In the case of the A antigen we have an additional sugar that is linked via the alpha 13 linkage between the Galactose and this and acetyl galactose amine. In the case of the B antigen we have this galactose linked via the alpha one three linkage to another galactose. And that's what differentiates these three types of antigens. So we see that the antigens in the ABL system are all glycosylated glycoproteins. And what that means is not only do we have the protein on the antigen, we also have this oligosaccharide as shown in this diagram. Now it turns out that the terminal sugar residues on the antigen determines the type of blood group as we discussed just a moment ago.