The monoclonal antibody 8B5 reacts with the CCP1/2-SP fragment of human MASP-2. MASP-2 is a trypsin-like serine protease and plays an important role in the initiation of the MBL complement activation pathway. Three pathways of complement activation have been reported: the antibody-dependent classical pathway, the antibody-independent alternative pathway and the lectin pathway. Activation of each pathway involves formation of serine protease complexes, which results in activation of the central complement component C3. In the lectin pathway, mannose binding-lectin (MBL)-associated serine proteases (MASPs) form complexes with polymeric lectin molecules which are involved in pattern recognition. Upon binding of the recognition molecules to carbohydrates on the surface of micro organisms, MASPs are converted to their active forms and initiate complement activation. Three types of human MASP have been reported. MASP-1, MASP-2 and MASP-3. Mannan-binding lectin (MBL) and ficolins, in complex with MBL-associated serin proteases (MASPs), are capable of activation the complement system, thus mediating the destruction of infectious agents. MASP-2 cleaves C4 and C2 and is crucial for the activation of downstream complement components.