Coculture with autologous myotubes of cytotoxic T cells isolated from muscle in inflammatory myopathies

T‐cell lines were expanded from muscle of 10 patients with polymyositis, 5 with inclusion body myositis, 5 with dermatomyositis, and 5 with other muscle diseases. All cell lines uniformly expressed T‐cell antigens, but not natural killer cell or B‐cell antigens. The proportion of helper (CD4⁺) and cytotoxic (CD8⁺) T cells in the expanded lines was variable and showed no correlation with the diagnosis. Sixteen cell lines (6 polymyositis, 4 inclusion body myositis, 5 dermatomyositis, 1 other muscle disease) consisted predominantly of CD8⁺ T cells. None of these lines displayed natural killer‐like cytotoxicity but all were capable of lectin‐dependent cytotoxicity. Three of 6 polymyositis, 1 of 4 inclusion body myositis, and 1 of 5 dermatomyositis lines showed low but statistically significant cytotoxicity against autologous myotubes (6 to 27% specific ⁵¹Cr release; effector‐target ratio, 20:1). The results demonstrate that functionally competent cytotoxic T cells can be expanded from muscle affected by inflammatory myopathies and are consistent with the hypothesis that some cytotoxic T cells recognize an autoantigen on myotubes. Further studies of this experimental system may define the molecular mechanism of T cell‐mediated muscle fiber injury and may help to identify the relevant antigens.