CHANGES IN CELL-SURFACE GLYCOSYLATION IN ALPHA-1,3-GALACTOSYLTRANSFERASE KNOCKOUT AND ALPHA-1,2-FUCOSYL-TRANSFERASE TRANSGENIC MICE

Background. Inactivation of the alpha 1,3-galactosyltransferase (GalT) gene by homologous recombination (knockout [KO] mice) and competition for the enzyme's N-acetyllactosamine substrate by transgenically expr essed alpha 1,2-fucosyltransferase (H-transferase) are two genetic app roaches to elimination of the Gal alpha 1,3Gal (alpha Gal) epitope, wh ich is the major xenoantigen in pigs against which humans have preform ed antibodies. Such genetic manipulations often have unpredictable res ults. Methods. A panel of 19 selected lectins was used to characterize the changes in cell surface glycosylation in GalT KO and II-transfera se transgenic mice, compared with nontransgenic littermate controls. R esults. GalT RO mice showed complete elimination of the alpha Gal epit ope, as reported previously. Surprisingly, however, this was associate d with only a modest increase in N-acetyllaetosamine residues and had little other effect on the pattern of lectin binding. In contrast, the pattern of lectin binding to II-transferase transgenic mouse cells wa s more profoundly disturbed and indicated, in addition to the expected expression of H substance and suppression of the alpha Gal epitope, t hat there was a marked reduction in alpha 2,3-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 w ere able to bind underlying carbohydrate structures (sialylated Tn and Forssman antigens) that are normally cryptic antigens on H-transferas e transgenic mouse spleen and cardiac endothelial cells, probably as a consequence of the reduction in the electronegativity of the cell sur face due to reduced sialylation. As humans have preformed anti-Tn and anti-Forssman antibodies, it is possible that these structures may bec ome targets of the xenograft rejection process, including hyperacute r ejection.