Immunohistochemical Analysis of Human Vallate Taste Buds

Abstract

The morphology of the vallate papillae from postmortem human samples was investigated with immunohistochemistry. Microscopically, taste buds were present along the inner wall of the papilla, and in some cases in the outer wall as well. The typical taste cell markers PLCβ2, GNAT3 (gustducin) and the T1R3 receptor stain elongated cells in human taste buds consistent with the Type II cells in rodents. In the human tissue, taste bud cells that stain with Type II cell markers, PLCβ2 and GNAT3, also stain with villin antibody. Two typical immunochemical markers for Type III taste cells in rodents, PGP9.5 and SNAP25, fail to stain any taste bud cells in the human postmortem tissue, although these antibodies do stain numerous nerve fibers throughout the specimen. Car4, another Type III cell marker, reacted with only a few taste cells in our samples. Finally, human vallate papillae have a general network of innervation similar to rodents and antibodies directed against SNAP25, PGP9.5, acetylated tubulin and P2X3 all stain free perigemmal nerve endings as well as intragemmal taste fibers. We conclude that with the exception of certain molecular features of Type III cells, human vallate papillae share the structural, morphological, and molecular features observed in rodents.

Keywords: P2X3; PLCb2; SNAP25; glossopharyngeal; gustducin; taste bud.

Figure 1.

Semi-schematic drawing of a human tongue showing location of the lingual taste papillae. All samples for the current study were taken from the row of circumvallate papillae including both the central papilla and more lateral ones.

Figure 2.

Immunocytochemistry for cell-type specific markers. Horizontal sections through the vallate papilla. (A–D) Triple label for Villin (red; A and C) and the Type II markers GNAT3 (gustducin; blue; A and B), and PLCβ2 (green; A and D). (E–J) Longitudinal sections of vallate papillae where dorsal is to the left. (E–G) Double label for SNAP25 (red; E and F) and Car4 (green; E and G). SNAP25 labels nerve fibers well but does not obviously label any taste cells. Car4 labels only rare taste cells (arrow G). (H–J) T1R3 (Tas1R3) labels several elongate taste cells in nearly every taste bud. Note the presence of taste buds on both sides of the crypt in J.

Figure 3.

Double and triple labeling for cell and nerve fiber markers. (A, A′) Horizontal section of the papilla; (B–E) Longitudinal sections where dorsal is to the right. (A, A′) Nerve fibers stained with acetylated tubulin (red) densely innervate taste buds as well as nontaste epithelium between the taste buds. Type II taste cells, marked by staining for PLCβ2 (green) and GNAT3 (Gustducin, blue) populate virtually all taste buds. In addition scattered GNAT3-positive superficial epithelial cells (arrows A′) appear between some taste buds. (B–E) Longitudinal sections of vallate papillae where dorsal is to the right. Note that in this plane of sections, taste buds are oriented at an angle to the surface of the epithelium, so that their taste pore is somewhat more dorsal than the base of the bud. (B) PGP95 stained (red) fibers innervate taste buds as well as surrounding epithelium. Some GNAT3 positive (green) cells appear to contact the PGP9.5-positive nerve fibers. (C–E) The dense network of intragemmal nerve fibers is stained by both SNAP25 (green; C and D) and P2X3 (green; E). These nerve fibers surround and apparently contact the Type II cells marked by GNAT3 (red; C and D) or PLCβ2 (red; E).

Figure 4.

Innervation of the papillary epithelium. Longitudinal sections; dorsal to the left. (A) PGP immunoreactive (green) fibers (arrows) extensively innervate the papillary trench wall below the taste bud (TB) shown at the left side of the image. PLCβ2 red. (B) Substance P immunoreactive fibers (green) sparsely innervate the epithelium and are mostly confined to basal regions or the subepithelial mucosa. PLCβ2 red. (C) In rare cases, Substance P immunoreactive nerve fibers (green) appear to contact the basal process of PLCβ2 immunoreactive (red) taste cells. Scale bar = 25 µm all panels.