ficolin2

Ficolin-2, also known as L-ficolin, is a soluble pattern-recognition protein of the innate immune system in humans. It belongs to the ficolin family, a group of collagen-like lectins that can initiate the lectin pathway of the complement system.

Biogenesis and distribution: Ficolin-2 is encoded by the FCN2 gene and is produced primarily by the liver. In the bloodstream it circulates as oligomeric complexes containing collagen-like stalks and a fibrinogen-like recognition domain, enabling multivalent binding to targets on microbial surfaces.

Function: Ficolin-2 binds to acetylated compounds and various carbohydrate patterns present on pathogens. Upon binding, it associates with MASP family proteases, notably MASP-2, to activate the lectin complement pathway, leading to cleavage of C4 and C2 and subsequent opsonization and downstream effector responses. It also contributes to the clearance of apoptotic cells and immune complexes and can modulate inflammatory processes.

Clinical and genetic aspects: Variation in FCN2 affects serum levels and functional activity of ficolin-2. Common polymorphisms are linked with altered susceptibility to infections, sepsis, and some inflammatory or autoimmune conditions in certain populations. Deficiency or low levels may predispose individuals to infection, particularly in immunocompromised groups such as neonates or the elderly.

Relation to other proteins: Ficolin-2 is one of three human ficolins, along with ficolin-1 (M-ficolin) and ficolin-3 (H-ficolin). All contribute to the lectin pathway by recognizing microbial ligands and engaging MASP proteases.