The monoclonal antibody GN4 recognizes human Ficolin-2, also known as L-ficolin. Ficolins are a family of pattern recognition molecules containing both a collagen-like domain and a fibrinogen-like domain that are capable of activating the complement system, through association with MASPs, on the surface of microorganisms. In human, three Ficolins are known: Ficolin-1 (M-ficolin), Ficolin-2 (L-ficolin), and Ficolin-3 (H-ficolin). Ficolin-1, is mainly expressed bymonocytes, granulocytes andlung cells and is present locally in areas of inflammation.Ficolin-2 (also L-ficolin, ficolin L, EBP-37 or hucolin) is produced primarily by the liver. The association between Ficolin-2 and MASPs/sMAP is Ca2+-dependent. MASPs in Ficolin-2-MASP complexes have proteolytic activities for C4, C2 and C3. Ficolin-2 also shows opsonic activity.