Conditional up-regulation of MHC class I in skeletal muscle leads to self-sustaining autoimmune myositis and myositis-specific autoantibodies

In the human inflammatory myopathies (polymyositis and dermatomyositis), th e early, widespread appearance of MHC class I on the surface of muscle cell s and the occurrence of certain myositis-specific autoantibodies are striki ng features. We have used a controllable muscle-specific promoter system to up-regulate MHC class I in the skeletal muscles of young mice. These mice develop clinical, biochemical, histological, and immunological features ver y similar to human myositis. The disease is inflammatory, limited to skelet al muscles, self-sustaining, more severe in females, and often accompanied by autoantibodies, including, in some mice, autoantibodies to histidyl-tRNA synthetase, the most common specificity found in the spontaneous human dis ease, anti-Jo-1. This model suggests that an autoimmune disease may unfold in a highly specific pattern as the consequence of an apparently nonspecifi c event-the sustained up-regulation of MHC class I in a tissue-and that the specificity of the autoantibodies derives not from the specificity of the stimulus, but from the context, location, and probably the duration of the stimulus. This model further suggests that the presumed order of events as an autoimmune disease develops needs to be reconsidered.