Analysis of Activity of Mannan-Binding Lectin, an Initiator of the Lectin Pathway of the Complement System

The innate immune system has traditionally been described as the first line of the body's defense against invasive pathogens. Such a response then leads to an inflammatory response which may also include coagulation. Activation of the innate immune response is mediated by pattern recognition molecules, which may be membrane-bound (e.g., cell-associated Toll-like receptors, NOD-like receptors, and RIG-I-like receptors) or soluble proteins. Recognition of foreign or altered structures in the body by some of the soluble pattern recognition receptors may lead to activation of the complement system and thus trigger one of the innate antimicrobial defense mechanisms. Such complement-activating soluble pattern recognition molecules include the collectins (lectins, i.e., carbohydrate-binding proteins, that use a collagen helix for stabilization of the molecule), i.e., mannan-binding lectin (MBL, also known as mannose-binding lectin), collectin K1 (CL-K1), and collectin L1 (CL-L1), and the ficolins (proteins that contain a fibrinogen-like domain and use a collagen helix for stabilization of the molecule), i.e., H-ficolin, L-ficolin, and M-ficolin (1, 2).