Monoclonal antibody analysis of mononuclear cells in myopathies. II: Phenotypes of autoinvasive cells in polymyositis and inclusion body myositis.

In 6 cases of polymyositis and 6 of inclusion body myositis, phenotypes of mononuclear cells focally surrounding and invading muscle fibers were analyzed. By localizing the T8, T4, and Ia markers with direct immunofluorescence and acid phosphatase enzyme cytochemically in the same sections, five different phenotypes were simultaneously identified in a given section: T8+ and T4+ cells that were either activated (Ia+) or not activated (Ia-), and acid phosphatase--reactive and Ia+ macrophages. This approach permitted the separate and quantitative assessment of the distributions of the different phenotypes among the invading versus the surrounding cells. In both polymyositis and inclusion body myositis, the invading cells were selectively enriched in the T8+ phenotype. One-third of all invading cells and one-half of the invading T8+ cells were activated. T4+ cells were more abundant among the surrounding than the invading cells, and only a small proportion of the T4+ cells were activated. These findings are especially significant in view of the cytotoxic capability of the T8+ cells and because histocompatibility factors permit T8+ but not T4+ cells to recognize an antigen on muscle fibers. Macrophages accounted for 21 to 31% of the cells invading or surrounding nonnecrotic fibers. For purposes of comparison, we also analyzed mononuclear cells in necrotic fibers: 80% of these cells were macrophages, and only 20% were T cells. The findings indicate that in polymyositis and inclusion body myositis, nonnecrotic muscle fibers are injured by autoinvasive T8+ cells that act in concert with macrophages. Further, the findings strongly imply previous sensitization of clones of T cells to muscle fiber-associated surface antigen(s).