The role of non-professional liver-resident APCs for inhibition of immune-mediated hepatitis in the mouse liver

Objectives: A single injection of concanavalin A (ConA) to mice induces acute Th1-mediated hepatitis. Tolerance against ConA rechallenge develops within 8 days and is mediated by IL–10-producing CD25+Foxp3+ regulatory T cells (Tregs). This study was intended to identify the contribution of hepatocytes (HC) to ConA tolerance by inducing a regulatory phenotype in naïve T cells. Methods: HC or splenic DC were isolated from saline- or ConA-pretreated wt, IL–10-, IFNγ-, IRF–1- or B7H1-deficient mice. Subsequently, HC or DC were co-cultured with splenic CD4+ responder T cells from wt, DEREG or IL–10 KO mice and stimulated with anti-CD3 for 48 hours. Cytokine release into the supernatant was measured by ELISA. Frequencies of CD4+Foxp3+ Tregs were quantified by FACS analysis. Results: Naïve CD4+ wt T cells co-cultured with ConA-tolerant wt HC showed significantly increased IL–10 levels indicating a tolerant phenotype. T cells were identified as major source of IL–10. In contrast, splenic DC from ConA-tolerant mice failed to induce IL–10 release in naïve wt T cells. However, CD4+ wt T cells co-cultured with ConA-primed B7H1-, IFNγ- or IRF–1-deficient HC released significantly lower levels of IL–10 compared to co-cultivation with ConA-tolerant wt HC. Moreover, Foxp3 expression was elevated in co-cultures of T cells from DEREG mice with ConA-tolerant HC compared to non-primed HC. Additionally, ConA-tolerant HC promoted the TGFβ-driven conversion of naïve wt T cells. Conclusions: We showed that HC from ConA-tolerant mice might act as non-professional APCs, since these cells were able to induce a regulatory T cell phenotype which is characterised by elevated IL–10 release. This process might depend firstly on an intact IFNγ-dependent Th1 response and secondly on the co-inhibitory interaction PD–1/B7H1. The failure of splenic DC to induce IL–10 expression indicates that the generation of an IL–10 producing T cell subset is restricted to liver-resident non-professional APCs.