Fucose is a hexose deoxy sugar with the chemical formula C6H12O5. It is found on N-linked glycans on the mammalian, insect and plant cell surface, and is the fundamental sub-unit of the fucoidan polysaccharide. α(1→3) linked core fucose is a suspected carbohydrate antigen for IgE-mediated allergy. Two structural features distinguish fucose from other six-carbon sugars present in mammals: the lack of a hydroxyl group on the carbon at the 6-position (C-6) (thereby making it a deoxy sugar) and the L-configuration. It is equivalent to 6-deoxy-L-galactose. In the fucose-containing glycan structures, fucosylated glycans, fucose can exist as a terminal modification or serve as an attachment point for adding other sugars. In human N-linked glycans, fucose is most commonly linked α-1,6 to the reducing terminal β-N-acetylglucosamine. However, fucose at the non-reducing termini linked α-1,2 to galactose forms the H antigen, the substructure of the A and B blood group antigens. Fucose is released from fucose-containing polymers by an enzyme called α-fucosidase. Fucosylation of antibodies has been established to reduce binding to the Fc receptor (FcgammaRIIIA) of Natural Killer cells and thereby reduce antigen-dependent cellular cytotoxicity. Therefore therapeutic antibodies that are designed to recruit the immune system to cancers cells ave been manufactured in cell lines deficient in the enzyme for core fucosylation (FUT8) and thereby enhancing the in vivo cell killing.