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1.  Epigenetic regulation of high glucose-induced proinflammatory cytokine productionin monocytes by curcumin 
Diabetes is a pro-inflammatory state. We have previously shown increased monocyte pro-inflammatory cytokines in patients with Type 1 and Type 2 diabetes. High glucose induces pro-inflammatory cytokines via epigenetic changes. Curcumin, a polyphenol responsible for the yellow color of the spice turmeric, is known to exert potent anti-inflammatory activity in vitro. Recent studies indicate that it may regulate chromatin remodeling by inhibiting histone acetylation. In this study, we aimed to test the effect of curcumin on histone acetylation and pro-inflammatory cytokine secretion under high-glucose conditions in human monocytes. Human monocytic (THP-1) cells were cultured in presence of mannitol (osmolar control, mannitol) or normoglycemic (NG, 5.5 mmol/L glucose) or hyperglycemic (HG, 25 mmol/L glucose) conditions in absence or presence of curcumin (1.5-12.5μM) for 72 h. Cytokine level, nuclear factor κB (NF-κB) transactivation, histone deacetylases (HDACs) activity, histone acetylases (HATs) activity were measured by western blots, qRT-PCR, ELISA, Immunofluorescence (IF) staining. HG significantly induced histone acetylation, NF-κB activity and pro-inflammatory cytokine (IL-6, TNF-α and MCP-1) release from THP-1 cells. Curcumin suppressed NF-κB binding and cytokine release in THP-1 cells. Also, since p300 histone acetyltransferase is a coactivator of NF-κB, we examined its acetylation. Curcumin treatment also significantly reduced HAT activity, level of p300 and acetylated CBP/p300 gene expression, and induced histone deacetylase 2 (HDAC2) expression by curcumin. These results indicate that curcumin decreases HG-induced cytokine production in monocytes via epigenetic changes involving NF-κB. In conclusion, curcumin supplementation by reducing vascular inflammation may prevent diabetic complications.
doi:10.1016/j.jnutbio.2010.03.014
PMCID: PMC3010508  PMID: 20655188
Acetylation; Deacetylation; p300; HDAC2; NF-κB
2.  High Glucose Induces Toll-Like Receptor Expression in Human Monocytes 
Diabetes  2008;57(11):3090-3098.
OBJECTIVE—Hyperglycemia-induced inflammation is central in diabetes complications, and monocytes are important in orchestrating these effects. Toll-like receptors (TLRs) play a key role in innate immune responses and inflammation. However, there is a paucity of data examining the expression and activity of TLRs in hyperglycemic conditions. Thus, in the present study, we examined TLR2 and TLR4 mRNA and protein expression and mechanism of their induction in monocytic cells under high-glucose conditions.
RESEARCH DESIGN AND METHODS—High glucose (15 mmol/l) significantly induced TLR2 and TLR4 expression in THP-1 cells in a time- and dose-dependent manner (P < 0.05). High glucose increased TLR expression, myeloid differentiation factor 88, interleukin-1 receptor–associated kinase-1, and nuclear factor-κB (NF-κB) p65-dependent activation in THP-1 cells. THP-1 cell data were further confirmed using freshly isolated monocytes from healthy human volunteers (n = 10).
RESULTS—Pharmacological inhibition of protein kinase C (PKC) activity and NADPH oxidase significantly decreased TLR2 and TLR4 mRNA and protein (P < 0.05). Knocking down both TLR2 and TLR4 in the cells resulted in a 76% (P < 0.05) decrease in high-glucose–induced NF-κB activity, suggesting an additive effect. Furthermore, PKC-α knockdown decreased TLR2 by 61% (P < 0.05), whereas inhibition of PKC-δ decreased TLR4 under high glucose by 63% (P < 0.05). Small inhibitory RNA to p47Phox in THP-1 cells abrogated high-glucose–induced TLR2 and TLR4 expression. Additional studies revealed that PKC-α, PKC-δ, and p47Phox knockdown significantly abrogated high-glucose–induced NF-κB activation and inflammatory cytokine secretion.
CONCLUSIONS—Collectively, these data suggest that high glucose induces TLR2 and -4 expression via PKC-α and PKC-δ, respectively, by stimulating NADPH oxidase in human monocytes.
doi:10.2337/db08-0564
PMCID: PMC2570406  PMID: 18650365
3.  Sera from patients with active systemic lupus erythematosus patients enhance the toll-like receptor 4 response in monocyte subsets 
Background
Systemic Lupus Erythematosus (SLE) is an auto-immune disease whose complex pathogenesis remains unraveled. Here we aim to explore the inflammatory ability of SLE patients’ sera upon peripheral blood (PB) monocyte subsets and myeloid dendritic cells (mDCs) obtained from healthy donors.
Methods
In this study we included 11 SLE patients with active disease (ASLE), 11 with inactive disease (ISLE) and 10 healthy controls (HC). PB from healthy donors was stimulated with patients’ sera, toll-like receptor (TLR) 4 ligand – lipopolysaccharide or both. The intracellular production of TNF-α was evaluated in classical, non-classical monocytes and mDCs, using flow cytometry. TNF-α mRNA expression was assessed in all these purified cells, after sera treatment.
Results
We found that sera of SLE patients did not change spontaneous TNF-α production by monocytes or dendritic cells. However, upon stimulation of TLR4, the presence of sera from ASLE patients, but not ISLE, significantly increased the intracellular expression of TNF-α in classical and non-classical monocytes. This ability was related to titers anti-double stranded DNA antibodies in the serum. High levels of anti-TNF-α in the patients’ sera were associated with increased TNF-α expression by co-cultured mDCs. No relationship was found with the levels of a wide variety of other pro-inflammatory cytokines. A slight increase of TNF-α mRNA expression was observed in these purified cells when they were cultured only in the presence of SLE serum.
Conclusions
Our data suggest that SLE sera induce an abnormal in vitro TLR4 response in classical and non-classical monocytes, reflected by a higher TNF-α intracellular expression. These effects may be operative in the pathogenesis of SLE.
doi:10.1186/s12950-015-0083-2
PMCID: PMC4451730  PMID: 26038677
Systemic lupus erythematosus; Serum; Cytokines; Toll like receptor 4; Classical monocytes; Non-classical monocytes; Myeloid dendritic cells
4.  Modulation of monocyte activation in patients with rheumatoid arthritis by leukapheresis therapy. 
Journal of Clinical Investigation  1993;91(3):862-870.
