Lipoteichoic acid may affect the pathogenesis of bile duct damage in primary biliary cirrhosis

Exploring Advanced Therapies for Primary Biliary Cholangitis: Insights from the Gut Microbiota-Bile Acid-Immunity Network

Primary biliary cholangitis (PBC) is a cholestatic liver disease characterized by immune-mediated injury to small bile ducts. Although PBC is an autoimmune disease, the effectiveness of conventional immunosuppressive therapy is disappointing. Nearly 40% of PBC patients do not respond to the first-line drug UDCA. Without appropriate intervention, PBC patients eventually progress to liver cirrhosis and even death. There is an urgent need to develop new therapies. The gut-liver axis emphasizes the interconnection between the gut and the liver, and evidence is increasing that gut microbiota and bile acids play an important role in the pathogenesis of cholestatic diseases. Dysbiosis of gut microbiota, imbalance of bile acids, and immune-mediated bile duct injury constitute the triad of pathophysiology in PBC. Autoimmune cholangitis has the potential to be improved through immune system modulation. Considering the failure of conventional immunotherapies and the involvement of gut microbiota and bile acids in the pathogenesis, targeting immune factors associated with them, such as bile acid receptors, microbial-derived molecules, and related specific immune cells, may offer breakthroughs. Understanding the gut microbiota-bile acid network and related immune dysfunctions in PBC provides a new perspective on therapeutic strategies. Therefore, we summarize the latest advances in research of gut microbiota and bile acids in PBC and, for the first time, explore the possibility of related immune factors as novel immunotherapy targets. This article discusses potential therapeutic approaches focusing on regulating gut microbiota, maintaining bile acid homeostasis, their interactions, and related immune factors.

Streptococcal infection and autoimmune diseases

Excessive activation of immune cells by environmental factors, such as infection or individual genetic risk, causes various autoimmune diseases. Streptococcus species are gram-positive bacteria that colonize the nasopharynx, respiratory tract, gastrointestinal tract, genitourinary tract, and skin. Group A Streptococcus (GAS) species cause various symptoms, ranging from mild infections, such as tonsillitis and pharyngitis, to serious infections, such as necrotizing fasciitis and streptococcal toxic shock syndrome. The contribution of GAS infections to several autoimmune diseases, including acute rheumatic fever, vasculitis, and neuropsychiatric disorders, has been studied. In this review, we focus on the association between streptococcal infections and autoimmune diseases, and discuss current research on the mechanisms underlying the initiation and progression of autoimmune diseases.

Bacterial culture and immunohistochemical detection of bacteria and endotoxin in cats with suppurative cholangitis-cholangiohepatitis syndrome

OBJECTIVE

To characterize the frequency and type of bacterial infection by culture- and immunohistochemical (IHC)-based methods and determine the impact of infection on clinical features and survival time in cats with suppurative cholangitis-cholangiohepatitis syndrome (S-CCHS).

ANIMALS

168 client-owned cats with S-CCHS (cases).

PROCEDURES

Clinical features, bacterial culture results, culture-inoculate sources, and survival details were recorded. Cases were subcategorized by comorbidity (extrahepatic bile duct obstruction, cholelithiasis, cholecystitis, ductal plate malformation, biopsy-confirmed inflammatory bowel disease, and biopsy-confirmed pancreatitis) or treatment by cholecystectomy or cholecystoenterostomy. Culture results, bacterial isolates, Gram-stain characteristics, and IHC staining were compared among comorbidities. Lipoteichoic acid IHC staining detected gram-positive bacterial cell wall components, and toll-like receptor expression IHC reflected pathologic endotoxin (gram-negative bacteria) exposure.

