO+T cells was sorted into each well of a 96-well PCR plate using a flow cytometer. cDNA from individual cells was prepared, and then the cDNA was nonspecifically amplified. The product was then amplified by PCR using gene-specific primers to analyze cytokine and activation marker expression.
Results:
Cytokine and activation marker expression by individual CD4+CD45RO+T cells from RA synovial tissues was analyzed using a single-cell RT-PCR method. Expression of mRNAs was analyzed in 152 individual synovial tissue CD4+CD45RO+ T cells sorted from three RA patients in which T-cell receptor (TCR) Cβ mRNA was detected. Frequencies of CD4+ memory T cells expressing cytokine and activation marker mRNA in RA synovium are shown in Table 1. IL-2, IL-4, and IL-6 were not expressed by the synovial tissue CD4+CD45RO+ T cells, whereas 2-20% of cells expressed the other cytokine mRNAs.
Few correlations between cytokine and activation marker mRNAs were observed. Notably, no cells contained both IFN-γ and LT-α mRNAs, cytokines that are thought to define the T-helper (Th)1 phenotype [9]. However, the frequency of TRANCE-positive cells in IL-10-positive cells was significantly higher than that in IL-10-negative cells (Table 2). Moreover, the frequency of TRANCE-positive cells in TNF-α-positive cells was also significantly higher than that in TNF-α-negative cells.
Varying percentages of CD4+ memory T cells expressed CC and CXC chemokine receptors. The frequency of CCR5-positive cells in IFN-γ-positive cells was significantly higher than that in IFN-γ-negative cells, whereas the frequency of CCR6-positive cells in LT-α-positive cells was significantly higher than that in LT-α-negative cells, and the frequency of CCR7-positive cells in IL-10-positive cells was significantly higher than that in IL-10-negative cells. Furthermore, the frequency of CXCR4-positive cells in TRANCE-positive cells was significantly higher than that in TRANCE-negative cells.
Expression of cytokine and activation marker mRNAs was also analyzed in 48 individual peripheral blood CD4+CD45RO+ T cells from two RA patients. IL-2, IL-4, IL-6, and LT-α were not expressed by the peripheral CD4+CD45RO+ T cells, whereas 4-17% of cells expressed the other markers. The most striking difference between synovial tissue and peripheral blood CD4+ memory T cells was the presence of LT-α expression in the former, but not in the latter. IFN-γ and TNF-α were not expressed by normal peripheral blood CD4+ memory T cells, although they were expressed by RA peripheral blood CD4+ memory T cells.
Discussion:
The present study employed a single-cell PCR technology to analyze cytokine expression by unstimulated RA synovial tissue CD4+ memory T cells immediately after isolation, without in vitro manipulation. The results confirm the Th1 nature of rheumatoid inflammation. It is noteworthy that no individual synovial CD4+ memory T cells expressed both IFN-γ and LT-α mRNAs, even though these are the prototypic Th1 cytokines [9]. These results imply that, in the synovium, regulation of IFN-γ and LT-α must vary in individual cells, even though both Th1 cytokines can be produced.
The present data showed that CCR5 expression correlated with IFN-γ but not with LT-α expression by synovial CD4+ memory T cells. It has been reported that CCR5 expression is upregulated in RA synovial fluid and synovial tissue T cells [10,11,12] and that CCR5 Δ 32 deletion may have an influence on clinical manifestations of RA [13], suggesting that CCR5 might play an important role in RA. Recently, it has been claimed that CCR5 was preferentially expressed by Th1 cell lines [14,15]. However, in the present study CCR5 was not expressed by all IFN-γ-expressing cells. Moreover, CCR5 expression did not correlate with expression of LT-α by RA synovial CD4+ memory T cells. Therefore, it is unclear whether CCR5 is a marker of Th1 cells in RA synovium.
IL-10 expression correlated with CCR7 expression by RA synovial CD4+ memory T cells. Recently, it was reported [16] that in the blood CCR7+CD4+ memory T cells express lymph-node homing receptors and lack immediate effector function, but efficiently stimulate dendritic cells. These cells may play a unique role in the synovium as opposed to in the blood. By producing IL-10, they might have an immunoregulatory function. In addition, IL-10 expression also correlated with expression of TRANCE. Although it is possible that IL-10 produced by these cells inhibited T-cell activation in the synovium, TRANCE expressed by these same cells might function to activate dendritic cells and indirectly stimulate T cells, mediating inflammation in the synovium. These results imply that individual T cells in the synovium might have different, and sometimes opposite functional activities.
LT-α expression correlated with CCR6 expression by synovial CD4+ memory T cells. It has been reported that CCR6 is expressed by resting peripheral memory T cells [17], whereas LT-α expression is associated with the presence of lymphocytic aggregates in synovial tissue [7]. The correlation between the expression of these two markers therefore suggests the possibility that CCR6 may play a role in the development of aggregates of CD4+ T cells that are characteristically found in rheumatoid synovium.
TRANCE is known to be expressed by activated T cells, and can stimulate dendritic cells and osteoclasts [18]. Of note, TRANCE-mediated activation of osteoclasts has recently been shown [19] to play an important role in the damage to bone that is found in experimental models of inflammatory arthritis. It is therefore of interest that TRANCE was expressed by 3-16% of the RA synovial CD4+ memory T cells. Of note, 67% of TNF-α-positive cells expressed TRANCE. In concert, TNF-α and TRANCE expressed by this subset of CD4+ memory T cells might make them particularly important in mediating the bony erosions that are characteristic of RA.
Interestingly, there was a correlation between expression of IFN-γ and IL-10 in RA peripheral blood CD4+ memory T cells. In RA peripheral blood, CD154 expression correlated with that of CXCR3 by CD4+ memory T cells. It has been claimed [15] that CXCR3 is preferentially expressed by in vitro generated Th1 cells. However, in the present study CXCR3 did not correlate with IFN-γ expression. Although IFN-γ and TNF-α mRNAs were expressed in vivo by peripheral blood CD4+ T cells from RA patients, LT-α mRNA was not detected, whereas IFN-γ , TNF-α , and LT-α were not detected in samples from healthy donors. These findings indicate that RA peripheral blood CD4+ memory T cells are stimulated in vivo, although they do not express LT-α mRNA. The present studies indicate that the frequencies of CD4+ memory T cells that expressed IFN-γ in the blood and in the synovium are comparable. These results imply that activated CD4+ memory T cells migrate between blood and synovium, although the direction of the trafficking is unknown. The presence of LT-α mRNA in synovium, but not in blood, indicates that CD4+ memory cells are further activated in the synovium, and that these activated CD4+ memory T cells are retained in the synovium until LT-α mRNA decreases.
In conclusion, CD4+ memory T cells are biased toward Th1 cells in RA synovium and peripheral blood. In the synovium, IFN-γ and LT-α were produced by individual cells, whereas in the rheumatoid blood no LT-α-producing cells were detected. Furthermore, there were modest correlations between individual cells that expressed particular cytokines, such as IL-10, and certain chemokine receptor mRNAs.
PMCID: PMC17818  PMID: 11056676
chemokine receptor; cytokine; rheumatoid arthritis; T lymphocyte
10.  Plasma and synovial fluid microRNAs as potential biomarkers of rheumatoid arthritis and osteoarthritis 
Introduction
MicroRNAs (miRNAs), endogenous small noncoding RNAs regulating the activities of target mRNAs and cellular processes, are present in human plasma in a stable form. In this study, we investigated whether miRNAs are also stably present in synovial fluids and whether plasma and synovial fluid miRNAs could be biomarkers of rheumatoid arthritis (RA) and osteoarthritis (OA).
