Primary Biliary Cirrhosis (PBC) is a chronic autoimmune liver disease mostly seen in middle aged women characterized by progressive non-suppurative destruction of small bile ducts resulting in intrahepatic cholestasis, parenchymal injury, and ultimately end stage liver disease. Despite major breakthroughs in our understanding of PBC, there remains only one FDA-approved agent for treatment: ursodeoxycholic acid (UDCA) to which one third of patients are unresponsive.
Biochemical response to treatment with UDCA is associated with excellent survival rates in PBC patients. However, there is a need for alternative treatments for non-responders. Results from human epidemiological and genetic studies as well as preclinical studies in PBC animal models have provided a strong impetus for the development of new therapeutic agents. In this review, we discuss the recent advances in translational research in PBC focusing on promising therapeutic approaches, namely immune-based targeted therapies and agents targeting the synthesis and circulation of bile acids.
We are in a new era for the development of novel therapies for PBC. Data on fibrates, budesonide, and obeticholic acid offer encouragement for non-responders to UDCA.
Primary Biliary Cirrhosis; ursodeoxycholic acid; FXR agonists; biologics
Although natural killer T (NKT) cells were discovered over 20 years ago, our understanding of their immunobiology continues to evolve and surprise. NKT cells are T lymphocytes: they arise in the bone marrow, are selected in the thymus, and express a T cell receptor. Unlike classic T cells, however, they are not strictly “adaptive” immune cells: in particular, as a population they express a very narrow range of T cell receptors. The vast majority of mouse NKT cells, for example, express the Vα14-J281 chain and only a finite number of Vβ chains (1). In addition, they express NK cell surface markers, such as NK 1.1. Moreover, unlike classical T cells, they are not restricted by MHC Class I or Class II, but by an MHC-like molecule, CD1d (2). Furthermore, NKT cells do not recognize peptides in the context of CD1d, but rather specialized lipids (3). Functionally NKT cells also reflect major differences from conventional T cells: they are able to produce both classic Th1 (IFN-γ) and Th2 (IL-4) cytokines without prior peripheral stimulation, but when stimulated by their glycolipid antigens downregulate TCR, expand, and divert to a Th1 phenotype (4). Like classical T cells, they are selected in the thymus by a self-molecule: however, it is not a protein, but a trihexosylceramide, iGb3, bound to CD1d (5). Mice deficient in iGb3 demonstrated a severe deficiency of NKT cells, illustrating its critical role in NKT cells selection and survival (5). These features of NKT cells place them into the expanding category of “innate-like” lymphocytes (6). “Innate” immunity has classically been defined by “stereotypical” responses mediated by invariant receptors to defined ligands: for example, the signaling and functional responses of TLR4 when bound to its ligand, LPS. Since the overall TCR repertoire of NKT cells is so limited, the population as a whole responds “innately” to just a few lipid antigens, rather than retaining a population-capability to respond to the full universe of T cell antigens. Finally, and of great interest to the field of hepatic immunity, NKT cells do not circulate freely, but tend to home to and reside for life in specific tissues such as the liver, where they compose ~30% of the intrahepatic lymphoid pool (7).
Shotgun proteomics is a powerful analytic method to characterize complex protein mixtures in combination with multi-dimensional liquid chromatography-tandem mass spectrometry (LC-MS/MS). We have used this platform for proteomic characterization of apoptotic bodies in efforts to define the complex protein mixtures found in primary cultures of human intrahepatic biliary epithelial cells (HiBEC), human renal proximal tubular epithelial cells, human bronchial epithelial cells, isolated intrahepatic biliary epithelial cells from explanted primary biliary cirrhosis (PBC) and control liver, using a total of 24 individual samples. Further, as additional controls and for purposes of comparison, proteomic signatures were also obtained from intact cells and apoptotic bodies. The data obtained from LC-MS/MS, combined with database searches and protein assembly algorithms, allowed us to address significant differences in protein spectral counts and identify unique pathways that may be a component to the induction of the signature inflammatory cytokine response against BECs, including the Notch signaling pathway, IL8, IL6, CXCR2 and integrin signaling. Indeed there are 11 proteins that localize specifically to apoptotic bodies of HiBEC and 8 proteins that were specifically absent in HiBEC apoptotic bodies. In conclusion, proteomic analysis of BECs from PBC liver compared to normal liver are significantly different, suggesting that an immunological attack affects the repertoire of proteins expressed and that such cells should be thought of as living in an environment undergoing continuous selection secondary to an innate and adaptive immune response, reflecting an almost “Darwinian” bias.