RESULTS

Clinical features were similar among cases except for more frequent abdominal pain and lethargy in cats with positive culture results and pyrexia, abdominal pain, and hepatomegaly for cats with polymicrobial infections. Bacteria were cultured in 93 of 135 (69%) cats, with common isolates including Enterococcus spp and Escherichia coli. IHC staining was positive in 142 of 151 (94%) cats (lipoteichoic acid, 107/142 [75%]; toll-like receptor 4, 99/142 [70%]). With in-parallel interpretation of culture and IHC-based bacterial detection, 154 of 166 (93%) cats had bacterial infections (gram-positive, 118/154 [77%]; gram-negative, 111/154 [72%]; polymicrobial, 79/154 [51%]). Greater frequency of bacterial isolation occurred with combined tissue, bile, and crushed cholelith inoculates. Infection and gram-positive bacterial isolates were associated with significantly shorter long-term survival times.

CLINICAL RELEVANCE

S-CCHS was associated with bacterial infection, pathologic endotoxin exposure, and frequent polymicrobial infection in cats. Combined tissue inoculates improved culture detection of associated bacteria.

The Gut-Liver Axis in Cholestatic Liver Diseases

The gut-liver axis describes the physiological interplay between the gut and the liver and has important implications for the maintenance of health. Disruptions of this equilibrium are an important factor in the evolution and progression of many liver diseases. The composition of the gut microbiome, the gut barrier, bacterial translocation, and bile acid metabolism are the key features of this cycle. Chronic cholestatic liver diseases include primary sclerosing cholangitis, the generic term secondary sclerosing cholangitis implying the disease secondary sclerosing cholangitis in critically ill patients and primary biliary cirrhosis. Pathophysiology of these diseases is not fully understood but seems to be multifactorial. Knowledge about the alterations of the gut-liver axis influencing the pathogenesis and the outcome of these diseases has considerably increased. Therefore, this review aims to describe the function of the healthy gut-liver axis and to sum up the pathological changes in these cholestatic liver diseases. The review compromises the actual level of knowledge about the gut microbiome (including the mycobiome and the virome), the gut barrier and the consequences of increased gut permeability, the effects of bacterial translocation, and the influence of bile acid composition and pool size in chronic cholestatic liver diseases. Furthermore, therapeutic implications and future scientific objectives are outlined.

Gut-Liver Axis and Inflammasome Activation in Cholangiocyte Pathophysiology

The Nlrp3 inflammasome is a multiprotein complex activated by a number of bacterial products or danger signals and is involved in the regulation of inflammatory processes through caspase-1 activation. The Nlrp3 is expressed in immune cells but also in hepatocytes and cholangiocytes, where it appears to be involved in regulation of biliary damage, epithelial barrier integrity and development of fibrosis. Activation of the pathways of innate immunity is crucial in the pathophysiology of hepatobiliary diseases, given the strong link between the gut and the liver. The liver secretes bile acids, which influence the bacterial composition of the gut microbiota and, in turn, are heavily modified by microbial metabolism. Alterations of this balance, as for the development of dysbiosis, may deeply influence the composition of the bacterial products that reach the liver and are able to activate a number of intracellular pathways. This alteration may be particularly important in the pathogenesis of cholangiopathies and, in particular, of primary sclerosing cholangitis, given its strong association with inflammatory bowel disease. In the present review, we summarize current knowledge on the gut–liver axis in cholangiopathies and discuss the role of Nlrp3 inflammasome activation in cholestatic conditions.

The Pathogenic Factors from Oral Streptococci for Systemic Diseases

The oral cavity is suggested as the reservoir of bacterial infection, and the oral and pharyngeal biofilms formed by oral bacterial flora, which is comprised of over 700 microbial species, have been found to be associated with systemic conditions. Almost all oral microorganisms are non-pathogenic opportunistic commensals to maintain oral health condition and defend against pathogenic microorganisms. However, oral Streptococci, the first microorganisms to colonize oral surfaces and the dominant microorganisms in the human mouth, has recently gained attention as the pathogens of various systemic diseases, such as infective endocarditis, purulent infections, brain hemorrhage, intestinal inflammation, and autoimmune diseases, as well as bacteremia. As pathogenic factors from oral Streptococci, extracellular polymeric substances, toxins, proteins and nucleic acids as well as vesicles, which secrete these components outside of bacterial cells in biofilm, have been reported. Therefore, it is necessary to consider that the relevance of these pathogenic factors to systemic diseases and also vaccine candidates to protect infectious diseases caused by Streptococci. This review article focuses on the mechanistic links among pathogenic factors from oral Streptococci, inflammation, and systemic diseases to provide the current understanding of oral biofilm infections based on biofilm and widespread systemic diseases.

