The Role Of Rat Platelet And Platelet Phospholipase A₂ In Host Defense Bacteria Infection

AbstractObjective: To explore the role of rat platelet and platelet phospholipase A2 (PLA2) in host defense bacteria infection. To understand further in the function of platelet and platelet PLA2, and to provide important information of developing new antibacterial agents. Methods: We studied the bactericidal activity and mechanism of rat platelet and platelet PLA2 in three levels: systemic level, cellular level and molecular level. (1) We measured the bactericidal activities, PLA2 activity of plasma and PLA2 mRNA in blood collected serially from rat before and after intravenous injection of Staphylococcus aureus. (2) Platelets were isolated from normal rat blood, and were stimulated by several agents to release PLA2, then measured the bactericidal activities. The pure rabbit platelet PLA2 bactericidal spectrum was compared with that of rat platelet. (3) Platelet PLA2 cDNA was cloned from rat whole blood. All known cDNA and gene data of mammalian platelet and pancreatic PLA2 were analyzed to understand the properties of molecular evolution of mammlian platelet PLA2. Results: (1) After injection of bacteria, The PLA2 activity of plasma collected at 3h rose 27 fold, and possessed potent bactericidal activity towards Gram-positive bacteria such as S. aureus, MRSA, E. faecalis, but exhibited low activity toward Gram-negative bacteria such as E.coli, and the mRNA in blood also rose to peak at 1h. (2) PLA2 released from platelet upon stimulation with thrombin had potent bactericidal activity toward Gram-positive bacteria, but no effect toward Gram-negative bacteria. The bactericidal spectrum of pure rabbit platelet PLA2 was similar to the one of rat platelet. (3) A new cDNA of rat platelet PLA2 was cloned from rat whole blood, and deposited with GenBank under the accession number AF365363. The molecular evolution of platelet PLA2 was faster than pancreatic PLA2. Therefore platelet PLA2 evolved to a basic molecule with more positive charge residues, and possessed bactericidal activity. Conclusions: Rat platelet and platelet PLA2 play an important role in host defense bacteria infection.