The monoclonal antibody 4H5 recognizes human Ficolin-3, also known as H-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 by monocytes, granulocytes and lung cells and is present locally in areas of inflammation.
Ficolin-3 (also Hakata antigen, H-ficolin or ficolin H) is produced by the liver and by the lung. Ficolin-3 is associated with three types of MASPs and sMAP, this complex activates C4, C2 and C3 in the fluid phase.