The mechanism suggested by Agostinis et al. aPL recognizes domain I of β2GPI and stabilizes on the cell surface. This is followed by binding of complement factor C1q resulting in the activation of the complement system. The formed anaphylatoxins will cause cell damage and induce a prothrombotic phenotype, leading to both thrombosis and pregnancy failure. Deleting the CH2 part, responsible for binding C1q, prevents complement activation by competing with aPL for binding domain I of β2GPI. Professional illustration by Paulette Dennis.