Inhibition of the activation of Hageman factor (factor XII) by β2-glycoprotein I

Abstract

Abstract β 2 -Glycoprotein I (apolipoprotein H), a constituent of normal human plasma, has been shown to inhibit the generation of amidolytic activity in plasma that has been exposed to negatively charged agents. Studies with purified Hageman factor (factor XII) demonstrate that this inhibitory property is directed against the activation of Hageman factor. In this study β 2 -glycoprotein I inhibited the kaolin-induced generation of clot-promoting properties in solutions of Hageman factor. This effect was localized to an interaction between β 2 -glycoprotein I and kaolin. In contrast, once Hageman factor was activated by kaolin, its clot-promoting properties were not inhibited by β 2 -glycoprotein I. Further, β 2 -glycoprotein inhibited the generation of amidolytic activity against H-d-prolyl-l-phenylalanyl-l-arginine p -nitroanilide dihydrochloride in mixtures of Hageman factor and ellagic acid. The specificity of the action of β 2 -glycoprotein I was confirmed by its neutralization by immunoglobulin fractions of antiserums directed against this protein.