Methods
We measured concentrations of miR-16, miR-132, miR-146a, miR-155 and miR-223 in synovial fluid from patients with RA and OA, and those in plasma from RA, OA and healthy controls (HCs) by quantitative reverse transcription-polymerase chain reaction. Furthermore, miRNAs in the conditioned medium of synovial tissues, monolayer fibroblast-like synoviocytes, and mononuclear cells were examined. Correlations between miRNAs and biomarkers or disease activities of RA were statistically examined.
Results
Synovial fluid miRNAs were present and as stable as plasma miRNAs for storage at -20°C and freeze-thawing from -20°C to 4°C. In RA and OA, synovial fluid concentrations of miR-16, miR-132, miR-146a, and miR-223 were significantly lower than their plasma concentrations, and there were no correlation between plasma and synovial fluid miRNAs. Interestingly, synovial tissues, fibroblast-like synoviocytes, and mononuclear cells secreted miRNAs in distinct patterns. The expression patterns of miRNAs in synovial fluid of OA were similar to miRNAs secreted by synovial tissues. Synovial fluid miRNAs of RA were likely to originate from synovial tissues and infiltrating cells. Plasma miR-132 of HC was significantly higher than that of RA or OA with high diagnosability. Synovial fluid concentrations of miR-16, miR-146a miR-155 and miR-223 of RA were significantly higher than those of OA. Plasma miRNAs or ratio of synovial fluid miRNAs to plasma miRNAs, including miR-16 and miR-146a, significantly correlated with tender joint counts and 28-joint Disease Activity Score.
Conclusions
Plasma miRNAs had distinct patterns from synovial fluid miRNAs, which appeared to originate from synovial tissue. Plasma miR-132 well differentiated HCs from patients with RA or OA, while synovial fluid miRNAs differentiated RA and OA. Furthermore, plasma miRNAs correlated with the disease activities of RA. Thus, synovial fluid and plasma miRNAs have potential as diagnostic biomarkers for RA and OA and as a tool for the analysis of their pathogenesis.
doi:10.1186/ar3013
PMCID: PMC2911870  PMID: 20470394
11.  Resistin in rheumatoid arthritis synovial tissue, synovial fluid and serum 
Annals of the Rheumatic Diseases  2006;66(4):458-463.
Background
Resistin is a newly identified adipocytokine which has demonstrated links between obesity and insulin resistance in rodents. In humans, proinflammatory properties of resistin are superior to its insulin resistance‐inducing effects.
Objectives
To assess resistin expression in synovial tissues, serum and synovial fluid from patients with rheumatoid arthritis, osteoarthritis and spondylarthropathies (SpA), and to study its relationship with inflammatory status and rheumatoid arthritis disease activity.
Methods
Resistin expression and localisation in synovial tissue was determined by immunohistochemistry and confocal microscopy. Serum and synovial fluid resistin, leptin, interleukin (IL)1β, IL6, IL8, tumour necrosis factor α, and monocyte chemoattractant protein‐1 levels were measured. The clinical activity of patients with rheumatoid arthritis was assessed according to the 28 joint count Disease Activity Score (DAS28).
Results
Resistin was detected in the synovium in both rheumatoid arthritis and osteoarthritis. Staining in the sublining layer was more intensive in patients with rheumatoid arthritis compared with those with osteoarthritis. In rheumatoid arthritis, macrophages (CD68), B lymphocytes (CD20) and plasma cells (CD138) but not T lymphocytes (CD3) showed colocalisation with resistin. Synovial fluid resistin was higher in patients with rheumatoid arthritis than in those with SpA or osteoarthritis (both p<0.001). In patients with rheumatoid arthritis and SpA, serum resistin levels were higher than those with osteoarthritis (p<0.01). Increased serum resistin in patients with rheumatoid arthritis correlated with both CRP (r = 0.53, p<0.02), and DAS28 (r = 0.44, p<0.05), but not with selected (adipo) cytokines.
Conclusion
The upregulated resistin at local sites of inflammation and the link between serum resistin, inflammation and disease activity suggest a role for resistin in the pathogenesis of rheumatoid arthritis.
doi:10.1136/ard.2006.054734
PMCID: PMC1856051  PMID: 17040961
12.  c-Fms-mediated differentiation and priming of monocyte lineage cells play a central role in autoimmune arthritis 
Introduction
Tyrosine kinases are key mediators of multiple signaling pathways implicated in rheumatoid arthritis (RA). We previously demonstrated that imatinib mesylate--a Food and Drug Administration (FDA)-approved, antineoplastic drug that potently inhibits the tyrosine kinases Abl, c-Kit, platelet-derived growth factor receptor (PDGFR), and c-Fms--ameliorates murine autoimmune arthritis. However, which of the imatinib-targeted kinases is the principal culprit in disease pathogenesis remains unknown. Here we examine the role of c-Fms in autoimmune arthritis.
Methods
We tested the therapeutic efficacy of orally administered imatinib or GW2580, a small molecule that specifically inhibits c-Fms, in three mouse models of RA: collagen-induced arthritis (CIA), anti-collagen antibody-induced arthritis (CAIA), and K/BxN serum transfer-induced arthritis (K/BxN). Efficacy was evaluated by visual scoring of arthritis severity, paw thickness measurements, and histological analysis. We assessed the in vivo effects of imatinib and GW2580 on macrophage infiltration of synovial joints in CIA, and their in vitro effects on macrophage and osteoclast differentiation, and on osteoclast-mediated bone resorption. Further, we determined the effects of imatinib and GW2580 on the ability of macrophage colony-stimulating factor (M-CSF; the ligand for c-Fms) to prime bone marrow-derived macrophages to produce tumor necrosis factor (TNF) upon subsequent Fc receptor ligation. Finally, we measured M-CSF levels in synovial fluid from patients with RA, osteoarthritis (OA), or psoriatic arthritis (PsA), and levels of total and phosphorylated c-Fms in synovial tissue from patients with RA.
Results
GW2580 was as efficacious as imatinib in reducing arthritis severity in CIA, CAIA, and K/BxN models of RA. Specific inhibition of c-Fms abrogated (i) infiltration of macrophages into synovial joints of arthritic mice; (ii) differentiation of monocytes into macrophages and osteoclasts; (iii) osteoclast-mediated bone resorption; and (iv) priming of macrophages to produce TNF upon Fc receptor stimulation, an important trigger of synovitis in RA. Expression and activation of c-Fms in RA synovium were high, and levels of M-CSF were higher in RA synovial fluid than in OA or PsA synovial fluid.
Conclusions
These results suggest that c-Fms plays a central role in the pathogenesis of RA by mediating the differentiation and priming of monocyte lineage cells. Therapeutic targeting of c-Fms could provide benefit in RA.
doi:10.1186/ar2940
PMCID: PMC2875666  PMID: 20181277
13.  Active synovial matrix metalloproteinase-2 is associated with radiographic erosions in patients with early synovitis 
Arthritis Research  2000;2(2):145-153.
Serum and synovial tissue expression of the matrix metalloproteinase (MMP)-2 and -9 and their molecular regulators, MMP-14 and TIMP-2 was examined in 28 patients with inflammatory early synovitis and 4 healthy volunteers and correlated with the presence of erosions in the patients. Immunohistological staining of MMP-2, MMP-14 and TIMP-2 localized to corresponding areas in the synovial lining layer and was almost absent in normal synovium. Patients with radiographic erosions had significantly higher levels of active MMP-2 than patients with no erosions, suggesting that activated MMP-2 levels in synovial tissue may be a marker for a more aggressive synovial lesion.
