Differentiation of Epithelial cells to M Cells in Response to Bacterial Colonization on the Follicle-Associated Epithelium of Peyer's Patch in Rat Small Intestine

Abstract

ABSTRACT. To clarify the relationship between M cells and intestinal microflora, histoplanimetrical investigation into the bacterial colonization and the differentiation to M cells was carried out in rat Peyer's patch under physiological conditions. The follicle-associated epithelium (FAE), except for the narrow area of apical region, was closely covered with both neighboring intestinal villi and a thick mucous layer, the latter of which also filled the intervillous spaces as well as the space between the FAE and the neighboring intestinal villi. Indigenous bacteria adhered almost constantly to the narrow areas of apical regions of both intestinal villi and the FAE. Bacterial colonies were occasionally located on the basal to middle region of FAE, where M cells also appeared, forming large pockets. When bacterial colonies were located on the basal to middle region of FAE, bacteria with the same morphological characteristics also proliferated in the intervillous spaces neighboring the Peyer's patch. In cases with no bacterial colonies on the basal to middle region of FAE, however, M cells were rare in the FAE. Histoplanimetrical analysis showed the similar distribution pattern of bacterial colonies on the FAE and M cells in the FAE. M cells ultrastructurally engulfed indigenous bacteria, which were then transported to the pockets. These results suggest that indigenous bacterial colonization on the FAE stimulates the differentiation of M cells in the FAE under physiological conditions. The uptake of bacteria by M cells might contribute the regulation of the development of indigenous bacterial colonies in the small intestine.

Persorption Mechanisms of Luminal Antigenic Particulates via Apoptotic Epithelial Cells of Intestinal Villi into Systemic Blood Circulation in Orally Immunized Rats

“…In rat Peyer's patches, the FAE except for the narrow area of the apical region is covered with follicle-associated intestinal villi. The narrow space between the FAE and adjacent villi is filled with thick mucous [3]. These findings are also confirmed in our study.…”

“…In the present study, no SEs reached the FAEs in any experimental groups because of prevention of diffusion of SEs by both the adjacent follicle-associated intestinal villi and mucous. This finding strongly supposes the hypothesis [3] that most M cells are away from the stream of luminal contents and that the situation of M cells in the FAE is unsuitable for constant monitoring of luminal food antigens under physiological conditions in animals.…”

“…Moreover, M cells are predominantly distributed in the basal to middle regions rather than the apical regions of the FAEs in Peyer's patches of rats, rabbits, humans and mice [3,22,30,35], of rabbit cecal lymphoid patches [22], and of chicken cecal tonsils [23]. On the other hand, detailed histoplanimetrical study suggests that the appearance of M cells is closely correlated with bacterial colonization in the FAE of rat Peyer's patches [3]. The engulfment of bacteria by M cells in the rabbit appendix requires the bacteria to be able to access the FAE [26].…”

Histoplanimetrical Study on the Relationship between the Cell Kinetics of Villous Columnar Epithelial Cells and the Proliferation of Indigenous Bacteria in Rat Small Intestine

“…In addition, from the present study, the expansion of indigenous bacterial colonies to occupy half the height of the intervillous spaces resulted in increased migration speed of villous columnar epithelial cells compared with those in environments without development of indigenous bacterial colonies. The indigenous bacteria preferentially settle on the epithelial cells of the narrow apical portions of both the intestinal villi and the domes of mucosal lymphatic follicles [8,9,17]. The passing time of apoptotic epithelial cells with indigenous bacteria through the narrow spaces of the apical portions of intestinal villi is calculated to be within several hours from both the villous length and the lifespan of the BrdU-labeled villous columnar epithelial cells in Experiment 1.…”

“…During this migration process, apoptosis is induced in the villous columnar epithelial cells, which are ultimately exfoliated into the intestinal lumen [13,30,34,40,41]. The fundamental settlement place of indigenous bacteria is the apical portions of both the intestinal villi and the domes of lymphatic follicles in Peyer's patches in the rat small intestine [8,17]. These apices are unstable sites where apoptotic epithelial cells are incessantly shed into the intestinal lumen.…”