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 Ulex europaeus agglutinin I (UEA₁) (10 μg/ml) was found to increase the rate constant of CL^? efflux into 100mM Na⁺ oxalate media by about 40% in erythrocytes taken from antigen H donors. In 100 mMK ⁺ oxalate, 150 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^? efflux by UEA₁ was completely blocked by 10 μM 4,4′-dllsothiocyanato-stilbene-2,2′-disulfonic acid (DIDS) indicating that the effect of the lectin is mediated by the anion exchanger of human erythrocytes (band 3 protein). In antigen A₁ erythrocytes no significant stimulation of anion exchange by UEA₁ was seen. The activation of Cl^? efflux was completely 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, replacing part of extracellular chloride by bicarbonate did not considerably alter the (previously reported) stimulatory effect of UEA₁ on red blood cell Ca⁺⁺ uptake. This suggests that the acceleration of anion exchange and of Ca⁺⁺ uptake by UEA₁, respectively, are mediated by different mechanisms. It is concluded that UEA₁ activates anion exchange of human erythrocytes most probably by a direct interaction with H antigens present on extracellular domains of the band 3 protein. © 1993 Wiley-Liss, Inc.