ELEVATED SERUM LEVELS OF INTERLEUKIN-1 RECEPTOR ANTAGONIST IN POLYMYOSITIS DERMATOMYOSITIS - A BIOLOGIC MARKER OF DISEASE-ACTIVITY WITH A POSSIBLE ROLE IN THE LACK OF ACUTE-PHASE PROTEIN RESPONSE/

Objective. To determine whether the lack of acute-phase protein (APP) response in numerous patients with polymyositis/dermatomyositis (PM/DM ) is related to an imbalance between cytokines and cytokine inhibitors . Methods. Levels of C-reactive protein (CRP), interleukin-1/beta (IL- 1 beta), tumor necrosis factor alpha (TNF alpha), IL-6, IL-1 receptor antagonist (IL-1ra), TNF soluble receptor 55 kd (sTNFR 55 kd), and sTN FR 75 kd were tested in the serum of 15 patients with PM/DM, 14 patien ts with spondylarthropathies (SPA), and 12 healthy blood donors. Serum IL-1 beta, TNF alpha, IL-6, IL-1ra, sTNFR were measured by specific i mmunoassays. Results. Serum levels of CRP were lower in PM/DM patients than in SPA patients. Normal or slightly elevated CRP values were fou nd in 10 of the 15 PM/DM patients, 7 of whom had active myositis. Seru m IL-6 levels were significantly higher in SPA patients than in PM/DM patients, whereas serum IL-1ra and sTNFR levels were significantly hig her in PM/DM than in SPA patients. IL-1ra levels were particularly ele vated in patients with active myositis and decreased in response to tr eatment. Conclusion. These differences in cytokine levels, particularl y IL-1ra, between PM/DM and SPA patients are indicative of distinct pa thogenic mechanisms. High levels of IL-1ra may account for the weak AP P response in some PM/DM patients. Our results suggest that measuremen t of IL-1ra, together with clinical examination, may provide useful in formation for the followup of PM/DM patients.