Immune response to lipopolysaccharide in primary biliary cirrhosis and autoimmune diseases

Emperipolesis mediated by CD8+ T cells correlates with biliary epithelia cell injury in primary biliary cholangitis

Primary biliary cholangitis (PBC) is an autoimmune disease characterized by chronic destruction of the bile ducts. A major unanswered question regarding the pathogenesis of PBC is the precise mechanisms of small bile duct injury. Emperipolesis is one of cell-in-cell structures that is a potential histological hallmark associated with chronic hepatitis B. This study aimed to clarify the pathogenesis and characteristics of emperipolesis in PBC liver injury. Sixty-six PBC patients, diagnosed by liver biopsy combined with laboratory test, were divided into early-stage PBC (stages I and II, n = 39) and late-stage PBC (stages III and IV, n = 27). Emperipolesis was measured in liver sections stained with haematoxylin-eosin. The expressions of CK19, CD3, CD4, CD8, CD20, Ki67 and apoptosis of BECs were evaluated by immunohistochemistry or immunofluorescence double labelling. Emperipolesis was observed in 62.1% of patients with PBC, and BECs were predominantly host cells. The number of infiltrating CD3⁺ and CD8⁺ T cells correlated with the advancement of emperipolesis (R²  = 0.318, P < .001; R²  = 0.060, P < .05). The cell numbers of TUNEL-positive BECs and double staining for CK19 and Ki67 showed a significant positive correlation with emperipolesis degree (R²  = 0.236, P < .001; R²  = 0.267, P < .001). We conclude that emperipolesis mediated by CD8⁺ T cells appears to be relevant to apoptosis of BEC and thus may aggravate the further injury of interlobular bile ducts.

Toll-like receptors in pathophysiology of liver diseases

Toll-like receptors (TLRs) are pattern recognition receptors that participate in host defense by recognizing pathogen-associated molecular patterns alongside inflammatory processes by recognizing damage associated molecular patterns. Given constant exposure to pathogens from gut, strict control of TLR-associated signaling pathways is essential in the liver, which otherwise may lead to inappropriate production of pro-inflammatory cytokines and interferons and may generate a predisposition to several autoimmune and chronic inflammatory diseases. The liver is considered to be a site of tolerance induction rather than immunity induction, with specificity in hepatic cell functions and distribution of TLR. Recent data emphasize significant contribution of TLR signaling in chronic liver diseases via complex immune responses mediating hepatocyte (i.e., hepatocellular injury and regeneration) or hepatic stellate cell (i.e., fibrosis and cirrhosis) inflammatory or immune pathologies. Herein, we review the available data on TLR signaling, hepatic expression of TLRs and associated ligands, as well as the contribution of TLRs to the pathophysiology of hepatic diseases.

Preventive administration of UDCA after liver transplantation for primary biliary cirrhosis is associated with a lower risk of disease recurrence

BACKGROUND & AIMS

Recurrence of primary biliary cirrhosis (PBC) after liver transplantation (LT) is not rare and can occasionally lead to severe graft dysfunction and retransplantation. Ursodeoxycholic acid (UDCA) is a safe and effective treatment for PBC. However, whether preventive administration of UDCA after LT could lower the incidence of PBC recurrence is unknown.

METHODS

Patients transplanted for PBC in five French and Swiss centers from 1988 to 2010 were included. Most patients from a single center received UDCA (10-15 mg/kg/d) preventively. Recurrence of PBC was histologically defined from biopsies routinely performed at 1, 5, 10, and 15 years of follow-up, and at any time when clinically indicated.

RESULTS

A total of 90 patients with a 1-year minimum follow-up were studied retrospectively, including 19 (21%) patients receiving preventive UDCA. The mean follow-up was 12 years. Recurrence was diagnosed in 48 (53%) patients. The recurrence rates at 5, 10, and 15 years were 27%, 47%, and 61%, respectively. In a multivariate proportional hazards model adjusted for potential confounders and risk factors, preventive UDCA was the only factor affecting the risk of recurrence significantly (HR=0.32; 95% CI: 0.11-0.91). The 5, 10, and 15-year rates of recurrence were 11%, 21%, and 40%, respectively, under preventive UDCA, and 32%, 53%, and 70%, respectively, without preventive UDCA. Seven patients with recurrence (15%) progressed to cirrhosis, requiring retransplantation in one. However, neither recurrence nor preventive UDCA had a significant impact on survival.

