Studies on macromolecular activators of phagocytosis from platelets (MAPPs) using anti MAPP murine monoclonal...

1-MAPP(290 kD) and s-MAPP(150 kD) are glycoproteins which have been shown to be involved in released products from platelets (PRPr) and to activate monocyte and neutrophil phagocytosis via the Fc receptors. Three IgG 2a (kappa) murine monoclonal antibodies against 1-MAPP and nine IgG1 (kappa) antibodies against s-MAPP have been raised. By affinity chromatography using these monoclonal antibodies, active MAPPs were obtained from the supernatant of outdated platelet concentrates in the presence of 60% saturated ammonium sulphate and from PRPr-rich medium, and substantial amounts of non-functioning immunoreactive MAPPs were obtained from the precipitate. Fab fragments of one of the two anti 1-MAPP and of two of the four anti s-MAPP monoclonal antibodies inhibited the function of their corresponding MAPPs, but none of them could inhibit the other MAPPs. 1-MAPP and s-MAPP in the platelets were visualized by indirect fluorescent antibody technique using Fab fragments of the antibodies.