CD23 molecule acts as a galactose-binding lectin in the cell aggregation of EBV-transformed human B-cell lines

Epstein-Barr virus (EBV)-transformed human B-cell lines, L-KT9and DH3 cells express CD23 antigen, and grow in a mixture ofsingle and aggregated cells. The CD23 molecule has high aminoacid sequence homology with C-type lectin and recently we haveshown that the solubilized CD23 molecule can really interactwith galactose residues on glycoproteins. In this study, therefore,we tested whether CD23 antigen on the cell surface really actsas a galactose-binding lectin in the aggregation of these cells.The EBV-transformed cells (L-KT9) were separated into an aggregated-cell-richfraction and a single-cell-rich fraction. Aggregated cells disaggregatedafter removal of galactose by ß-galactosidase treatment,whereas single cells made large aggregation on sialidase treatment,and this aggregation was inhibited in the presence of asialo-fetuin.On the other hand, naturally aggregated cells become singlecells with anti-CD23 monoclonal antibody (mAB) as well as thesoluble form of CD23, but not with anti-CD21 mAB. In addition,L-KT9 and DH3 cells bound to asialo-fetuin-coupled Sepharose(ASF-Sepharose) and this binding was significantly inhibitedby pre-treatment of cells with anti-CD23, but not with anti-CD21or other antiadhesion molecules. From these results, we concludethat the naturally aggregated state of EBV-transformed cellsoccurs mainly through the interaction of CD23 as a lectin moleculeand galactose residues as its ligand. CD23 molecule cell aggregation EBV-transformed B cells glycosidase treatment low-affinity IgE receptor