apoptosis; shotgun proteomics; apoptotic bodies; biliary epithelial cells
The interleukin (IL)-12/IL-23 mediated Th1/Th17 signaling pathway has been associated with the etiopathogenesis of primary biliary cirrhosis (PBC). To address the cytokine microenvironment specifically in the liver, we examined the localized expression of cytokine subunits and their corresponding receptors using previously optimized immunohistochemistry with an extensive panel of antibodies directed at IL-12p70, IL-12p35, IFN-γ, IL-12RB2, IL-23p40, IL-23p19, IL-17 and IL-23R using liver from PBC (n=51) and non-PBC (n=80) control liver disease patients. Multiple portal tracts in each patient were blindly evaluated and individually scored. We report herein that although IL-12/Th1 and IL-23/Th17 staining were detected in all of the liver sections, they were primarily localized around the damaged interlobular bile ducts in PBC. Most importantly, Th17 skewing was prominent in advanced PBC patients with intensive secretion of IL-23p19 by inflamed hepatocytes around IL-23R, IL-12RB2, and IFN-γ expressing degenerated cholangiocytes. Our novel finding on the direct association of Th17 skewing and disease severity illustrates the significance of the IL-23/Th17 pathway in the perpetuation of IL-12/Th1-mediated immunopathology in PBC. Furthermore, localized IL-23p19 production by hepatocytes may enhance pro-fibrotic Th17 signaling and pro-inflammatory IFN-γ production that contribute to PBC pathology. In conclusion, our data emphasize the pathogenic relevance of IL-12/Th1 and IL-23/Th17 in the evolution of PBC. Of significance, however, the shift from a Th1 to a Th17 imbalance at advanced stages of the disease suggests the necessity to consider modulation of the IL-23/Th17 pathway as a potential target for therapeutic intervention.
immunohistochemistry; Th1; IL-12; Th17; IL-23; primary biliary cirrhosis
There are several murine models described with features similar to human primary biliary cirrhosis (PBC). Amongst these models, the one which has the closest serologic features to PBC is a mouse with a T cell-restricted expression of the dominant negative transforming growth factor β receptor type II (dnTGFβRII). Our work has demonstrated that CD8+ T cells from dnTGFβRII mice transfer autoimmune cholangitis to Rag1-/- recipients. However, it remained unclear whether the autoimmune cholangitis was secondary to an intrinsic function within CD8+ T cells or due to the abnormal TGFβR environment within which CD8+ T cells were generated. To address this mechanistic issue, we utilized our dnTGFβRII, OT-I/Rag1-/-, OT-II/Rag1-/- mice and in addition generated OT-I/dnTGFβRII/Rag1-/-, and OT-II/dnTGFβRII/Rag1-/- mice in which the entire T cell repertoire was replaced with ovalbumin (OVA) specific CD8+ or CD4+ T cells, respectively. Importantly, neither the parental OT-I/dnTGFβRII/Rag1-/- mice and/or OT-II/dnTGFβRII/Rag1-/- mice developed cholangitis. However, adoptive transfer demonstrated that only transfer of CD8+ T cells from dnTGFβRII mice but not CD8+ T cells from OT-I/Rag -/- mice or from OT-I/dnTGFβRII/Rag1-/- mice transferred disease. These data were not secondary to absence of CD4+ T cell help since a combination of CD8+ T cells from OT-I/dnTGFβRII/Rag1-/- and CD4+ T cells from OT II/dnTGFβRII/Rag1-/- or CD8+ T cells from OT-I/dnTGFβRII/Rag1-/- with CD4+ T cells from OT-II/Rag1-/- mice failed to transfer disease. In conclusion, defective TGFβRII signaling, in addition to clonal CD8+ T cells that target biliary cells, are required for induction of autoimmune cholangitis.
