[Myositis-specific autoantibodies]

Idiopathic inflammatory myopathies are a group of acquired skeletal muscle diseases that include polymyositis, dermatomyositis, and inclusion body myositis. Studies have shown many myositis-specific autoantibodies (MSAs) that are useful for the diagnoses as well as classification of idiopathic inflammatory myopathies, because they have been shown to correlate with distinct clinical phenotypes. Anti-Jo-1, anti-PL-7, anti-PL-12, anti-EJ, anti-KS, anti-OJ, anti-Ha, and anti-Zo antibodies target aminoacyl tRNA synthetases, and represent anti-synthetase syndrome. Anti-synthetase syndrome is characterized by myositis, interstitial lung disease, arthritis, fever, Raynaud's phenomenon, and mechanic's hands. Anti-Mi-2, anti-MDA5 (anti-CADM140), anti-TIF1 (anti-155/140, anti-p155), anti-NXP-2 (anti-MJ), and anti-SAE antibodies are specific for dermatomyositis. In particular, anti-MDA5 antibodies are clinically associated with amyopathic dermatomyositis developing into rapidly progressive interstitial lung disease, whereas anti-TIF1 and anti-NXP-2 antibodies are closely correlated with cancer-associated dermatomyositis in adults. In addition, anti-TIF1 and anti-NXP-2 antibodies are predominant MSAs found in juvenile dermatomyositis, and the latter was correlated with a high incidence of calcinosis. Furthermore, anti-SRP and anti-3-hydroxy-3-methylglutaryl-coenzyme A (anti-HMG-CoA) antibodies have been found in patients with necrotizing myopathy. Moreover, a recent study suggested the presence of autoantibodies to a 43-kDa muscle protein in patients with inclusion body myositis. Although the pathogenic role of MSAs remains unknown, recent studies have shown that myositis autoantigens are expressed at high levels in regenerating muscle fibers, which may initiate or amplify autoimmune responses in idiopathic inflammatory myopathies.