After binding of complement and antibody on the surface of encapsulated bacteria, the process of phagocytosis by polymorphonuclear leukocytes/macrophages is enhanced by all of the following opsonins, except?: (A) C3b complement protein, (B) IgG antibody, (C) Mannose binding lectin (MBL), (D) CD11b/CD18
Answer is D. The efficiency of phagocytosis is greatly enhanced when microbes are coated with opsonins for which the phagocytes express high-affinity receptors. The major opsonins are immunoglobulin G (IgG) antibodies, the C3b breakdown product of complement, and ceain plasma lectins, notably mannose-binding lectin and collectins, all of which are recognized by specific receptors on leukocytes. CD11b/CD18 (MAC-1) is macrophage integrin which help in binding of microbes to macrophages, and are not opsonins.