The Role of MASP-1/3 in Complement Activation
The complement system, which consists of more than 30 plasma and cell surface proteins, is activated by three pathways: the classical, lectin, and alternative pathways, leading to the generation of opsonins and pathogen destruction. In the lectin pathway, mannose-binding lectin (MBL) and ficolins act as pattern recognition molecules for pathogens, resulting in the activation of MBL-associated serine proteases (MASPs: MASP-1, MASP-2, and MASP-3). Among these proteases, MASP-2 is a key enzyme that cleaves C4 and C2 to assemble a C3 convertase (C4b2a). However, the physiological function of MASP-1 and MASP-3 remains unclear. To investigate the roles of MASP-1 and MASP-3, we generated a MASP-1- and MASP-3-deficient (M1/3 KO) mouse model and found that the deficient mice lacked alternative pathway activation because factor D (Df) remained as a proenzyme in the serum. MASP-1 and MASP-3 were able to convert the proenzyme of Df to an active form in vitro. In addition, MASP-1 was able to activate MASP-2 and MASP-3 as C1r activates C1s. Thus, MASP-1 and MASP-3 seem to be involved in activation of both the lectin and alternative pathways.
KeywordsAlternative Pathway Lectin Pathway Carbohydrate Recognition Domain Alternative Pathway Activation Pattern Recognition Molecule
- Banda NK, Takahashi M, Levitt B, Glogowska M, Nicholas J, Takahashi K, Stahl GL, Fujita T, Arend WP, Holers VM (2010) Essential role of complement mannose-binding lectin-associated serine proteases-1/3 in the murine collagen antibody-induced model of inflammatory arthritis. J Immunol 185:5598–5606CrossRefGoogle Scholar
- Schwaeble WJ, Lynch NJ, Clark JE, Marber M, Samani NJ, Ali YM, Dudler T, Parent B, Lhotta K, Wallis R et al (2011) Targeting of mannan-binding lectin-associated serine protease-2 confers protection from myocardial and gastrointestinal ischemia/reperfusion injury. Proc Natl Acad Sci USA 108:7523–7528CrossRefGoogle Scholar
- Vorup-Jensen T, Petersen SV, Hansen AG, Poulsen K, Schwaeble W, Sim RB, Reid KB, Davis SJ, Thiel S, Jensenius JC (2000) Distinct pathways of mannan-binding lectin (MBL)- and C1-complex autoactivation revealed by reconstitution of MBL with recombinant MBL-associated serine protease-2. J Immunol 165:2093–2100CrossRefGoogle Scholar
- Zundel S, Cseh S, Lacroix M, Dahl MR, Matsushita M, Andrieu JP, Schwaeble WJ, Jensenius JC, Fujita T, Arlaud GJ, Thielens NM (2004) Characterization of recombinant mannan-binding lectin-associated serine protease (MASP)-3 suggests an activation mechanism different from that of MASP-1 and MASP-2. J Immunol 172:4342–4350CrossRefGoogle Scholar