Clinical importance of antibodies against platelet activating factor in antiphospholipid syndrome manifestations

Background We assessed whether antibodies against platelet activating facto r (PAF) are related to the presence of antiphospholipid syndrome (APS) clin ical manifestations, in particular thrombosis, in patients with connective tissue diseases. Materials and methods Anti-PAF, anticardiolipin (aCL), anti beta 2 glycopro tein I (anti beta 2GPI) and antiphosphatidylcholine (anti-PC) antibodies we re determined in 52 patients with APS, 29 patients with systemic lupus eryt hematosus (SLE) aCL but without APS, 30 patients with SLE without aCL, and 30 patients with scleroderma. A new enzyme-linked immunosorbent assay (ELIS A) was developed for determining anti-PAF antibodies in a bovine serum-free fashion. Results The ELISA showed high specificity. Homologous inhibition experiment s showed 60-70% inhibition. Anti-PAF antibodies were found in 18/52 APS pat ients, 10/29 SLE/aCL(+) patients, 9/30 SLE/aCL(-) patients and 3/30 sclerod erma patients. Anti-PAF antibodies were significantly associated with anti- PC antibodies (odds ratio [OR] 12.7, P < 0.01), and there was a modest asso ciation with immunoglobulin G (IgG) aCL (OR 3.1, P > 0.10), but not with Ig M aCL or anti beta 2GPI. Three SLE/aCL(+) patients and five SLE/aCL(-) pati ents had clinical manifestations characteristic of APS. All these patients had anti-PAF antibodies, while none had high titres of aCL or anti beta 2GP I antibodies and only one had anti-PC antibodies. Among the combined APS an d SLE groups, the presence of anti-PAF antibodies was significantly associa ted with clinical manifestations which are characteristic of APS (OR 2.6, P = 0.02). The effect was independent of IgG aCL and anti beta 2GPI antibodi es. Conclusions Anti-PAF antibodies are common in APS and SLE and comprise an i ndependent factor for the development of thrombosis. Several patients exper iencing thromboses have anti-PAF antibodies without other antiphospholipid specificities.