Affinity purified anti-cardiolipin and anti-DNA antibodies

Recent studies have raised questions concerning the specificity of anticardiolipin antibodies and their relationship to anti-DNA antibodies, the lupus anticoagulant, the biological false positive test for syphilis, and reagin, the antibody detected in syphilis. In an attempt to answer some of these questions, 3 IgG and 2 IgM affinity purified anticardiolipin antibodies, as well as 3 affinity purified anti-DNA antibodies were studied. Affinity purified anti-cardiolipin antibodies showed high binding to negatively charged phospholipids but not to ssDNA by solid phase radioimmunoassay. On the other hand, affinity purified anti-DNA antibodies did not bind cardiolipin. Inhibition experiments showed that negatively charged phospholipids and VDRL liposomes inhibited the binding of anticardiolipin antibodies to phosphatidylserine, but ssDNA, alpha-glycerol phosphate and hyaluronic acid did not. Similar studies of sera from patients with high anticardiolipin antibody levels supported the results obtained with affinity purified anticardiolipin antibodies. These results suggest that anticardiolipin antibodies bind negatively charged phospholipids and there appears to be little crossreactivity with DNA or unrelated negatively charged polymers such as hyaluronic acid. Both the negatively charged phosphodiester group and glyceride portions of the phospholipid molecules appear important for their antigenicity. Four of the 5 affinity purified anti-cardiolipin antibodies had lupus anticoagulant activity providing further evidence to suggest that these 2 groups of antibodies have the same or very similar specificities. Studies of sera from 3 patients with syphilis showed that VDRL liposomes inhibited reagin activity to a greater extent than did cardiolipin. On the other hand, in patients with autoimmune disorders, cardiolipin inhibited anticardiolipin antibody activity to a greater extent than did VDRL liposomes.(ABSTRACT TRUNCATED AT 250 WORDS)