Definition of IFN-γ-related pathways critical for chemically-induced systemic autoimmunity

IFN-gamma is essential for idiopathic and murine mercury-induced systemic autoimmunity (mHgIA), and heterozygous IFN-gamma(+/-) mice also exhibit reduced disease. This suggests that blocking specific IFN-gamma-related pathways that may only partially inhibit IFN-gamma production or function will also suppress autoimmunity. To test this hypothesis, mice deficient in genes regulating IFN-gamma expression (Casp1, Nlrp3, Il12a, Il12b, Stat4) or function (Ifngr1, Irf1) were examined for mHgIA susceptibility. Absence of either Ifngr1 or Irf1 resulted in a striking reduction of disease, while deficiency of genes promoting IFN-gamma expression had modest to no effect. Furthermore, both Irf1- and Ifng-deficiency only modestly reduced the expansion of CD44(hi) and CD44(hi)CD55(lo) CD4(+) T cells, indicating that they are not absolutely required for T cell activation. Thus, there is substantial redundancy in genes that regulate IFN-gamma expression in contrast to those that mediate later signaling events. These findings have implications for the therapeutic targeting of IFN-gamma pathways in systemic autoimmunity. (C) 2012 Elsevier Ltd. All rights reserved.