Receptors involved in the phagocytosis of senescent and diamide-oxidized human RBCs

Senescent RBCs bear IgG and C3 opsonins that are three to four times less than required for similar phagocytosis of experimentally opsonized RBCs.

Studies were performed to determine the phagocyte receptors involved in phagocytosis in vitro. The effect of clustering of opsonins and oxidative damage in the sequestration of RBCs was studied by exposing RBCs to BS3 (bis[sulfosuccinimidyl]-suberate) and diamide (azodicarboxylic acid bis[dimethyl-amide]).

Sequestration of senescent RBCs was inhibited by the treatment of lymphokine-activated monocytes with N-acetyl-D-galactoseamine (GalNAc), arginine-glycine-aspartic acid (RGD), or antibodies to CR3, FcgammaRI, FcgammaRII, leukocyte response integrin (LRI), and integrin-associated protein (IAP). Exposure to BS3 alone did not enhance phagocytosis. The addition of serum resulted in opsonin binding. The level of opsonization required for sequestration was higher than on senescent RBCs and was only marginally inhibited by blocking CR3, FcgammaRI and FcgammaRII. Diamide treatment alone did not lead to sequestration. Diamide-treated RBCs exposed to serum bound opsonin much as did senescent RBCs, and sequestration was inhibited by GalNAc, RGD, and antibodies to CR3, FcgammaRI, FcgammaRII, LRI, and IAP.

Membrane alterations resulting in the binding of opsonins and the sequestration of senescent RBCs may be similar to those that occur on diamide-oxidized RBCs. They suggest the need for cooperative events among oxidation, clustering and cross-linking, and serum opsonization.