One of the hallmarks in rheumatoid arthritis (RA) is the intense activation of the monocyte-macrophage system. In the present investigation, the modulation of blood monocyte activation was studied with regard to the secretion of cytokines and inflammatory mediators, and to the expression of cytokine receptors. Patients with severe active RA underwent repeated leukapheresis procedures that removed all circulating monocytes. Highly enriched monocyte preparations from the first and third leukapheresis were studied. There were striking differences between the two monocyte populations. Cells obtained from the first leukapheresis constitutively released large amounts of prostaglandin E2 (PGE2), neopterin, interleukin 1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha). In particular, IL-1 beta and neopterin production were further enhanced by stimulation with either interferon-gamma (IFN-gamma) or TNF-alpha without a synergistic effect. In contrast, cells derived from the third leukapheresis procedure showed a close to normal activation status with only low levels of cytokine and mediator production as well as a reduced response to cytokine stimulation. The number of the receptors for IFN-gamma and TNF-alpha was not changed between first and third leukapheresis. However, TNF-binding capacity was only detectable upon acid treatment of freshly isolated monocytes. A further upregulation was noted upon 24 h in vitro culture, suggesting occupation of membrane receptors and receptor down-regulation by endogenously produced TNF-alpha. Northern blot analysis of cytokine gene expression was in good correlation with the amount of mediators determined on the protein level. These data indicate that cells of the monocyte-macrophage system are already highly activated in the peripheral blood in RA patients with active disease. These cells can be efficiently removed by repeated leukapheresis and are replenished by monocytes that have, with respect to cytokine and mediator production, a considerably lower activation status.
Images
PMCID: PMC288038  PMID: 8450066
5.  High Insulin and Leptin Increase Resistin and Inflammatory Cytokine Production from Human Mononuclear Cells 
BioMed Research International  2012;2013:487081.
Resistin and the proinflammatory cytokines, such as TNF-α, IL-6, and IL-1β, produced by adipocytes, and macrophages, are considered to be important modulators of chronic inflammation contributing to the development of obesity and atherosclerosis. Human monocyte-enriched mononuclear cells, from ten healthy individuals, were exposed to high concentrations of insulin, leptin, and glucose (alone or in combination) for 24 hours in vitro. Resistin, TNF-α, IL-6, and IL-1β production was examined and compared to that in untreated cells. High insulin and leptin concentrations significantly upregulated resistin and the cytokines. The subsequent addition of high glucose significantly upregulated resistin and TNF-α mRNA and protein secretion, while it did not have any effect on IL-6 or IL-1β production. By comparison, exposure to dexamethasone reduced TNF-α, IL-6, and IL-1β production, while at this time point it increased resistin protein secretion. These data suggest that the expression of resistin, TNF-α, IL-6, and IL-1β from human mononuclear cells, might be enhanced by the hyperinsulinemia and hyperleptinemia and possibly by the hyperglycemia in metabolic diseases as obesity, type 2 diabetes, and atherosclerosis. Therefore, the above increased production may contribute to detrimental effects of their increased adipocyte-derived circulating levels on systemic inflammation, insulin sensitivity, and endothelial function of these patients.
doi:10.1155/2013/487081
PMCID: PMC3591160  PMID: 23484124
6.  CD56+ monocytes have a dysregulated cytokine response to lipopolysaccharide and accumulate in rheumatoid arthritis and immunosenescence 
Arthritis Research & Therapy  2013;15(5):R139.
Introduction
Peripheral blood monocytes are no longer regarded as a homogeneous cell population, but can be differentiated both phenotypically and functionally into various subpopulations. In rheumatoid arthritis, the subpopulation of CD14bright/CD16+ monocyte is expanded and prone towards generation of Th17 cells. CD56+ monocytes represent a different subpopulation, which is also expanded in conditions associated with autoimmunity like inflammatory bowel diseases. The aim of the study was the quantification and functional characterization of the CD56+ monocyte subset in rheumatoid arthritis (RA).
Methods
Frequencies of peripheral blood monocyte subpopulations were analyzed by flow cytometry in 86 healthy controls and 75 RA patients. In 16 patients, anti-tumor necrosis factor (TNF) therapy was initiated, and the CD56+ monocyte frequency was monitored longitudinally. Lipopolysaccharide (LPS)-induced cytokine production of CD56+ and CD56– monocytes was determined by intracellular staining or cytokine secretion assays.
Results
In healthy individuals, 8.6% ± 0.6 of the monocytes co-expressed CD56, with the majority of CD56+ monocytes being CD14bright (7.9% ± 0.5), while only a minor population was CD14dim (0.7% ± 0.1). We found a strong positive correlation between an individual’s age and the frequency of CD56+ monocytes. Upon stimulation with LPS, CD56+ monocytes became more frequently positive for TNF, IL-10 and IL-23 than CD56– monocytes. In addition, CD56+ monocytes spontaneously produced more reactive oxygen intermediates than CD56- monocytes. In RA patients, the frequency of CD56+ monocytes was significantly higher than in healthy controls (12.2% ± 0.9 vs. 7.9% ± 0.5, p = 0.0002), and this difference most pronounced in RA patients below 40 years of age (11.1% ± 1.6 vs. 4.1% ± 0.4, P < 0.0001). Treatment of the patients with an anti-TNF blocking agent significantly reduced CD56+ monocyte frequencies (baseline 12.4% vs. 24 weeks treatment 8.0%, P = 0.0429), and the magnitude of this decrease was found to correlate with the change in disease activity under the therapy.
Conclusion
The CD14bright/CD56+ monocyte subset is expanded in aging individuals as well as in patients with RA. The pro-inflammatory production of cytokines and reactive oxygen species as well as the elimination of those cells in patients with a good response towards TNF inhibiting agents indicates a possible contribution of those monocytes in the inflammatory response in RA.
doi:10.1186/ar4321
PMCID: PMC3978677  PMID: 24286519
7.  Fisetin Inhibits Hyperglycemia-Induced Proinflammatory Cytokine Production by Epigenetic Mechanisms 
Diabetes is characterized by a proinflammatory state, and several inflammatory processes have been associated with both type 1 and type 2 diabetes and the resulting complications. High glucose levels induce the release of proinflammatory cytokines. Fisetin, a flavonoid dietary ingredient found in the smoke tree (Cotinus coggygria), and is also widely distributed in fruits and vegetables. Fisetin is known to exert anti-inflammatory effects via inhibition of the NF-κB signaling pathway. In this study, we analyzed the effects of fisetin on proinflammatory cytokine secretion and epigenetic regulation, in human monocytes cultured under hyperglycemic conditions. Human monocytic (THP-1) cells were cultured under control (14.5 mmol/L mannitol), normoglycemic (NG, 5.5 mmol/L glucose), or hyperglycemic (HG, 20 mmol/L glucose) conditions, in the absence or presence of fisetin. Fisetin was added (3–10 μM) for 48 h. While the HG condition significantly induced histone acetylation, NF-κB activation, and proinflammatory cytokine (IL-6 and TNF-α) release from THP-1 cells, fisetin suppressed NF-κB activity and cytokine release. Fisetin treatment also significantly reduced CBP/p300 gene expression, as well as the levels of acetylation and HAT activity of the CBP/p300 protein, which is a known NF-κB coactivator. These results suggest that fisetin inhibits HG-induced cytokine production in monocytes, through epigenetic changes involving NF-κB. We therefore propose that fisetin supplementation be considered for diabetes prevention.
