Carbohydrate Research, 228 (1992) 289-291 Elsevier Science Publishers B.V., Amsterdam 289 Further definition of the size of the blood group-i antigenic determinant using a chemically synthesised octasaccharide of poly-N-acetyllactosamine type* Ten Feizi, Elizabeth F. Hounsell, Glycoconjugates Section, Clinical Research Centre. Watford Road, Harrow, Middlesex, HAI 3UJ (United Kingdom) Jocelyne Alais, Alain Veyrieres+, and Serge David Institut a’e Chimie Mokculaire d’Orsay, U. R. A. du C. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM N. R.S. D. 0462. UniversitP Paris-&d, Brit. 420, F-91405 Orsay (France) (Received June 26th, 1991; accepted in revised form January 23rd, 1992) ABSTRACT In earlier studies, the minimum structure which inhibited the binding of anti-i to an i-active glycoprotein was the linear Disaccharide, j?-D-Galp-(1 +4)-/3-D-GlcpNAc-(1 +3)-D-Gal. There was an in- creasing hierarchy of inhibitory activities in the linear tetrasaccharide, B-D-Galp-(1 +4)-/?-D-GlcpNAc- (1 -+3)-B-D-Galp-( 1 +4)-&D-GlcNAc, its methyl 8_glycoside, and in the methyl &glycoside of the hexa- saccharide. The linear octasaccharide methyl j?-glycoside in this series is approximately only half zyxwvutsrqponmlkjih as active as the hexasaccharide methyl /3-glycoside. Analyses by high resolution ‘H-n.m.r. of these two oligosaccharides indicated that they have similar conformations in solution, and there is no evidence for the occurrence of inter-molecular interactions which might partially hinder the binding of anti-i to the octasaccharide methyl /7-glycoside. These results are consistent with the size of the i antigen being in the region of a hexasaccharide. It is proposed that the methyl aglycon group of the hexasaccharide methyl B-glycoside confers an above normal activity by presenting a hydrophobic area for additional contact in the vicinity of the antibody- combining site. INTRODUCTION The i and I antigens are carbohydrate determinants of human erythrocytes recognised by monoclonal autoantibodies in sera of patients with an autoirmnune haemolytic disorder, cold agglutinin syndrome’. The expression of the i antigen, which predominates on the erythrocytes of the foetus and neonate, diminishes during the first year of life, while expression of the I antigen increases. These antigens are not confined to human erythrocytes but are expressed in a variety of human and animal cells, and their levels change in embryonic development, cell differentiation, and oncogenesis’*‘. By haemagglutination inhibition and quantitative precipitation using mucin-type * T.F., E.F.H., J.A., and A.V. congratulate Professor S. David on the occasion of his 70th birthday and thank him for the stimulus he has given for the collaborations between our two laboratories. ’ Present address: Laboratoire de Chimie des Glucides, T74-E6, Universitt Pierre et Marie Curie, 4 Place Jussieu, F-75252 Paris, France. 0008-6215/921$05.00 @ 1992 - Elsevier Science Publishers B.V. All rights reserved.