primary biliary cirrhosis; murine models; autoimmunity; cholangitis
Antimitochondrial autoantibodies (AMA), the serological hallmark of primary biliary cirrhosis (PBC) are directed against the lipoyl domain of the E2 subunit of pyruvate dehydrogenase (PDC-E2). However, comprehensive analysis of the amino acid residues of PDC-E2 lipoyl beta sheet with AMA specificity is lacking. Herein, we postulated that specific residues within the lipoyl domain are critical to AMA recognition by maintaining conformational integrity. We systematically replaced each of 19 residue peptides of the inner lipoyl domain with alanine and analyzed these mutants for reactivities against 60 PBC and 103 control sera. Based on these data, we then constructed mutants with 2, 3, or 4 replacements and, in addition, probed the structure of the substituted domains using thiol-specific spin labeling and electron paramagnetic resonance (EPR) of a 5Ile-> Ala and 12Ile->Ala double mutant. Single alanine replacement at 5Ile, 12Ile and 15Glu significantly reduced AMA recognition. In addition, mutants with 2, 3, or 4 replacements at 5Ile, 12Ile and 15Glu reduced AMA reactivity even further. Indeed, EPR reveals a highly flexible structure within the 5Ile and 12Ile double-alanine mutant. Autoreactivity is largely focused on specific residues in the PDC-E2 lipoyl domain critical in maintaining the lipoyl loop conformation necessary for AMA recognition. Collectively, the AMA binding studies and EPR analysis demonstrate the necessity of the lipoyl beta sheet structural conformation in anti-PDC-E2 recognition.
Autoantibodies; primary biliary cirrhosis; xenobiotics; conformational structure
The treatment of primary biliary cirrhosis (PBC) with conventional immunosuppressive drugs has been relatively disappointing and there have been few efforts in defining a role for the newer biological agents useful in rheumatoid arthritis and other systemic autoimmune diseases. In this study we took advantage of dnTGF-βRII mice, a mouse model of autoimmune cholangitis, to address the therapeutic efficacy of B cell depletion using anti-CD20. Mice were treated at either 4–6 weeks of age or beginning at 20–22 weeks of age with IP injections of anti-CD20 every two weeks. We quantitated B cell levels in all mice as well as antimitochondrial antibodies (AMA), serum and hepatic levels of pro-inflammatory cytokines and histopathology of liver and colon. In mice whose treatment was initiated at 4–6 weeks of age, anti-CD20 therapy demonstrated a significant lower incidence of liver inflammation associated with reduced numbers of activated hepatic CD8+ T cells. However, colon inflammation was exacerbated. In contrast, in mice treated at 20–22 weeks of age, anti-CD20 therapy had relatively little effect on either liver or colon disease. As expected all treated animals had reduced levels of B cells, absence of AMA, and increased levels in sera of TNFα, IL-6 and CCL2 (MCP-1). These data suggest potential usage of anti-CD20 in early PBC resistant to other modalities, but raise the cautionary note regarding the use of anti-CD20 in IBD.
Autoimmune cholangitis; Primary biliary cirrhosis; B cells
There have been several descriptions of mouse models that manifest select immunological and clinical features of autoimmune cholangitis with similarities to primary biliary cirrhosis in humans. Some of these models require immunization with complete Freund's adjuvant, whereas others suggest that a decreased frequency of T regulatory cells (Tregs) facilitate spontaneous disease. We hypothesized that anti-mitochondrial antibodies (AMA) and development of autoimmune cholangitis would be found in mice genetically deficient in components essential for the development and homeostasis of Foxp3+ Tregs. Therefore, we examined Scurfy (Sf) mice, animals that have a mutation in the gene encoding the Foxp3 transcription factor which results in a complete abolition of Foxp3+ Tregs. Indeed at 3-4 weeks of age, 100% of animals manifest high titer serum AMA of all isotypes. Further, mice have moderate to severe lymphocytic infiltrates surrounding portal areas with evidence of biliary duct damage, and dramatic elevation of cytokines in serum and mRNAs encoding cytokines in liver tissue, including TNF-α, IFN-γ, IL-6, IL-12 and IL-23. In conclusion, the lack of functional Foxp3 is a major predisposing feature for loss of tolerance that leads to autoimmune cholangitis. These findings reflect on the importance of regulatory T cells in other murine models as well as in patients with PBC.
