ARTHRITIS & RHEUMATISM Vol. 54, No. 6, June 2006, pp 2004–2009 DOI 10.1002/art.21883 © 2006, American College of Rheumatology Unusually High Frequency of Autoantibodies to PL-7 Associated With Milder Muscle Disease in Japanese Patients With Polymyositis/Dermatomyositis Yoshioki Yamasaki, 1 Hidehiro Yamada, 2 Toshiko Nozaki, 2 Jun Akaogi, 2 Cody Nichols, 1 Robert Lyons, 1 Anthony Chin Loy, 1 Edward K. L. Chan, 1 Westley H. Reeves, 1 and Minoru Satoh 1 Objective. Autoantibodies to aminoacyl transfer RNA synthetases, such as histidyl (Jo-1), threonyl (PL- 7), alanyl (PL-12), glycyl (EJ), and isoleucyl (OJ), are closely associated with a subset of patients with polymyositis/dermatomyositis (PM/DM) complicated by interstitial lung disease (ILD). Anti–Jo-1 is by far the most common, found in 15–25% of patients with PM/ DM, whereas the other types are found in only 3% of these patients. In this study, the clinical associations of these autoantibodies in Japanese patients with PM/DM were investigated. Methods. The diagnoses of PM/DM and amyo- pathic DM (ADM) were based on the Bohan and Peter criteria and Sontheimer’s definition, respectively. Sera from 36 Japanese patients with PM/DM (13 with PM, 20 with DM, 3 with ADM) were screened by immunopre- cipitation and by enzyme-linked immunosorbent assay (for Jo-1). Clinical and laboratory data were collected. Results. The frequencies of autoantibodies to Jo-1 (22%) and to EJ, OJ, and PL-12 (3–6%) were similar to those found in previous studies, including studies of Japanese subjects. However, anti–PL-7 was found in 17% of patients, in contrast to a frequency of 1–4% in previous studies (P < 0.02–0.0002). The 6 anti–PL-7– positive patients were not related, and no skewing in year or month of disease development, place of resi- dence or work, or occupation was found. All patients had ILD, consistent with the clinical features of antisynthetase-positive patients. The patients with anti– PL-7 had lower serum muscle enzyme levels and milder muscle weakness (P < 0.05) compared with anti–Jo-1– positive patients. Conclusion. Anti–PL-7 was found at an unusually high frequency in this group of Japanese patients with myositis. Although anti–PL-7, similar to anti–Jo-1, is associated with PM/DM with ILD, muscle involvement in the patients with anti–PL-7 appeared to be milder than that in the anti–Jo-1 subset. Certain autoantibodies, such as anti-Sm in sys- temic lupus erythematosus (SLE) and anti– topoisomerase I in systemic sclerosis (SSc; scleroderma), are associated with particular diagnoses and are useful clinical markers. In addition, some autoantibodies are tightly linked with a specific clinical subset of the disease. Anti–Jo-1 antibodies, which recognize the cyto- plasmic amino acid–charging enzyme histidyl transfer RNA (tRNA) synthetase, are a disease marker of polymyositis/dermatomyositis (PM/DM) associated with a unique clinical subset, characterized by myositis, inter- stitial lung disease (ILD), arthritis, mechanic’s hands, and Raynaud’s phenomenon (1). Interestingly, auto- antibodies to all other aminoacyl tRNA synthetases, including threonyl (PL-7), alanyl (PL-12), glycyl (EJ), isoleucyl (OJ), and asparaginyl (KS), are associated with the same syndrome, which has been designated antisyn- thetase syndrome (1). Anti–Jo-1 antibodies, found in 15–25% of PM/DM patients, are by far the most common among the antisynthetase antibodies; all other types are usually Supported by NIH grants R01-AR-40391, and M01R00082. 1 Yoshioki Yamasaki, MD, Cody Nichols, MD, Robert Lyons, BS, Anthony Chin Loy, BS, Edward K. L. Chan, PhD, Westley H. Reeves, MD, Minoru Satoh, MD, PhD: University of Florida, Gaines- ville; 2 Hidehiro Yamada, MD, PhD, Toshiko Nozaki, MD, Jun Akaogi, MD, PhD: St. Marianna University School of Medicine, Kawasaki, Japan. Address correspondence and reprint requests to Minoru Satoh, MD, PhD, Division of Rheumatology and Clinical Immunology, University of Florida, PO Box 100221, Gainesville, FL 32610-0221. E-mail: satohm@ufl.edu. Submitted for publication July 13, 2005; accepted in revised form February 27, 2006. 2004