Inflammation and the Gut-Liver Axis in the Pathophysiology of Cholangiopathies

Cholangiocytes, the epithelial cells lining the bile ducts, represent the unique target of a group of progressive diseases known as cholangiopathies whose pathogenesis remain largely unknown. In normal conditions, cholangiocytes are quiescent and participate to the final bile volume and composition. Following exogenous or endogenous stimuli, cholangiocytes undergo extensive modifications of their phenotype. Reactive cholangiocytes actively proliferate and release a set of proinflammatory molecules, which act in autocrine/paracrine manner mediating the cross-talk with other liver cell types and innate and adaptive immune cells. Cholangiocytes themselves activate innate immune responses against gut-derived microorganisms or bacterial products that reach the liver via enterohepatic circulation. Gut microbiota has been implicated in the development and progression of the two most common cholangiopathies, i.e., primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC), which have distinctive microbiota composition compared to healthy individuals. The impairment of intestinal barrier functions or gut dysbiosis expose cholangiocytes to an increasing amount of microorganisms and may exacerbate inflammatory responses thus leading to fibrotic remodeling of the organ. The present review focuses on the complex interactions between the activation of innate immune responses in reactive cholangiocytes, dysbiosis, and gut permeability to bacterial products in the pathogenesis of PSC and PBC.

Increased Intestinal Permeability and Decreased Barrier Function: Does It Really Influence the Risk of Inflammation?

Background

Increased intestinal permeability due to barrier dysfunction is supposed to cause microbial translocation which may induce low-grade inflammation in various diseases. However, this series of events has not been comprehensively evaluated yet.

Summary

Intestinal epithelial barrier dysfunction and increased permeability have been described in patients with inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), alcoholic liver disease, nonalcoholic steatohepatitis (NASH), liver cirrhosis, acute pancreatitis, primary biliary cholangitis (PBC), type 1 and type 2 diabetes, chronic kidney disease, chronic heart failure (CHF), depression, and other diseases. Most clinical reports used either permeability assays of challenge tests or measurement of circulating bacterial markers like endotoxin for assessment of 'the leaky gut'. The intestinal permeability assessed by the challenge tests has often been related to the changes of tight junction proteins in the epithelium or circulating endotoxin levels. In patients with IBD, alcoholic liver disease, NASH, liver cirrhosis, PBC, obstructive jaundice, severe acute pancreatitis, and CHF, endotoxemia and proinflammatory cytokinemia have been found in addition to increased permeability. In the serum of patients with IBS and depression, antiflagellin antibodies and antilipid A antibodies were detected, respectively, together with increased permeability and proinflammatory cytokinemia. The site of infection, which is localized to the intestine in IBD and IBS, includes various extraintestinal organs in other diseases. The relation of gut dysbiosis to intestinal barrier dysfunction has gradually been clarified.

Key Messages

Although no direct cause-and-effect relationship has been confirmed, all clinical and experimental data suggest the importance of intestinal hyperpermeability in the inflammatory changes of various diseases. Increased intestinal permeability is a new target for disease prevention and therapy. Considering the close relationship of 'the leaky gut' and gut dysbiosis to the major diseases, we can conclude that meticulous dietetic and probiotic approaches to recover healthy microbiota have the potential to make a breakthrough in the management of these diseases tomorrow.

Increased Intestinal Permeability and Decreased Barrier Function: Does It Really Influence the Risk of Inflammation?

