Assay for Estimation of the Functional Activity of the Mannan-Binding Lectin Pathway of the Complement System

Mannan-binding lectin (MBL) is a soluble pattern recognition molecule of the innate immune system. It is found in plasma in complex with MBL-associated serine proteases (MASPs). When MBL recognizes foreign, e.g., the surface of some microorganisms, or altered host surfaces the MASPs are activated and this will in turn lead to the initiation of the complement system, i.e., activation of complement by the MBL pathway. This will end up in increased phagocytosis of the microorganism and killing by insertion of pore structures in the membrane of the microorganisms. Lack of MBL seems significant in specific situations, e.g., in immunocompromised individuals were MBL is important in battling infections and, e.g., in ischemia/reperfusion injuries were MBL can have a negative inflammatory generating, and thus tissue destructive role, as it recognizes epitopes emerging in the ischemic tissue. It may thus be relevant in several situations to test for the presence of the MBL pathway in human sera. Here we describe a functional assay for estimation of MBL pathway activity by detection of complement factor deposition onto microtiter plate wells coated with a physiological relevant ligand for MBL.