Lectin interactions with α‐galactosylated xenoantigens

α‐Galactosylated xenoantigens (Galα1‐3Galβ1‐4GlcNAcβ1 and Galα1‐3Galβ1‐4GlcNAcβ1‐3Galβ1‐4Glc) are often detected with the α‐Gal specific lectin Griffonia simplicifolia 1 isolectin B4 (GS1 B4). However, this lectin exhibits a broad and variable specificity for carbohydrates terminating in α‐Gal. Thus, both false positive and false negative results may occur when GS1 B4 is used to determine natural antigens in xeno (pig‐to‐primate) transplantation research. To refine the tools for detecting α‐galactosylated antigens we have studied the binding of various α‐galactophilic lectins to α‐galactosylated neoglycoproteins. The lectins were: Euonymus europaeus agglutinin (EEA), Griffonia simplicifolia 1 isolectin B4 (GS1 B4), Maclura pomifera agglutinin (MPA) and Pseudomonas aeruginosa agglutinin (PA‐IL). Although both GS1 B4 and MPA strongly bound glycoconjugates terminating in Gal there seems to be some differentiation in their sugar binding preferences. MPA was the only lectin that showed high affinity for the pentasaccharide Galα1‐3Galβ1‐4GlcNAcβ1‐3Galβ1‐4Glc and for the Galα‐glycans on non‐primate thyroglobulin. The length of the xenoantigenic carbohydrate chain may influence the nature of the inhibition when a simple sugar is used to inhibit GS1 B4 binding to the xenoantigen. Inhibition studies of MPA GS1 B4 interaction further suggest that both lectins attach to the same site of the carbohydrate antigen and that GS1 B4 in addition binds to at least one other site that has no affinity for MPA. When lectins are used for recognition and investigation of natural Galα‐antigens, we propose that GS1 B4 and MPA should accompany each other.