Immunological and ultrastructural observations on the role of lymphoid cells in the pathogenesis of polymyositis.

Abstract

Muscle biopsies from two cases of polymyositis were examined with the electron microscope, particular attention being given to the inflammatory cells in the lesions. Lymphocytes which were enlarged and possibly “activated” were found in contact with the endothelium of small venules; they were also seen apparently traversing the vessel wall. Venular endothelial cells were often swollen with reduplication of the basement membrane. Perivascular and interstitial cells comprised small lymphocytes, larger transforming lymphocytes with distinctive morphological features, pleomorphic macrophages and a few plasma cells and granulocytes. In one case cells resembling primitive lymphoid cells were found internal to the basement membrane of several muscle fibres. Peripheral blood lymphocytes from both patients were stimulated on incubation with a crude muscle homogenate. The lymphocytes also appeared to be cytotoxic to cultures of foetal human striated muscle. The significance of these findings is considered in relationship to the pathogenesis of the muscle fibre damage in polymyositis.