CONCLUSIONS

Preventive treatment with UDCA reduces the risk of PBC recurrence after LT.

Primary biliary cirrhosis: From bench to bedside

Primary biliary cirrhosis (PBC) is a chronic non-suppurative destructive intrahepatic cholangitis leading to cirrhosis after a protractive non cirrhotic stage. The etiology and pathogenesis are largely unknown and autoimmne mechanisms have been implicated to explain the pathological lesions. Many epitopes and autoantigens have been reported as crucial in the pathophysiology of the disease and T and B cells abnormalities have been described, the exact pathways leading to the destruction of small intrahepatic ductules are mostly speculative. In this review we examined the various epidemiologal and geoepidemiological data as well as the complex pathogenetic aspects of this disease, focusing on recent in vivo and in vitro studies in this field. Initiation and progression of PBC is believed to be a multifactorial process with strong infuences from the patient’s genetic background and by various environmental factors. The role of innate and adaptive immunity, including cytokines, chemokines, macrophages and the involvement of apoptosis and reactive oxygen species are outlined in detailed. The current pathogenetic aspects are presented and a novel pathogenetic theory unifying the accumulated clinical information with in vitro and in vivo data is formulated. A review of clinical manifestations and immunological and pathological diagnosis was presented. Treatment modalities, including the multiple mechanisms of action of ursodeoxycholate were finally discussed.

Liver alkaline phosphatase: a missing link between choleresis and biliary inflammation

Several lines of evidence show that serum alkaline phosphatase (AP) is not only a signpost of cholestasis but also a surrogate marker of the severity of primary biliary cirrhosis and primary sclerosing cholangitis. In the present opinion article, we review and discuss the putative role of liver AP in health and in cholestatic diseases. In inflammatory cholestatic conditions, loss of activity of liver AP (resulting from its relocation from canaliculi and the acidic milieu) might promote hyper-adenosine triphosphate-bilia, lipopolysaccharide overload, and subsequent exacerbation and perpetuation of inflammation. Drugs that can restore the polarity of hepatocytes and canalicular export of bile acids or act as bile alkalinity modifiers are predicted to exert anti-inflammatory effects and to benefit both primary biliary cirrhosis and primary sclerosing cholangitis. Oral administration of intestinal AP could be a valid therapeutic intervention that deserves further study under experimental conditions as well as in human diseases. Overall, the key role of the liver microenvironment that might shape the different facets of the inflammatory processes in fibrosing cholangiopathies is highlighted.

Association analysis of toll-like receptor 4 polymorphisms in Japanese primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is characterized by portal inflammation and immune-mediated destruction of intrahepatic bile ducts that often result in liver failure. Toll-like receptor (TLR) 4 recognizes lipopolysaccharides of Gram-negative bacteria. Infectious agents have been suspected to play a crucial role in PBC pathogenesis since TLR4 expression was found in bile duct epithelial cells and periportal hepatocytes in liver tissues of PBC. To assess the potential contribution of TLR4 SNPs to the development of this disease, we genotyped five SNPs in TLR4 in 261 PBC patients and 359 controls using a TaqMan assay. No significant positive associations with either PBC susceptibility or progression were uncovered. These results indicate that TLR4 polymorphisms do not play a prominent role in the development of PBC in Japanese patients.

Ursodeoxycholic acid and bile-acid mimetics as therapeutic agents for cholestatic liver diseases: an overview of their mechanisms of action

Chronic cholestasis and liver inflammation are the two main pathophysiological components of the two major classes of disease - primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) - leading to bile duct destruction and ultimately to cirrhosis and liver failure. Ursodeoxycholic acid (UDCA), initially introduced as a therapeutic approach to counteract the cholestatic components to PBC and PSC, was subsequently shown to exhibit unexpected anti-inflammatory and immunomodulatoty properties. The use of farnesoid X receptor (FXR) and TGR5 agonists in various animal models have confirmed early observations indicating that bile acids are not only toxicants and inflammagens, but also repressors of innate and adaptive immunity. Obeticholic acid is a bile-acid mimetic, with no toxic or inflammagen behavior, that strongly activates FXR to combat the toxic effects of high concentrations of bile acid. Because UDCA is not an FXR agonist, its combination with obeticholic acid could be a promising tool for the treatment of PBC and PSC. In this overview, the biological properties of UDCA, NorUDCA and FXR agonists are highlighted, as well as their overlapping mechanisms of action in inflammatory biliary disorders.

