The Interaction of β₂ Glycoprotein-I and Heparin and Its Effect on β₂ Glycoprotein-I Antiphospholipid Antibody Cofactor Function in Plasma

Summary

β₂ glycoprotein-I (β₂GPI), a cofactor for antiphospholipid antibody (aPA) binding, binds to many anionic macromolecules including heparin. The nature of this interaction with heparin is not well understood and its effect on the purported biological functions of β₂GPI is unknown.

We have examined the interactions of dermatan sulphate (DS) and different pharmaceutical preparations of heparin with β₂GPI by crossed immunoelectrophoresis (CIE) and investigated the effect of these agents on plasma levels of p2GPI antigen (β₂GPI: Ag) by a standardised enzyme linked immunosorbent assay (ELISA). P2GPI aPA cofactor activity (β₂GPI:Cof) was also measured using a modified solid phase an-ti-phosphatidylserine (aPS) ELISA. CIE results confirmed a heparin-β₂GPI interaction with unfractionated (UF) heparin. β₂GPI:Ag levels were unaffected by any of the preparations investigated. There were no significant differences in β₂GPI:Cof activities of the samples containing LMW heparins or DS but levels of β₂GPI:Cof were increased in samples containing UF sodium and calcium heparin preparations (0.5 IU/ml Monoparin, p <0.05, and 10 IU/ml Liquemin and Calcipa-rine, p <0.05).

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