Sf mouse; Primary Biliary Cirrhosis; Tregs; Interleukin 12; CD8 T lymphocyte
Antimitochondrial antibodies (AMA) directed against the lipoyl domain of the E2 subunit of pyruvate dehydrogenase (PDC-E2) are detected in 95% of patients with PBC and are present before onset of clinical disease. The recent demonstration that AMA recognize xenobiotic modified PDC-E2 with higher titers than native PDC-E2, raises the possibility that the earliest events involved in loss of tolerance are related to xenobiotic modification. We hypothesized that reactivity to such xenobiotics would be predominantly IgM and using sera from a large cohort of PBC patients and controls (n=516), we examined in detail sera reactivity against either SAc-conjugated bovine serum albumin (BSA), recombinant PDC-E2 (rPDC-E2) or BSA alone. Further, we also defined the relative specificity to the SAc moiety using inhibition ELISA; SAc conjugate and rPDC-E2 specific affinity purified antibodies were also examined for antigen specificity, isotype and cross-reactivity. Reactivity to SAc conjugates is predominantly IgM; such reactivity reflects a footprint of previous xenobiotic exposure. Indeed, this observation is supported by both direct binding, cross reactivity, and inhibition studies. In both early and late stage PBC, the predominant Ig isotype to SAc is IgM, with titers higher with advanced stage disease. We also note that there was a higher level of IgM reactivity to SAc in early stage versus late stage PBC. Interestingly, this finding is particularly significant in light of the structural similarity between SAc and the reduced form of lipoic acid, a step which is similar to the normal physiological oxidation of lipoic acid. We submit that specific modifications of the disulfide bond within the lipoic-acid-conjugated PDC-E2 moiety, i.e. by an electrophilic agent renders PDC-E2 immunogenic in a genetically susceptible host.
Tolerance; electrophiles; lipoic acid; environment and autoimmunity
Dominant negative TGF-β receptor II (dnTGF-βRII) mice spontaneously develop an autoimmune cholangitis resembling human primary biliary cirrhosis (PBC). Interestingly, the dominant negative TGF-β receptor is expressed by both CD4+ and CD8+ T cells and leads to greatly reduced (but not absent) TGF-β signaling resulting in T cell intrinsic cell mediated autoimmunity. However, the mechanisms of the T cell dysregulation remain unclear. Recently it has been shown that TGF-β signaling is intimately involved with miRNA biogenesis and control. Herein we show that lack of T cell TGF-β signaling leads to down regulation of T cell miRNAs but upregulation of the key inflammatory miRNA 21. Furthermore, the expression of miR-21 from hepatic effector CD8+ T cells is significantly higher than in the same subsets isolated from spleen and mesenteric lymph nodes of the dnTGF-βRII mice. Previous studies indicate that miR-21 increases the synthesis of IFN-γ and IL-17A by T cells and suppresses apoptosis via programmed cell death protein 4 (PDCD4). Data presented herein demonstrate that transfecting w.t. B6 T cell subsets with miR-21 resulted in upregulation of the inflammatory cytokines TNF-α and IFN-γ, thus partly replicating the dnTGF-βRII T cell phenotype. In conclusion, these data suggest miR-21 plays a critical role in the production of pro-inflammatory cytokines in dnTGFβRII mice, which could be a contributing factor for the development of the organ-specific autoimmune cholangitis and colitis in this murine model of human PBC.
Primary biliary cirrhosis; inflammatory bowel disease; autoimmunity; cholangitis; colitis; microRNA; miR-21
We have previously reported that mice with a dominant negative transforming growth factor β receptor restricted to T cells (dnTGFβRII mice) develop an inflammatory biliary ductular disease that strongly resembles human primary biliary cirrhosis (PBC). Furthermore, deletion of the gene encoding interleukin (IL)-12p40 resulted in a strain (IL-12p40−/−dnTGFβRII) with dramatically reduced autoimmune cholangitis. To further investigate the role of the IL-12 cytokine family in dnTGFβRII autoimmune biliary disease, we deleted the gene encoding the IL-12p35 subunit from dnTGFβRII mice, resulting in an IL-12p35−/− dnTGFβRII strain which is deficient in two members of the IL-12 family, IL-12 and IL-35. In contrast to IL-12p40−/− mice, the IL-12p35−/− mice developed liver inflammation and bile duct damage with similar severity but delayed onset as the parental dnTGFβRII mice. The p35−/− mice also demonstrated a distinct cytokine profile characterized by a shift from a Th1 to a Th17 response. Strikingly, liver fibrosis was frequently observed in IL-12p35−/− mice. In conclusion, IL-12p35−/− dnTGFβRII mice, histologically and immunologically, reflect key features of PBC, providing a useful generic model to understand the immunopathology of human PBC.
