Antiglycyl tRNA synthetase is an unusual autoantibody specificity associated with polymyositis and dermatomyositis complicated by interstitial lung disease. We report here autoantibodies to glycyl tRNA synthetase in a patient with systemic lupus erythematosus and interstitial lung disease. During the course of her disease, the patient developed elevated muscle enzymes and worsening pulmonary function. A quantitative immunoprecipitation technique was developed to evaluate the relationship between autoantibody production and clinical manifestations in this patient. Increasing serum antiglycyl tRNA synthetase antibody levels correlated with the severity of the patient's interstitial lung disease and with the level of creatine phosphokinase. These results suggest that certain autoantibodies, such as antiglycyl tRNA synthetase, might reflect an underlying pathologic process (in this case, myositis and interstitial lung disease) irrespective of disease diagnosis, and that quantitative immunoprecipitation may be a useful technique for investigating the relationship between specific autoantibody production and organ involvement in systemic autoimmune disease. Quantitation of these autoantibodies may be useful clinically in monitoring disease activity and/or response to therapy.
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