Page 106 - Veterinary Immunology, 10th Edition
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FIG. 4.6 Complement activation by the lectin pathway.
Complement-activating lectins include mannose-binding lectin
(MBL) and a family of proteins called ficolins. MBL attaches to
mannose or N-acetylglucosamine on the walls of bacteria, fungi,
and protozoa. It does not bind to mammalian glycoproteins. Once
bound, MBL activates a serum protease called MASP-2. (MASP
stands for MBL-associated serine protease.) Activated MASP-2, in
turn, acts on the complement component C4, splitting it into C4a
and C4b. This exposes a thioester group on the C4b that generates a
reactive carbonyl group that binds the C4b to the microbial surface
(Fig. 4.7). Another complement component, C2, then binds to the
C4b to form a complex, C4b2. The bound C2 is then cleaved by
MASP-2 to generate C4b2b (Box 4.1).
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