Structural and functional aspects of complement activation by mannose-binding protein.

Serum mannose-binding protein (MBP) is the first component of the lectin pathway of the complement cascade. It binds to sugars on the surface of pathogenic microorganisms and triggers complement fixation by activating an associated serine protease, designated MBP-associated serine protease-2 (MASP-2). Recent studies have provided insight into the interactions between MBP and MASP-2 that trigger complement activation. MBP/MASP complexes share many features with the C1 complex of the classical pathway. The relatively simple MBP/MASP complexes serve as useful models for understanding activation of the classical pathway of the complement cascade.