A critical role for immature muscle precursors in myositis.

The innate and adaptive immune responses contribute to the development of inflammatory myopathies; the innate immune system does so through activation of the type I interferon and Toll-like receptor pathways. Dendritic cells have a pivotal role in the development of both adaptive and innate immune responses. Equipped with a range of pattern-recognition receptors, dendritic cells link innate and adaptive immunity. This Perspectives article discusses novel concepts in myositis, focusing on immature muscle precursors. Of interest, the immature muscle precursors involved in regeneration are associated with upregulation of HLA class I antigens and myositis-associated autoantigens, as well as activation of the Toll-like receptor pathway and production of type I interferon, and could have a critical contribution to the pathogenesis of myositis. These regenerating immature muscle cells might also be a target of the immune response in myositis, thereby explaining why muscle regeneration is not effective in the context of such inflammation.