Mannose complement activation

Figure 15.1 Complement activation pathways. The classical, lectin and alternative pathways converge into a final common pathway when C3 convertase (C3 con) cleaves C3 into C3a and C3b. Ab = antibody, Ag = antigen, Cl-INH = Cl inhibitor, MAC = membrane attack complex, MASP = MBL-associated serine protease, MBL = mannose-binding lectin, P = properdin. Overbar indicates activation.

Lectin pathway, stimulated by binding to a lectin. Lectins belong to a family of proteins called collectins, which are present in blood and bind to bacteria. One lectin, known as the mannose binding lectin (MBL), binds to a sequence of mannose sugars that are part of the carbohydrate on the cell surface of some bacteria. It is the lectin-bacteria complex that activates one of the complement proteins. The components of the pathway are prefixed with a C and a number. 

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