Human monoclonal anti-phospholipid antibodies selectively bind to membrane phospholipid and β₂-glycoprotein I (β₂-GPI) on apoptotic cells

The ability of an anti-phospholipid (LJ1) and an anti-β₂-GPI (RSP-57) human MoAb to bind to apoptotic but not viable cells was demonstrated in this study. Both MoAbs were derived from patients with systemic lupus erythematosus and anti-phospholipid antibody syndrome. The parallel analysis of the specificity and affinity of four anti-phospholipid human MoAbs suggests that the binding of LJ1 MoAb to apoptotic cells is a specific property of this MoAb. RSP-57 MoAb recognizes apoptotic cells through β₂-GPI which becomes available for binding after the interaction with negatively charged phospholipids. This observation provides evidence that the binding of human anti-phospholipid antibodies to apoptotic cells occurs in both a β₂-GPI-dependent and independent way and involves a restricted group of epitopes. The finding that LJ1 and RSP-57 MoAbs bind apoptotic cells underlines the property of these MoAbs to act as cell membrane markers of apoptosis. Major pathological implications derive from the observation that LJ1 and RSP-57 MoAbs recognize epitopes expressed on ‘early’ apoptotic cells. The interference with the in vivo clearance and processing of apoptotic cells is a potential pathogenic mechanism of these antibodies.