Background

Increased intestinal permeability due to barrier dysfunction is supposed to cause microbial translocation which may induce low-grade inflammation in various diseases. However, this series of events has not been comprehensively evaluated yet.

Summary

Intestinal epithelial barrier dysfunction and increased permeability have been described in patients with inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), alcoholic liver disease, nonalcoholic steatohepatitis (NASH), liver cirrhosis, acute pancreatitis, primary biliary cholangitis (PBC), type 1 and type 2 diabetes, chronic kidney disease, chronic heart failure (CHF), depression, and other diseases. Most clinical reports used either permeability assays of challenge tests or measurement of circulating bacterial markers like endotoxin for assessment of 'the leaky gut'. The intestinal permeability assessed by the challenge tests has often been related to the changes of tight junction proteins in the epithelium or circulating endotoxin levels. In patients with IBD, alcoholic liver disease, NASH, liver cirrhosis, PBC, obstructive jaundice, severe acute pancreatitis, and CHF, endotoxemia and proinflammatory cytokinemia have been found in addition to increased permeability. In the serum of patients with IBS and depression, antiflagellin antibodies and antilipid A antibodies were detected, respectively, together with increased permeability and proinflammatory cytokinemia. The site of infection, which is localized to the intestine in IBD and IBS, includes various extraintestinal organs in other diseases. The relation of gut dysbiosis to intestinal barrier dysfunction has gradually been clarified.

Key Messages

Although no direct cause-and-effect relationship has been confirmed, all clinical and experimental data suggest the importance of intestinal hyperpermeability in the inflammatory changes of various diseases. Increased intestinal permeability is a new target for disease prevention and therapy. Considering the close relationship of 'the leaky gut' and gut dysbiosis to the major diseases, we can conclude that meticulous dietetic and probiotic approaches to recover healthy microbiota have the potential to make a breakthrough in the management of these diseases tomorrow.

Involvement of commensal bacteria may lead to dysregulated inflammatory and autoimmune responses in a mouse model for chronic nonsuppurative destructive cholangitis

BACKGROUND

We previously reported a mouse model of primary biliary cirrhosis (PBC)-like chronic nonsuppurative destructive cholangitis (CNSDC), in which frequent injections of Streptococcus intermedius induced CNSDC and autoantibody production. The present study was performed to verify the model by examining 1) the reappearance of the PBC-like CNSDC after lymphocyte transfer from model to naïve mice, 2) the involvement of autophagy, and 3) the influence of the strain difference.

METHODS

Mice were inoculated with S. intermedius weekly for 8 weeks, then sacrificed to obtain samples. Spleen cells obtained from S. intermedius-inoculated mice were transferred to RAG2(-/-) mice.

RESULTS

CNSDC and elevated serum level of anti-gp210 titers were observed in S. intermedius-inoculated C57BL/6 mice, similar to the results of our previous report using BALB/c mice. Portal inflammation was induced in the livers of RAG2(-/-) mice by the transfer of spleen cells from S. intermedius-inoculated C57BL/6 mice. Among the inflammatory cells in the RAG2(-/-) mice, CD3-positive cells were predominant. Autophagosome-like structures were detected histologically, in the cytoplasm of infiltrated cells around the bile ducts in the livers of S. intermedius-inoculated both C57BL/6 and BALB/c mice. In S. intermedius-inoculated C3H/HeJ mice, inflammation in the portal area was less extensive than that in the hepatic parenchyma.

CONCLUSION

Bacterial component(s) and sequentially upregulated innate and acquired immune responses, accompanied by autophagy, might trigger CNSDC, via autoimmune mechanisms. Throughout the generation of bacteria-triggered PBC-like CNSDC, strain difference may influence the response to S. intermedius-inoculation in the liver.

Animal models of biliary tract injury

PURPOSE OF REVIEW

Cholestatic liver diseases with bile duct injury and biliary fibrosis account for a significant percentage of patients with end-stage liver disease and undergoing liver transplantation. A number of different animal models have been established and have added substantially to our understanding of the molecular mechanisms underlying this group of chronic liver diseases. In the present review, we discuss recent findings and new insight derived from different animal models of biliary tract injury and fibrosis.

