Expression of HLA-DR and its enhancing molecules in muscle fibers in polymyositis

Polymyositis (PM) is an autoimmune inflammatory muscle disease of unknown c ause in which cellular immunity is thought to play an important pathogenic role. Class II major histocompatibility complex (class II MHC: human leukoc yte antigen (HLA)-DR operates as a cofactor of antigen presentation in immu nological responses. There has been a major debate over whether muscle fibe rs themselves synthesize and express HLA-DR molecules and play a role in an tigen presentation in PM pathogenesis. In this study, we demonstrated that most muscle fibers from patients with PM synthesized and expressed HLA-DR m olecules on their surface. Human leukocyte antigen-DR expression was highly specific to PM. In addition, class II transactivator (CIITA), human leukoc yte antigen DM (HLA-DM), and invariant chain (li), which are indispensable for expression of mature HLA-DR molecules and for antigen processing and pr esentation, were co-expressed. One of the cytokines that could induce this expression is interferon-gamma (IFN-gamma), released by activated lymphocyt es. Our results indicate that in PM muscle fibers synthesize and express HL A-DR molecules and may contribute to the inflammatory responses together wi th lymphocytes. (C) 2000 John Wiley & Sons, Inc. Muscle Nerve 23: 385-392, 2000.