The Role Of Th-1and Th-17Cytokines In The Pathogenesis Of Murine Autoimmune Cholangitis And Colitis

Primary biliary cirrhosis is a chronic autoimmune liver disease characterized by chronic non-suppurative destructive cholangitis of small bile ducts, high titer antimitochondrial autoantibodies (AMA) in serum. The destruction of small bile ducts is mediated by a multi-lineage innate immune responses combination with the adaptive immune response. Autoreactive CD4+T and CD8+T cells specifically infiltrated around portal tracts. Additionally, natural killer T cell, dendritic cells and other antigen presentation cells performed a regulatory function on adaptive immune responses. Meanwhile, cytokines as important molecular participated in regulating the immune balance of PBC. There is a Thl cytokines profile predominance in serum and liver of PBC patients, accompanied by elevated level of typical Th1cytokines, IFN-γ. Meanwhile, in PBC patients, it was determined that IL-17A positive cells infiltrated around in portal tracts, too. But the precise role of IFN-γ and IL-17A in the pathogenesis of PBC needs to be clarified.Inflammatory bowel diseases (IBD) are chronic, relapsing inflammatory disorders of the gastrointestinal tract and epithelial injury. Crohn’s disease and ulcerative colitis constitute the two main subtypes of IBD. IBD patients typically suffered from diarrhoea, abdominal pain, rectal bleeding and malnutrition. The pathogenesis of IBD is mediated by genomic and mucosal immune dysfunctional. It has been suggested that cytokines directly participated on this process. In Crohn’s disease, cytokines profiles are bias towards Th1cells. Additionally, Th17cells also have a critical role in the intestinal diseases. Meanwhile, genome wide association studies (GWAS) studies showed IL-12is linked to the pathogenesis of Crohn’s disease.Due to the limitation of the clinical study, investigators dedicated to establish primary biliary cirrhosis in experimental animals, in which they could define the role of these factors in the pathogenesis of PBC directly. Our previous work demonstrated that IL-2Rα deficient (IL-2Rα-/-) mice could spontaneously develop autoimmune cholangitis, similar to human PBC, both in immunological and histological characteristics. Meanwhile, IL-2Rα-/-mice is also a classically Crohn’s disease murine model. Our previous studies also showed autoimmune cholangitis was mediated by CD8+T cells, and CD4+T cells participated in the disorder of colitis in IL-2Rα-/-mice. Simultaneously, there was a high level of Th1cell associated cytokines, IFN-γ, and the hallmark of Th17cytokines, IL-17A, in the serum of IL-2Rα-/-mice. Meanwhile, other inflammatory cytokines, such as IL-6and IL-12p40could be detected in the serum.In this study, we took advantage of IL-2Rα-/-mice to address the precise role of IFN-γ and IL-17A in the natural history of autoimmune cholangitis and colitis. Two major parts are shown as followed:Part Ⅰ. The role of IFN-γ and IL-17A of Cholangitis versus Colitis in IL-2Rα-/-/-mice1.1Deletion of IFN-γ in IL-2Rα-/-mice did not affect neither autoimmune cholangitis or colitis.We backcrossed IFN-γ-/-mice onto IL-2Rα-/-mice to generate IFN-γ-/-IL-2Rα-/-mice, then utilized HE staining to detect the histological change of liver and colon tissue sections. There was no significant differences either in cholangitis or colitis between IFN-γ-/-IL-2Rα-/-mice and IL-2Rα-/-mice. Meanwhile, liver mononuclear cells did not change, accordance with histological examination.1.2Deletion of IL-17A in IL-2Rα-/-mice exacerbated autoimmune cholangitis but ameliorated colitis.We generated IL-17A-/-IL-2Rα-/-mice through breeding IL-17A-/-mice with IL-2Rα-/-mice. Then the histological of liver and colon tissue were examined through HE staining. The cholangitis exacerbated in IL-17A deficient IL-2Rα-/-mice, in the aspect of portal inflammation, lobular inflammation and bile duct damage. Meanwhile, pathogenic CD8+T cells increased evidently, accompanied with high amounts of IFN-γ. Interestingly, deletion of IL-17A ameliorated the colitis due to the decline of the number of pathogenic effector/memory CD4+T cells.Conclusion Ⅰ:Our study showed that IL-17A but not IFN-γ played a protective role in autoimmune cholangitis of IL-2Rα-/-mice, and IL-17A played a proinflammatory role in inflammatory bowel disease. So in the clinical study, recombinant IL-17A may be the potential therapy for PBC patients, but also take caution against such use in IBD.Part Ⅱ. The role of IL-12p40of Colitis in IL-2Rα-/-miceWe backcrossed the IL-12p40-/-mice on IL-2Rα-/-mice to gain the IL-12p40-/-IL-2Rα-/-mice, then the histological of colitis was detected. Deletion of IL-12p40ameliorated the colitis. And resulted in the decreased of pathogenic CD4+T cells, accompanied by the down regulation of IL-17A, and up regulation of IFN-γ.Conclusion Ⅱ:IL-12p40played a pathogenic role in colitis in the IL-2Rα-/-mice through IL-17A pathway. It was suggested the existence of other potential cytokines participating in regulating the secretion of IFN-y in IL-2Rα-/-mice in spite of IL-12.