Lectin pathway

The lectin pathway or MBL pathway is a type of cascade reaction in the complement system, similar in structure to the classical complement pathway,^[1] in that, after activation, it proceeds through the action of C4 and C2 to produce activated complement proteins further down the cascade. In contrast to the classical complement pathway, the lectin pathway does not recognize an antibody bound to its target. The lectin pathway starts with mannose-binding lectin (MBL) or ficolin binding to certain sugars.

In this pathway, mannose-binding lectin binds to mannose, glucose, or other sugars with 3- and 4-OH groups placed in the equatorial plane, in terminal positions on carbohydrate or glycoprotein components of microorganisms including bacteria such as Salmonella, Listeria, and Neisseria strains. Fungal pathogens such as Candida albicans and Cryptococcus neoformans as well as some viruses such as HIV-1 and Respiratory syncytial virus (RSV) are bound by MBL.

Mannan-binding lectin, also called mannose-binding protein, is a protein belonging to the collectin family that is produced by the liver and can initiate the complement cascade by binding to pathogen surfaces.