Primary biliary cirrhosis; murine models; autoimmunity; cholangitis
Collectively, the data in both humans and murine models of human primary biliary cirrhosis (PBC) suggest that activated T cells, particularly CD8 T cells, play a critical role in biliary cell destruction. Under physiological conditions, T cell activation involves two critical signals that involve the MHC and a set of co-stimulatory molecules which include a receptor on T cells coined cytotoxic T lymphocyte antigen 4 (CTLA-4). Germane to the studies reported herein, signaling via CTLA-4 has the potential to modulate co-stimulation and induce inhibitory signals. In this study we have taken advantage of our well-defined murine model of PBC in which mice are immunized with 2-octynoic acid coupled to BSA, leading to the production of high titer anti-mitochondrial autoantibodies and portal cellular infiltrates. To investigate the potential of CTLA-4 Ig as an immunotherapeutic agent, we treated mice both before and after induction of autoimmune cholangitis. Firstly, we demonstrate that CTLA-4 Ig treatment begun one day before 2-OA-BSA immunization, completely inhibits the manifestations of cholangitis, including AMA production, intra-hepatic T cell infiltrates and bile duct damage. However, and more critically, treatment with CTLA-4 Ig initiated after the development of autoimmune cholangitis in previously immunized mice, also resulted in significant therapeutic benefit, including reduced intra-hepatic T cell infiltrates and biliary cell damage, although AMA levels were not altered. These data suggest that an optimized regimen with CTLA-4 Ig has the potential to serve as an investigative therapeutic tool in patients with PBC.
Primary biliary cirrhosis; cytotoxic T lymphocyte antigen 4; Abatacept autoimmunity; cholangitis
autoimmune cholangitis; epigenetics; environment; DNA methylation; PBC
Autophagy is a physiological cellular mechanism that degrades and recycles proteins and other molecules to maintain an adequate amino acid level during nutritional starvation of the cell. Autophagy is involved in cellular homeostasis and differentiation, as well as in tissue remodeling, aging, cancer, and other diseases. Under particular environmental conditions, autophagy can also be a contributor to programmed cell death, or can act as a defense mechanism for the elimination of intracellular bacteria and viruses. According to recent experimental data, autophagy may be implicated in autoimmunity by promotion of major histocompatibility complex (MHC) class II presentation of cytosolic antigens and control of T lymphocyte homeostasis, and its induction by Th1 cytokines and perhaps by specific serum autoantibodies. We review herein the role of autophagy in immune function and its possible contribution to breakdown of tolerance and development of autoimmunity.
Apoptosis; autoimmunity; autophagy
Primary biliary cirrhosis (PBC) is an autoimmune disease of the liver characterized by progressive bile duct destruction eventually leading to cirrhosis and liver failure. The serological hallmark of the disease is the presence of circulating antimitochondrial antibodies (AMA). These reflect the presence of autoreactive T and B cells to the culprit antigens, the E2 subunits of mitochondrial 2-oxo-acid dehydrogenase enzymes, chiefly pyruvate dehydrogenase (PDC-E2). The disease results from a combination of genetic and environmental risk factors. Genetic predisposition is indicated by the higher familial incidence of the disease particularly among siblings and the high concordance rate among monozygotic twins. Environmental triggering events appear crucial to disrupt a pre-existing unstable immune tolerance of genetic origin allowing, after a long latency, the emergence of clinical disease. Initiating mimotopes of the vulnerable epitope of the PDC-E2 autoantigen can be derived from microbes that utilize the PDC enzyme or, alternatively, environmental xenobiotics/chemical compounds that modify the structure of native proteins to make them immunogenic. A further alternative as a source of antigen is PDC-E2 derived from apoptotic cells. In the effector phase the biliary ductular cell, by reason of its proclivity to express the antigen PDC-E2 in the course of apoptosis, undergoes a multilineage immune attack comprised of CD4+ and CD8+ T cells and antibody. In this article, we critically review the available evidence on etiopathogenesis of PBC and present interpretations of complex data, new developments and theories, and nominate directions for future research.