doi:10.1155/2012/639469
PMCID: PMC3539716  PMID: 23320034
8.  SOCS1 regulates the IFN but not NFκB pathway in TLR-stimulated human monocytes and macrophages 
SOCS1 can regulate TLR-mediated signal transduction, yet mechanistic studies in murine macrophages have been confusing and contradictory. This study has used an adenoviral transfection system to determine the role of SOCS1 in the regulation of TNFα production by activated human monocytes. Monocytes were infected with AdV-SOCS1 or with an empty vector control, AdV-GFP, for 24 h prior to activation with the TLR4 ligand, LPS. SOCS1 did not regulate TNFα mRNA or protein production within the first two hours of TLR4 activation. However, SOCS1 suppressed the sustained production of TNFα by primary human monocytes and synovial fluid macrophages ex vivo. In addition, SOCS1 regulated the production of IL-6, but not IL-10, by monocytes. Analysis of the early signaling pathway downstream of TLR4 demonstrated that SOCS1 had no regulatory effect on the activation or on the DNA binding capacity of NFκB. The late effects of LPS are mediated in part through the MyD88-independent pathway activating IRF3 and initiating the production of IFNβ. In response to adenoviral infection and prior to LPS exposure, monocytes expressed enhanced levels of IFNβ and Myxovirus A (MxA) mRNA, an anti-viral molecule characterizing IFNβ activity. These two genes were reduced in AdV-SOCS1-infected cells. Further, SOCS1 regulated IFN-dependent pathways in LPS-activated cells as evidenced by reduced IFNβ production and STAT1 phosphorylation.
Using AdV-infection to dissect SOCS1 control of IFN-dependent pathways, this study suggests that SOCS1-regulation of the IFN-dependent component of the LPS-induced TLR4 signaling pathway may contribute to the down-regulation of inflammatory cytokine production by AdV-SOCS1-infected human monocytes.
PMCID: PMC3430718  PMID: 19017994
Human; Inflammation; Signal Transduction; TNF; Toll-like receptor
9.  Interleukin 10(IL-10) inhibits cytokine synthesis by human monocytes: an autoregulatory role of IL-10 produced by monocytes 
The Journal of Experimental Medicine  1991;174(5):1209-1220.
In the present study we demonstrate that human monocytes activated by lipopolysaccharides (LPS) were able to produce high levels of interleukin 10 (IL-10), previously designated cytokine synthesis inhibitory factor (CSIF), in a dose dependent fashion. IL-10 was detectable 7 h after activation of the monocytes and maximal levels of IL-10 production were observed after 24-48 h. These kinetics indicated that the production of IL-10 by human monocytes was relatively late as compared to the production of IL-1 alpha, IL-1 beta, IL-6, IL-8, tumor necrosis factor alpha (TNF alpha), and granulocyte colony-stimulating factor (G-CSF), which were all secreted at high levels 4-8 h after activation. The production of IL-10 by LPS activated monocytes was, similar to that of IL-1 alpha, IL-1 beta, IL-6, IL-8, TNF alpha, granulocyte-macrophage colony-stimulating factor (GM-CSF), and G-CSF, inhibited by IL-4. Furthermore we demonstrate here that IL-10, added to monocytes, activated by interferon gamma (IFN-gamma), LPS, or combinations of LPS and IFN-gamma at the onset of the cultures, strongly inhibited the production of IL-1 alpha, IL-1 beta, IL-6, IL-8, TNF alpha, GM-CSF, and G-CSF at the transcriptional level. Viral-IL-10, which has similar biological activities on human cells, also inhibited the production of TNF alpha and GM-CSF by monocytes following LPS activation. Activation of monocytes by LPS in the presence of neutralizing anti-IL-10 monoclonal antibodies resulted in the production of higher amounts of cytokines relative to LPS treatment alone, indicating that endogenously produced IL-10 inhibited the production of IL-1 alpha, IL-1 beta, IL-6, IL-8, TNF alpha, GM-CSF, and G-CSF. In addition, IL-10 had autoregulatory effects since it strongly inhibited IL-10 mRNA synthesis in LPS activated monocytes. Furthermore, endogenously produced IL-10 was found to be responsible for the reduction in class II major histocompatibility complex (MHC) expression following activation of monocytes with LPS. Taken together our results indicate that IL-10 has important regulatory effects on immunological and inflammatory responses because of its capacity to downregulate class II MHC expression and to inhibit the production of proinflammatory cytokines by monocytes.
PMCID: PMC2119001  PMID: 1940799
10.  Functional Activity of Monocytes and Macrophages in HTLV-1 Infected Subjects 
The Human T lymphotropic virus type-1 (HTLV-1) infects predominantly T cells, inducing proliferation and lymphocyte activation. Additionally, HTLV-1 infected subjects are more susceptible to other infections caused by other intracellular agents. Monocytes/macrophages are important cells in the defense against intracellular pathogens. Our aims were to determine the frequency of monocytes subsets, expression of co-stimulatory molecules in these cells and to evaluate microbicidal ability and cytokine and chemokine production by macrophages from HTLV-1 infected subjects. Participants were 23 HTLV-1 carriers (HC), 22 HAM/TSP patients and 22 healthy subjects (HS) not infected with HTLV-1. The frequencies of monocyte subsets and expression of co-stimulatory molecules were determined by flow cytometry. Macrophages were infected with L. braziliensis or stimulated with LPS. Microbicidal activity of macrophages was determined by optic microscopy. Cytokines/chemokines from macrophage supernatants were measured by ELISA. HAM/TSP patients showed an increase frequency of intermediate monocytes, but expression of co-stimulatory molecules was similar between the groups. Macrophages from HTLV-1 infected individuals were infected with L. braziliensis at the same ratio than macrophages from HS, and all the groups had the same ability to kill Leishmania parasites. However, macrophages from HTLV-1 infected subjects produced more CXCL9 and CCL5, and less IL-10 than cells from HS. While there was no correlation between IFN-γ and cytokine/chemokine production by macrophages, there was a correlation between proviral load and TNF and CXCL10. These data showed a dissociation between the inflammatory response and microbicidal ability of macrophages from HTLV-1 infected subjects. While macrophages ability to kill an intracellular pathogen did not differ among HTLV-1 infected subjects, these cells secreted high amount of chemokines even in unstimulated cultures. Moreover the increasing inflammatory activity of macrophages was similar in HAM/TSP patients and HC and it was related to HTLV-1 proviral load rather than the high IFN-γ production observed in these subjects.
