Further evidence for the presence of anti-protein S autoantibodies in patients with systemic lupus erythematosus

Acquired protein S (PS) deficiency in systemic lupus erythematosus (SLE) ha s been previously reported, but its mechanism and its possible thrombotic r ole have not been established. The aim of our study was to provide further evidence for auto-immune PS deficiency in 27 Tunisian SLE patients, using P S-specific enzyme-linked immunosorbent assay (ELISA) and surface plasmon re sonance technology (SPR). PS deficiencies for PS activity, free PS or total PS, respectively, were found in 19, 18 and 12 patients. A significant corr elation (r = -0.475, P < 0.016) was found between free/total PS ratio and C 4bBP levels, suggesting a role of inflammation in free PS deficiency. Immun oglobulin IgG antibodies to PS were detected in four patients by both ELISA and SPR, in six patients only by ELISA, and in two patients only by SPR. S ignals for anti-PS IgG by ELISA and SPR were, however, significantly correl ated (r = 0,549, P = 0.003). These results suggest that an auto-immune mech anism could account for low PS activity in patients with SLE. Ante-antibodi es to PS may form immune complexes, inducing increased clearance of PS or i nterfering with the protein C-protein S system. (C) 2000 Lippincott William s & Wilkins.