The
carbohydrate epitope Gal alpha 1-3Gal beta 1-4GlcNAc-R (alpha-galactosyl) is abundantly expressed on cells of non-primate mammals, prosimians and New World monkeys, where it is synthesized by the
enzyme alpha 1,3-galactosyltransferase (alpha 1,3GT). Old World monkeys, apes and humans lack alpha 1,3GT and hence do not synthesize alpha-galactosyl
epitopes. Instead, these species produce a natural antibody, anti-Gal, which interacts specifically with alpha-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 alpha-galactosyl
epitopes on the
glycoproteins of virus propagated in cells that either produce or lack alpha 1,3GT. As predicted, virus propagated in Vero cells (derived from the African green monkey, an Old World monkey) did not express alpha-galactosyl
epitopes. In contrast, virus propagated in mouse 3T3 cells (EEE3T3) expressed approximately 80 alpha-galactosyl
epitopes per virion on both the E1 and the E2 envelope
glycoproteins. Thus, expression of the
alpha-galactosyl epitope on virions paralleled that on host cells. The binding of anti-Gal antibody to these
epitopes on EEE3T3 virions partially neutralized virus infectivity, raising the possibility that anti-Gal production in hosts may influence the initial infectious stage of viruses expressing alpha-galactosyl
epitopes.