IFNγ and CTLA-4 Drive Hepatic CD4 T-Cell Tolerance and Protection From Autoimmunity in Mice

BACKGROUND & AIMS: The liver has a distinct capacity to induce immune tolerance to hepatic antigens. Although liver tolerance can be advantageous for preventing autoimmune and inflammatory diseases, it also can be detrimental by preventing immune surveillance of infected or malignant cells. Here, we investigated the immune mechanisms that establish hepatic tolerance. METHODS: Tolerance was investigated in C-reactive protein (CRP)-myelin basic protein (MBP) mice expressing the neuro-antigen MBP in hepatocytes, providing profound resistance to MBP-induced neuroinflammation. Tolerance induction was studied after transfer of MBP-specific CD4 T cells into CRP-MBP mice, and tolerance mechanisms were tested using depleting or blocking antibodies. RESULTS: Although tolerant CRP-MBP mice display increased numbers of forkhead box P3 thorn regulatory T cells, we here found them not essential for the maintenance of hepatic tolerance. Instead, upon MBP recognition in the liver, MBP-specific T cells became activated to produce interferon (IFN)gamma, which, in turn, induced local up-regulation of recruitment molecules, including Chemokine (C-X-C motif) ligand9 and its receptor C-X-C motif chemokine receptor3, facilitating endothelial translocation and redirection of MBP-specific T cells into the hepatic parenchyma. There, the translocated MBP-specific CD4 T cells partly converted into interleukin 10-producing type 1 regulatory T cells, and significantly up-regulated the expression of immune checkpoint molecules, notably cytotoxic T-lymphocyte-associated protein 4 (CTLA-4). Intriguingly, although liver tolerance was not affected by impairment of interleukin 10 signaling, concomitant blockade of IFN gamma and CTLA-4 abrogated hepatic tolerance induction to MBP, resulting in neuroinflammatory autoimmune disease in these mice. CONCLUSIONS: IFN gamma-mediated redirection of autoreactive CD4 T cells into the liver and up-regulation of checkpoint molecules, including CTLA-4, were essential for tolerance induction in the liver, hence representing a potential treatment target for boosting or preventing liver tolerance.

Automated summary

This study investigated the immune mechanisms that establish liver tolerance. It was found that MBP-specific T cells were activated to produce IFN-gamma in the liver, which induced the up-regulation of recruitment molecules and redirected the T cells into the liver parenchyma. Some of the translocated T cells converted into regulatory T cells producing IL-10 and up-regulated the expression of immune checkpoint molecules. The up-regulation of IFN gamma and immune checkpoint molecules, including CTLA-4, were essential for tolerance induction in the liver.