APS PATIENT SERA PREFERENTIALLY RECOGNIZE THE FIRST DOMAIN OF b2-GLYCOPROTEIN I.

Patricia A. McNeeley, Edward J. Victoria, David Marquis, Jacqueline F. Crisologo, Darlene C. Tuyay and Matthew D. Linnik.

La Jolla Pharmaceutical Company, San Diego, CA 92121 USA

Surface plasmon resonance was used to study the interaction between immobilized b2GPI and serum from 67 patients diagnosed with primary or secondary antiphospholipid syndrome (APS). The patients all had GPL scores > 20 in a standard solid phase ACA ELISA. Sera from 23 normal indiviuals and two commercial pooled sources were also tested. The sera were assessed by direct binding to baculovirus expressed human b2GPI containing "sushi" domains 1-5 and a domain-deletion mutant of human b2GPI containing domains 2-5 using a BIAcore biosensor. The integrity and purity of the b2GPI preparations were demonstrated electrophoretically, by N-terminal microsequencing and mass spectrometry. The amount of each protein immobilized and the reproducibility of binding was determined with a rabbit polyclonal anti-human b2GPI antibody. Immobilized haptoglobin was used as a negative control. The median equilibrium response (reflective of both b2GPI binding and titer of antibody in the serum) for domains 1-5 were 687 and 389 for patient and control sera respectively. A three-fold or greater selectivity for binding to domains 1-5 versus domains 2-5 was exhibited by 87% (58/67) of the APS patient sera while 32% (8/25) of the normal controls displayed the same preference. These results suggest that sera from a majority of APS patients bind preferentially to domain 1-containing b2GPI.

Presented at the 8th International Symposium on Antiphospholipid Antibodies, Sapporo, Japan, Oct. 6-9, 1998.