COMPLEMENT ACTIVATION IN HUMAN SERUM BY LIPOSOME-ENCAPSULATED HEMOGLOBIN - THE ROLE OF NATURAL ANTIPHOSPHOLIPID ANTIBODIES

In exploring the occurrence and mechanism of liposome-encapsulated hem oglobin (LEH)-induced complement (C) activation, we found that normal human serum contained low titers of IgG and IgM class natural antibodi es with reactivity against LEH, and that the amount of vesicle-bound I gM significantly correlated with LEH-induced C consumption. IgM bindin g to LEH was inhibited by phosphocholine and ATP, but not by choline c hloride. These data suggest that naturally occurring antibodies play a key role in LEH-induced C activation, and that a major portion of the se antibodies are directed against the phosphate moiety on the phospho lipid headgroups of liposome bilayers.