The hallmark of primary biliary cirrhosis (PBC) is the presence of autoreactive T and B cell responses that target biliary epithelial cells (BEC). We have previously demonstrated that biliary cell cytotoxicity is dependent upon the initiation of innate immune responses followed by chronic adaptive as well as bystander mechanisms. Critical to these mechanisms are the interactions between natural killer (NK) cells and BEC. We have taken advantage of our ability to isolate relatively pure viable preparations of liver-derived NK cells, BEC, and endothelial cells, and studied the interactions between NK cells and BEC and focused on the mechanisms that activate autoreactive T cells, their dependence on IFN-γ, and the expression of BEC MHC class I and class II molecules. Importantly, we demonstrate herein that at a high NK/BEC ratio, NK cells are cytotoxic for autologous BECs, but are not dependent on autoantigen, but yet still activate autoreactive CD4+ T cells in the presence of antigen presenting cells (APC). In contrast, at a low NK/BEC ratio, BECs are not lysed, but IFN-γ production is induced, which facilitates expression of MHC class I and class II molecules on BEC and, interestingly, protects them from lysis upon subsequent exposure to autoreactive NK cells. Furthermore, IFN-γ secreted from NK cells after exposure to autologous BECs is essential for this protective function and enables autoreactive CD4+ T cells to become cytopathic. In conclusion, our data reveal that NK cell mediated innate immune responses are likely critical at the initial stage of PBC, but also facilitate and maintain the chronic cytopathic effect of autoantigen-specific T cells, essential for progression of disease.

Understanding the mechanisms of chronic inflammation in primary biliary cholangitis (PBC) is essential for successful treatment. Earlier work has demonstrated that patients with PBC have reduced expression of the anion exchanger 2 (AE2) on biliary epithelial cells (BEC) and deletion of AE2 gene has led to a PBC-like disorder in mice. To directly address the role of AE2 in preventing PBC pathogenesis, we took advantage of our ability to isolate human BEC and autologous splenic mononuclear cells (SMC). We studied the influence of hydrophobic bile acids, in particular, glycochenodeoxycholic acid (GCDC), on AE2 expression in BEC and the subsequent impact on the phenotypes of BEC and local inflammatory responses. We demonstrate herein that GCDC reduces AE2 expression in BEC through induction of reactive oxygen species (ROS), which enhances senescence of BEC. In addition, a reduction of AE2 levels by either GCDC or another AE2 inhibitor upregulates expression of CD40 and HLA-DR as well as production of IL-6, IL-8 and CXCL10 from BEC in response to toll like receptor ligands, an effect suppressed by inhibition of ROS. Importantly, reduced AE2 expression enhances the migration of autologous splenic mononuclear cells (SMC) towards BEC. In conclusion, our data highlight a key functional role of AE2 in the maintenance of the normal physiology of BEC and the pathogenic consequences of reduced AE2 expression, including abnormal intrinsic characteristics of BEC and their production of signal molecules that lead to the chronic inflammatory responses in small bile ducts.

DNA methylation is the conversion of cytosine to 5-methylcytosine, leading to changes in the interactions between DNA and proteins. Methylation of cytosine-guanine (CpG) islands (CGIs) is associated with gene expression silencing of the involved promoter. Although studies focussing on global changes or a few single loci in DNA methylation have been performed in dogs with certain diseases, genome-wide analysis of DNA methylation is required to prospectively identify specific regions with DNA methylation change. The hypothesis of this study was that next-generation sequencing with methylation-specific signatures created by sequential digestion of genomic DNA with SmaI and XmaI enzymes can provide quantitative information on methylation levels. Using blood from healthy dogs and cells obtained from canine lymphoma cell lines, approximately 100,000CpG sites across the dog genome were analysed with the novel method established in this study. CpG sites in CGIs broadly were shown to be either methylated or unmethylated in normal blood, while CpG sites not within CpG islands (NCGIs) were largely methylated. Thousands of CpG sites in lymphoma cell lines were found to gain methylation at normally unmethylated CGI sites and lose methylation at normally methylated NCGI sites. These hypermethylated CpG sites are located at promoter regions of hundreds of genes, such as TWIST2 and TLX3. In addition, genes annotated with 'Homeobox' and 'DNA-binding' characteristics have hypermethylated CpG sites in their promoter CGIs. Genome-wide quantitative DNA methylation analysis is a sensitive method that is likely to be suitable for studies of DNA methylation changes in cancer, as well as other common diseases in dogs.

Summary There is increasing interest in the role of T cell exhaustion and it is well known that the natural history of chronic hepatitis C virus infection (HCV) is modulated by CD8+ T cell immunobiology. There are many pathways that alter the presence of exhaustive T cells and, in particular, they are functionally impaired by inhibitory receptors, such as programmed death-1 (PD-1) and T cell immunoglobulin and mucin domain-containing protein 3 (Tim-3). We obtained spleen, liver and peripheral blood (before and after splenectomy) lymphoid cells from 25 patients with HCV-related cirrhosis undergoing liver transplantation for end-stage disease or splenectomy for portal hypertension. In all samples we performed an extensive phenotypic study of exhaustion markers [PD-1, Tim-3, interferon (IFN)-γ) and their ligands (PD-L1, PD-L2, galectin-9] in CD8 + T cell subpopulations (both total and HCV-specific) and in antigen-presenting cells (APC; monocytes and dendritic cells). In the spleen, total and HCV-specific CD8+ T cells demonstrated enhanced markers of exhaustion, predominantly in the effector memory subpopulation. Similarly, splenic APC over-expressed inhibitory receptor ligands when compared to peripheral blood. Finally, when peripheral blood CD8 + T cells were compared before and after splenectomy, markers of exhaustion were reduced in splenic CD8 + T cells and APC. Our data in HCV-related cirrhosis suggest that CD8 + T cells in the spleen manifest a significantly higher exhaustion compared to peripheral blood and may thus contribute to the failure to control HCV. Counteracting this process may contribute to inducing an effective immune response to HCV.

SummaryOne of the major obstacles in dissecting the mechanism of pathology in human primary biliary cirrhosis (