Figure 1.

Biosynthetic pathways of Lewis antigens starting from type 1 lacto series core chains. Starting from type 1 core chains, an α1, 2-fucosyltransferase (Se) transfers fucose (Fuc) to the terminal galactose (Gal), resulting in the H-1 antigen (H1). H-1 antigen is a target for GalNAc- or Gal-transferases (in blood group A or B individuals) or remains unmodified (in blood group O individuals). These intermediates the are modified for the fucosylation step by an α1,3/4-fucosyltransferase (Le), resulting in the difucosylated histo-blood group antigens ALe^b, ALe^b and Le^b. Non-secretors are unable to produce an active Se product, and are only targets for the Le gene product Le^a.