mannan-binding lectin pathway (MLB pathway)

^[1]^[2]

Function

one of 3 pathways of complement activation
uses mannose-binding lectin (MBL2) to activate the classical complement pathway independently of antibody
MBL binds mannose & N-acetylglucosamine (Ca+2-dependent) expressed on the surface of certain pathogens, including acapsular gram-positive & gram-negative bacteria, mycobacteria, viruses, yeast, parasites & protozoa
upon recognition of antigen, MBL2 adopts a conformational change that leads to activation of serine proteases MASP1 & MASP2^[1]
after activation, MASP2 cleaves C4 to generate the classical C3 convertase C4b2a
MASP1 has the ability to cleave C3 suggesting it might activate the complement alternative pathway directly
following generation of the classical C3 convertase C4b2a by the MLB2-MASP1-MASP2 complex, complement activation occurs as in the classical complement cascade with possible activation of the complement alternative pathway
the mannan-binding lectin pathway is regulated by C1 inhibitor & alpha-2 macroglobulin

specific antigen antibody complexes can activate the mannan-binding lectin pathway
IgG that lack terminal galactose residues IgG-G0 found in plasma of patients with rheumatoid arthritis & other disorders interact in MLB2 & activate the mannan-binding lectin pathway
defects in mannan-binding lectin pathway increase susceptibility to infection by Neisseria

↑ ^1.0 ^1.1 Henry's Clinical Diagnosis & Management by Laboratory Methods, 21st edition, McPherson RA & Pincus MR (es), W.B. Saunders Co., Philadelphia, PA. 2007
↑ Medical Knowledge Self Assessment Program (MKSAP) 15, American College of Physicians, Philadelphia 2009