Etiopathogenesis of primary biliary cirrhosis: an overview of recent developments

Substantial advancements in the field of primary biliary cirrhosis (PBC) research have broadened our understanding of this enigmatic disease. Genome-wide studies have identified several new candidate genes involved in the immunoregulatory process, particularly those responsible for antigen presentation and lymphocyte signaling. Examples include the HLA class-II region and genes implicated in IL12-JAK/STAT signaling, and the NF-κB and TNF signaling pathways. Environmental triggers appear to disrupt the pre-existing, unstable immune tolerance in genetically susceptible individuals, and molecular mimics of the PBC-specific autoantigen (PDC) may be derived from microbes or xenobiotic compounds, which modify native proteins, making them immunogenic. Although the vast majority of patients with PBC are AMA-positive, a variety of disease-specific antinuclear antibodies have been recognized in conferring a worse clinical outcome. There has also been a revived interest in the role of antibody-secreting B cells in murine models suggesting that depletion of these cells paradoxically exacerbates cholangiopathy. Biliary specificity in PBC is most likely driven by the uniqueness of cholangiocyte apoptosis in which the PDC-E2 autoantigen undergoes differential glutathiolation. Cholangiocytes also possess the ability to phagocytose neighboring apoptotic cells, present intact immunoreactive antigen, and undergo attack from autoantibodies, the innate immune system, and autoreactive lymphocytes. Cellular senescence and a lack of functioning T-regulatory cells are proposed mechanisms by which this multi-lineage process is thought to be enhanced. This review summarizes these key advances as the true complexities of the disease process begin to be unraveled.

Altered biliary epithelial cell and monocyte responses to lipopolysaccharide as a TLR ligand in patients with primary biliary cirrhosis

OBJECTIVE

Lipopolysaccharide (LPS) is suspected to trigger primary biliary cirrhosis (PBC) in susceptible individuals, yet the precise mechanism of its effect in PBC remains largely unknown. The aim of this study was to investigate altered responses to LPS ligand for Toll-like receptors (TLRs) in pathogenesis of PBC in vivo and in vitro.

MATERIAL AND METHODS

In vivo, we investigated levels of LPS and pro-inflammatory cytokines in sera and expression of LPS receptors in liver tissues from 162 patients with PBC, 325 patients with other liver diseases and 80 healthy controls. In vitro, altered responses to LPS on monocytes and cultured human biliary epithelial cells (BECs) from patients with PBC were determined.

RESULTS

Significantly higher levels of LPS in patients with PBC were detected, compared with patients with other liver diseases and healthy controls. Immunohistochemically, expression of TLR4, CD14, CD68 and NF-κB was significantly enhanced in liver tissues from patients with PBC. Before LPS stimulation, we found significantly higher serum levels of tumor necrosis factor-α, interleukin (IL)-1β, IL-6 and IL-8 in patients with PBC than those in healthy controls. After LPS stimulation, TLR4 expression and pro-inflammatory cytokine production in CD14-positive monocytes and cultured BEC from patients with PBC increased significantly.

CONCLUSIONS

These results indicated that patients with PBC were prone to exhibit higher serum LPS level, hypersensitivity of monocytes and BEC to LPS, and enhanced production of pro-inflammatory cytokines. LPS altered expression of TLR4, CD14 and NF-κB on monocytes and BEC, which may be implicated in the pathogenesis and progression of PBC.

The role of lipopolysaccharide/toll-like receptor 4 signaling in chronic liver diseases

Toll-like receptor 4 (TLR4) is a pattern recognition receptor that functions as lipopolysaccharide (LPS) sensor and whose activation results in the production of several pro-inflammatory, antiviral, and anti-bacterial cytokines. TLR4 is expressed in several cells of healthy liver. Despite the constant confrontation of hepatic TLR4 with gut-derived LPS, the normal liver does not show signs of inflammation due to its low expression of TLR4 and ability to modulate TLR4 signaling. Nevertheless, there is accumulating evidence that altered LPS/TLR4 signaling is a key player in the pathogenesis of many chronic liver diseases (CLD). In this review, we first describe TLR4 structure, ligands, and signaling. Later, we review liver expression of TLR4 and discuss the role of LPS/TLR4 signaling in the pathogenesis of CLD such as alcoholic liver disease, nonalcoholic fatty liver disease, chronic hepatitis C, chronic hepatitis B, primary sclerosing cholangitis, primary biliary cirrhosis, hepatic fibrosis, and hepatocarcinoma.