Author Summary
HTLV-1 predominantly infects T cells, inducing cell proliferation and activation. While there is a larger amount of studies regarding T cells functions in HTLV-1 infected subjects, little is known about innate immunity. We evaluated monocyte and macrophage functions in HTLV-1 infected subjects. We observed that HAM/TSP patients have an increased frequency of intermediate monocytes, but expression of co-stimulatory molecules in these cells was similar between HTLV-1 infected subjects and healthy subjects (HS). Additionally, the microbicidal ability of macrophages from HTLV-1 infected subjects to kill Leishmania braziliensis is preserved, and these cells showed inflammatory profile, producing more CXCL9 and CCL5, and less IL-10 than macrophages from HS. It was important to determine if the exacerbated ability of macrophages to secrete cytokine was due to IFN-γ production. While there was no correlation between IFN-γ levels by PBMCs and cytokine/chemokine production by macrophages, there was a direct correlation between proviral load and TNF and CXCL10 levels. Our data indicate that despite the high production of proinflammatory mediators, macrophages from HTLV-1 infected subjects kill an intracellular pathogen in similar levels than cells from HS and pointed out for the role of viral factors inducing the inflammatory response in these cells.
doi:10.1371/journal.pntd.0003399
PMCID: PMC4270688  PMID: 25521499
11.  Maggot secretions suppress pro-inflammatory responses of human monocytes through elevation of cyclic AMP 
Diabetologia  2009;52(9):1962-1970.
Aims/hypothesis
Maggots of the blowfly Lucilia sericata are used for the treatment of chronic wounds. As monocytes may contribute to the excessive inflammatory responses in such wounds, this study focussed on the effects of maggot secretions on the pro-inflammatory activities of these cells.
Methods
Freshly isolated monocytes were incubated with a range of secretions for 1 h and then stimulated with lipopolysaccharides (range 0–100 ng/ml) or lipoteichoic acid (range 0–5 µg/ml) for 18 h. The expression of cell surface molecules, cytokine and chemokine levels in culture supernatants, cell viability, chemotaxis, and phagocytosis and killing of Staphylococcus aureus were measured.
Results
Maggot secretions dose-dependently inhibited production of the pro-inflammatory cytokines TNF-α, IL-12p40 and macrophage migration inhibitory factor by lipopolysaccharides- and lipoteichoic acid-stimulated monocytes, while enhancing production of the anti-inflammatory cytokine IL-10. Expression of cell surface receptors involved in pathogen recognition remained unaffected by secretions. In addition, maggot secretions altered the chemokine profile of monocytes by downregulating macrophage inflammatory protein-1β and upregulating monocyte chemoattractant protein-1 and IL-8. Nevertheless, chemotactic responses of monocytes were inhibited by secretions. Furthermore, maggot secretions did not affect phagocytosis and intracellular killing of S. aureus by human monocytes. Finally, secretions induced a transient rise in the intracellular cyclic AMP concentration in monocytes and Rp-cyclic AMPS inhibited the effects of secretions.
Conclusions/interpretation
Maggot secretions inhibit the pro-inflammatory responses of human monocytes through a cyclic AMP-dependent mechanism. Regulation of the inflammatory processes by maggots contributes to their beneficial effects on chronic wounds.
doi:10.1007/s00125-009-1432-6
PMCID: PMC2723663  PMID: 19575178
Chemokines; Chemotaxis; Chronic wounds; Cyclic AMP; Cytokines; Inflammation; Phagocytosis; Signal transduction
12.  Effects of Porphyromonas gingivalis and Escherichia coli lipopolysaccharides on mononuclear phagocytes. 
Infection and Immunity  1997;65(8):3248-3254.
The mononuclear phagocyte plays an important role in the regulation of microbe-induced inflammation, in part through its ability to secrete mediators, particularly cytokines, in response to microorganisms and their products. To evaluate the effects of the microbial flora associated with chronic adult periodontitis on cytokine induction, lipopolysaccharide (LPS) from the periodontopathogen Porphyromonas gingivalis was used to stimulate naive and phorbol ester-primed U937 monocytic cells, as well as elutriated human peripheral blood monocytes. We assessed the effect of this LPS, in comparison to that of LPS from Escherichia coli, on cell proliferation, cytokine induction, and surface expression of the LPS receptor CD14. P. gingivalis LPS stimulated proliferation of U937 cells at concentrations of greater than 1 ng/ml, while E. coli LPS inhibited proliferation. Phorbol myristic acid (PMA)-treated U937 cells and elutriated monocytes responded to E. coli LPS activation by producing tumor necrosis factor alpha (TNF-alpha) mRNA and protein; however, P. gingivalis LPS induced greater numbers of TNF-alpha mRNA-positive cells and higher (P < 0.05) levels of protein than did E. coli LPS. Both cell types expressed interleukin-1 beta (IL-1beta) mRNA and protein in response to either LPS treatment. Compared with E. coli LPS, P. gingivalis LPS induced significantly (P < 0.05) higher numbers of IL-1 mRNA-positive U937 cells and elutriated monocytes, as well as production of significantly more (P < 0.05) IL-1 protein by the monocytes. The PMA-treated U937 cells and the monocytes produced high levels of IL-1 receptor antagonist mRNA and protein which were only marginally affected by the LPS preparations. While E. coli LPS induced expression of CD 14 on the surface of PMA-primed U937 cells and monocytes, P. gingivalis LPS exhibited a significantly (P < 0.05) greater ability to enhance receptor levels. Our results indicate that P. gingivalis LPS can activate the mononuclear phagocyte for proliferation, cytokine production, and CD14 expression, providing evidence for the potential of this bacterial component to act as a critical regulatory factor in the chronic inflammatory response associated with periodontitis.
PMCID: PMC175459  PMID: 9234782
13.  Heat shock protein 70 down-regulates the production of toll-like receptor-induced pro-inflammatory cytokines by a heat shock factor-1/constitutive heat shock element-binding factor-dependent mechanism 
Background
Heat shock protein 70 (Hsp70) is an intracellular chaperone protein with regulatory and cytoprotective functions. Hsp70 can also be found in the extracellular milieu, as a result of active secretion or passive release from damaged cells. The role of extracellular Hsp70 is not fully understood. Some studies report that it activates monocytes, macrophages and dendritic cells through innate immune receptors (such as Toll-like receptors, TLRs), while others report that Hsp70 is a negative regulator of the inflammatory response. In order to address this apparent inconsistency, in this study we evaluated the response of human monocytes to a highly purified recombinant Hsp70.
