Demonstration of the interaction between the CD23 molecule and the galactose residue of glycoproteins.

The CD23 molecule is a low-affinity receptor for IgE and has a marked homology in amino acid sequence with C-type animal lectins, including asialoglycoprotein receptor. We tested whether the CD23 antigen can indeed interact with the sugar chain of glycoproteins. Detergent extract of the membrane component from Epstein-Barr Virus (EBV)-transformed human B-cell line, L-KT9 cells, was incubated with asialofetuin (ASF)-coupled Sepharose, and bound proteins were effectively eluted by 0.3 M lactose or galactose which were among the competitive sugars tested. In this eluate, the CD23 molecule was detected by an immunoblotting technique. Because fetuin has both an N- and O-type sugar chain on the molecule, we tested which type of sugar chain can interact with CD23. The CD23 molecule interacted with asialocasein having a sugar chain with the Gal-GalNAc structure with asialobovine submaxillary mucin having the GalNAc structure, and also with ASF; however, it faintly interacted with ASF after removal of the O-type sugar chain by beta-elimination. These results showed that the CD23 molecule can, indeed, interact with the galactose residue, especially with the Gal-GalNAc rather than the Gal-GlcNAc structure of the terminal sugar chain of glycoproteins.