Anticardiolipin and complement activation: relation to clinical symptoms.

Anticardiolipin antibodies which seldom occur in healthy persons are frequently found in systemic lupus erythematosus (SLE). Their presence, especially at high levels (greater than 10 units) are often accompanied by thromboembolic manifestations as well as thrombocytopenia and recurrent abortions. The incidence of cardiolipin antibodies was as great in SLE as in women with clinically unexplained recurrent abortions. The anticardiolipin levels remained unchanged in most patients for long periods and were remarkably unaffected by disease activity and therapy. On the other hand, in several cases the activated partial thromboplastin time which was prolonged in most patients with persistently high cardiolipin antibody levels, approached normal during treatment with prednisolone and salicylic acid. This seemed to facilitate a successful outcome of pregnancy. Absorption of sera with cardiolipin and other negatively charged phospholipids but not with uncharged phospholipids abolished the anticardiolipin activity in enzyme linked immunosorbent assay. In most sera with cardiolipin antibody levels greater than 10 units complement activation by the classical pathway could be demonstrated. Whether the anticardiolipin antibodies contributed to complement activation could not be determined.