Profile and cross-reactivities of antiphospholipid antibodies in systemic lupus erythematosus and syphilis.

Antiphospholipid antibodies have been determined in two groups of 48 sera from patients with systemic lupus erythematosus (SLE) and syphilis. Using an ELISA, IgG anticardiolipin (CL), antiphosphatidyl serine (PS) and antiphosphatidyl ethanolamine (PEA), antibodies have been detected with the same frequency in both groups of patients. Titres of antiphosphatidyl serine (PS) (p less than 0.005) and PEA antibodies (p less than 0.05) were significantly higher in the syphilitic sera compared to the SLE sera. Anticardiolipin binding activity of both groups of sera could be inhibited by preincubation with phosphatidic acid, phosphatidyl serine, phosphatidyl glycerol and cardiolipin antigens, but the inhibiting ratio of phosphatidyl antigen was significantly higher (p less than 0.01) in the SLE group. These data suggest that anticardiolipin auto-antibodies present in SLE sera are very similar to the "reagins" or antibodies to cardiolipin seen in syphilitic sera. IgG anticardiolipin antibodies may be an epiphenomenon and are probably not implicated in the pathogenesis of the thrombotic diathesis seen preferentially in some patients with SLE.