Primary biliary cirrhosis: a 2010 update

Primary biliary cirrhosis (PBC) is a chronic inflammatory autoimmune disease that mainly targets the cholangiocytes of the interlobular bile ducts in the liver. The condition primarily affects middle-aged women. Without treatment, PBC generally progresses to cirrhosis and eventually liver failure over a period of 10-20 years. PBC is a rare disease with prevalence of less than 1/2000. PBC is thought to result from a combination of multiple genetic factors and superimposed environmental triggers. The contribution of the genetic predisposition is evidenced by the familial clustering. Several risk factors, including exposure to infectious agents and chemical xenobiotics, have been suggested. Ursodeoxycholic acid (UDCA) is currently the only FDA-approved medical treatment for PBC. When administered at doses of 13-15 mg/kg/day, a majority of patients with PBC have a normal life expectancy without additional therapeutic measures. One out of three patients does not adequately respond to UDCA therapy and may need additional medical therapy and/or liver transplantation. This review summarises current knowledge on the epidemiology, ethiopathogenesis, clinical, and therapeutic aspects of PBC.

Bile salts control the antimicrobial peptide cathelicidin through nuclear receptors in the human biliary epithelium

BACKGROUNDS & AIMS

Under normal conditions, the biliary tract is a microbial-free environment. The absence of microorganisms has been attributed to various defense mechanisms that include the physicochemical and signaling actions of bile salts. Here, we hypothesized that bile salts may stimulate the expression of a major antimicrobial peptide, cathelicidin, through nuclear receptors in the biliary epithelium.

METHODS

The expression of cathelicidin was analyzed in human liver samples by immunostaining and reverse-transcription quantitative polymerase chain reaction. The regulation of cathelicidin expression by the endogenous bile salt, chenodeoxycholic acid, and by the therapeutic bile salt, ursodeoxycholic acid (UDCA), was assessed in human biliary epithelial cells in which endogenous nuclear receptor expression was blunted by siRNA or dominant-negative strategies.

RESULTS

In the human liver, biliary epithelial cells show intense immunoreactivity for cathelicidin and for the vitamin D receptor. In cultured biliary epithelial cells, chenodeoxycholic acid and UDCA induce cathelicidin expression through 2 different nuclear receptors: the farnesoid X receptor and the vitamin D receptor, respectively. Importantly, vitamin D further increases the induction of cathelicidin expression by both bile salts. In a prototypical inflammatory biliary disease (ie, primary biliary cirrhosis), we document that hepatic expressions of the vitamin D receptor and of cathelicidin significantly increased with UDCA therapy.

CONCLUSIONS

Our results indicate that bile salts may contribute to biliary tract sterility by controlling epithelial cell innate immunity. They further suggest that in inflammatory biliary diseases, which involve bacterial factors, a strategy systematically combining UDCA with vitamin D would increase therapeutic efficacy.

Altered expression of TLR homolog RP105 on monocytes hypersensitive to LPS in patients with primary biliary cirrhosis

BACKGROUNDS/AIMS

Toll-like receptors (TLRs) have emerged as a key component of the innate immune system that triggers antimicrobial responses. Altered monocyte responses to ligands for TLRs have been reported in patients with primary biliary cirrhosis (PBC), yet the precise mechanism remains unknown.

METHODS

We investigated in vitro responses to a TLR4 ligand, lipopolysaccharide (LPS), using peripheral blood mononuclear cells and monocytes from 25 patients with PBC, 10 patients with chronic viral hepatitis (CVH), and 20 healthy individuals.

