IL-12 down-regulates autoantibody production in mercury-induced autoimmunity

In genetically susceptible H-2(s) mice, subtoxic doses of mercuric chloride (HgCl₂) induce a complex autoimmune syndrome characterized by the production of anti-nucleolar IgG Abs, lymphoproliferation, increased serum levels of IgG1 and IgE Abs, and renal Ig deposits. Mercury-induced autoimmunity in H-2(s) mice provides a useful model for chemically related autoimmunity in humans. The increase in serum IgG1 and IgE, which are under IL-4 control, suggests a role for the Th2 subset in this syndrome. The IL-12 cytokine induces T cell proliferation and IFN-γ production and is necessary for differentiation of naive T cells into the Th1 subset. To gain an understanding of T cell control in this syndrome and, in particular, Th1/Th2 regulation, we assessed the effect of IL-12 administration in mercury- induced autoimmunity. Groups of A.SW mice (H-2(s)) received HgCl₂ plus IL- 12, HgCl₂ alone, or IL-12 alone. IL-12 treatment resulted in a dramatic reduction of the anti-nucleolar Ab titers. IL-12 also inhibited the HgCl₂- induced serum IgG1 increase, but, in contrast, did not significantly affect IgE induction in this model. This observation may be related to our unexpected finding that IL-12 further potentiated the HgCl₂-triggered IL-4 induction in this model. The levels of renal Ig deposits were similar in mice receiving HgCl₂ alone or HgCl₂ plus IL-12. Our results indicate that IL-12 can down-regulate the autoimmune component of this experimental syndrome and that the various manifestations of mercury-induced autoimmunity are independently regulated.