Differential expression of carbohydrate blood-group antigens on rat taste-bud cells: relation to the functional marker alpha-gustducin.

An afferent nerve fiber supplying a taste bud receives input from several taste receptor cells, yet is predominantly responsive to one of the classic taste qualities (salt, acid, sweet, or bitter). This specificity requires recognition between taste receptor cells and nerve fibers that may be mediated by surface markers correlating with function. In an effort to identify potential markers, we used immunofluorescence and confocal microscopy to examine expression of the oligosaccharide blood-group antigens Lewis(b), A, and H type 2 in taste buds of the rat oral cavity. We compared the distributions of these antigens with that of alpha-gustducin, a G-protein subunit implicated in responses to sweet- and bitter-tasting substances. The A and Lewis(b) antigens were present only on spindle-shaped cells whose apical processes reached the taste pore. These antigens were not present on epithelial cells surrounding taste buds, and Lewis(b) was not found elsewhere in the digestive tract. Lewis(b) and A were not removed by lipid extraction, suggesting that they are present on glycoproteins rather than glycolipids. All Lewis(b)-positive cells expressed alpha-gustducin, but only a fraction of alpha-gustducin-positive cells expressed Lewis(b). The fraction of taste-bud cells expressing Lewis(b) decreased in the order: vallate papillae > foliate papillae > nasoincisor duct. The epiglottis had almost no taste-bud cells that expressed Lewis(b). The A antigen appeared on taste-bud cells that also expressed alpha-gustducin in the order: foliate and vallate papillae > nasoincisor duct and epiglottis > fungiform papillae. In addition, the A antigen was present on many cells that lacked alpha-gustducin in foliate and vallate papillae. In vallate papillae, cells expressed either A or Lewis(b), but not both. Lewis(b) appears to be restricted to differentiated light cells that also express alpha-gustducin and may be involved in intercellular interactions of these cells.