Systemic CD4 T cell tolerance induction in the liver depends on interferon-γ and CTLA-4

Introduction/Objectives:

We have previously shown that ectopic expression of myelin basic protein (MBP) in the liver can prevent autoimmune encephalomyelitis (EAE); however, the mechanisms explaining how the liver can effectively protect distant tissues are not entirely clear.

Methods:

MBP-specific tg4 T cells were adoptively transferred into CRP-MBP mice expressing MBP in the liver. Molecules associated with hepatic tolerance induction were identified by immunophenotyping of tg4 T cells retained from the liver. Inhibitory antibodies were used to test the importance of the identified molecules for the protection from autoimmune disease in CRP-MBP mice.

Results:

Transferred tg4 T cells accumulated in the livers of CRP-MBP recipients, as compared to non-transgenic littermates (> 10-fold). This accumulation was facilitated by hepatic re-stimulation of tg4 T cells, resulting in increased IFN-γ production, and subsequent activation of the CXCL9 – CXCR3 axis, which enables endothelial transmigration. The accumulated tg4 T cells in the livers of CRP-MBP mice showed a significant up-regulation of several co-inhibitory receptors together with IFN-γ, including Lag-3, PD-1, Tim-3, TIGIT and, most notably, CTLA-4. However, blockade of CTLA-4 by in vivo administration of an anti-CTLA-4 antibody did not impair tolerance. In contrast, blockade of IFN-γ reduced expression of CXCR3 and CXCL9 and prevented hepatic accumulation of tg4 T cells, resulting in partial impairment of systemic tolerance and development of mild EAE. Intriguingly, concomitant blockade of IFN-γ and CTLA-4 completely abolished tolerance to MBP and induced severe EAE.

Conclusion:

Our findings demonstrate that systemic CD4 T cell tolerance induction in the liver and protection from autoimmune disease depends on 1) IFN-γ-mediated transmigration of circulating autoreactive T cells into the liver parenchyma and 2) up-regulation of multiple co-inhibitory receptors, notably CTLA-4.