Extracellular lectin functioning as a pattern-recognition receptor in innate immunity. Binds the sugar moieties of pathogen-associated molecular patterns (PAMPs) displayed on microbes and activates the lectin pathway of the complement system. May also activate monocytes through a G protein-coupled receptor, FFAR2, inducing the secretion of interleukin-8/IL-8. Binds preferentially to 9-O-acetylated 2-6-linked sialic acid derivatives and to various glycans containing sialic acid engaged in a 2-3 linkage (By similarity). Homotrimer. Interacts with elastin/ELN. Interacts (via Fibrinogen C-terminal domain) with FFAR2. Interacts with CRP; may regulate monocyte activation by FCN1. Found on the monocyte and granulocyte surface. Highly expressed in liver and spleen. The fibrinogen C-terminal domain mediates calcium-dependent binding to carbohydrates and tethering to the cell surface in monocytes and granulocytes. The domain undergoes a conformational switch at pH under 6.2, and looses its carbohydrate-binding ability. Belongs to the ficolin lectin family.