The lectin pathway of recognition and activation. Either MBL or serum ficolin bind to surface ...

The lectin pathway of recognition and activation. Either MBL or serum ficolin bind to surface terminal carbohydrates that have either mannose or N-acetylgalactosamine as a nonreducing terminus on the pathogen. These sugars are internal structures in human glycoproteins and glycolipids but are terminal structures on pathogens, so they are accessible only on pathogens. Mannose-binding lectin-associated serine protease-2 (MASP-2) binds to the MBL and cleaves C2 and C4, creating C2a and C2b and C4a and C4b. C2b and C4a diffuse away and C2aC4b forms the same C3 convertase that was in the classical pathway. MASP-1 can become associated but cleaves C2 only and thus may enhance the pathway but does not work independently.