Studies on phospholipids in the action of a lupus coagulation inhibitor.
Plasma from a patient with early manifestations of disseminated lupus erythematosus, a prolonged partial thromboplastin time with kaolin, mildly prolonged prothrombin time, and a circulating inhibitor affecting the assay of several clotting factors was investigated. The most sensitive test for the inhibitor was found to be the Russell viper venom time without phospholipid. A decrease in phospholipid concentration as well as decreased sodium chloride levels both significantly enhanced the effect of the inhibitor in several coagulation tests. Of various phospholipid substitutes tested phosphatidyl ethanolamine was the most effective in partially correcting for the inhibitor. The inhibitor was not localized to the patient's platelets, which were also found to partially neutralize its effect. Since lupus erythematosus is sometimes accompanied by thrombocytopenia the coagulation disorder may be aggravated by such a deficiency of phospholipid. The inhibitor appears to act by preventing binding of phospholipid to the Xa/V/thromboplastin complex. It was characterized as a gamma globulin of mixed class.