Diamide enhances phagocytosis of human red cells in a complement- and anti band 3 antibody-dependent process

Human red cells treated with 20-200 microM diamide were opsonized by serum and phagocytized by adherent monocytes. Phagocytosis was dependent on complement. It was enhanced by supplementing whole serum and was restored by supplementing complement-inactivated serum with naturally occurring antibodies which bind to the major integral protein of the human red cell, band 3 protein. Diamide induced oligomers of anti band 3 reactive oligomers, and enhanced anti band 3 binding to red cells. Complement C3 binding paralleled that of anti band 3 and exceeded it by two orders of magnitude. Thus, naturally occurring antibodies have functional properties which were not abolished by other serum Ig and may be involved together with complement in the clearance of red cells subjected to oxidant stress.