The chemical structures of the ABH antigens and two additional antigens (alpha 1,3 galactosyl epitope and Forssman antigen) are shown. As opposed to the ABH antigens, which possess a fucose linked to the galactose by alpha 1,2 glycosidic linkage, the alpha 1,3 galactosyl epitope and Forssman antigen do not possess the fucose. The A antigen and Forssman antigen possess a GalNAc linked to the galactose by alpha 1,3 linkage, whereas the B antigen and alpha 1,3 galactosyl epitope possess a galactose linked to the galactose by alpha 1,3 linkage.