MYOSIN-INDUCED AUTOIMMUNE POLYMYOSITIS IN THE RAT

Experimental autoimmune myositis (EAM) was induced in Lewis rats by im munization with partially purified and purified skeletal myosin. Altho ugh clinical signs such as muscle weakness were very mild, multiple in flammatory lesions in the skeletal muscle, but not in the heart, were found by histological examination. Immunohistochemical staining reveal ed that muscle fiber-infiltrating cells were CD8(+) and CD11b(+) cells and that CD3(+), TCR alpha beta(+), B and NK cells were mainly locate d in the endomysium and interfiber connective tissue. These findings w ere in contrast to those obtained in experimental autoimmune encephalo myelitis lesions in which CD4(+) cells predominate over CD8(+) cells. T cells and sera isolated from myosin-immunized animals responded vigo rously to myosin. However, neither sensitized lymphoid cells mainly co mprising CD4(+) cells nor purified anti-myosin immunoglobulin G mediat ed the disease into naive rats, suggesting that T cells other than CD4 (+) cells such as CD8(+) cells may be the final effector. Taken togeth er, EAM induced in Lewis rats is similar to human polymyositis (PM). E AM can serve as a good model for human PM and give insight into the pa thogenesis of the disease. (C) 1997 Elsevier Science B.V.