Immunohistochemical characterization of the mononuclear cells infiltrating muscle of patients with inflammatory and noninflammatory myopathies.

The immunopathogenetic mechanisms associated with the development of inflammatory myopathies are not well defined. In order to identify cells in affected muscle tissue, mononuclear cells infiltrating muscle biopsies from patients with inflammatory myopathies and controls with other neuromuscular diseases were analyzed in situ by an avidin-biotin immunoperoxidase technique. Serial frozen sections were stained for cells expressing total T, helper-induced T, suppressor-cytotoxic T, B, monocyte/macrophage, and HLA-DR phenotypes. A significant increase in the percentage of helper-inducer T cells are noted in the inflammatory myopathies when compared to the disease control group. Furthermore, most of the mononuclear cells in the inflammatory myopathy biopsies were HLA-DR positive, suggesting that the infiltrating T lymphocytes were activated. No significant differences in mononuclear cell distributions were found when the inflammatory myopathy group was broken down into individual groups of patients with polymyositis, polymyositis with associated connective tissue disease, and dermatomyositis.