Introduction:
In cancer the gelatinases [matrix metalloproteinase (MMP)-2 and MMP-9] have been shown to be associated with tissue invasion and metastatic disease. In patients with inflammatory arthritis the gelatinases are expressed in the synovial membrane, and have been implicated in synovial tissue invasion into adjacent cartilage and bone. It is hypothesized that an imbalance between the activators and inhibitors of the gelatinases results in higher levels of activity, enhanced local proteolysis, and bone erosion.
Objectives:
To determine whether the expression and activity levels of MMP-2 and MMP-9, and their regulators MMP-14 and tissue inhibitor of metalloproteinase (TIMP), are associated with early erosion formation in patients with synovitis of recent onset.
Patients and method:
A subset of 66 patients was selected from a larger early synovitis cohort on the basis of tissue availability for the study of synovial tissue and serum gelatinase expression. Patients with peripheral joint synovitis of less than 1 years' duration were evaluated clinically and serologically on four visits over a period of 12 months. At the initial visit, patients underwent a synovial tissue biopsy of one swollen joint, and patients had radiographic evaluation of hands and feet initially and at 1year. Serum MMP-1, MMP-2, MMP-9, MMP-14, and TIMP-1 and TIMP-2 levels were determined, and synovial tissue was examined by immunohistology for the expression of MMP-2 and MMP-9, and their molecular regulators. Gelatinolytic activity for MMP-2 and MMP-9 was quantified using a sensitive, tissue-based gel zymography technique. Four healthy individuals underwent closed synovial biopsy and their synovial tissues were similarly analyzed.
Results:
Of the 66 patients studied, 45 fulfilled American College of Rheumatology criteria for rheumatoid arthritis (RA), with 32 (71%) being rheumatoid factor positive. Of the 21 non-RA patients, seven had a spondylarthropathy and 14 had undifferentiated arthritis. Radiographically, 12 of the RA patients had erosions at multiple sites by 1 year, whereas none of the non-RA patients had developed erosive disease of this extent. In the tissue, latent MMP-2 was widely expressed in the synovial lining layer and in areas of stromal proliferation in the sublining layer and stroma, whereas MMP-9 was expressed more sparsely and focally. MMP-14, TIMP-2, and MMP-2 were all detected in similar areas of the lining layer on consecutive histologic sections. Tissue expression of MMP-14, the activator for pro-MMP-2, was significantly higher in RA than in non-RA patients (8.4 ± 5 versus 3.7 ± 4 cells/high-power field; P = 0.009). In contrast, the expression of TIMP-2, an inhibitor of MMP-2, was lower in the RA than in the non-RA samples (25 ± 12 versus 39 ± 9 cells/high-power field; P = 0.01). Synovial tissue expressions of MMP-2, MMP-14, and TIMP-2 were virtually undetectable in normal synovial tissue samples. The synovial tissue samples of patients with erosive disease had significantly higher levels of active MMP-2 than did those of patients without erosions (Fig. 1). Tissue expression of MMP-2 and MMP-9, however, did not correlate with the serum levels of these enzymes.
With the exception of serum MMP-2, which was not elevated over normal, serum levels of all of the other MMPs and TIMPs were elevated to varying degrees, and were not predictive of erosive disease. Interestingly, MMP-1 and C-reactive protein, both of which were associated with the presence of erosions, were positively correlated with each other (r = 0.42; P < 0.001).
Discussion:
MMP-2 and MMP-9 are thought to play an important role in the evolution of joint erosions in patients with an inflammatory arthritis. Most studies have concentrated on the contribution of MMP-9 to the synovitis, because synovial fluid and serum MMP-9 levels are markedly increased in inflammatory arthropathies. Previously reported serum levels of MMP-9 have varied widely. In the present sample of patients with synovitis of recent onset, serum MMP-9 levels were elevated in only 21%. Moreover, these elevations were not specific for RA, the tissue expression of MMP-9 was focal, and the levels of MMP-9 activity were not well correlated with early erosions. Although serum MMP-2 levels were not of prognostic value, high synovial tissue levels of MMP-2 activity were significantly correlated with the presence of early erosions. This may reflect augmented activation of MMP-2 by the relatively high levels of MMP-14 and low levels of TIMP-2 seen in these tissues. We were able to localize the components of this trimolecular complex to the synovial lining layer in consecutive tissue sections, a finding that is consistent with their colocalization.
In conclusion, we have provided evidence that active MMP-2 complexes are detectable in the inflamed RA synovium and may be involved in the development of early bony erosions. These results suggest that strategies to inhibit the activation of MMP-2 may have the potential for retarding or preventing early erosions in patients with inflammatory arthritis.
PMCID: PMC17808  PMID: 11062605
early synovitis; erosion; metalloproteinase; matrix metalloproteinase-2; rheumatoid arthritis
14.  Protection against cartilage and bone destruction by systemic interleukin-4 treatment in established murine type II collagen-induced arthritis 
Arthritis Research  1999;1(1):81-91.
Destruction of cartilage and bone are hallmarks of human rheumatoid arthritis (RA), and controlling these erosive processes is the most challenging objective in the treatment of RA. Systemic interleukin-4 treatment of established murine collagen-induced arthritis suppressed disease activity and protected against cartilage and bone destruction. Reduced cartilage pathology was confirmed by both decreased serum cartilage oligomeric matrix protein (COMP) and histological examination. In addition, radiological analysis revealed that bone destruction was also partially prevented. Improved suppression of joint swelling was achieved when interleukin-4 treatment was combined with low-dose prednisolone treatment. Interestingly, synergistic reduction of both serum COMP and inflammatory parameters was noted when low-dose interleukin-4 was combined with prednisolone. Systemic treatment with interleukin-4 appeared to be a protective therapy for cartilage and bone in arthritis, and in combination with prednisolone at low dosages may offer an alternative therapy in RA.
Introduction:
Rheumatoid arthritis (RA) is associated with an increased production of a range of cytokines including tumour necrosis factor (TNF)-α and interleukin (IL)-1, which display potent proinflammatory actions that are thought to contribute to the pathogenesis of the disease. Although TNF-α seems to be the major cytokine in the inflammatory process, IL-1 is the key mediator with regard to cartilage and bone destruction. Apart from direct blockade of IL-1/TNF, regulation can be exerted at the level of modulatory cytokines such as IL-4 and IL-10. IL-4 is a pleiotropic T-cell derived cytokine that can exert either suppressive or stimulatory effects on different cell types, and was originally identified as a B-cell growth factor and regulator of humoral immune pathways. IL-4 is produced by activated CD4+ T cells and it promotes the maturation of Th2 cells. IL-4 stimulates proliferation, differentiation and activation of several cell types, including fibroblasts, endothelial cells and epithelial cells. IL-4 is also known to be a potent anti-inflammatory cytokine that acts by inhibiting the synthesis of proinflammatory cytokines such as IL-1, TNF-α, IL-6, IL-8 and IL-12 by macrophages and monocytes. Moreover, IL-4 stimulates the synthesis of several cytokine inhibitors such as interleukin-1 receptor antagonist (IL-1Ra), soluble IL-1-receptor type II and TNF receptors IL-4 suppresses metalloproteinase production and stimulates tissue inhibitor of metalloproteinase-1 production in human mononuclear phagocytes and cartilage explants, indicating a protective effect of IL-4 towards extracellular matrix degradation. Furthermore, IL-4 inhibits both osteoclast activity and survival, and thereby blocks bone resorption in vitro. Of great importance is that IL-4 could not be detected in synovial fluid or in tissues. This absence of IL-4 in the joint probably contributes to the disturbance in the Th1/Th2 balance in chronic RA.
