Fig. 1.

Proposed structural states of β2GPI and the transition to cellular binding. The schematic above demonstrates the potential interactions between cell surfaces, β2GPI and antibodies in APS. The proposed schemes are intensely debated in the field. The top scheme shows antibody binding to a closed β2GPI with this causing β2GPI to open and bind cell membranes. The middle scheme shows β2GPI opening due to environmental factors with an antibody later binding. The bottom scheme shows circular β2GPI binding a cell membrane, opening and dimerization by an antibody. Debate exists as to which of these schemes is the most physiologically relevant.