The Autoimmune Myopathies

The autoimmune myopathies (also known as myositis) comprise an important group of disorders in which skeletal muscle is one of the primary targets of the autoimmune response. The immune responses in these disorders target a limited set of ubiquitously expressed autoantigens, and there is a striking association of specific autoantibodies with distinct clinical phenotypes. Several features of these diseases, including the association with cancer, the induction of disease in response to statins, and the preferential expression of myositis-specific autoantigens in regenerating but not resting muscle cells, have provided important insights into the initiating and propagating mechanisms. Emerging data suggest a model of disease in which initiation and propagation may be separated in time and, potentially, space. In this model, increased expression of myositis-specific autoantigens in regenerating cells focuses immune injury on cells healing muscle injury, establishing a self-sustaining loop of immune-mediated muscle injury and repair. Such loops may be amenable to novel therapeutic interventions.