1. Rega Institute for Medical Research, Laboratory of Molecular Immunology, University of Leuven, Minderbroedersstraat 10, B-3000 Leuven, Belgium, Department of Clinical Biochemistry, University of Antwerp, Universiteitsplein 1, B-2610 Wilrijk, Belgium, and Oxford Glycobiology Institute, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K.