Development Of Autoimmune Hepatitis In TAM Receptor-deficient Mice

Although the liver is an immunoprivileged site, autoimmune liver diseases, such as autoimmune hepatitis (AIH), develop globally in diverse ethnic groups. AIH is a progressive inflammatory liver disorder, which is often diagnosed late in its progression, and usually results in severe consequences for the patients. Unfortunately, the etiology of AIH and the mechanisms leading to immune liver damage are poorly understood. One reason for this lack of knowledge is the absence of reliable animal models that show persistent autoimmune destruction of the liver parenchyma. Here, we demonstrate that TAM receptor tyrosine kinases (Tyro3, Axl and Mer) knockout mice develop spontaneous AIH that reflects persistent autoimmune liver damage and may represent a reliable model to elucidate the pathophysiology of AIH. In this study, we analyzed the phenotype of AIH in Tyro3-/-Axl-/-Mer-/-(TAM-/-) triple mutant mice and investigated the mechanisms leading to the immune liver damage.We firstly found evident hepatomegaly in TAM-/-mice. The liver size increased progressively as TAM-/-mice aged, and reached up to5-fold that of wild controls at12months age. In accordance with the hepatomegaly, a progressive elevation of ALT and AST activities was found in sera of the TAM-/-mice, which suggests that the liver was damaged. Mean values of ALT and AST in sera of the TAM-/-mice were approximately8-fold that of WT controls at12months age. Histological analysis revealed an inflammatory phenotype characteristic for massive cellular infiltrations in parenchymal regions of TAM-/-liver. The colonies of infiltrated cells grew larger as mice aged. Further characterization showed that the infiltrated cells contained lymphocytes and marophages. The infiltrated lymphocytes in the TAM-/-liver were predominantly B cells and CD4+T cells, but relatively few CD8+T cells. The macrophages in TAM-/-liver consisted of those derived from circulating monocytes and resident Kupffer cells.The generation of autoantibodies characteristic for AIH patients suggests that TAM-/-mice develop AIH. We further investigated the mechanisms leading to autoimmune liver damage. We found that major proinflammatory cytokines, such as IL-1β, IL-6, TNF-α, IFN-α and IFN-β, were significantly upregulated in TAM-/-liver. Moreover, expression of inflammatory feature cell adhesion molecules, such as ICAM-1and P-selectin and E-selectin, was also dramatically upregulated in the TAM-/-liver. The upregulation of inflammatory feature molecules may result from the activation of NF-κB, as IκB was dramatically decreased and phosphorylated NF-κB was sharply increased in the TAM-/-liver. We also provided evidence that TNF-α induced hepatocyte death. Interestingly, IFN-α/IFN-β alone did not induce hepatocyte death, but they significantly enhance TNF-α-induced hepatocyte death, through upregulating TNF-α receptor1(TNFR1) expression.Finally, we demonstrated that Bone marrow transplantation repaired the liver damage in TAM-/-mice. WT bone marrow cells transferred into irradiated TAM-/-mice reduced dramatically TNF-α level in the liver. The liver weight was significantly decreased, and serum ALT and AST activities were back to normal level. The results suggest that transfer of bone marrow transplantation might be a feasible treatment consideration for AIH.