Anti-threonyl-tRNA synthetase, a second myositis-related autoantibody.

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Abstract
An autoantibody known as PL-7 was found in the serum of 4 patients with myositis and 1 with a systemic lupus erythematosus-like syndrome. The PL-7 antigen is an 80,000 dalton polypeptide that coprecipitates with tRNA. In aminoacylation reactions, PL-7 IgG inhibited the charging of tRNA with threonine but had little or no effect on charging with other amino acids. Experimental antibodies raised against purified threonyl-tRNA synthetase recognized the same 80,000 dalton polypeptide, but tRNA was not coprecipitated. PL-7 antibody is apparently directed at threonyl-tRNA synthetase. Different antigenic sites are recognized by the human and experimental autoantibodies. The findings emphasize the link between myositis and autoimmunity to tRNA-related structures.