The role of non-professional liver APCs for tolerance induction in the mouse model of concanavalin A-induced liver injury

Objectives: A single injection of concanavalin A (ConA) in mice induces acute Th1-mediated hepatitis. Tolerance against ConA rechallenge develops within 8 days mediated by IL-10-producing CD4+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 were isolated from saline- or ConA-pretreated wt, IL-10-, IRF-1- or B7H1-deficient mice. Subsequently, HC were co-cultivated with splenic CD4+ responder T cells from wt, DEREG or IL-10 KO mice and stimulated with both anti-CD3 and anti-CD28 for 48 hours. Cytokine release into the supernatant was measured by ELISA. Frequencies of CD4+CD25+GFP+ Tregs were quantified by FACS analysis.

Results: Naïve CD4+ wt T cells co-cultivated with ConA primed wt HC showed significantly decreased IL-2 levels and significantly elevated IL-10 levels indicating a tolerant phenotype. T cells were identified as major source of IL-10. However, CD4+ wt T cells co-cultivated with ConA primed IL-10-, B7H1-, or IRF-1-deficient HC released significantly lower levels of IL-10 compared to co-cultivation with ConA primed wt HC. Moreover, GFP expression, correlating with FoxP3 expression, was significantly elevated in co-cultures of T cells from DEREG mice with ConA primed HC compared to non-primed HC whereas the activation marker CD25 was significantly down-regulated upon co-cultivation with HC from ConA-tolerant mice.

Conclusions: We demonstrated that HC from ConA tolerant mice might act as non-professional APCs, since these cells were able to induce a regulatory T cell phenotype mainly by increased proliferation of Tregs. This process might depend firstly on an intact IFNγ-dependent Th1 response and secondly on the co-inhibitory interaction PD-1/B7H1.