RECENT FINDINGS

Cholangiocytes do not undergo epithelial to mesenchymal transition and do not contribute to the pool of biliary fibroblasts involved in extracellular matrix deposition. Rather cholangiocytes can acquire a reactive phenotype activating fibrogenesis through secretion of proinflammatory and profibrogenic mediators. Bile acid homeostasis is controlled by a gut-liver axis playing a crucial role in the adaptive response to bile duct injury and cholestasis. The nuclear factor-kappa B and hedgehog signaling pathways play a critical role in cholestatic liver injury and the emergence of liver cancer. Nuclear receptors are key mediators of adaptive response mechanisms in cholestasis and potential therapeutical targets.

SUMMARY

Recent progress and mechanistic insights from mouse models have added to our understanding of the molecular mechanisms underlying cholestatic liver and biliary tract injury and pointed to new therapeutic options.

Enhanced innate immune responsiveness and intolerance to intestinal endotoxins in human biliary epithelial cells contributes to chronic cholangitis

BACKGROUND

Pattern recognition receptors (PRRs) orchestrate the innate immune defence in human biliary epithelial cells (BECs). Tight control of PRR signalling provides tolerance to physiological amounts of intestinal endotoxins in human bile to avoid constant innate immune activation in BECs.

AIMS

We wanted to determine whether inappropriate innate immune responses to intestinal endotoxins contribute to the development and perpetuation of chronic biliary inflammation.

METHODS

We examined PRR-mediated innate immune responses and protective endotoxin tolerance in primary BECs isolated from patients with primary sclerosing cholangitis (PSC), alcoholic liver disease and patients without chronic liver disease. Expression studies comprised northern blots, RT-PCR, Western blots and immunocytochemistry. Functional studies comprised immuno-precipitation Western blots, FACS for endotoxin uptake, and NF-κB activation assays and ELISA for secreted IL-8 and tumour necrosis factor (TNF)-α.

RESULTS

Primary BECs from explanted PSC livers showed reversibly increased TLR and NOD protein expression and activation of the MyD88/IRAK signalling complex. Consecutively, PSC BECs exhibited inappropriate innate immune responses to endotoxins and did not develop immune tolerance after repeated endotoxin exposures. This endotoxin hyper-responsiveness was probably because of the stimulatory effect of abundantly expressed IFN-γ and TNF-α in PSC livers, which stimulated TLR4-mediated endotoxin signalling in BECs, leading to increased TLR4-mediated endotoxin incorporation and impaired inactivation of the TLR4 signalling cascade. As TNF-α inhibition partly restored protective innate immune tolerance, endogenous TNF-α secretion probably contributed to inappropriate endotoxin responses in BECs.

CONCLUSION

Inappropriate innate immune responses to intestinal endotoxins and subsequent endotoxin intolerance because of enhanced PRR signalling in BECs probably contribute to chronic cholangitis.

The autoimmunity of primary biliary cirrhosis and the clonal selection theory

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disease in which an immune-mediated injury targets the small intrahepatic bile ducts. PBC is further characterized by highly specific serum antimitochondrial autoantibodies (AMA) and autoreactive T cells, a striking female predominance, a strong genetic susceptibility, and a plethora of candidate environmental factors to trigger the disease onset. For these reasons PBC appears ideal to represent the developments of the clonal selection theory over the past decades. First, a sufficiently potent autoimmunogenic stimulus in PBC would require the coexistence of numerous pre-existing conditions (mostly genetic, as recently illustrated by genome-wide association studies and animal models) to perpetuate the destruction of the biliary epithelium by the immune system via the persistence of forbidden clones. Second, the proposed modifications of mitochondrial autoantigens caused by infectious agents and/or xenobiotics well illustrate the possibility that peculiar changes in the antigen structure and flexibility may contribute to tolerance breakdown. Third, the unique apoptotic features demonstrated for cholangiocytes are the ideal setting for the development of mitochondrial autoantigen presentation to the immune system through macrophages and AMA thus turning the non traditional mitochondrial antigen into a traditional one. This article will review the current knowledge on PBC etiology and pathogenesis in light of the clonal selection theory developments.

