Cell-Mediated Cytotoxicity and Childhood Dermatomyositis

Nine children with inflammatory myopathy were studied for evidence of cell-mediated cytotoxicity. Seven patients had clinical childhood dermatomyositis (CDM), one had mixed connective-tissue disease, and one juvenile rheumatoid arthritis, but all had evidence in the biopsy specimen of muscle inflammation. Blood was simultaneously taken from age- and sex-matched controls. After separation on a Ficoll-Hypaque column, monocytes and mixed lymphocytes from each subject were added to monolayers of human skeletal muscle cells for intervals up to 72 hours. The monolayers were washed and incubated with amino acid hydrolysate labeled with carbon 14. After washing, the myocytes were harvested, solubilized, and measured for¹⁴C uptake. The counts per minute per milligram of protein were directly proportional to muscle cell viability. There was no substantial difference in the viability of myocytes exposed to either monocytes or mixed lymphocytes from patients or controls.