• Y Ogawa, H Sakamoto, M Oryu, M Shinnou, N Sakamoto, W Yanghong, R Khatun, and M Nishioka.
• Third Department of Medicine, Kagawa Medical University, Kita-gun, Japan.
• Thromb. Res. 2000 Mar 1; 97 (5): 297-306.

AbstractMacromolecular activators of phagocytosis from platelets (MAPP: 1-MAPP and s-MAPP) are released from activated fresh platelets and enhance leukocyte phagocytosis via the Fcgamma receptors. In this study, production of MAPP was investigated in lysate of freeze-thawed stored platelets (PL). Incubation of PL and thrombin with precursors of MAPP (pre-MAPP: pre-1-MAPP and pre-s-MAPP) produced 1-MAPP and s-MAPP, whereas products released from stored platelets by stimulation with thrombin or collagen did not produce MAPP after incubation with pre-MAPP. The action of thrombin in MAPP formation with PL and pre-MAPP was inhibited by antithrombin III and heparin, and sequential incubation studies indicated that the key site of action of thrombin was on a component of PL. Other serine proteases such as trypsin could be substituted for thrombin in this reaction, whereas the action of thrombin was specific when whole platelets were used instead of PL. Gel filtration of PL before and after treatment with thrombin suggested that a macromolecule in PL (PMA-I) is digested by thrombin and liberates a 700 to 800 Da substance (PMA-II) which converts pre-MAPP to MAPP.

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