Biliary innate immunity: function and modulation

Biliary innate immunity is involved in the pathogenesis of cholangiopathies in patients with primary biliary cirrhosis (PBC) and biliary atresia. Biliary epithelial cells possess an innate immune system consisting of the Toll-like receptor (TLR) family and recognize pathogen-associated molecular patterns (PAMPs). Tolerance to bacterial PAMPs such as lipopolysaccharides is also important to maintain homeostasis in the biliary tree, but tolerance to double-stranded RNA (dsRNA) is not found. In PBC, CD4-positive Th17 cells characterized by the secretion of IL-17 are implicated in the chronic inflammation of bile ducts and the presence of Th17 cells around bile ducts is causally associated with the biliary innate immune responses to PAMPs. Moreover, a negative regulator of intracellular TLR signaling, peroxisome proliferator-activated receptor-γ (PPARγ), is involved in the pathogenesis of cholangitis. Immunosuppression using PPARγ ligands may help to attenuate the bile duct damage in PBC patients. In biliary atresia characterized by a progressive, inflammatory, and sclerosing cholangiopathy, dsRNA viruses are speculated to be an etiological agent and to directly induce enhanced biliary apoptosis via the expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Moreover, the epithelial-mesenchymal transition (EMT) of biliary epithelial cells is also evoked by the biliary innate immune response to dsRNA.

Long-term bacterial exposure can trigger nonsuppurative destructive cholangitis associated with multifocal epithelial inflammation

Bacterial infection has become a focus of attention in the pathogenesis of primary biliary cirrhosis (PBC). We earlier reported that the bacterial lipoteichoic acid was detected at the sites of inflammation around damaged bile ducts in the livers of PBC, and PBC patients' sera showed high titers against streptococcal histone-like protein. Here, we investigated whether chronic bacterial exposure could trigger PBC-like epithelial cell damage in normal mouse. BALB/c mice were repeatedly inoculated with various bacteria for 8 weeks. At 1 week (Group 1) and 3, 4, or 20 months (long term; Group 2) after the final inoculation, mice were killed to obtain samples. In the livers of the Streptococcus intermedius (S.i.)-inoculated mice in Group 1, cellular infiltration was predominantly observed around the bile ducts over the hepatic parenchyma. In the S.i.-inoculated mice in Group 2, portal but not parenchymal inflammation was observed in the livers, and periductal cellular infiltrates were detected in the salivary glands. Both S.i.-inoculated Groups 1 and 2 BALB/c mice sera had antibodies against HuCCT1 biliary epithelial cells, anti-nuclear antibodies, and anti-gp210 antibodies, but not anti-mitochondrial antibodies. Immunoreactivity to histone-like DNA-binding protein of S.i. (S.i.-HLP) was detectable around the sites of chronic nonsuppurative destructive cholangitis in the portal area in the livers of both S.i.-inoculated Groups 1 and 2 BALB/c mice. Furthermore, anti-S.i.-HLP antibody bound to synthetic gp210 peptide, as well. Bacteria triggered PBC-like cholangitis, multifocal epithelial inflammation, and autoantibody production. Bacteria are likely involved in the pathogenesis of PBC and of associated multifocal epithelial inflammation.

Inflammation and biliary tract injury

PURPOSE OF REVIEW

Primary biliary cirrhosis, primary sclerosing cholangitis and biliary atresia are thought to be immune-mediated cholangiopathies, however, gaps in knowledge remain with regard to the immunopathogenesis of these diseases.

