Autoantibodies to small nuclear and cytoplasmic ribonucleoproteins in japanese patients with inflammatory muscle disease

Objective. To elucidate the profile and clinical significance of autoantibodies to small nuclear and small cytoplasmic ribonucleoproteins in Japanese patients with polymyositis and dermatomyositis (PM/DM). Methods. Radioimmunoprecipitation assays were performed with sera from 91 patients with various inflammatory muscle diseases and from 254 control patients with other rheumatic diseases. Patients with PM/DM were categorized according to autoantibody specificities, and clinical comparisons were made. Results. Antibodies to aminoacyl transfer RNA (tRNA) synthetases and the signal recognition particle (SRP) were found to be specific for PM/DM. PM/DM patients with antibodies to 3 aminoacyl‐tRNA synthetases (histidyl, threonyl, and glycyl) appeared to form a distinct clinical subset, associated with chronic interstitial lung disease, polyarthritis, and myositis, while 3 patients with antibodies that bound the SRP had severe myositis that was resistant to corticosteroid therapy. In general, the frequency and clinical correlations of anti—aminoacyl‐tRNA synthetase antibodies in Japanese patients were similar to those in North American populations. In contrast, among this Japanese cohort, the occurrence of anti‐PM/ScI appeared to be reduced in frequency, whereas anti‐Ku and anti—U2 RNP antibodies were accentuated in patients with overlap syndromes. Conclusion. We conclude that racial groups differ somewhat in their characteristic autoimmune responses to individual autoantigens. These differences could reflect variation in immunogenetic background or different etiologic mechanisms which might occur at different geographic locations.