A novel host defense mechanism mediated by a cornplex of host defense lectin and serine protease in innate immunity

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Mannose-binding lectin (MBL) and ficolins am host defense lectins involved in innate immunity. MBL and ficolins am complexed with serine pryteases termed MASP. Upon binding of the complexes to carbohydrates on pathogens MASP activates C4 and C2 of the complement system via the lectin pathway. Three types of MASP (MASP 1, -2 and -3) and a truncated protein of MASP 2 termed sMAP am present in human and mouse. Of the components associated with the host defense leans, MASP-2 is involved in activating C4 and C2, but functions of the others are unknown. Recently, human MASP 1/3 preparations have been shown to activate factor IX of the coagulation system, suggesting a linkage of the host defense lectins to the coagulation system in innate immunity. The aim of this project was to investigate the possible involvement of the host defense lectins in the coagulation system. We obtained the following results.(1). Both MBL-MASP and L-ficolin-MASP isolated from human serum activated factor IX. MASP-1/3 preparations activated factor IX in solid phase as well as fluid phase. Recombinant MASP-1 strongly activated factor IX. (2). Human MASP-1 activated fibrinogen. (3). Zymosan treated with human serum stimulated the coagulation system more than zymosan did. Addition of MASP-1/3 did not affect the coagulation time.(4). MBL binds to Salmonella typhimurium TV119.Incubation of human plasma with TV 119 did not cause a formation of a fibrin gel around the colonies.