Autoantibodies to myeloperoxidase in Brown Norway rats treated with mercuric chloride

Abstract

BACKGROUND: Mercuric chloride (HgCl2) induces an autoimmune syndrome in Brown Norway (BN) rats characterized by the presence of a number of autoantibodies, including antibodies to glomerular basement membrane. Tissue injury has previously been reported to be rare in this model, but in the accompanying paper we describe changes in a number of organs including a necrotizing leucocytoclastic vasculitis in the gut. Myeloperoxidase (MPO) is one of the target antigens for anti-neutrophil cytoplasm antibodies, that are present in the majority of patients with the human autoimmune disease systemic vasculitis and have been implicated in pathogenesis. There is at present, no animal model for anti-neutrophil cytoplasm antibody positive systemic vasculitis. EXPERIMENTAL DESIGN: Ten BN rats were given five injections of HgCl2, each of 1 mg/kg, over 10 days. Sequential serum samples were tested for autoantibodies to MPO using solid phase assays, indirect immunofluorescence on normal rat neutrophils, and Western blot analysis. The specificity of these antibodies in the solid phase assay was confirmed by inhibition studies with purified antigen, and by testing binding to uncoated plates. Sera from control animals treated with saline were also tested. RESULTS: BN rats given HgCl2 developed antibodies to MPO, which in Western blots bound to similar determinants to those bound by human anti-MPO antibodies. The anti-MPO antibodies resolved spontaneously, with a time course similar to that of the anti-glomerular basement membrane antibodies, but there was no correlation between the two antibody responses in individual animals. There was no anti-MPO activity in sera taken before HgCl2 was given, nor in sera from saline-treated controls. CONCLUSIONS: BN rats treated with HgCl2 develop anti-MPO antibodies. Together with the description in the accompanying paper of necrotizing vasculitis in these animals, these observations suggest that HgCl2-induced autoimmunity in the BN rat may provide a useful model of anti-neutrophil cytoplasm antibody positive systemic vasculitis.