Methods
Human peripheral blood monocytes were stimulated with Hsp70, alone or in combination with TLR agonists. Cytokines were quantified in culture supernatants, their mRNAs were measured by RT-PCR, and the binding of transcription factors was evaluated by electrophoretic mobility shift assay (EMSA). Kruskal-Wallis test or one-way or two-way ANOVA were used to analyze the data.
Results
The addition of Hsp70 to TLR-activated monocytes down-regulated TNF-α as well as IL-6 levels. This effect was independent of a physical interaction between Hsp70 and TLR agonists; instead it resulted of changes at the TNF-α gene expression level. The decrease in TNF-α expression correlated with the binding of HSF-1 (heat shock transcription factor 1, a transcription factor activated in response to Hsp70) and CHBF (constitutive HSE-binding factor) to the TNF-α gene promoter.
Conclusion
Extracellular Hsp70 negatively regulates the production of pro-inflammatory cytokines of monocytes exposed to TLR agonists and contributes to dampen the inflammatory response.
doi:10.1186/1476-9255-11-19
PMCID: PMC4105516  PMID: 25053922
Heat shock protein 70; Inflammatory response; HSF-1; CHBF; Toll-like receptors
14.  Suppressors of cytokine signalling (SOCS) are reduced in osteoarthritis 
Objectives
Suppressor of cytokine signalling (SOCS) proteins are inhibitors of cytokine signalling that function via the JAK/STAT pathway (Janus kinase/signal transducers and activators of transcription). Eight SOCS proteins, SOCS1–SOCS7 and CIS-1 (cytokine-inducible SH2-domain, with similar structure to the other SOCS proteins) have been identified, of which SOCS1, 2, and 3 and CIS-1 are the best characterised. A characteristic feature of osteoarthritis (OA) is increased production by articular chondrocytes of proinflammatory cytokines, such as interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNFα), which may be induced by mechanotransduction and contribute to cartilage destruction. In this study, we have compared the gene expression of SOCS1, 2, 3 and CIS-1 in healthy and OA human chondrocytes, and also analyzed the effects of IL-1β and TNFα on the levels of mRNA encoding these SOCS family members. In addition, SOCS2 protein production was assessed and the CpG methylation status of the SOCS2 promoter was analyzed to determine the role of epigenetics in its regulation.
Methods
Femoral heads were obtained after joint replacement surgery for late stage OA and hemiarthroplasty following a fracture of the neck of femur (#NOF). Chondrocytes from the superficial layer of OA cartilage and the deep zone of #NOF cartilage were isolated by sequential treatment with trypsin, hyaluronidase and collagenase B. Total DNA and RNA were extracted from the same chondrocytes, and the levels of SOCS1, 2, 3 and CIS-1 mRNA were determined by qRT-PCR. The percentage of methylation in the CpG sites of the SOCS2 proximal promoter was quantified by pyrosequencing. Alternatively, healthy chondrocytes were isolated from #NOF cartilage and cultured with and without a mixture of IL-1β and oncostatin M (OSM, both 2.5 ng/ml) or TNFα (10 ng/ml). The short-term cultures with single cytokine treatment were harvested 24 and 72 h after treatment, and the long-term cultures were maintained for 4–5 weeks until confluent with periodical cytokine stimulation. Total RNA was extracted and mRNA levels were determined by qRT-PCR.
Results
The SOCS2 and CIS-1 mRNA levels were reduced by approximately 10-fold in OA samples compared to control samples, while SOCS1 and SOCS3 showed similar expression patterns in OA and control chondrocytes. The SOCS2 and CIS-1 mRNA levels declined by 6-fold and 3-fold with long-term treatment with IL-1β and OSM in combination and TNFα, respectively. There was no significant difference in the CpG methylation status of the SOCS2 promoter between healthy and OA chondrocytes. Similarly, cytokine stimulation did not change the CpG methylation status of the SOCS2 promoter.
Conclusions
This study demonstrates the reduced expression of SOCS2 and CIS-1 in OA, while SOCS1 and SOCS3 were unaffected. The observation that long-term treatment with inflammatory cytokines attenuated the expression of SOCS2 and CIS-1 suggests a potential positive feedback mechanism, and a role of SOCS in the pathology of OA.
doi:10.1016/j.bbrc.2011.02.101
PMCID: PMC3937865  PMID: 21352802
Osteoarthritis (OA); Chondrocytes; Suppressors of cytokine signalling (SOCS); Cytokine-inducible SH2 protein (CIS-1); IL-1β; TNFα
15.  Priming of human monocytes for enhanced lipopolysaccharide responses: expression of alpha interferon, interferon regulatory factors, and tumor necrosis factor. 
Infection and Immunity  1993;61(8):3222-3227.
Culture of human monocytes with either granulocyte-macrophage colony-stimulating factor or gamma interferon (IFN-gamma) results in a primed state, during which these cells express heightened responses to bacterial lipopolysaccharide (LPS). The production of IFN-alpha in response to LPS by human monocytes has an absolute requirement for priming. Tumor necrosis factor (TNF) expression is also greatly enhanced in primed monocytes after LPS stimulation, but unlike IFN-alpha, TNF is readily expressed in unprimed monocytes as well. In an effort to determine the molecular events associated with IFN-alpha induction in this system, freshly isolated human monocytes were primed by culture with either IFN-gamma or granulocyte-macrophage colony-stimulating factor and then treated with LPS; expression of IFN-alpha subtype 2 (IFN-alpha 2), IFN regulatory factors (IRFs), and TNF was assessed by Northern (RNA blot) analysis. IRF-1 mRNA is expressed at high levels in monocytes and is regulated by both LPS and priming cytokines, but its expression alone does not correlate with the induction of IFN-alpha 2 expression. IRF-2 mRNA is expressed in a more gradual manner following LPS stimulation, implying a possible feedback mechanism for inhibiting IFN-alpha expression. However, nuclear run-on analysis indicates that IFN-alpha 2 is not transcriptionally modulated in this system, in striking contrast to TNF, which is clearly regulated at the transcriptional level. In addition, IFN-alpha 2 mRNA accumulation is superinduced when primed monocytes are treated with LPS plus cycloheximide, while TNF mRNA is relatively unaffected. The results demonstrate that priming can affect subsequent LPS-induced gene expression at different levels in human monocytes.
