ABH ANTIGENS AS RECOGNITION SITES FOR THE ACTIVATION OF RED-BLOOD-CELL ANION-EXCHANGE BY THE LECTIN ULEX-EUROPAEUS AGGLUTININ-I

The blood group antigen H (blood group O) and fucose-specific lectin U lex europaeus agglutinin I (UEA1) (10 mug/ml) was found to increase th e rate constant of Cl-efflux into 100 mM Na+ oxalate media by about 40 % in erythrocytes taken from antigen H donors. In 100 mM K+ oxalate, 1 50 mM Na+ pyruvate and in 150 mM Na+ acetate media the lectin elevated the rate constant of Cl- efflux by 20-50%. The acceleration of Cl- ef flux by UEA, was completely blocked by 10 muM 4,4'-diisothiocyanato-st ilbene-2,2'-disulfonic acid (DIDS) indicating that the effect of the l ectin is mediated by the anion exchanger of human erythrocytes (band 3 protein). In antigen Al erythrocytes no significant stimulation of an ion exchange by UEA, was seen. The activation of Cl- efflux was comple tely prevented by addition of 1 mM fucose to the medium. These results suggest that the effect of UEA1 is mediated through interaction with the fucose residues of H antigens. Increasing extracellular Ca++ from 0.5 to 5 mM in Na+ pyruvate or Na+ acetate media slightly reduced the acceleration of anion exchange by the lectin. On the other hand, repla cing part of extracellular chloride by bicarbonate did not considerabl y alter the (previously reported) stimulatory effect of UEA1 on red bl ood cell Ca++ uptake. This suggests that the acceleration of anion exc hange and of Ca++ uptake by UEA1, respectively, are mediated by differ ent mechanisms. It is concluded that UEA, activates anion exchange of human erythrocytes most probably by a direct interaction with H antige ns present on extracellular domains of the band 3 protein. (C) 1993 Wi ley-Liss, Inc.