CD4 and polymyositis: Although CD8+ T cells are the predominant immune cells in polymyositis associated with cytotoxicity, it was shown that CD4+ T cells can also cause muscle cell injury directly through Fas cell surface death receptor and its ligand FasL (transmembrane proteins that belong to the TNF family) that are expressed on both infiltrating lymphocytes and muscle fibers on muscle tissue from polymyositis patients [119].