Images
PMCID: PMC280991  PMID: 8335353
16.  Maggot Secretions Skew Monocyte-Macrophage Differentiation Away from a Pro-Inflammatory to a Pro-Angiogenic Type 
PLoS ONE  2009;4(11):e8071.
Background
Maggots of the blowfly Lucilia sericata are used for the treatment of chronic wounds. Earlier we reported maggot secretions to inhibit pro-inflammatory responses of human monocytes. The aim of this study was to investigate the effect of maggot secretions on the differentiation of monocytes into pro-inflammatory (MØ-1) and anti-inflammatory/pro-angiogenic macrophages (MØ-2) as these cells play a central role in wound healing.
Methodology/Principal Findings
Freshly isolated monocytes were incubated with secretions and GM-CSF or M-CSF for 6 days and then stimulated with LPS or LTA for 18 h. The expression of cell surface molecules and the levels of cytokines, chemokines and growth factors in supernatants were measured. Our results showed secretions to affect monocyte-macrophage differentiation leading to MØ-1 with a partial MØ-2-like morphology but lacking CD163, which is characteristic for MØ-2. In response to LPS or LTA, secretions-differentiated MØ-1 produced less pro-inflammatory cytokines (TNF-α, IL-12p40 and MIF) than control cells. Similar results were observed for MØ-2 when stimulated with low concentrations of LPS. Furthermore, secretions dose-dependently led to MØ-1 and MØ-2 characterized by an altered chemokine production. Secretions led to MØ-2, but not MØ-1, producing enhanced levels of the growth factors bFGF and VEGF, as compared to control cells. The expression of cell-surface receptors involved in LPS/LTA was enhanced by secretions, that of CD86 and HLA-DR down-regulated, while receptors involved in phagocytosis remained largely unaffected.
Conclusions
Maggot secretions skew the differentiation of monocytes into macrophages away from a pro-inflammatory to a pro-angiogenic type.
doi:10.1371/journal.pone.0008071
PMCID: PMC2778998  PMID: 19956650
17.  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
18.  Palmitate and insulin synergistically induce IL-6 expression in human monocytes 
Background
Insulin resistance is associated with a proinflammatory state that promotes the development of complications such as type 2 diabetes mellitus (T2DM) and atherosclerosis. The metabolic stimuli that initiate and propagate proinflammatory cytokine production and the cellular origin of proinflammatory cytokines in insulin resistance have not been fully elucidated. Circulating proinflammatory monocytes show signs of enhanced inflammation in obese, insulin resistant subjects and are thus a potential source of proinflammatory cytokine production. The specific, circulating metabolic factors that might stimulate monocyte inflammation in insulin resistant subjects are poorly characterized. We have examined whether saturated nonesterified fatty acids (NEFA) and insulin, which increase in concentration with developing insulin resistance, can trigger the production of interleukin (IL)-6 and tumor necrosis factor (TNF)-α in human monocytes.
Methods
Messenger RNA and protein levels of the proinflammatory cytokines IL-6 and TNF-α were measured by quantitative real-time PCR (qRT-PCR) and Luminex bioassays. Student's t-test was used with a significance level of p < 0.05 to determine significance between treatment groups.
Results
Esterification of palmitate with coenzyme A (CoA) was necessary, while β-oxidation and ceramide biosynthesis were not required, for the induction of IL-6 and TNF-α in THP-1 monocytes. Monocytes incubated with insulin and palmitate together produced more IL-6 mRNA and protein, and more TNF-α protein, compared to monocytes incubated with palmitate alone. Incubation of monocytes with insulin alone did not affect the production of IL-6 or TNF-α. Both PI3K-Akt and MEK/ERK signalling pathways are important for cytokine induction by palmitate. MEK/ERK signalling is necessary for synergistic induction of IL-6 by palmitate and insulin.
Conclusions
High levels of saturated NEFA, such as palmitate, when combined with hyperinsulinemia, may activate human monocytes to produce proinflammatory cytokines and support the development and propagation of the subacute, chronic inflammatory state that is characteristic of insulin resistance. Results with inhibitors of β-oxidation and ceramide biosynthesis pathways suggest that increased fatty acid flux through the glycerolipid biosynthesis pathway may be involved in promoting proinflammatory cytokine production in monocytes.
doi:10.1186/1475-2840-9-73
PMCID: PMC2988002  PMID: 21054880
19.  A critical role of nitric oxide in human immunodeficiency virus type 1-induced hyperresponsiveness of cultured monocytes. 
Molecular Medicine  1996;2(4):460-468.
BACKGROUND: Human immunodeficiency virus type 1 (HIV-1) infection leads to a general exhaustion of the immune system. Prior to this widespread decline of immune functions, however, there is an evident hyperactivation of the monocyte/macrophage arm. Increased levels of cytokines and other biologically active molecules produced by activated monocytes may contribute to the pathogenesis of HIV disease both by activating expression of HIV-1 provirus and by direct effects on cytokine-sensitive tissues, such as lung or brain. In this article, we investigate mechanisms of hyperresponsiveness of HIV-infected monocytes. MATERIALS AND METHODS: The study was performed on monocyte cultures infected in vitro with a monocytetropic strain HIV-1ADA. Cytokine production was induced by stimulation of cultures with lipopolysaccharides (LPS) and measured by ELISA. To study involvement of nitric oxide (NO) in the regulation of cytokine expression, inhibitors of nitric oxide synthase (NOS) or chemical donors of NO were used. RESULTS: We demonstrate that infection with HIV-1 in vitro primes human monocytes for subsequent activation with LPS, resulting in increased production of pro-inflammatory cytokines tumor necrosis factor (TNF) and interleukin 6 (IL-6). This priming effect can be blocked by Ca(2+)-chelating agents and by the NOS inhibitor L-NMMA, but not by hemoglobin. It could be reproduced on uninfected monocyte cultures by using donors of NO, but not cGMP, together with LPS. CONCLUSIONS: NO, which is expressed in HIV-1-infected monocyte cultures, induces hyperresponsiveness of monocytes by synergizing with calcium signals activated in response to LPS stimulation. This activation is cGMP independent. Our findings demonstrate the critical role of NO in HIV-1-specific hyperactivation of monocytes.
Images
PMCID: PMC2230172  PMID: 8827716
20.  Palmitate Induced IL-6 and MCP-1 Expression in Human Bladder Smooth Muscle Cells Provides a Link between Diabetes and Urinary Tract Infections 
PLoS ONE  2010;5(5):e10882.
Background
Urinary tract infections (UTI) are more frequent in type-2 diabetes mellitus patients than in subjects with normal glucose metabolism. The mechanisms underlying this higher prevalence of UTI are unknown. However, cytokine levels are altered in diabetic patients and may thus contribute to the development of UTI. Increased levels of free fatty acids (FFA), as observed in obese patients, can induce IL-6 production in various cell types.
