Expression and subcellular distribution of toll-like receptors TLR4, TLR5 and TLR9 on the gastric epithelium in Helicobacter pylori infection

Abstract

Toll-like receptors (TLRs) expressed by mucosal epithelium play an essential role in the defense against microbes by recognizing conserved bacterial molecules. For the first time TLR4, TLR5 and TLR9 have been microanatomically localized in patients with noninflamed gastric mucosa and Helicobacter pylori gastritis by immunohistochemistry. Because polarized expression of TLRs in apical and basolateral epithelial compartments is thought to modulate mucosal immunity, subcellular TLR distribution by gastric epithelium was investigated using confocal microscopy. TLR4, TLR5 and TLR9 were expressed by gastric epithelium in antrum and corpus of all patients with H. pylori gastritis (n = 14) and with noninflamed gastric mucosa (n = 5). TLR4 was expressed at the apical and the basolateral pole of the gastric epithelium as well in noninflamed gastric mucosa as in H. pylori gastritis. TLR5 and TLR9 expression in the noninflamed gastric mucosa was identical to that of TLR4 with localization at the apical and the basolateral epithelial pole. However, in H. pylori gastritis TLR5 and TLR9 expression on the gastric epithelium changed to an exclusive basolateral localization without detectable expression at the apical pole. In the human stomach, the gastric epithelium expressed TLR4, TLR5 and TLR9, which gives it the possibility to interact with H. pylori. Furthermore, gastric epithelial TLR4 expression is highly polarized in an apical and a basolateral compartment, whereas TLR5 and TLR9 polarization seems to be a process dynamically influenced by H. pylori infection. This polarized and dynamically regulated gastric epithelial expression of TLRs supports a sentinel role for these receptors in the mucosal immunity to H. pylori.

Fig. 1

Toll-like receptor expression in noninflamed gastric mucosa and chronic active H. pylori gastritis determined by immunohistochemistry Gastric epithelial cells as well in noninflamed gastric mucosa (a–c) as in chronic active H. pylori gastritis (d–f,j,k) express TLR4, TLR5 and TLR9. Epithelial TLR4 and TLR5 expression is accentuated in the glandular neck region (a,b,d,e). TLR9 expression was predominantly localized at the gastric surface epithelium (c,f). TLR4 and TLR9 expression by gastric epithelium tends to be stronger in H. pylori gastritis (d,f) than in the noninflamed gastric mucosa (a,c). TLR5 shows a strong expression by gastric epithelium as well in the noninflamed mucosa (b) as in chronic active H. pylori gastritis (e). Fig j and k show TLR5 and TLR9 expression by gastric epithelium in H. pylori gastritis in more detail. Negative controls for TLR4, TLR5 and TLR9 show no staining (g–i) TLR4 and TLR5 stain mononuclear cells in the lamina propria of H. pylori gastritis (d,e). Many neutrophils in chronic active H. pylori gastritis express TLR4 and some neutrophils express TLR9 (arrows, m). TLR5, however, is not found on neutrophils (arrows; l). Magnification: a–d, f × 20; e × 40; g–k × 100.

Fig. 2

Subcellular distribution of Toll-like receptors in gastric epithelium in noninflamed gastric mucosa and chronic active H. pylori gastritis determined by confocal microscopy Fluorescence microscopy shows TLR4 expression by gastric epithelium at the apical and at the basolateral epithelial pole. This expression pattern was identical in the (a) noninflamed gastric mucosa and (b) in H. pylori gastritis. In H. pylori infection the bacterium was directly attached to TLR4 expressed at the apical epithelial pole (b), which was confirmed by vertical confocal scanning sections (b inset). TLR5 (c, overview; d, detail) and TLR9 (g overview; h, detail) expression in the noninflamed gastric mucosa is identical to TLR4 with expression at the apical and at the basolateral pole of the gastric epithelium. However, in chronic active H. pylori gastritis gastric epithelium with directly overlying H. pylori expressed TLR5 (e, overview; f, detail) and TLR9 (i, overview; j, detail) exclusively at the basolateral pole of the gastric epithelial cells. No TLR5 and TLR9 expression at the apical pole was detectable, so that the apical cell borders are no more visible. TLR expression shows a red fluorescence. Nuclei and H. pylori are stained with DAPI and are pseudocoulored in blue and green, respectively.