RECENT FINDINGS

In this review, we highlight recent investigations pertaining to the role of both innate and adaptive immunity in bile duct damage. In innate immunity, evidence is presented for the contribution of cholangiocyte toll-like receptor stimulation promoting the ongoing inflammatory response. Innate-like lymphocytes may also be critical in the early phases of small bile duct injury found in primary biliary cirrhosis. With regard to adaptive immunity, the role of specific gene deficiencies in the susceptibility to immune-mediated cholangiopathies is reviewed. Furthermore, recent work analyzing the effector mechanisms of adaptive immunity leading to bile duct epithelial apoptosis are outlined.

SUMMARY

Understanding the intricacies of the inflammatory mechanisms culminating in bile duct epithelial injury are crucial to the future development of therapies aimed at halting the ongoing biliary tract destruction found in immune-mediated cholangiopathies. A paucity of research studies on primary sclerosing cholangitis was noted in this review and future research efforts should focus on primary sclerosing cholangitis, in addition to primary biliary cirrhosis and biliary atresia.

Pathogenesis of primary biliary cirrhosis

Autoimmune phenomena have been recognized in primary biliary cirrhosis (PBC) for more than 50 years and the specificity of the characteristic responses directed at highly conserved mitochondrial antigens determined in detail over the past 20. Effecter autoreactive immune responses are characterized and potential mechanisms of breakdown of tolerance to self proposed. Elements of the clinical pattern of PBC, including the recurrence of the disease across HLA boundaries after liver transplantation, remain difficult to reconcile with a simple autoimmune model. Alternative (but not necessary mutually exclusive) pathogenetic models have been outlined, including a potential role for retroviral pathogens and directly cytopathic effects.

A possible role of histone-like DNA-binding protein of Streptococcus intermedius in the pathogenesis of bile duct damage in primary biliary cirrhosis

Bacterial infection has become a focus of attention in the pathogenesis of primary biliary cirrhosis (PBC). It was reported that anti-histone autoantibody was detected in PBC, suggesting that bacterial histone-like DNA-binding protein (HLP) may be involved in the pathogenesis of PBC. To identify bacterial species in PBC to confirm this possibility, serum reactivity to bacterial cells was studied by ELISA. The IgM class Streptococcus intermedius titers were significantly higher in PBC than chronic hepatitis due to hepatitis C virus (CH-C) and healthy subjects. Among the streptococci, S. intermedius was selected for further study. The antigenic peptide of S. intermedius of HLP was synthesized to examine the serum reactivity to Si-HLP. IgM class anti-Si-HLP peptide titers were significantly higher in PBC. Immunoreactivity to anti-Si-HLP was detected in the cytoplasm of biliary epithelial cells and inflammatory cells in the portal area in PBC patients' livers. Streptococci, especially S. intermedius, might play a key role in the pathogenesis of PBC, possibly involving HLP.

Lipoteichoic acid may affect the pathogenesis of PBC-like bile duct damage and might be involved in systemic multifocal epithelial inflammations in chronic colitis-harboring TCRalpha-/-xAIM-/- mice

Background

Chronic colitis-harboring TCRα^−/− × AIM^−/− mice showed PBC-like bile duct damage in the liver. Bacterial infection is one of the candidates for the pathogenesis of PBC. We demonstrated that the bacterial cell wall component lipotheicoic acid (LTA)was detected at sites of inflammation around damaged bile ducts in PBC patients. The aim of this study was to investigate the pathophysiology of the liver and other organs in TCRα^−/− × AIM^−/− mice.

Methods

Thirteen female TCRα^−/− × AIM^−/− mice were sacrificed at 24 weeks of age. The liver, stomach, small intestine, colon, pancreas, kidney and spleen were studied for pathological examination. Using anti-LTA antibody as the primary antibody,an immunohistochemical study was carried out.

Results

In the liver, LTA was mainly detected in the portal area with inflammation, and some of the cytoplasm of hepatocytes. Inflammations were also observed in the stomach, intestine, pancreas and kidney. Throughout the gastrointestinal tract, from the stomach to the colon, LTA was detected in the epithelium at sites of inflammation. Furthermore, LTA was detected around both pancreatic ducts with inflammation and distal renal tubules with inflammation.

