Autoantibodies to aminoacyl-transfer RNA synthetases for isoleucine and glycine. Two additional synthetases are antigenic in myositis.

Autoantibodies to three of the aminoacyl-transfer RNA (tRNA) synthetases have been reported (for histidine, threonine, and alanine). Most patients with these autoantibodies have polymyositis, and the majority also have interstitial lung disease. This study examined the question of whether autoantibodies to other aminoacyl-tRNA synthetases occur in the sera of myositis patients. We tested sera from patients with myositis with unidentified anticytoplasmic antibodies that immunoprecipitate tRNA for the ability to inhibit the aminoacyl-tRNA synthetases for the remaining 17 amino acids. Three sera showed strong inhibitory activity for a synthetase. OJ and NJ sera (and IgG) significantly inhibited isoleucyl-tRNA synthetase activity, each with 94% inhibition at the screening dilution, whereas other test sera and controls all inhibited less than 50%. OJ and NJ sera immunoprecipitated identical patterns of tRNA, and identical, complex patterns of high m.w. polypeptides that were consistent with the multienzyme synthetase complex of which isoleucyl-tRNA synthetase is a part. EJ serum (and IgG) significantly inhibited glycyl-tRNA synthetase, and immunoprecipitated a unique pattern of transfer RNA, and a strong predominant protein band of 77 kDa. These data strongly suggest that OJ and NJ have autoantibodies to isoleucyl-tRNA synthetase, and that EJ has antibodies to glycyl-tRNA synthetase. The findings of signs of muscle involvement in all three patients, and severe interstitial lung disease in OJ, strengthens the association of antisynthetases with these conditions.