RECOGNITION OF TYPE-1 CHAIN OLIGOSACCHARIDES AND LACTO-SERIES GLYCOLIPIDS BY AN ANTIBODY TO HUMAN SECRETORY COMPONENT

Binding of the mouse IgM antibody 6C4 is lost after treatment of human free secretory component with peptide N-glycosidase F (Bakos et al. ( 1991) J. Immunol. 146, 162-168) or periodate, suggesting that asparagi ne-linked oligosaccharides contain the epitope recognized by this anti body, Inhibition of antibody binding to free secretory component by mi lk oligosaccharides established that lacto-N-tetraose is the minimum s tructure recognized by the antibody, but larger oligosaccharides with terminal Gal beta 1-3GlcNAc sequences bind with much higher affinity, Antibody binding is enhanced by substitution with the Lewis Fuc alpha 1-4 and is inhibited by Fuc alpha 1-2Gal substitution, Free secretory component, however, does not bind other antibodies that recognize Le(a ) or Le(b) oligosaccharides, and binding is lost after digestion with a beta-galactosidase that cleaves Gal beta 1-3 linkages but not after digestion with alpha-L-fucosidase. Therefore, the major epitope recogn ized by 6C4 on free secretory component is probably not an asparagine- linked Le(a) oligosaccharide, The antibody also binds to human milk la ctoferrin, some human mucins, and lacto-series glycolipids including I II4 alpha Fuc-lactotetraosyl ceramide and lactotetraosyl ceramide, Bas ed on affinity chromatography of oligosaccharides released from free s ecretory component, the epitope recognized by antibody 6C4 is present on approximately 3.5% of the asparagine-linked oligosaccharides. (C) 1 995 Academic Press, Inc.