DOMAIN 1-SPECIFIC ANTI-ß2GPI ANTIBODIES FROM APS PATIENTS CONTRIBUTE TO LUPUS ANTICOAGULANT ACTIVITY

Patricia A. McNeeley, Jill M. Sansone, G. Michael Iverson, Keith A. Cockerill and Matthew D. Linnik
La Jolla Pharmaceutical Company, 6455 Nancy Ridge Dr. San Diego, CA 92121

Autoantibodies directed against ß2GPI have been implicated in the thrombotic events characteristic of APS. Previous work from our laboratories has demonstrated that the amino terminal domain of ß2GPI (domain 1) contains the immunodominant epitopes for these ß2GPI-dependent antiphospholid antibodies.

In the current study we evaluated the lupus anticoagulant (LA) activity of domain 1 specific antibodies using a commercially available dilute Russell viper venom time assay (American Diagnostica, Inc). When added to pooled normal human plasma at concentrations from 3 to 100mg/ml, eight of eight anti-domain 1 antibodies affinity purified from APS patient plasmas were positive for LA activity. In addition, 18 of 26 APS patient plasmas (69%) were positive for LA activity when mixed 1:1 with pooled normal human plasma. The LA activity was confirmed as coagulation time was corrected by addition of excess phospholipid. The plasmas positive for LA activity were also positive in a standard GPL assay and a ß2GPI binding ELISA. Seven APS plasmas with high LA activity were retested after the domain 1 antibodies had been specifically immunoabsorbed from the plasma using insoluble domain 1 on agarose beads. In all cases the removal of domain 1-specific anti-ß2GPI antibodies caused a decrease in LA activity. These data demonstrate that anti-ß2GPI activity can be removed from APS plasma using immobilized insoluble domain 1 and that removal of these antibodies attenuates lupus anticoagulant activity.

Accepted for presentation at the
1st Tutzing Antiphospholipid Conference
Bavaria, Germany
April 22-25, 2002.