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

Summary. 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 2 a (κ) murine monoclonal antibodies against 1-MAPP and nine IgG1 (κ) 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 By affinity chromatography using these monoclonal antibodies, active MAPPs were obtained from the supernatant of outdated platelet concentrates in the presence of 60% saturated ammonium sulphate and from PRPr-rich medium, and substantial amounts of non-functioning immunoreactive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.