The disaccharide Galalpha1-3Gal is found on more than 45 different molecules on the endothelium of porcine cells and has recently attracted considerable interest, being the major target, recognized by xenoreactive antibodies. In this study, the distribution and topology of Galalpha1-3Gal on porcine endothelial cells was examined to access whether some Galalpha1-3Gal-containing molecules might be preferentially recognized by antibodies binding to Galalpha1-3Gal. Thirteen percent of the Galalpha1-3Gal was found on glycolipid and 87% on glycoproteins. Of all the glycoproteins and glycolipids containing Galalpha1-3Gal, two molecules, fibronectin and the integrin beta1 subunit, were most intensely labeled by galactose oxidase, suggesting that these molecules may be preferentially exposed on the apical surface of the endothelium. Binding of anti-Galalpha1-3Gal antibodies to endothelial cell surfaces significantly diminished labeling of fibronectin and the integrin beta1 subunit by galactose oxidase, indicating that these glycoproteins are targets for the antibodies when binding to intact porcine cells. (C) 2003 Elsevier Science (USA). All rights reserved.