Factors of the Lectin Pathway of Complement Activation and Their Clinical Associations in Neonates

Figure 1

The three major pathways of complement activation. These pathways differ crucially in their initiating events: the classical pathway depends on antibody recognition and binding to C1q; the alternative pathway depends on low-level spontaneous hydrolysis of C3 being stabilised by bacterial polysaccharides and so forth; and the lectin pathway depends on the recognition of saccharides by ficolins and certain collectins (MBL, CL-11). The common end result is the generation of C3a and C3b from C3; the classical and lectin pathways produce C4b2a as the C3 convertase, whereas that role is played by C3bBb in the alternative pathway. C1 inhibitor (C1inh) and C4-binding protein (C4bp) are downregulators of both classical and lectin pathways; H factor is an inhibitor of the early phase of alternative pathway, modified from [11].