Collagen-induced arthritis (CIA) is a widely used model of arthritis that displays several features of human RA. Recently it was demonstrated that the onset of CIA is under stringent control of IL-4 and IL-10. Furthermore, it was demonstrated that exposure to IL-4 during the immunization stage reduced onset and severity of CIA. However, after cessation of IL-4 treatment disease expression increased to control values.
Aims:
Because it was reported that IL-4 suppresses several proinflammatory cytokines and matrix degrading enzymes and upregulates inhibitors of both cytokines and catabolic enzymes, we investigated the tissue protective effect of systemic IL-4 treatment using established murine CIA as a model. Potential synergy of low dosages of anti-inflammatory glucocorticosteroids and IL-4 was also evaluated.
Methods:
DBA-1J/Bom mice were immunized with bovine type II collagen and boosted at day 21. Mice with established CIA were selected at day 28 after immunization and treated for days with IL-4, prednisolone, or combinations of prednisolone and IL-4. Arthritis score was monitored visually. Joint pathology was evaluated by histology, radiology and serum cartilage oligomeric matrix protein (COMP). In addition, serum levels of IL-1Ra and anticollagen antibodies were determined.
Results:
Treatment of established CIA with IL-4 (1 μg/day) resulted in suppression of disease activity as depicted in Figure 1. Of great interest is that, although 1 μg/day IL-4 had only a moderate effect on the inflammatory component of the disease activity, it strongly reduced cartilage pathology, as determined by histological examination (Fig. 1). Moreover, serum COMP levels were significantly reduced, confirming decreased cartilage involvement. In addition, both histological and radiological analysis showed that bone destruction was prevented (Fig. 1). Systemic IL-4 administration increased serum IL-1Ra levels and reduced anticollagen type II antibody levels. Treatment with low-dose IL-4 (0.1 μg/day) was ineffective in suppressing disease score, serum COMP or joint destruction. Synergistic suppression of both arthritis severity and COMP levels was noted when low-dose IL-4 was combined with prednisolone (0.05 mg/kg/day), however, which in itself was not effective.
Discussion:
In the present study, we demonstrate that systemic IL-4 treatment ameliorates disease progression of established CIA. Although clinical disease progression was only arrested and not reversed, clear protection against cartilage and bone destruction was noted. This is in accord with findings in both human RA and animal models of RA that show that inflammation and tissue destruction sometimes are uncoupled processes. Of great importance is that, although inflammation was still present, strong reduction in serum COMP was found after exposure to IL-4. This indicated that serum COMP levels reflected cartilage damage, although a limited contribution of the inflamed synovium cannot be excluded.
Increased serum IL-1Ra level (twofold) was found after systemic treatment with IL-4, but it is not likely that this could explain the suppression of CIA. We and others have reported that high dosages of IL-1Ra are needed for marked suppression of CIA. As reported previously, lower dosages of IL-4 did not reduce clinical disease severity of established CIA. Of importance is that combined treatment of low dosages of IL-4 and IL-10 appeared to have more potent anti-inflammatory effects, and markedly protected against cartilage destruction. Improved anti-inflammatory effect was achieved with IL-4/prednisolone treatment. In addition, synergistic effects were found for the reduction of cartilage and bone destruction. This indicates that systemic IL-4/prednisolone treatment may provide a cartilage and bone protective therapy for human RA.
Effects in mice of treatment with interleukin-4 or control on disease activity, cartilage damage and bone destruction. Mice were treated intraperitoneally for 7 days with either vehicle (control) or 1 μg/day interleukin-4 (IL-4). CIA, collagen-induced arthritis. *P < 0.05, versus control, by Mann-Whitney U test.
PMCID: PMC17779  PMID: 11056663
bone destruction; cartilage oligomeric matrix protein levels; collagen-induced arthritis; interleukin-4; prednisolone
15.  The immunoreceptor tyrosine-based activation motif (ITAM) -related factors are increased in synovial tissue and vasculature of rheumatoid arthritic joints 
Arthritis Research & Therapy  2012;14(6):R245.
Introduction
The immunoreceptor tyrosine-based activation motif (ITAM) pathway provides osteoclast co-stimulatory signals and regulates proliferation, survival and differentiation of effector immune cells. In the osteoclast, the receptors Triggering Receptor Expressed on Myeloid cells 2 (TREM2) and Osteoclast Associated Receptor (OSCAR) and their respective adaptor proteins, DAP12 and FcRγ mediate ITAM signals and induce calcium signaling and the crucial transcription factor, NFATc1. In rheumatoid arthritis (RA), OSCAR expression by monocytes is inversely correlated with disease activity. Additionally, serum levels of OSCAR are reduced in RA patients versus healthy controls suggesting that expression and secretion or cleavage of soluble (s) OSCAR is immune modulated. Recent data suggest that endothelial cells may also be a source of OSCAR.
Methods
ITAM receptors, their adaptor proteins, and NFATc1 and cathepsin K were detected in human synovial tissues by immunohistochemistry. Synovial tissues from patients with active RA were compared with tissue from patients in remission, osteoarthritis (OA) patients and healthy individuals. OSCAR was measured by immunoassay in synovial fluids recovered from active RA and OA patients. Endothelial cells were cultured with or without 5 ng/mL TNF-α or IL-1β over 72 hours. Temporal expression of OSCAR mRNA was assessed by qRT PCR and OSCAR protein in the supernatant was measured by ELISA.
Results
Significantly higher (P < 0.05) NFATc1-positive inflammatory cell aggregates were found in active RA tissues than in healthy synovial tissue. Similarly, the percentage of OSCAR, FcRγ, DAP12 and TREM2 positive cells was significantly higher in active RA tissues compared to the healthy synovial tissue. Notably, OSCAR was strongly expressed in the microvasculature of the active RA tissues (9/9), inactive RA (8/9) weakly in OA (4/9) but only in the lumen of healthy synovial tissue (0/8). OSCAR levels were detected in synovial fluids from both RA (47 to 152 ng/mL) and OA (112 to 145 ng/mL) patients. Moreover, OSCAR mRNA expression and soluble OSCAR release was stimulated by TNF-α and IL1-β in cultured endothelial cells.
Conclusions
Increased levels of ITAM related factors were present in synovial tissue from active RA joints compared to OA and healthy joints. OSCAR was strongly expressed by the vasculature of active RA patients and membrane bound and soluble OSCAR was stimulated by inflammatory mediators in endothelial cells in vitro.
doi:10.1186/ar4088
PMCID: PMC3674611  PMID: 23146195
16.  Ectopic Lymphoid Structures Support Ongoing Production of Class-Switched Autoantibodies in Rheumatoid Synovium 
PLoS Medicine  2009;6(1):e1.
Background
Follicular structures resembling germinal centres (GCs) that are characterized by follicular dendritic cell (FDC) networks have long been recognized in chronically inflamed tissues in autoimmune diseases, including the synovium of rheumatoid arthritis (RA). However, it is debated whether these ectopic structures promote autoimmunity and chronic inflammation driving the production of pathogenic autoantibodies. Anti-citrullinated protein/peptide antibodies (ACPA) are highly specific markers of RA, predict a poor prognosis, and have been suggested to be pathogenic. Therefore, the main study objectives were to determine whether ectopic lymphoid structures in RA synovium: (i) express activation-induced cytidine deaminase (AID), the enzyme required for somatic hypermutation and class-switch recombination (CSR) of Ig genes; (ii) support ongoing CSR and ACPA production; and (iii) remain functional in a RA/severe combined immunodeficiency (SCID) chimera model devoid of new immune cell influx into the synovium.
