The idiopathic inflammatory myopathies (IIM) are systemic autoimmune diseases that have predominant mononuclear inflammatory cell infiltrates in the skeletal muscle. The cells that are typically involved in the pathogenesis of disease are B-lymphocytes, T-lymphocytes, macrophages, dendritic cells, and natural killer cells. However, in addition to these immune cells, cells of nonimmunologic origin, such as myocytes, may be directly involved in the immune response. The local milieu also consists of distinct cytokine and chemokine profiles considered related to type 1 interferon stimulation. Tumor necrosis factor and interleukin 1 are also prominent, proinflammatory cytokines involved in the evolution of IIM. Although the pathologic processes involved in IIM have yet to be fully elucidated, we understand the inflammatory milieu is a model of dynamic flux made of diverse cytokine and chemokine expressions leading to alterations in muscle fiber structure and function.
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