Autoantibodies; Autoreactive T cells; 2-oxoacid dehydrogenase; Biliary epithelial cells; Primary biliary cirrhosis
C-type lectin receptors are pattern recognition receptors that are critical for autoimmunity and the immune response. Mincle is a C-type lectin receptor expressed by a variety of antigen presenting cells including macrophages, neutrophils, dendritic cells and B cells; a variety of stimuli including stress are known to induce the expression of Mincle. Mincle is an FcRγ-associated activation receptor that senses damaged cells and upon ligation induces activated macrophages to produce inflammatory cytokines. Recently, while several studies have reported that Mincle plays an important role in macrophage responses to fungal infection its function on B cells remains to be defined. In efforts to elucidate the function of Mincle expressed by B cells, we studied the expression of Mincle on subsets of B cells and analyzed cytokines and synthesized immunoglobulin upon ligation of Mincle. The expression of Mincle on CD27−CD19+ naïve B cells is significantly higher than CD27+CD19+ memory B cells. The stimulation of TLR9 ligand induced Mincle expression on B cells. Furthermore, co-stimulation of TLR9 and Mincle ligand reduced IgG and IgA production from B cells without a significant change in the inflammatory cytokines TNFα, IL-6, IL-8 and IL-10. Our data identifies Mincle as a potentially critical player in human B cell responses.
C-type lectin; Mincle; Toll-like receptor
dnTGFβRII mice, expressing a dominant negative form of TGFβ receptor II under control of the CD4 promoter, develop autoimmune colitis and cholangitis . We previously observed that deficiency in IL-12p40 led to a marked diminution of inflammation in both the colon and the liver. To distinguish whether IL-12p40 mediated protection acted via the IL-12 or IL-23 pathways, we generated an IL-23p19−/− dnTGFβRII strain deficient in IL-23 but not in IL-12; mice were longitudinally followed for changes in the natural history of disease and immune responses. Interestingly, IL-23p19−/− mice demonstrate dramatic improvement in their colitis but no changes in biliary pathology; mice also manifest reduced Th17 cell populations and unchanged IFN-γ levels. We submit that the IL-12/Th1 pathway is essential for biliary disease pathogenesis, while the IL-23/Th17 pathway mediates colitis. To further assess the mechanism of the IL-23 mediated protection from colitis, we generated an IL-17A−/− dnTGFβRII strain deficient in IL-17, a major effector cytokine produced by IL-23-dependent Th17 cells. Deletion of the IL-17A gene did not affect the severity of either cholangitis or colitis, suggesting that the IL-23/Th17 pathway contributes to the colon disease in an IL-17-independent manner. These results affirm that the IL-12/Th1 pathway is critical to biliary pathology in dnTGFβRII mice while the colitis is caused by a direct effect of IL-23.
Primary biliary cirrhosis; murine models; autoimmunity; cholangitis; colitis
In our previous work, including analysis of more than 10,000 sera from control patients and patients with a variety of liver diseases, we have demonstrated that with the use of recombinant autoantigens, antimitochondrial autoantibodies (AMA) are only found in PBC and that a positive AMA is virtually pathognomonic of either PBC or future development of PBC. Although the mechanisms leading to the generation of AMA are enigmatic, we have postulated that xenobiotic-induced and/or oxidative modification of mitochondrial autoantigens is a critical step leading to loss of tolerance. This thesis suggests that a severe liver oxidant injury would lead to AMA production. We analyzed 217 serum samples from 69 patients with acute liver failure (ALF) collected up to 24 months post-ALF, compared with controls, for titer and reactivity with the E2 subunits of pyruvate dehydrogenase (PDC-E2), branched chain 2-oxo-acid dehydrogenase (BCOADC-E2) and 2-oxo-glutarate dehydrogenase (OGDC-E2). AMA were detected in 28/69 (40.6%) ALF patients with reactivity found against all of the major mitochondrial autoantigens. In addition, and as further controls, sera were also analyzed for autoantibodies to gp210, Sp100, centromere, chromatin, soluble liver antigen (SLA), tissue transglutaminase (tTG) and deaminated gliadin peptides (DGP) where the most frequently detected non-mitochondrial autoantibody was against tTG (57.1% of ALF patients). In conclusion, the strikingly high frequency of AMA in ALF supports the thesis that oxidative stress-induced liver damage may lead to AMA induction. The rapid disappearance of AMA in these patients provides further support for the contention that PBC pathogenesis requires additional factors including genetic susceptibility.