Methods and Findings
Using immunohistochemistry (IHC) and quantitative Taqman real-time PCR (QT-PCR) in synovial tissue from 55 patients with RA, we demonstrated that FDC+ structures invariably expressed AID with a distribution resembling secondary lymphoid organs. Further, AID+/CD21+ follicular structures were surrounded by ACPA+/CD138+ plasma cells, as demonstrated by immune reactivity to citrullinated fibrinogen. Moreover, we identified a novel subset of synovial AID+/CD20+ B cells outside GCs resembling interfollicular large B cells. In order to gain direct functional evidence that AID+ structures support CSR and in situ manufacturing of class-switched ACPA, 34 SCID mice were transplanted with RA synovium and humanely killed at 4 wk for harvesting of transplants and sera. Persistent expression of AID and Iγ-Cμ circular transcripts (identifying ongoing IgM-IgG class-switching) was observed in synovial grafts expressing FDCs/CD21L. Furthermore, synovial mRNA levels of AID were closely associated with circulating human IgG ACPA in mouse sera. Finally, the survival and proliferation of functional B cell niches was associated with persistent overexpression of genes regulating ectopic lymphoneogenesis.
Conclusions
Our demonstration that FDC+ follicular units invariably express AID and are surrounded by ACPA-producing plasma cells provides strong evidence that ectopic lymphoid structures in the RA synovium are functional and support autoantibody production. This concept is further confirmed by evidence of sustained AID expression, B cell proliferation, ongoing CSR, and production of human IgG ACPA from GC+ synovial tissue transplanted into SCID mice, independently of new B cell influx from the systemic circulation. These data identify AID as a potential therapeutic target in RA and suggest that survival of functional synovial B cell niches may profoundly influence chronic inflammation, autoimmunity, and response to B cell–depleting therapies.
Costantino Pitzalis and colleagues show that lymphoid structures in synovial tissue of patients with rheumatoid arthritis support production of anti-citrullinated peptide antibodies, which continues following transplantation into SCID mice.
Editors' Summary
Background.
More than 1 million people in the United States have rheumatoid arthritis, an “autoimmune” condition that affects the joints. Normally, the immune system provides protection against infection by responding to foreign antigens (molecules that are unique to invading organisms) while ignoring self-antigens present in the body's own tissues. In autoimmune diseases, this ability to discriminate between self and non-self fails for unknown reasons and the immune system begins to attack human tissues. In rheumatoid arthritis, the lining of the joints (the synovium) is attacked, it becomes inflamed and thickened, and chemicals are released that damage all the tissues in the joint. Eventually, the joint may become so scarred that movement is no longer possible. Rheumatoid arthritis usually starts in the small joints in the hands and feet, but larger joints and other tissues (including the heart and blood vessels) can be affected. Its symptoms, which tend to fluctuate, include early morning joint pain, swelling, and stiffness, and feeling generally unwell. Although the disease is not always easy to diagnose, the immune systems of many people with rheumatoid arthritis make “anti-citrullinated protein/peptide antibodies” (ACPA). These “autoantibodies” (which some experts believe can contribute to the joint damage in rheumatoid arthritis) recognize self-proteins that contain the unusual amino acid citrulline, and their detection on blood tests can help make the diagnosis. Although there is no cure for rheumatoid arthritis, the recently developed biologic drugs, often used together with the more traditional disease-modifying therapies, are able to halt its progression by specifically blocking the chemicals that cause joint damage. Painkillers and nonsteroidal anti-inflammatory drugs can reduce its symptoms, and badly damaged joints can sometimes be surgically replaced.
Why Was This Study Done?
Before scientists can develop a cure for rheumatoid arthritis, they need to know how and why autoantibodies are made that attack the joints in this common and disabling disease. B cells, the immune system cells that make antibodies, mature in structures known as “germinal centers” in the spleen and lymph nodes. In the germinal centers, immature B cells are exposed to antigens and undergo two genetic processes called “somatic hypermutation” and “class-switch recombination” that ensure that each B cell makes an antibody that sticks as tightly as possible to just one antigen. The B cells then multiply and enter the bloodstream where they help to deal with infections. Interestingly, the inflamed synovium of many patients with rheumatoid arthritis contains structures that resemble germinal centers. Could these ectopic (misplaced) lymphoid structures, which are characterized by networks of immune system cells called follicular dendritic cells (FDCs), promote autoimmunity and long-term inflammation by driving the production of autoantibodies within the joint itself? In this study, the researchers investigate this possibility.
What Did the Researchers Do and Find?
The researchers collected synovial tissue from 55 patients with rheumatoid arthritis and used two approaches, called immunohistochemistry and real-time PCR, to investigate whether FDC-containing structures in synovium expressed an enzyme called activation-induced cytidine deaminase (AID), which is needed for both somatic hypermutation and class-switch recombination. All the FDC-containing structures that the researchers found in their samples expressed AID. Furthermore, these AID-containing structures were surrounded by mature B cells making ACPAs. To test whether these B cells were derived from AID-expressing cells resident in the synovium rather than ACPA-expressing immune system cells coming into the synovium from elsewhere in the body, the researchers transplanted synovium from patients with rheumatoid arthritis under the skin of a special sort of mouse that largely lacks its own immune system. Four weeks later, the researchers found that the transplanted human lymphoid tissue was still making AID, that the level of AID expression correlated with the amount of human ACPA in the blood of the mice, and that the B cells in the transplant were proliferating.
What Do These Findings Mean?
These findings show that the ectopic lymphoid structures present in the synovium of some patients with rheumatoid arthritis are functional and are able to make ACPA. Because ACPA may be responsible for joint damage, the survival of these structures could, therefore, be involved in the development and progression of rheumatoid arthritis. More experiments are needed to confirm this idea, but these findings may explain why drugs that effectively clear B cells from the bloodstream do not always produce a marked clinical improvement in rheumatoid arthritis. Finally, they suggest that AID might provide a new target for the development of drugs to treat rheumatoid arthritis.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0060001.
This study is further discussed in a PLoS Medicine Perspective by Rene Toes and Tom Huizinga
The MedlinePlus Encyclopedia has a page on rheumatoid arthritis (in English and Spanish). MedlinePlus provides links to other information on rheumatoid arthritis (in English and Spanish)
The UK National Health Service Choices information service has detailed information on rheumatoid arthritis
The US National Institute of Arthritis and Musculoskeletal and Skin Diseases provides Fast Facts, an easy to read publication for the public, and a more detailed Handbook on rheumatoid arthritis
The US Centers for Disease Control and Prevention has an overview on rheumatoid arthritis that includes statistics about this disease and its impact on daily life
doi:10.1371/journal.pmed.0060001
PMCID: PMC2621263  PMID: 19143467
17.  Multiple mechanisms support oligoclonal T cell expansion in rheumatoid synovitis. 
Molecular Medicine  1997;3(7):452-465.
