[Idiopathic Inflammatory Myopathy and Anti-aminoacyl-tRNA Synthetase Antibody].

Anti-aminoacyl-tRNA synthetase (ARS) antibodies (anti-Jo-1, anti-PL-7, anti-PL-12, anti-EJ, anti-KS, anti-OJ, anti-Ha, and anti-Zo antibodies) are found in 25 to 40% of myositis patients. The patients with these antibodies have anti-synthetase syndrome with one or more of the following clinical features: myositis, interstitial lung disease, arthritis, fever, Raynaud's phenomenon, and mechanic's hands. In Japan, health insurance coverage of treatments for patients in whom the "anti-ARS antibodies," anti-Jo-1, anti-PL-7, anti-PL-12, anti-EJ, and anti-KS are detected by enzyme-linked immunosorbent assay was approved by the Ministry of Health, Labour and Welfare in 2014. Recently, clinical features have been discovered to be heterogeneous. Patients with the anti-PL-7, anti-PL-12, anti-KS, and anti-OJ antibodies exhibit interstitial lung disease rather than myositis. Interstitial lung disease is related to the prognosis of this syndrome. Regarding histopathological findings of the muscle, perimysial connective tissue fragmentation with positive staining for alkaline phosphatase is the characteristic feature. Myonuclear actin filament inclusions are also detected. A recent work demonstrated that immunization of mice with histidyl-tRNA synthetase results in muscle inflammation consistent with myositis. These findings promote understanding of the pathological mechanism of the development of myositis associated with anti-ARS antibodies.