[Recent progress of molecular immunology on inflammatory myopathy]

The pathogenesis of polymyositis(PM), T-cell-mediated disease, and dermatomyositis(DM), humoral immunity-mediated disease, has not been clearly understood. Retroviruses(HIV, HTLV-I) may play a important role in some PM/DM patients. HTLV-I provirus was detected in infiltrating CD4+ lymphocytes, but not within the muscle fibers by PCR in situ hybridization. It is suggested that HTLV-I-associated PM is not due to direct, persistent infection of the muscle fiber by the virus, but to a T-cell-mediated immunological process triggered by the HTLV-I-infected cells. Inclusion body myositis(IBM) is characterized pathologically by vacuolated muscle fibers containing paired-helical filaments(PHFs) similar to Alzheimer-disease brain. Furthermore, prion protein and mRNA are abnormally accumulated in IBM muscle.