RESULTS

After stimulation with LPS, we found significantly higher amounts of IL-1beta, IL-6, and IL-8 production in PBC patients. Through the TLR4 signaling pathway, activation of NF-kappaB and expression of MyD88 mRNA were significantly increased in PBC patients, and the level of TLR4 expression was significantly increased on PBC monocytes as compared with CVH patients and controls. Of significance, the surface expression of RP105, which has recently been shown to be involved in negative regulation of TLR4 signaling, on PBC monocytes was significantly decreased in comparison with CVH patients (P=0.016) and controls (P<0.001).

CONCLUSIONS

These results suggest that expression of RP105 and TLR4 is altered on PBC monocytes, which appear to be hypersensitive to LPS, resulting in increased secretion of pro-inflammatory cytokines.

Genes and (auto)immunity in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a chronic autoimmune cholestatic liver disease most commonly encountered in postmenopausal women; it is characterized by high-titer serum autoantibodies to mitochondrial antigens, elevated serum IgM, progressive destruction of intrahepatic bile ducts, and ultimately liver cirrhosis and failure. The cytopathic mechanisms leading to the selective destruction of intrahepatic cholangiocytes are still largely unknown. The current theory on the pathogenesis of PBC indicated that environmental factors might trigger autoimmunity in genetically susceptible individuals. In fact, genetic predisposition is critical to disease onset and progression, yet peculiar among autoimmune diseases, as indicated by the lack of a strong association with major histocompatibility complex haplotypes. Further, the recently reported concordance rate among monozygotic twins strengthens the importance of genetic factors, while also indicating that additional factors, possibly infectious agents or xenobiotics, intervene to trigger the disease. In this review, the available data regarding the genetic factors associated with PBC susceptibility and progression, as well as the available evidence regarding the immunomediated pathogenesis of PBC, will be critically illustrated and discussed.

Altered monocyte responses to defined TLR ligands in patients with primary biliary cirrhosis

The role of the adaptive immune response, with regard to the development of autoantibodies, has been extensively studied in primary biliary cirrhosis (PBC). However, the importance of innate immunity has been noted only recently. Based on the proposed role of microorganisms in the pathogenesis of the disease, we hypothesize that patients with PBC possess a hyper-responsive innate immune system to pathogen-associated stimuli that may facilitate the loss of tolerance. To address this issue, we isolated peripheral blood monocytes from 33 patients with PBC and 26 age-matched healthy controls and stimulated such cells in vitro with defined ligands for toll-like receptor (TLR) 2 (lipoteichoic acid; LTA), TLR3 (polyIC), TLR4 (lipopolysaccharide; LPS), TLR5 (flagellin), and TLR9 (CpG-B). Supernatant fluids from the cultures were analyzed for levels of 5 different pro-inflammatory cytokines, interleukin (IL)-1beta, IL-6, IL-8, IL-12p70, and TNF-alpha. After in vitro challenge with TLR ligands, PBC monocytes produced higher relative levels of pro-inflammatory cytokines, particularly IL-1beta, IL-6, IL-8, and TNF-alpha, compared with controls. In conclusion, monocytes from patients with PBC appear more sensitive to signaling via select TLRs, resulting in secretion of selective pro-inflammatory cytokines integral to the inflammatory response that may be critical in the breakdown of self-tolerance.

Genetic polymorphisms of toll-like receptor 9 influence the immune response to CpG and contribute to hyper-IgM in primary biliary cirrhosis

The serum hallmark of primary biliary cirrhosis (PBC) is the presence of anti-mitochondrial antibodies (AMA), found in 95% of patients. However, nearly every patient with PBC, including those who are AMA-negative, has an elevation in serum IgM. This hyper-IgM is neither representative of other Ig isoforms, nor is due to the levels of AMA. In fact, we have recently reported that the hyper-IgM is an innate immune response and can be induced with CpG-B with concurrent up-regulation of toll-like receptor 9 (TLR9). Based on these observations, we performed a two-tier study. First, we quantitated TLR9 genotypes in patients with PBC and controls and correlated these data with the B cell response to CpG-B. Second, based on these data, we performed an extensive TLR9 genotyping in a large cohort of patients and controls. We report herein that the 2848 AA TLR9 genotype is associated with enhanced gene expression and higher frequency of intracellular IgM(+) B cells following CpG stimulation. Interestingly, however, despite the functional association, there is no difference in the distribution of TLR9 genotypes between patients and controls. Our data emphasize the importance of dissecting the innate immune response in PBC.