C-protein in the skeletal muscle induces severe autoimmune polymyositis inLewis rats

To obtain a good animal model for polymyositis, we previously induced exper imental autoimmune myositis (EAM) in Lewis rats by immunization with partia lly purified skeletal myosin. However, the nature of EAM-inducing antigen(s ) in the partially purified myosin preparation remains unclear because it m ay contain several myositogenic antigens. In the present study, we further purified myosin and C-protein from partially purified myosin preparations a nd examined their EAM-inducing ability. It was revealed that immunization w ith both C-protein and purified myosin elicited EAM, which was essentially the same as that induced by partially purified myosin. However, their myosi togenic ability was quite different. C-protein induced severe EAM of high h istological grade and lesion frequency, whereas purified myosin induced onl y mild EAM. Immunohistochemical staining of C-protein-induced lesions demon strated that muscle fiber-infiltrating cells were CD8 beta(+) T cells and m acrophages and that CD4(+) cells were mainly located in the endomysium and interfiber connective tissue. Collectively, these findings suggest that C-p rotein in the skeletal muscle is the major myositogenic antigen and induces inflammatory lesions mimicking those of human polymyositis. (C) 1999 Elsev ier Science B.V. All rights reserved.