Conclusions

The development of inflammations in the liver as well as extensive organs, strongly suggests a close relationship between bile duct damage and systemic multifocal epithelial inflammations, perhaps involving bacterial LTA, in TCRα^−/− × AIM^−/− mice.

Biliary innate immunity and cholangiopathy

The intrahepatic biliary tree is a conduit of bile which contains pathogen-associated molecular patterns (PAMPs) such as lipopolysaccharide (LPS) originated from intestinal flora. Human biliary epithelial cells (BEC) express toll-like receptors (TLR) and intracellular adaptor molecules and secrete antibiotic peptides and (pro)inflammatory cytokines via the activation of nuclear transcription factors. However, although human bile contains several PAMPs in normal as well as diseased livers, PAMPs physiologically do not elicit an inflammatory response in the biliary tree, suggesting that tolerance against commensal PAMPs including LPS (endotoxin tolerance) is important in maintaining the homeostasis of biliary innate immunity. Negative regulators of intracellular TLR signalings, peroxisome proliferator activating receptor-gamma (PPAR-gamma) and IRAK-M, are associated with the endotoxin tolerance in BEC. In vivo, PPAR-gamma and IRAK-M are ubiquitously expressed in intrahepatic biliary epithelium, while the expression of PPAR-gamma is reduced in damaged bile ducts of primary biliary cirrhosis (PBC). In addition to antibiotic peptides, several cytokines andchemokines are also secreted from BEC as an innate immune response and these humoral components participate in attracting immunocytes and modulating peribiliary cytokine milieu. BEC have receptors for several cytokines and the expression of TLR in BEC is affected by cytokines, suggesting that biliary innate immunity is regulated by an acquired immunity. A T-helper (Th)1-type cytokine, interferon-gamma, downregulates PPAR-gamma and upregulates TLR, and consequently increases the susceptibility of biliary innate immunity. Because periductal cytokine milieu in PBC is Th1-dominant, the increased susceptibility to PAMPs may be associated with the development of cholangiopathy in PBC. Biliary innate immunity is speculated to be associated with the pathogenesis of biliary diseases as well as the defense against biliary microbial infection.

Systemic Multifocal Epithelial Inflammations Associated with PBC-like Bile Duct Damage in Chronic Colitis Harboring TCR / xAIM / Mice: Does Lipoteichoic Acid Affect the Pathogenesis of Epithelial Inflammation Followed by Fibrosis?

Autoimmune disorder and associated multifocal organ inflammations such as dry gland syndrome are occasionally observed; however, their etiologies are not clearly understood. We previously reported that chronic colitis-harboring TCR alpha(-/-) x AIM(-/-) mice show primary biliary cirrhosis (PBC)-like bile duct damage in the liver. Gram-positive bacterial infection is one of the candidates for the pathogenesis of PBC. We also reported that the bacterial cell wall component lipoteichoic acid (LTA) was detected at the sites of inflammation around damaged bile ducts in PBC patients. On the basis of these facts, we hypothesized that LTA might affect the pathogenesis of bile duct damage in the livers of TCR alpha(-/-) x AIM(-/-) mice. LTA was detected not only in the portal area with inflammation in the liver but also throughout the gastrointestinal tract, from the stomach to the colon, and especially in the epithelium at sites of inflammation. In addition, LTA was detected around both pancreatic ducts with inflammation and at the distal renal tubules with inflammation in TCR alpha(-/-) x AIM(-/-) mice. Furthermore, in the liver, pancreas, kidney, and colon, fibrous stroma were detected at the sites of LTA-positive inflammation foci. Bacterial LTA might affect the pathogenesis of epithelial inflammation followed by fibrosis in systemic multifocal epithelial inflammations in chronic colitis-harboring TCR alpha(-/-) x AIM(-/-) mice with PBC-like bile duct damage.