Monoclonal antibody analysis of mononuclear cells in myopathies. IV: Cell‐mediated cytotoxicity and muscle fiber necrosis

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Abstract
Cell-mediated muscle fiber injury occurs in inclusion body myositis (IBM), polymyositis (PM), and even in Duchenne dystrophy (DD). Most of the autoaggressive cells are T cells and macrophages, but some are killer/natural killer (K/NK) cells. We here compare the frequencies per 1,000 muscle fibers of endomysial K/NK cells of varying cytotoxicity with those of T cells and macrophages in 8 cases each of IBM, PM, and DD. Two-micrometer serial cryostat sections were analyzed. The Leu-4 marker, present on all T cells and some K/NK cells, and the Leu-7 and Leu-11 markers, present on K/NK cells, were localized by paired immunofluorescence. Macrophages were demonstrated by the acid phosphatase reaction. In IBM, PM and DD, the respective average cell counts per 1,000 muscle fibers were: Leu-4+7− cells (T cells not expressing a K/NK marker)—710, 530, and 59; Leu-4+7+ cells (K/NK cells of low K/NK cytotoxicity)—294, 163, and 13; Leu-4−7+ cells (K/NK cells of intermediate cytotoxicity)—32, 10, and 2; and macrophages—292, 251, and 38. Leu 11+ K/NK cells that have the highest killing activity were virtually absent in all cases. The data suggest a limited role for antigen and major histocompatibility complex unrestricted K/NK cells, as compared with antigen-specific and major histocompatibility complex-restricted T cells, in IBM and PM. Further, the findings cast doubt on the significance of either T cells or K/NK cells in mature muscle in DD. We also determined the frequencies of nonnecrotic muscle fibers invaded by mononuclear cells (i.e., fibers affected by cell-mediated cytotoxicity) and of necrotic fibers, for these frequencies are indicators of two major mechanisms of muscle fiber injury in myopathies. Nonnecrotic invaded fibers were 5.5 times more frequent than necrotic fibers in IBM; the converse was true in DD; and the two mechanisms were equally frequent in PM.

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