Use of an enzyme-linked immunosorbent assay and of inhibition studies to distinguish between antibodies to cardiolipin from patients with syphilis or autoimmune disorders.

We report a VDRL-enzyme-linked immunosorbent assay (ELISA) that enabled us to distinguish between the antibodies to cardiolipin from patients with autoimmune disorders and those from patients with syphilis. Additional studies using inhibition experiments with phospholipid liposomes, as well as ELISAs with a variety of phospholipid antigens, showed that antibodies to phospholipids from patients with syphilis bind cardiolipin (best when presented as the VDRL antigen) but exhibited little cross-reactivity with negatively charged phospholipids. On the other hand, antibodies to phospholipids from patients with autoimmune disorders exhibited little or no binding to the VDRL antigen but cross-reacted with both cardiolipin and negatively charged phospholipids. These findings may explain why antibodies to phospholipids only from patients with autoimmune disorders may have lupus anticoagulant activity and why they are associated with thrombosis, fetal loss, and thrombocytopenia.