Interaction of giant phospholipid vesicles containing cardiolipin and cholesterol with beta2-glycoprotein-I and anti-beta2-glycoprotein-I antibodies.

Antiphospholipid syndrome is characterized with thrombotic events and/or pregnancy morbidity and antiphospholipid antibodies (aPL). The most common antigen for aPL is beta2-glycoprotein-I (beta(2)GPI), a plasma protein binding to negatively charged phospholipids. The influence of aPL on coagulation is not well understood. Giant phospholipid vesicles (GPVs) are a convenient in vitro system for studying interactions between phospholipid membranes and proteins resulting in the change of the vesicles' configuration. We aimed to set up an in vitro model and to study changes in the morphology of GPVs with high content of cardiolipin upon addition of beta(2)GPI and/or IgG fraction of a patient with antiphospholipid syndrome (APS). Addition of the IgG fraction of the APS patient caused lateral segregation of the membrane inclusions and adhesion of GPVs. Addition of beta(2)GPI caused adhesion of GPVs. Addition of both, the patient IgG fraction and beta(2)GPI caused adhesion of vesicles to the glass slides and to each other, formation of pores and burst of vesicles. Our results indicate that adhesion of the cardiolipin-containing vesicles does not seem specific for added proteins, rather, it indicates electrostatic and curvature-mediated interactions between the membrane constituents.