Mannan-binding lectin-associated serine protease-2 (MASP-2) is the effector protease of the lectin pathway of complement activation. It circulates in complex with pattern-recognition molecules (e.g., MBL, ficolins, collectins). Upon binding of these molecules to pathogen- or damage-associated molecular patterns, MASP-2 is auto-activated and cleaves complement components C4 and C2 to form the C3 convertase (C4b2a), initiating the complement cascade.