Tolerance; Oxidative injury; Self-reactivity; Epitopes
Although the etiology of primary biliary cirrhosis (PBC) remains enigmatic, there are several pieces of data supporting the thesis that a strong genetic predisposition and environmental factors interact to produce a selective loss of tolerance. The striking female predominance of PBC has suggested that this sex predisposition may be secondary to epigenetic alterations on the X chromosome. In the present study, we rigorously defined the X chromosome methylation profile of CD4, CD8, and CD14 cells from 30 PBC patients and 30 controls. Genomic DNA from sorted CD4, CD8, and CD14 subpopulations was isolated, sonicated, and immunoprecipitated for analysis of methylation. All products were hybridized to a custom-tiled four-plex array containing 27,728 CpG islands annotated by UCSC and 22,532 well-characterized RefSeq promoter regions. Furthermore, bisulfite sequencing was then used for validation on a subsequent group of independent samples from PBC patients and controls. Thence, expression levels of selected X-linked genes were evaluated by quantitative real-time PCR with cDNA samples from all subjects.
We report herein that a total of 20, 15, and 19 distinct gene promoters reflected a significant difference in DNA methylation in CD4+ T, CD8+ T, and CD14+ cells in patients with PBC. Interestingly, there was hypermethylation of FUNDC2 in CD8+ T cells and a striking demethylation of CXCR3 in CD4+ T cells, which inversely correlated with CXCR3 expression levels in CD4+ T cells from early-stage PBC patients.
Our data provides a set of genes with epigenetic alteration likely to be indicators of autoimmunity and emphasizes the role of CXCR3 in the natural history of PBC.
Electronic supplementary material
The online version of this article (doi:10.1186/s13148-015-0098-9) contains supplementary material, which is available to authorized users.
X chromosome; Primary biliary cirrhosis; CXCR3
Substantial evidence supports dysregulated B cell immune responses in patients with primary biliary cirrhosis (PBC), including the presence of serum anti-mitochondrial antibodies (AMAs). However, recent reports from murine models of PBC suggest that B cells may also provide regulatory function and indeed the absence of B cells in such models leads to exacerbation of disease. The vast majority of patients with PBC have readily detectable antimitochondrial antibodies, but a minority (<5%), are AMA negative (AMA−) even with recombinant diagnostic technology. This issue prompted us to examine the nature of B cell infiltrates surrounding the portal areas in AMA positive (AMA+) and AMA− patients since they display indistinguishable clinical features. Of importance was the finding that the degree of bile duct damage around the portal areas was significantly milder in AMA+ PBC than those seen in AMA− PBC patients. The portal areas from AMA− patients had a significant increase of CD5+ cells infiltrating the ductal regions and the levels of B cell infiltrates were worse in the early phase of bile duct damage. The frequency of positive portal areas and the magnitude of CD5+ and CD20+ cellular infiltrates within areas of ductal invasion is associated with the first evidence of damage of biliary duct epithelia, but becomes reduced in the ductopenia stage, with the exception of CD5+ cells which remain sustained and predominate over CD20+ cells. In conclusion, our data suggest a putative role of B cell autoimmunity in regulating the portal destruction characteristic of PBC.
B cells; CD20; CD5; Primary biliary cirrhosis
Psoriatic arthritis (PsA) is a chronic inflammatory disease characterized by
clinical features that include bone loss and epidermal hyperplasia. Aberrant cytokine
expression has been linked to joint and skin pathology; however, it is unclear which
cytokines are critical for disease initiation. IL-17A participates in many pathologic
immune responses; however, its role in PsA has not been fully elucidated.
To determine the role of IL-17A in epidermal hyperplasia and bone destruction
associated with psoriatic arthritis.
An in vivo gene transfer approach was used to investigate the
role of IL-17A in animal models of inflammatory (Collagen-induced arthritis) and
non-inflammatory (RANKL-gene transfer) bone loss.
