The antigens Ii, SSEA-1 and ABH are in interrelated system of carbohydrate differentiation antigens expressed on glycosphingolipids and glycoproteins.

Immunochemical studies using a group of monoclonal human auto-antibodies (anti-I and anti-i cold agglutinins) and a mouse hybridoma antibody (anti-SSEA-1) have revealed an interrelated system of carbohydrate antigens which also involves the major blood group antigens. The I and i antigens are expressed on branched and linear oligosaccharides respectively built of repeating N-acetyllactosamine units. These structures may serve as backbones to which specific monosaccharides are added to form the differentiation antigen termed SSEA-1 and the blood group H, A and B antigens. The expression of these carbohydrate antigens changes dramatically during (a) early embryogenesis in the mouse, (b) erythrocyte maturation and (c) gastric carcinogenesis in man. It is envisaged that these changing antigenicities reflect the stepwise addition or deletion of monosaccharides as a result of altered balance of glycosyl transferases. We now face the challenge of investigating the functions of these changing carbohydrate structures.