BACKGROUND: The synovial T cell infiltrate in rheumatoid arthritis (RA) is diverse but contains clonally expanded CD4+ populations. Recent reports have emphasized that RA patients have a tendency to develop CD4+ T cell oligoclonality which also manifests in the peripheral blood. Clonal dominance in the tissue may thus result from antigen specific stimulation in the synovial membrane or may reflect the infiltration of expanded clonotypes present throughout the lymphoid system. We have explored to what extent clonal populations amongst tissue CD4+ T cells display joint specificity as defined by their restriction to the joint, their persistence over time, and their expression of markers indicative for local activation. MATERIALS AND METHODS: Matched samples of peripheral blood and synovial fluid or synovial tissue were collected from 14 patients with active RA and CD4+ IL-2R+ and CD4+ IL-2R- T cells from both compartments were purified. Clonal populations of CD4+ T cells were detected by RT-PCR amplification of T cell receptor (TCR) transcripts with BV and BJ specific primers followed by size fractionation and direct sequencing of dominant size classes of TCR transcripts. RESULTS: Clonal CD4+ T cells were detected in the synovial fluid and synovial tissue of all patients. All patients carried synovial clonotypes that were undetectable in the blood but were present in independent joints or at several non-adjacent areas of the same joint. These joint restricted CD4+ clonotypes were generally small in size, were preferentially found in the IL-2R+ subpopulation, and persisted over time. A second type of clonogenic T cells in the synovial infiltrate had an unrestricted tissue distribution and was present at similar frequencies amongst activated and nonactivated T cells in the blood and affected joints. Ubiquitous clonotypes isolated from two different patients expressed sequence homologies of the TCR beta chain. CONCLUSIONS: Two types of expanded CD4+ clonotypes contribute to the T cell infiltrate in rheumatoid synovitis. Differences in the distribution pattern and in molecular features suggest that distinct mechanisms are supporting the clonal outgrowth of these two groups of clonotypes. Clonally expanded T cells restricted to the joint but present in several independent joints appear to respond to locally residing antigens. Clonogenic cells with an unrestricted distribution pattern and widespread activation in the blood and tissue may react to a different class of antigens which appear to be shared by multiple patients. T cell recognition in RA may be involved at several different levels and may be related to more than one pathomechanism.
Images
PMCID: PMC2230222  PMID: 9260157
18.  Intra-Articular Fms-Like Tyrosine Kinase 3 Ligand Expression Is a Driving Force in Induction and Progression of Arthritis 
PLoS ONE  2008;3(11):e3633.
Background
One of the hallmarks of rheumatoid arthritis (RA) is hyperplasia and inflammation of the synovial tissue being characterized by in situ occurrence of highly differentiated leukocytes. Fms-like tyrosine kinase 3 (Flt3) has a crucial role in hematopoiesis, regulation of cell proliferation, differentiation and apoptosis. Typically, Flt3 is expressed on early myeloid and lymphoid progenitors and is activated by its soluble ligand (Flt3-L). The highly differentiated cellular pattern in the synovium of the RA patients made us hypothesize that Flt3-L, with its ability to induce proliferation and differentiation, could be of importance in induction and/or progression of arthritis.
Methodology/Principal Findings
To investigate occurrence of Flt3-L in RA we have measured its levels in matched serum and synovial fluid samples from 130 patients and 107 controls. To analyse the pro-inflammatory role of Flt3-L, we continuously overexpressed this protein locally in healthy mouse joints using homologous B-cell line transfected with Flt3-L gene. Additionally, recombinant Flt3-L was instillated intra-articularly in combination with peptidoglycans, a Toll Like Receptor 2-ligand with stong arthritogenic properties. Our results show significantly higher levels of Flt3-L in the synovial fluid as compared to serum levels in RA subjects (p = 0.0001). In addition, RA synovial fluid levels of Flt-3-L were significantly higher than these obtained from synovial fluids originating from non-inflammatory joint diseases (p = 0.022). Intra-articular administration of B-cell line transfected with Flt3-L gene resulted in highly erosive arthritis while inoculation of the same B-cell line without hyperexpression of Flt3-L did not induce erosivity and only in a minority of cases caused synovial proliferation! Flt3-ligand potentiated peptidoglycan induced arthritis as compared to mice injected with peptidoglycan alone (p<0.05).
Conclusions/Significance
Our findings indicate that Flt3-L is strongly expressed at the site of inflammation in human RA. It exerts both pro-inflammatory and tissue destructive properties once in the joint cavity. Owing to these properties, treatment attempts to neutralize this molecule should be considered in RA.
doi:10.1371/journal.pone.0003633
PMCID: PMC2575855  PMID: 18982072
19.  Synovial biology and T cells in rheumatoid arthritis 
Events that occur in rheumatoid arthritis synovial tissues are responsible for the signs and symptoms of joint inflammation and for the eventual destruction of articular and periarticular structures that lead to joint dysfunction and disability. The three most abundant cell populations in RA synovium are synovial macrophages (type A synoviocytes), synovial fibroblasts (type B synoviocytes) and infiltrating T lymphocytes. Other important cell populations include B lymphocytes, dendritic cells, plasma cells, mast cells and osteoclasts. Our current understanding of rheumatoid arthritis is moving beyond previous concepts that view this disease as the consequence of a specific and focused humoral or cellular autoimmune response to a single autoantigen. Rather, a new view of rheumatoid arthritis is emerging, which seeks to understand this disease as the product of pathologic cell–cell interactions occurring within a unique and defined environment, the synovium. T lymphocytes in rheumatoid arthritis synovium interact closely with dendritic cells, the most potent antigen-presenting cell population in the immune system. T cells also interact with monocytes and macrophages and cytokine-activated T cells may be, especially, suited to trigger production of the important cytokine TNFα by synovial macrophages. Recent evidence also suggests a potent bidirectional interaction between synovial T cells and synovial fibroblasts, which can lead to activation of both cell types. An important role for synovial B lymphocytes has been emphasized recently, both by experimental data and by results of clinical interventions. B cells in synovium can interact with fibroblasts as well as with other cells of the immune system and their potential role as antigen-presenting cells in the joint is as yet underexplored. Rheumatoid arthritis synovium may be one of the most striking examples of pathologic, organ-specific interactions between immune system cells and resident tissue cell populations. This view of rheumatoid arthritis also leads to the prediction that novel approaches to treatment will more logically target the intercellular communication systems that maintain such interactions, rather than attempt to ablate a single cell population.
doi:10.1016/j.pathophys.2005.07.005
PMCID: PMC3533491  PMID: 16112560
T cells; B cells; Fibroblasts; Dendritic cells; Monocytes
20.  Decreased levels of soluble receptor for advanced glycation end products in patients with rheumatoid arthritis indicating deficient inflammatory control 
Arthritis Research & Therapy  2005;7(4):R817-R824.
The receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin superfamily being expressed as a cell surface molecule and binding a variety of ligands. One of these ligands is high-mobility group box chromosomal protein 1, a potent proinflammatory cytokine, expression of which is increased in synovial tissue and in synovial fluid of rheumatoid arthritis (RA) patients. The interaction of high-mobility group box chromosomal protein 1 with cell-surface RAGE leads to an inflammatory response. In contrast, the presence of soluble RAGE (sRAGE) may abrogate cellular activation since the ligand is bound prior to interaction with the surface receptor.
Our aim was to analyse to what extent sRAGE is present in patients with chronic joint inflammation (RA) as compared with patients with non-inflammatory joint disease and with healthy subjects, and to assess whether there is an association between sRAGE levels and disease characteristics.
Matching samples of blood and synovial fluid were collected from 62 patients with RA with acute joint effusion. Blood from 45 healthy individuals, synovial fluid samples from 33 patients with non-inflammatory joint diseases and blood from six patients with non-inflammatory joint diseases were used for comparison. sRAGE levels were analysed using an ELISA.
RA patients displayed significantly decreased blood levels of sRAGE (871 ± 66 pg/ml, P < 0.0001) as compared with healthy controls (1290 ± 78 pg/ml) and with patients with non-inflammatory joint disease (1569 ± 168 pg/ml). Importantly, sRAGE levels in the synovial fluid of RA patients (379 ± 36 pg/ml) were lower than in corresponding blood samples and correlated significantly with blood sRAGE. Interestingly, a significantly higher sRAGE level was found in synovial fluid of RA patients treated with methotrexate as compared with patients without disease-modifying anti-rheumatic treatment.
We conclude that a decreased level of sRAGE in patients with RA might increase the propensity towards inflammation, whereas treatment with methotrexate counteracts this feature.
doi:10.1186/ar1749
PMCID: PMC1175032  PMID: 15987483
21.  Gene therapy for established murine collagen-induced arthritis by local and systemic adenovirus-mediated delivery of interleukin-4 
Arthritis Research  2000;2(4):293-302.
