Changes In Cell Surface Glycosylation In α1,3-galactosyltransferase Knockout And α1,2-fucosyltransferase Transgenic Mice

Background. Inactivation of the α1,3-galactosyltransferase (GalT) gene by homologous recombination (knockout [KO] mice) and competition for the enzyme's N-acetyllactosamine substrate by transgenically expressed α1,2-fucosyltransferase (H-transferase) are two genetic approaches to elimination of the Galα1,3Gal (αGal) epitope, which is the major xenoantigen in pigs against which humans have preformed antibodies. Such genetic manipulations often have unpredictable results. Methods. A panel of 19 selected lectins was used to characterize the changes in cell surface glycosylation in GalT KO and H-transferase transgenic mice, compared with nontransgenic littermate controls. Results. GalT KO mice showed complete elimination of the αGal epitope, as reported previously. Surprisingly, however, this was associated with only a modest increase in N-acetyllactosamine residues and had little other effect on the pattern of lectin binding. In contrast, the pattern of lectin binding to H-transferase transgenic mouse cells was more profoundly disturbed and indicated, in addition to the expected expression of H substance and suppression of the αGal epitope, that there was a marked reduction in α2,3-sialylation and exposure of the normally cryptic antigens, sialylated Tn and Forssman antigens. Similar changes in lectin reactivity with porcine aortic endothelial cells were induced by neuraminidase treatment. Conclusions. Lectins were able to bind underlying carbohydrate structures (sialylated Tn and Forssman antigens) that are normally cryptic antigens on H-transferase transgenic mouse spleen and cardiac endothelial cells, probably as a consequence of the reduction in the electronegativity of the cell surface due to reduced sialylation. As humans have preformed anti-Tn and anti-Forssman antibodies, it is possible that these structures may become targets of the xenograft rejection process, including hyperacute rejection.