Idiopathic inflammatory myopathies (IIM) can be classified according to key pathogenic mechanisms: humoral/complement-dominant entities (such as dermatomyositis and immune-mediated necrotizing myopathy), prototypical T-cell-dominant forms (polymyositis), and inclusion body myositis, which combines chronic CD8+ cytotoxicity with degenerative protein-aggregation pathology. Here, CD8A is linked to polymyositis.