Effects of platelet release products on neutrophilic Fc gamma receptors

Large and small macromolecular activators of phagocytosis from platelets (I-MAPP and s-MAPP, respectively), which function via the neutrophilic Fc gamma receptors (Fc gammaR) were refined from platelet release products by gel filtration and affinity chromatography with the use of an anti transferrin antibody column and the mechanism of phagocytosis activation was investigated. Flow cytometry revealed that 1-MAPP and s-MAPP did not increase the expression of neutrophilic Fc gammaRII (CD32) and Fc gammaRIII (CD16) antigens, whereas rosette formation of neutrophils with rabbit IgG-sensitized sheep erythrocytes (EA) in the presence of anti Fc gammaR antibodies suggested that both MAPPs increase the binding ability of Fc gammaRII. On the other hand, the enhancing effect of I-MAPP and s-MAPP on neutrophilic phagocytosis disappeared with the increase in phagocytosis by the phosphate-buffered saline control neutrophils when they were centrifuged with EA before incubation for phagocytosis. The enhanced phagocytosis, both by the two MAPPs and centrifugation, was canceled by treatment of the neutrophils with anti-CD32 Fab. The phagocytosis activatory effects of MAPP on neutrophils were canceled by anti-CD71 monoclonal antibody but not by transferrin.