To determine whether IL-4 is therapeutic in treating established experimental arthritis, a recombinant adenovirus carrying the gene that encodes murine IL-4 (Ad-mIL-4) was used for periarticular injection into the ankle joints into mice with established collagen-induced arthritis (CIA). Periarticular injection of Ad-mIL-4 resulted in a reduction in the severity of arthritis and joint swelling compared with saline- and adenoviral control groups. Local expression of IL-4 also reduced macroscopic signs of joint inflammation and bone erosion. Moreover, injection of Ad-mIL-4 into the hind ankle joints resulted in a decrease in disease severity in the untreated front paws. Systemic delivery of murine IL-4 by intravenous injection of Ad-mIL-4 resulted in a significant reduction in the severity of early-stage arthritis.
Introduction:
Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease that is characterized by joint inflammation, and progressive cartilage and bone erosion. Recent research has identified certain biologic agents that appear more able than conventional therapies to halt effectively the progression of disease, as well as ameliorate disease symptoms. One potential problem with the use of biologic agents for arthritis therapy is the need for daily or weekly repeat dosing. The transfer of genes directly to the synovial lining can theoretically circumvent the need for repeat dosing and reduce potential systemic side effects [1,2]. However, although many genes have been effective in treating murine CIA if administrated at a time before disease onset, local intra-articular or periarticular gene transfer has not been highly effective in halting the progression of established disease. IL-4, similar to tumor necrosis factor (TNF)-α and IL-1 inhibitors, has been shown be therapeutic for the treatment of murine CIA when administered intravenously as a recombinant protein, either alone or in combination with IL-10. IL-4 can downregulate the production of proinflammatory and T-helper (Th)1-type cytokines by inducing mRNA degradation and upregulating the expression of inhibitors of proinflammatory cytokines such as IL-1 receptor antagonist (IL-1Ra) [3,4]. IL-4 is able to inhibit IL-2 and IFN-γ production by Th1 cells, resulting in suppression of macrophage activation and the production of the proinflammatory cytokines IL-1, IL-6, IL-8, and TNF-α by monocytes and macrophages [4,5,6,7,8,9].
Objective:
In order to examine the therapeutic effects of local and systemic IL-4 expression in established CIA, an adenoviral vector carrying the gene for murine IL-4 (Ad-mIL-4) was generated. The ability of Ad-mIL-4 to treat established CIA was evaluated by local periarticular and systemic intravenous injection of Ad-mIL-4 into mice at various times after disease onset.
Materials and methods:
Male DBA/1 lacJ (H-2q) mice, aged 7-8 weeks, were purchased from The Jackson Laboratory (Bar Harbor, ME, USA). The mice were immunized intradermally at the base of tail with 100 μ g bovine type II collagen. On day 21 after priming, mice received a boost injection (intradermally) with 100 μ g type II collagen in incomplete adjuvant. For the synchronous onset of arthritis, 40 μ g lipopolysaccharide (Sigma, St Louis, MO, USA) was injected intraperitoneally on day 28. Ad-mIL-4 was injected periarticularly into the hind ankle joints of mice on day 32 or intravenously by tail vein injection on day 29. Disease severity was monitored every other day using an established macroscopic scoring system ranging from 0 to 4: 0, normal; 1, detectable arthritis with erythma; 2, significant swelling and redness; 3, severe swelling and redness from joint to digit; and 4, maximal swelling with ankylosis. The average of macroscopic score was expressed as a cumulative value for all paws, with a maximum possible score of 16 per mouse. Cytokine production by joint tissue or serum were assessed using enzyme-linked immunosorbent assay (ELISA; R&D Systems, Minneapolis, MN, USA).
Results:
To examine the therapeutic effects of IL-4 gene transfer in a murine model of arthritis, 5×108 particles of Ad-mIL-4 and enhanced green fluorescent protein (Ad-eGFP) were administered by periarticular injection into the ankle joints of mice with established disease 4 days after lipopolysaccharide injection. All mice had established disease at time of injection. As shown in Figure 1, the severity of arthritis (Fig. 1a), paw thickness (Fig. 1b), and the number of arthritic paws (Fig. 1c) were all significantly reduced in the Ad-mIL-4 group, compared with the saline- and Ad-eGFP-treated groups. Analysis of the bones in the ankle joints of control arthritic mice showed evidence of erosion with an associated monocytic infiltrate around the joint space compared with the Ad-mIL-4-treated and nonarthritic control joints. In addition, injection of the ankle joints in the hind legs resulted in a therapeutic effect in the front paws. A similar contralateral effect has been observed with adenoviral-mediated delivery of viral (v)-IL-10. Interestingly, a high level of murine IL-10 also was detected from the joint lysates of Ad-mIL-4-treated naïve and arthritic mice, with the production of endogenous IL-10 correlating with the dose of Ad-mIL-4. The administration of recombinant IL-4 protein systemically has been shown to be therapeutic in murine CIA models if given before disease onset. To examine the effect of systemic IL-4 delivered by gene transfer, 1×109 particles of Ad-mIL-4 were injected via the tail vein of collagen-immunized mice the day after lipopolysaccharide injection. Whereas the immunized control mice, injected with Ad-eGFP, showed disease onset on day 3 after lipopolysaccharide injection, Ad-mIL-4-treated mice showed a delay in disease onset and as a reduction in the total number of arthritic paws. Also, systemic injection of Ad-mIL-4 suppressed the severity of arthritis in CIA mice according to arthritis index.
Discussion:
Gene therapy represents a novel approach for delivery of therapeutic agents to joints in order to treat the pathologies associated with RA and osteoarthritis, as well as other disorders of the joints. In the present study we examined the ability of local periarticular and systemic gene transfer of IL-4 to treat established and early-stage murine CIA, respectively. We have demonstrated that both local and systemic administration of Ad-mIL-4 resulted in a reduction in the severity of arthritis, as well as in the number of arthritic paws. In addition, the local gene transfer of IL-4 reduced histologic signs of inflammation and of bone erosion. Interestingly, local delivery of Ad-mIL-4 was able to confer a therapeutic effect to the untreated, front paws through a currently unknown mechanism. In addition, both local and systemic expression of IL-4 resulted in an increase in the level of endogenous IL-10, as well as of IL-1Ra (data not shown). Previous experiments have shown that gene transfer of IL-10 and IL-1 and TNF inhibitors at the time of disease initiation (day 28) is therapeutic. However, delivery of these agents after disease onset appeared to have only limited therapeutic effect. In contrast, the present results demonstrate that IL-4, resulting from local periarticular and systemic injection of Ad-mIL-4, was able partially to reverse progression of established and early-stage disease, respectively. These results, as well as those of others, support the potential application of IL-4 gene therapy for the clinical treatment of RA.
PMCID: PMC17812  PMID: 11056670
adenoviral vectors; collagen-induced arthritis; gene therapy; IL-4; IL-10; rheumatoid arthritis
22.  Epithelial neutrophil activating peptide-78: a novel chemotactic cytokine for neutrophils in arthritis. 
Journal of Clinical Investigation  1994;94(3):1012-1018.
