The carbohydrate epitope Galα1-3Galβ1-4GlcNAc-R (α-galactosyl) is abundantly expressed on cells of non-primate mammals, prosimians and New World monkeys, where it is synthesized by the enzyme α1,3-galactosyltransferase (α1,3GT). Old World monkeys, apes and humans lack α1,3GT and hence do not synthesize α-galactosyl epitopes. Instead, these species produce a natural antibody, anti-Gal, which interacts specifically with α-galactosyl epitopes and which constitutes up to 1% of circulating immunoglobulins in humans. We have used eastern equine encephalitis (EEE) virus as a model to examine the differential expression of α-galactosyl epitopes on the glycoproteins of virus propagated in cells that either produce or lack α1,3GT. As predicted, virus propagated in Vero cells (derived from the African green monkey, an Old World monkey) did not express α-galactosyl epitopes. In contrast, virus propagated in mouse 3T3 cells (EEE) expressed approximately 80 α-galactosyl epitopes per virion on both the E1 and the E2 envelope glycoproteins. Thus, expression of the α-galactosyl epitope on virions paralleled that on host cells. The binding of anti-Gal antibody to these epitopes on EEE virions partially neutralized virus infectivity, raising the possibility that anti-Gal production in hosts may influence the initial infectious stage of viruses expressing α-galactosyl epitopes.


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