Therefore we studied the effects of the free fatty acid palmitate and bacterial lipopolysaccharide (LPS) on interleukin-6 (IL-6) and monocyte chemotactic protein-1 (MCP-1) expression and secretion in cultured human bladder smooth muscle cells (hBSMC).
Methodology/Principal Findings
Biopsies were taken from patients undergoing cystectomy due to bladder cancer. Palmitate or LPS stimulated hBSMC were analysed for the production and secretion of the IL-6, gp80, gp80soluble, gp130, MCP-1, pSTAT3, SOCS3, NF-κB and SHP2 by quantitative PCR, ELISA, Western blotting, and confocal immunofluorescence. In signal transduction inhibition experiments we evaluated the involvement of NF-κB and MEK1 in IL-6 and MCP-1 regulation. Palmitate upregulates IL-6 mRNA expression and secretion via NF-κB dependent pathways in a concentration- and time-dependent manner. MCP-1 was moderately upregulated by palmitate but was strongly upregulated by LPS involving NF-κB and MEK1 dependent pathways. Soluble IL-6 receptor (gp80soluble) was downregulated by palmitate and LPS, while membrane-bound gp80 was moderately upregulated. LPS increased SOCS3 and SHP2, whereas palmitate only induced SOCS3. Secondary finding: most of the IL-6 is secreted.
Conclusions/Significance
Bacterial infection (LPS) or metabolic alterations (palmitate) have distinct effects on IL-6 expression in hBSMC, (i) short term LPS induced autocrine JAK/STAT signaling and (ii) long-term endocrine regulation of IL-6 by palmitate. Induction of IL-6 in human bladder smooth muscle cells by fatty acids may represent a pathogenetic factor underlying the higher frequency and persistence of urinary tract infections in patients with metabolic diseases.
doi:10.1371/journal.pone.0010882
PMCID: PMC2878332  PMID: 20526368
21.  Highly Pathogenic Avian Influenza Virus H5N1 Infects Alveolar Macrophages without Virus Production or Excessive TNF-Alpha Induction 
PLoS Pathogens  2011;7(6):e1002099.
Highly pathogenic avian influenza virus (HPAIV) of the subtype H5N1 causes severe, often fatal pneumonia in humans. The pathogenesis of HPAIV H5N1 infection is not completely understood, although the alveolar macrophage (AM) is thought to play an important role. HPAIV H5N1 infection of macrophages cultured from monocytes leads to high percentages of infection accompanied by virus production and an excessive pro-inflammatory immune response. However, macrophages cultured from monocytes are different from AM, both in phenotype and in response to seasonal influenza virus infection. Consequently, it remains unclear whether the results of studies with macrophages cultured from monocytes are valid for AM. Therefore we infected AM and for comparison macrophages cultured from monocytes with seasonal H3N2 virus, HPAIV H5N1 or pandemic H1N1 virus, and determined the percentage of cells infected, virus production and induction of TNF-alpha, a pro-inflammatory cytokine. In vitro HPAIV H5N1 infection of AM compared to that of macrophages cultured from monocytes resulted in a lower percentage of infected cells (up to 25% vs up to 84%), lower virus production and lower TNF-alpha induction. In vitro infection of AM with H3N2 or H1N1 virus resulted in even lower percentages of infected cells (up to 7%) than with HPAIV H5N1, while virus production and TNF-alpha induction were comparable. In conclusion, this study reveals that macrophages cultured from monocytes are not a good model to study the interaction between AM and these influenza virus strains. Furthermore, the interaction between HPAIV H5N1 and AM could contribute to the pathogenicity of this virus in humans, due to the relative high percentage of infected cells rather than virus production or an excessive TNF-alpha induction.
Author Summary
Alveolar macrophages (AM), which reside in the alveolar lumen, usually dampen down the host immune response to incoming pathogens. However, they are thought to increase inflammation during highly pathogenic avian influenza virus (HPAIV) H5N1 infections, which cause severe and often fatal disease in humans. This is based on experiments with human macrophages cultured from monocytes rather than with human AM. Here we show that human AM, collected via broncho-alveolar lavage from healthy volunteers, can become infected with HPAIV H5N1. However, this results in neither induction of the pro-inflammatory cytokine TNF-alpha nor virus production. Therefore, AM are most likely not responsible for the excessive cytokine response or high viral load during human HPAIV H5N1 infections as assumed previously. These data significantly changes our insight into the pathogenesis of HPAIV H5N1 pneumonia in humans, indicating that other cells than AM must be responsible for the excessive pro-inflammatory cytokine profile observed during HPAIV H5N1 infections.
doi:10.1371/journal.ppat.1002099
PMCID: PMC3121882  PMID: 21731493
22.  Enzyme-Linked Immunospot Assays Provide a Sensitive Tool for Detection of Cytokine Secretion by Monocytes 
Blood monocytes as well as tissue-differentiated macrophages play a pivotal role in controlling immune reactions. Monocytes regulate the extent, nature, and duration of immune responses by secretion of cytokines. Interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), IL-10, and IL-12 are of particular interest, since IL-12 shifts the immune response towards a Th1 type, facilitating the production of, e.g., TNF-α and IL-6, while IL-10 counteracts Th1 responses and promotes the production of Th2-related cytokines such as IL-4. A tight regulation of these four cytokines keeps the balance and decides whether Th1 or Th2 will predominate in immune reactions. Enzyme-linked immunospot (ELISPOT) assays are among the most-sensitive and -specific methods available for cytokine research. They permit ex vivo identification of individual cells actively secreting cytokines. In the present study we prepared monocytes from healthy subjects' blood and adapted ELISPOT assays to define optimal conditions to detect and enumerate monocytes secreting IL-6, TNF-α, IL-10, and IL-12. The optimal time for monocyte incubation was 24 h, and optimal monocyte numbers (in cells per well) were 2,000 for IL-6, 1,000 for TNF-α, 50,000 for IL-10, and 100,000 for enumeration of IL-12 secreting monocytes. Among healthy subjects, 10% ± 5% of the monocytes secreted IL-6, 12% ± 12% secreted TNF-α, 0.1% ± 0.1% secreted IL-10, and 0.2% ± 0.3% secreted IL-12 (values are means ± standard deviations). In conclusion, ELISPOT assays constitute a valuable tool to enumerate monocytes secreting IL-6, TNF-α, IL-10, and IL-12 and probably to enumerate monocytes secreting other cytokines and proteins.
doi:10.1128/CDLI.8.6.1248-1257.2001
PMCID: PMC96257  PMID: 11687471
23.  IgE Cross-linking Critically Impairs Human Monocyte Function by Blocking Phagocytosis 
Background
IgE cross-linking triggers many cellular processes that drive allergic disease. While the role of IgE in mediating allergic responses is best described on basophils and mast cells, expression of the high-affinity IgE receptor on other innate immune cells, including monocytes, suggests that it may impact the function of these cells in allergic environments.
