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Pathogenesis of Polymyositis The pathogenesis of polymyositis involves a complex interplay of immune system dysfunction , autoimmunity , and muscle fiber damage . It is primarily considered a T-cell-mediated autoimmune disorder that targets muscle fibers , leading to chronic inflammation and muscle weakness. 1. Immune System Dysregulation Polymyositis is thought to be initiated by an abnormal immune response , where the body fails to recognize its own muscle tissues and begins attacking them. This response is primarily cell-mediated rather than antibody-mediated. 2. Role of CD8+ T-Cells Cytotoxic CD8+ T lymphocytes are the main effector cells. These T cells  recognize antigens presented on muscle fibers via MHC class I molecules , which are abnormally upregulated on the surface of muscle cells in polymyositis. The T cells then directly invade muscle fibers and release perforin and granzymes, leading to muscle cell necrosis (cell death). 3. Muscle Fiber Inju...