We and others have shown that cells obtained from inflamed joints of rheumatoid arthritis (RA) patients produce interleukin-8, a potent chemotactic cytokine for neutrophils (PMNs). However, IL-8 accounted for only 40% of the chemotactic activity for PMNs found in these synovial fluids. Currently, we have examined the production of the novel PMN chemotactic cytokine, epithelial neutrophil activating peptide-78 (ENA-78), using peripheral blood, synovial fluid, and synovial tissue from 70 arthritic patients. RA ENA-78 levels were greater in RA synovial fluid (239 +/- 63 ng/ml) compared with synovial fluid from other forms of arthritis (130 +/- 118 ng/ml) or osteoarthritis (2.6 +/- 1.8 ng/ml) (P < 0.05). RA peripheral blood ENA-78 levels (70 +/- 26 ng/ml) were greater than normal peripheral blood levels (0.12 +/- 0.04 ng/ml) (P < 0.05). Anti-ENA-78 antibodies neutralized 42 +/- 9% (mean +/- SE) of the chemotactic activity for PMNs found in RA synovial fluids. Isolated RA synovial tissue fibroblasts in vitro constitutively produced significant levels of ENA-78, and this production was further augmented when stimulated with tumor necrosis factor-alpha (TNF-alpha). In addition RA and osteoarthritis synovial tissue fibroblasts as well as RA synovial tissue macrophages were found to constitutively produce ENA-78. RA synovial fluid mononuclear cells spontaneously produced ENA-78, which was augmented in the presence of lipopolysaccharide. Immunohistochemical localization of ENA-78 from the synovial tissue of patients with arthritis or normal subjects showed that the predominant cellular source of this chemokine was synovial lining cells, followed by macrophages, endothelial cells, and fibroblasts. Synovial tissue macrophages and fibroblasts were more ENA-78 immunopositive in RA than in normal synovial tissue (P < 0.05). These results, which are the first demonstration of ENA-78 in a human disease state, suggest that ENA-78 may play an important role in the recruitment of PMNs in the milieu of the inflamed joint of RA patients.
Images
PMCID: PMC295150  PMID: 8083342
23.  Deficiency of CXCR2, but not other chemokine receptors, attenuates a murine model of autoantibody-mediated arthritis 
Arthritis and rheumatism  2010;62(7):1921-1932.
Objective
Chemokines coordinate leukocyte trafficking in homeostasis and during immune responses. Prior studies of their role in arthritis have employed animal models with both an initial adaptive immune response and an inflammatory effector phase. This study focused on chemokines and their receptors in the effector phase of arthritis using the K/BxN serum-transfer model.
Methods
A time-course microarray analysis of serum-transferred arthritis was performed, examining ankle, synovial fluid and peripheral blood. Upregulation of chemokines was confirmed by quantitative RT-PCR. The functional relevance of chemokine induction was assessed by transferring serum into mice deficient in CCR1–CCR7, CCR9, CXCR2, CXCR3, CXCR5, CX3CR1, CCL2 or CCL3. Further mechanistic analysis of CXCR2 involved treatment of arthritic mice with a CXCR2 antagonist, bone-marrow transfers with CXCR2+/− and CXCR2−/− donors and recipients, flow cytometry of synovial cells, and competition experiments measuring enrichment of CXCR2-expressing neutrophils in arthritic joints of mice with mixed CXCR2+/+ and CXCR2−/− bone-marrow.
Results
Gene-expression profiling revealed upregulation of the CXCR2 ligands CXCL1, CXCL2 and CXCL5 in the joint in parallel with disease activity. CXCR2−/− mice had attenuated disease relative to CXCR2+/− littermates, as did mice receiving the CXCR2 inhibitor, while deficiency of other chemokine receptors did not affect arthritis severity. CXCR2 was required only on hematopoietic cells and was widely expressed on synovial neutrophils. CXCR2-expressing neutrophils were preferentially recruited to arthritic joints in the presence of CXCR2-deficient neutrophils.
Conclusion
CXCR2 (but not other chemokine receptors) is critical for the development of autoantibody-mediated arthritis, exhibiting a cell-autonomous role in neutrophil recruitment to inflamed joints.
doi:10.1002/art.27470
PMCID: PMC2994550  PMID: 20506316
24.  Urokinase, a constitutive component of the inflamed synovial fluid, induces arthritis 
Arthritis Research & Therapy  2002;5(1):R9-R17.
Urokinase plasminogen activator (uPA) is an important regulator of fibrinolysis in synovial fluid. An increase of uPA activity and expression of its receptor have been reported in joints of patients with rheumatoid arthritis (RA). The aim of the present study was to assess the arthritogenic capacity of uPA and the mechanisms by which this effect is mediated. uPA was injected into the knee joints of healthy mice, and morphological signs of arthritis were assessed 4 days after the injection. The prerequisite of different leukocyte populations for the development of uPA-triggered arthritis was assessed by selective cell depletion. The inflammatory capacity of uPA was assessed in vitro. Finally, levels of uPA were measured in 67 paired blood and synovial fluid samples from RA patients. The synovial fluid from RA patients displayed higher levels of uPA compared with blood samples. Morphological signs of arthritis were found in 72% of uPA-injected joints compared with in only 18% of joints injected with PBS (P < 0.05). Synovitis was characterised by infiltration of CD4-Mac-1+ mononuclear cells, by the formation of pannus and by occasional cartilage destruction. The absence of monocytes and lymphocytes diminished the frequency of synovitis (P < 0.01), indicating an arthritogenic role of both these leukocyte populations. Synthetic uPA inhibitor downregulated the incidence of uPA-triggered arthritis by 50%. uPA induced arthritis, stimulating the release of proinflammatory cytokines IL-6, IL-1β and tumour necrosis factor alpha. Accumulation of uPA locally in the joint cavity is a typical finding in erosive RA. uPA exerts potent arthritogenic properties and thus may be viewed as one of the essential mediators of joint inflammation.
doi:10.1186/ar606
PMCID: PMC154426  PMID: 12716448
arthritis; inflammation; urokinase plasminogen activator
25.  Detailed analysis of the cell infiltrate and the expression of mediators of synovial inflammation and joint destruction in the synovium of patients with psoriatic arthritis: implications for treatment 
Annals of the Rheumatic Diseases  2006;65(12):1551-1557.
Background
The synovial tissue is a primary target of many inflammatory arthropathies, including psoriatic arthritis (PsA). Identification of proinflammatory molecules in the synovium may help to identify potentially therapeutic targets.
Objective
To investigate extensively the features of cell infiltration and expression of mediators of inflammation and joint destruction in the synovium of patients with PsA compared with patients with rheumatoid arthritis matched for disease duration and use of drugs.
Methods
Multiple synovial tissue biopsy specimens were obtained by arthroscopy from an inflamed joint in 19 patients with PsA (eight oligoarthritis, 11 polyarthritis) and 24 patients with rheumatoid arthritis. Biopsy specimens were analysed by immunohistochemistry to detect T cells, plasma cells, fibroblast‐like synoviocytes, macrophages, proinflammatory cytokines, matrix metalloproteinases and tissue inhibitor metalloproteinase‐1, adhesion molecules and vascular markers. Stained sections were evaluated by digital image analysis.
Results
The synovial infiltrate of patients with PsA and rheumatoid arthritis was comparable with regard to numbers of fibroblast‐like synoviocytes and macrophages. T cell numbers were considerably lower in the synovium of patients with PsA. The number of plasma cells also tended to be lower in PsA. The expression of tumour necrosis factor alpha (TNFα), interleukin (IL) 1β, IL6 and IL18 was as high in PsA as in rheumatoid arthritis. The expression of matrix metalloproteinases, adhesion molecules and vascular markers was comparable for PsA and rheumatoid arthritis.
Conclusion
These data show increased proinflammatory cytokine expression in PsA synovium, comparable to results obtained for rheumatoid arthritis, and support the notion that, in addition to TNFα blockade, there may be a rationale for treatments directed at IL1β, IL6 and IL18.
doi:10.1136/ard.2005.050963
PMCID: PMC1798447  PMID: 16728461

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