Objectives
To determine the effect of IgE cross-linking on the function of human monocytes.
Methods
Monocytes purified from healthy donor blood samples were cultured for 4–96 hr with media alone, a cross-linking anti-IgE antibody, or control IgG. Surface CD14 and CD64 expression and secreted cytokine concentrations were determined. Monocyte function was determined by assessing: 1) phagocytosis of E. coli or apoptotic HEp2 cells and 2) killing of intracellular E. coli. Select experiments were performed on monocytes obtained from participants with elevated versus normal serum IgE concentrations.
Results
IgE cross-linking on monocytes increased CD14 expression and induced secretion of TNF-á, IL-6, and autoregulatory IL-10. These effects were greatest in individuals with elevated serum IgE concentrations. In contrast, IgE cross-linking reduced CD64 expression and significantly impaired phagocytic function without disrupting the capacity of monocytes to kill bacteria.
Conclusion
IgE cross-linking drives monocyte pro-inflammatory processes and autoregulatory IL-10 in a serum IgE-dependent manner. In contrast, monocyte phagocytic function is critically impaired by IgE cross-linking. Our findings suggest that IgE cross-linking on monocytes may contribute to allergic disease by both enhancing detrimental inflammatory responses and concomitantly crippling phagocytosis, a primary mechanism utilized by these cells to resolve inflammation.
doi:10.1016/j.jaci.2012.11.037
PMCID: PMC3564054  PMID: 23374271
Monocyte; IgE; FcεRI; IgE cross-linking; Allergy; Pro-inflammatory; Autoregulatory; Phagocytosis; Apoptotic debris
24.  Abnormal Production of Pro- and Anti-Inflammatory Cytokines by Lupus Monocytes in Response to Apoptotic Cells 
PLoS ONE  2011;6(3):e17495.
Monocytes are a key component of the innate immune system involved in the regulation of the adaptive immune response. Previous studies have focused on apoptotic cell clearance abnormalities in systemic lupus erythematosus (SLE) monocytes. However, whether SLE monocytes might express unique patterns of cytokine secretion in response to apoptotic cells is still unknown. Here, we used monocytes from healthy controls and SLE patients to evaluate the production of TNF-α and TGF-β in response to apoptotic cells. Upon recognition of apoptotic material, monocytes from healthy controls showed prominent TGF-β secretion (mean ± SD: 824.6±144.3 pg/ml) and minimal TNF-α production (mean ± SD: 32.6±2.1 pg/ml). In contrast, monocytes from SLE patients had prominent TNF-α production (mean ± SD: 302.2±337.5 pg/ml) and diminished TGF-β secretion (mean ± SD: 685.9±615.9 pg/ml), a difference that was statistically significant compared to normal monocytes (p≤10−6 for TNF-α secretion, and p = 0.0031 for TGF-β, respectively). Interestingly, the unique cytokine response by SLE monocytes was independent of their phagocytic clearance efficiency, opsonizing autoantibodies and disease activity. We further showed that nucleic acids from apoptotic cells play important role in the induction of TNF-α by lupus monocytes. Together, these observations suggest that, in addition to potential clearance defects, monocytes from SLE patients have an abnormal balance in the secretion of anti- and pro-inflammatory cytokines in response to apoptotic cells. Since the abnormal cytokine response to apoptotic material in SLE is not related to disease activity and opsonizing autoantibodies, it is possible that this response might be an intrinsic property of lupus monocytes. The studies focus attention on toll-like receptors (TLRs) and their downstream pathways as mediators of this response.
doi:10.1371/journal.pone.0017495
PMCID: PMC3056659  PMID: 21423726
25.  Acute Alcohol Intake Induces SOCS1 and SOCS3 and Inhibits Cytokine-Induced STAT1 and STAT3 Signaling in Human Monocytes 
Background
Acute alcohol consumption is associated with induction of immuno-inhibitory cytokines and down-regulation of pro-inflammatory responses to various pathogens. We previously reported that alcohol activates janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling leading to IL-10 induction. The JAK-STAT pathway also activates its own negative regulators, suppressors of cytokine signaling (SOCS) 1 and SOCS3. SOCS proteins are inducible inhibitors that negatively regulate STAT3/STAT1 signaling pathways induced by cytokines, IL-6 or IFNs. Here we aimed to explore the effect of acute alcohol on induction of SOCS1/SOCS3 and regulation of STAT3/STAT1 pathways induced by IL-6 or IFNs in human monocytes.
Methods
Blood samples from normal volunteers were collected before and 24 hours after consumption of 2 ml vodka/kg body weight. For in vitro experiments human monocytes were pretreated with ethanol (EtOH) followed by stimulation with cytokines; proteins were analyzed by Western blot, nuclear protein binding to DNA by EMSA, and RNA by real time PCR.
Results: Acute in vivo or in vitro alcohol treatment increased both SOCS1 and SOCS3 RNA expression in monocytes. Alcohol treatment resulted in increased STAT3 and STAT1 DNA binding capacity. Activation of both STAT1 and STAT3 has been shown to induce SOCS1/3. We hypothesized that induction of SOCS proteins by alcohol in turn may lead to modulation of cytokine signaling through STAT1 and STAT3. Indeed, we observed significant down-regulation of IL-6-, IFNα- and IFNγ-induced STAT1 DNA binding as well as inhibition of IL-6- and IFNγ-induced STAT3 when alcohol was added to monocytes 3 hours prior to the cytokine stimulation. Consistent with inhibition of IL-6-induced STAT3 DNA binding in alcohol-pretreated cells, the levels of IL-6-dependent genes, MCP-1 and ICAM-1, was reduced after IL-6 stimulation. Similar to EtOH alone, combined EtOH+IL-6 simulation resulted in increased expression of both SOCS3 and SOCS1 genes.
Conclusion
While acute alcohol treatment alone activates STAT1/3 signaling pathways and induces SOCS3 and SOCS1 levels in monocytes, alcohol also leads to down-regulation of IL-6-, IFNα-, and IFNγ-induced signaling via STAT1/STAT3 pathways, likely through excessive SOCS activation.
doi:10.1111/j.1530-0277.2008.00726.x
PMCID: PMC4116614  PMID: 18616672
Toll-Like Receptor 4; Lipopolysacharide (LPS); In Vivo; In Vitro; Ethanol

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