Expression of tumor necrosis factor-α in muscles of polymyositis

We immunohistochemically examined biopsied muscles from nine untreated patients with polymyositis (PM) and five patients with other neuromuscular diseases (ONMD), using monoclonal antibodies to tumor necrosis factor-α (TNF-α) and lymphoid surface markers. In muscles of three patients with PM, we observed many TNF-α positive macrophages and lymphocytes in endomysium and around vessels in the muscles. By contrast, there were few, weakly TNF-α stained cells in muscles of three patients with ONMD. The ratio of TNF-α-positive cells to the muscle fibers and the ratio of TNF-α-positive cells to the mononuclear cells were significantly higher in PM compared with ONMD. In addition, we obsered atrophic muscle fibers more frequently in TNF-α-positive muscles than TNF-α-negative ones. We conclude that, at least, in a part of PM patients, TNF-α produced locally may contribute to the pathogenesis of PM.