Given the essential role of IL-15 in memory CD8+ T-cell survival and function and the pathogenic role of cytotoxic CD8+ T cells in polymyositis and inclusion-body myositis, we hypothesize that the skeletal muscle IL-15 promotes autoreactive CD8+ T-cell function, which contributes to the development of autoimmune myositis. The gene discussed is CD8A; the disease is polymyositis.