IMMUNIZATION OF A RABBIT WITH BETA(2)-GLYCOPROTEIN-I INDUCES CHARGE-DEPENDENT CROSS-REACTIVE ANTIBODIES THAT BIND ANIONIC PHOSPHOLIPIDS ANDHAVE SIMILAR REACTIVITY AS AUTOIMMUNE ANTIPHOSPHOLIPID ANTIBODIES

A rabbit immmunized with beta(2)-glycoprotein I (beta(2)-GPI) produced Abs that bind to negatively charged phospholipids and to beta(2)-GPI. After affinity purification of the Abs to beta(2)-GPI, the dual react ivity could still be detected. Adsorption studies with a phosphatidyls erine affinity column depleted phospholipid-reactive Abs, but beta(2)- GPI reactivity was retained. The same pattern of reactivity was found with culture supernatants from rabbit anti-beta(2)-GPI splenocytes fus ed with an immortalized rabbit cell line. The reactivity to negatively charged phospholipids is likely to involve ionic interactions, as hig h ionic strength buffers eliminated binding to anionic phospholipids, but not to beta(2)-GPI. Affinity-purified anti-phospholipid (aPL) Abs from four of seven autoimmune patients bound anionic phospholipids in the absence of beta(2)-GPI. However, in high ionic strength buffer, th is binding was abolished in three patients and significantly reduced i n the fourth. In contrast, affinity-purified aPL Abs from seven autoim mune patients bound to beta(2)-GPI-coated plates, and binding in high ionic strength buffer was reduced only moderately in three patients. T herefore, autoimmune-type aPL Abs display anti-beta(2)-GPI reactivity and charge-dependent binding to anionic phospholipids similar to affin ity-purified rabbit anti-beta(2)-GPI Abs.