Mercuric chloride-induced autoimmunity in the brown Norway rat. Cellular kinetics and major histocompatibility complex antigen expression.

HgCl2 induces an autoimmune syndrome in Brown Norway rats that involves synthesis of anti-glomerular basement membrane (GBM) antibodies and development of nephritis with high proteinuria. HgCl2-induced changes in the composition of leukocyte populations and in the expression of MHC antigens in lymphoid and nonlymphoid organs were investigated by flow cytometry and immunohistochemistry. An early increase of CD4+ splenocytes was followed by a transient proliferation of CD4+ as well as CD8+ and B lymphocytes in peripheral lymphoid organs; in contrast, progressive depletion of the thymic cortex was found. B lymphocyte activation involved mainly the IgG1 and IgE isotypes. Nonlymphoid organs were infiltrated by MHC class II antigen expressing CD4+ and CD8+ T lymphocytes and monocytes; secondary to infiltration, mainly epithelial cells, being the main target of infiltrating cells, showed increased expression of MHC antigens. In glomeruli a 2.7-fold increase of CD8+ lymphocytes occurred after HgCl2-administration. The diverse autoimmune phenomena observed in this study fit with the hypothesized involvement of T lymphocytes autoreactive with MHC class II antigens. Apart from anti-GBM autoantibodies, a role for autoreactive CD8+ T lymphocytes must be considered in the pathogenesis of the HgCl2-induced autoimmune syndrome.