Peculiar Composition of Epithelial Cells in Follicle-Associated Intestinal Crypts of Peyer’s Patches in the Rat Small Intestine

Abstract

The epithelial cell composition was investigated in the follicle-associated intestinal crypt (FAIC) of rat Peyer’s patches. The epithelium of the FAIC mainly consisted of columnar epithelial cells, goblet cells and Paneth cells. The characteristics of secretory granules in Paneth cells and goblet cells of both the FAIC and ordinary intestinal crypts (IC) were almost the same in periodic acid-Schiff (PAS) reaction, Alcian blue (AB) staining and the immunohistochemical detection of lysozymes and soluble phospholipase A2. Both goblet cells and Paneth cells were markedly less frequent on the follicular sides than on the anti-follicular sides of the FAIC. Goblet cells were also markedly less frequent in the follicle-associated epithelium (FAE) than in the ordinary intestinal villi (IV). Indigenous bacteria were more frequently adhered to FAE than to follicle-associated intestinal villi or IV. These findings suggest that the host defense against indigenous bacteria is inhibited on the follicular sides of FAIC, which might contribute to the preferential settlement of indigenous bacteria on the FAE; they also suggest that differentiation into secretory cells is inhibited in the epithelium of the follicular sides of FAIC, so that differentiation into M cells might be admitted in the FAE of rat Peyer’s patches. Furthermore, intermediate cells possessing characteristics of both Paneth cells and goblet cells were rarely found in the FAIC, but not in the IC. This finding suggests that the manner of differentiation into Paneth cells in the FAIC differs from that in the IC.

Differential expression of Toll-like receptor-2, -4 and -9 in follicle-associated epithelium from epithelia of both follicle-associated intestinal villi and ordinary intestinal villi in rat Peyer’s patches

“…In the present study, TLR-2 was detected in the MV in both FAIV and IV, but almost all MV of FAE were negative for TLR-2. Considering the previous finding suggesting that indigenous bacteria adhered more frequently to FAE than to epithelia of FAIV and IV [17], these findings suggest that FAE might provide the circumstances where indigenous bacteria more easily adhere and proliferate before their settlement by the near complete absence of TLR-2 expression. Furthermore, the level of TLR-2 expression in MV was lower in the epithelium of f-FAIV than in the epithelia of IV and af-FAIV.…”

“…Indigenous bacteria more frequently adhere to FAE than to epithelia of FAIV and IV [13, 17, 20]. In the rat small intestine, it is suggested that bacteria proliferating on the mucosal surface are recognized by TLR-2 expressed in MV of IV and that TLR-2-negative MV at the apices of IV probably contribute to the adhesion of indigenous bacteria at the villous apices [15].…”

“…These findings suggest that bacteria in the space between the FAE and the epithelium of f-FAIV might be more difficult for TLR-2-mediated recognition systems to recognize than bacteria in the ordinary intervillous spaces. Considering the previous findings suggesting that Paneth cells are limited numerically on the FAIC [17], the space between FAE and the epithelium of FAIV might provide a better environment for the proliferation of indigenous bacteria than the spaces among IVs.…”

“…All tissue blocks were immersion-fixed in 4.0% paraformaldehyde fixative in 0.1 M phosphate buffer (pH 7.4) for 24 hr at 4°C and then were snap-frozen in liquid nitrogen with reference to the embedding method described previously [17]. Four- µ m-thick sections were cut using a Coldtome HM505E (Carl Zeiss, Jena, Thüringen, Germany) and were placed on slide glasses precoated with 2% 3-aminopropyltriethoxysilane (Shin-Etsu Chemical Co., Tokyo, Japan) and stored at −30°C until use.…”

“…The lymphatic follicles probably monitor the development of bacterial colonies in the restricted areas around the lymphatic follicle in the rat small intestine [28]. In light of the finding that indigenous bacteria adhere to the follicle-associated epithelium (FAE) of Peyer’s patches more frequently than to the epithelia of intestinal villi [17], it has been speculated that the Peyer’s patches are equipped with different systems for regulating the settlement of indigenous bacteria from the mucosa with the exception of Peyer’s patches in the small intestine. However, the regulation system for indigenous bacteria in the Peyer’s patches remains unknown.…”