Kinetic studies of neutrophil phagocytosis. V. studies on the co-operation between the Fc and C3b receptors.

The co-operation between the Fc and C3b receptors of PMNs (neutrophil granulocytes) during phagocytosis has been studied by the effect of interference with either of the receptors. The significance of the Fc receptor for the mediation of internalization proposed by previous investigators was confirmed by the inhibition of both Fc- and C3b-mediated phagocytosis by Fc fragments of IgG and by Fab fragments of antiserum against the Fc part of IgG. C3b-receptor-mediated phagocytosis was inhibited by trypsin, granulocyte elastase, myeloperoxidase and HO. High concentrations of elastase and the combined action of HO and myeloperoxidase generated a C3b-receptor dysfunction, which implied that the destruction of C3b-receptor function also disturbed Fc-receptor function. The demonstrated C3b receptor dysfunction indicated that the Fc and C3b receptors were closely situated in the cellular membrane of the PMN. A hypothesis for co-operation between the two receptor types would be that the C3b receptor initially facilitates the adherence of an IgG-C3b-coated particle. Secondly, the C3b receptor would facilitate the IgG-Fc-receptor contact either by some kind of structural derangement to permit the entrance of the IgG-C3b complex or by removal of C3b from the Fc part of IgG.