IL-17A gene transfer induced the expansion of
precursors and a concomitant elevation of biomarkers indicative of bone resorption. This
occurred at a time preceding noticeable joint inflammation suggesting that IL-17A is
critical for the induction of pathological bone resorption through direct activation of
osteoclast precursors. Moreover, IL-17A induced a second myeloid population
CD11b+Gr1high neutrophil-like cells which was associated
with cutaneous pathology including epidermal hyperplasia, parakeratosis, and
Munro’s microabscesses formation.
Collectively, these data support that IL-17A can play a key role in the
pathogenesis of inflammation-associated arthritis and/or skin disease, as observed in
Interleukin-17A; psoriatic arthritis; osteoclasts
There has been increased interest in the role of B cells in the pathogenesis of primary biliary cirrhosis. Although the vast majority of patients with primary biliary cirrhosis have antimitochondrial antibodies, there is no correlation of antimitochondrial antibody titer and/or presence with disease severity. Further, in murine models of primary biliary cirrhosis, it has been suggested that depletion of B cells may exacerbate biliary pathology. To address this issue, we have focused on detailed phenotypic characterization of mononuclear cell infiltrates surrounding the intrahepatic bile ducts of patients with PBC, PSC, AIH, CH-C and GVHD, including CD3, CD4, CD8, CD20, CD38 and immunoglobulin classes, as well as double immunohistochemical staining for CD38 and IgM. Interestingly, CD20 B lymphocytes, which are a precursor of plasma cells, were found in scattered locations or occasionally forming follicle-like aggregations but were not noted at the proximal location of chronic nonsuppurative destructive cholangitis. In contrast, there was a unique and distinct coronal arrangement of CD38 cells around the intrahepatic ducts in primary biliary cirrhosis but not controls; the majority of such cells were considered plasma cells based on their expression of intracellular immunoglobulins, including IgM and IgG, but not IgA. Patients with primary biliary cirrhosis who manifest this unique coronal arrangement were those with significantly higher titers of antimitochondrial antibodies. These data collectively suggest a role of plasma cells in the specific destruction of intrahepatic bile ducts in primary biliary cirrhosis and highlight the increasing interest in plasma cells and autoimmunity.
antimitochondrial antibodies; primary biliary cirrhosis; plasma cells; coronal arrangement
Primary biliary cirrhosis (PBC) has been often coined a model autoimmune disease based on the homogeneity amongst patients, the frequency and similarity of antimitochondrial antibodies, including the highly directed immune response to pyruvate dehydrogenase (PDC-E2). A significant number of patients with PBC suffer from sicca and amongst these, there are patients who also have classic Sjogren's syndrome. Indeed, both PBC and Sjogren's syndrome are characterized by inflammation of target epithelial elements. Both diseases can be considered on the basis of a number of other related clinical aspects, including proposed unique apoptotic features of the target tissue, the role of secretory IgA, and the frequency with which both diseases overlap with each other. Indeed, PBC may be considered a Sjogren's syndrome of the liver, whereas Sjogren's syndrome can be equally discussed as PBC of the salivary glands. Dissection of the genetic predispositions for both diseases and especially the molecular basis of effector mechanisms, will become critical elements in developing new therapies.
Apoptosis; autoantibodies; epithelium; inflammation
Liver granuloma are recognized as specific histological features in primary biliary cirrhosis but their significance remains enigmatic. Similarly, there are limited data on the impact of hyper-IgM on granulomas while in both cases a role of B cells has been hypothesized. The present study investigates a significant number of tissue samples from PBC and control livers as well as other granulomatous diseases to investigate the representation of dendritic cells and the role of IgM in PBC-associated granulomas. We demonstrate that the classical cellular marker for dendritc cells CD11c is highly expressed in hepatic granulomas from PBC liver samples, along with markers of immature dendritic cells, i.e. CD11b, low MHC II, IL-23 and CCR7 and CD83 expression, and C1q high expression. PBC patients with granulomas had significantly higher serum IgM levels and PBC granulomas were surrounded by B and plasma cells. Using ad in vitro approach we further demonstrate that IgM inhibits LPS-induced maturation of myeloid dendritic cells, as well as LPS-induced activation of NF-κB and the expression of proinflammatory cytokines such as TNF-α, IL-12, and IFN-β. In conclusion, we propose that immature dendritic cells are key factors in liver granulomas and that the commonly observed hyper-IgM may contribute to their appearance in patients with PBC.