RECOVERY OF MACROMOLECULAR ACTIVATORS OF PHAGOCYTOSIS FROM PLATELETS (MAPP) PRODUCING AND RELEASING FUNCTION IN STORED HUMAN PLATELETS

Macromolecular activators of phagocytosis from platelets (MAPP) were n ot released from platelets prepared from platelet concentrates (PC) ob tained after anticoagulation with CPD solution and stored for more tha n 48 h. The MAPP activity which had escaped into the plasma disappeare d after 72 h of storage. After incubation in dialyzed and Ca2+-supplem ented plasma prepared from the same PC or from fresh peripheral blood, the platelets obtained after storage for 72 h released both MAPP (l-M APP and s-MAPP) upon thrombin stimulation, Gel filtration studies of t he plasma revealed that l-MAPP and s-MAPP were produced from the plate lets incubated in plasma fractions corresponding to l-MAPP and s-MAPP, respectively. These observations suggest that platelets accumulate pr ecursors of MAPP, pre-MAPP comprising pre-l-MAPP and pre-s-MAPP, in th e presence of Ca2+, and produce and release MAPP when stimulated with thrombin.