Immunocytochemical study of CD45 T cell isoforms in inflammatory myopathies

The CD45RO and CD45RA antigens subdivide the CD8⁺ and the CD4⁺ T cells into primed memory cells and unprimed virgin T cells, respectively. To assess the relative abundance of the CD8⁺ and the CD4⁺ T cells expressing the two CD45 isoforms in the major inflammatory myopathies, we immunophenotyped T cells in muscle specimens from patients with inclusion body myositis, polymyositis (PM), and dermatomyositis. The analysis was according to diagnosis and sites of cell accumulation: endomysial inflammatory cells focally surrounding and invading nonnecrotic fibers were analyzed in inclusion body myositis and PM and perivascular infiltrates in PM and dermatomyositis. In all diseases and at all sites of accumulation, the CD45RO⁺ memory T cells were predominant and the CD45RO/CD45RA ratio exceeded that in normal blood. In PM and inclusion body myositis, the marked enrichment of endomysial T cells in memory cells implicates time cells in the pathogenesis. The enrichment of perivascular T cells in dermatomyositis and PM in memory cells may be a result of enhanced transendothelial migratory capacity of these cells; alternatively, the virgin-to-memory cell conversion may occur after diapedesis.