ANTI-BETA-2-GLYCOPROTEIN-I AND ANTI-PROTHROMBIN ANTIBODIES IN PATIENTS WITH THE ANTIPHOSPHOLIPID SYNDROME - IMMUNOLOGICAL SPECIFICITY AND CLOTTING PROFILES

Lupus anticoagulant (LA) antibodies have been shown to be directed to protein-phospholipid complexes. In this study, we report on LA antibod ies from patients with the 'antiphospholipid' syndrome (APS), that are directed to :prothrombin and beta 2-glycoprotein I, but not to the co mplexes of these plasma proteins to anionic phospholipids. The anti-pr othrombin antibodies studied had different reactivities in two clottin g assays: the dilute Russell's viper venom time (dRVVT) and the dilute kaolin clotting time (dKCT). Anti-prothrombin and anti-beta 2-glycopr otein I (anti-beta 2GPI) antibodies, affinity-purified from one patien t with APS were not cross-reactive and had different effects in the dR VVT and dKCT clotting tests. Polyclonal anti-prothrombin antibodies, a ffinity-purified on a prothrombin column, from two patients with proth rombin reactivity in their plasma, have affinity constants to prothrom bin of 104 and 192 nM. The patient with affinity-purified antibodies t o prothrombin and beta 2GPI, had affinity constants to prothrombin and beta 2GPI, respectively, of 192 nM and 3030 nM, respectively. LA anti bodies are a heterogenous population of antibodies that have different immunological specificities and clotting test reactivities in differe nt patients.