Ultrastructural Study on the Epithelial Responses against Attachment of Indigenous Bacteria to Epithelial Membranes in Peyer's Pathes of Rat Small Intestine

Abstract

ABSTRACT. The ultrastructure of epithelial responses against the membrane adhesion of indigenous bacteria was investigated in the follicleassociated epithelium (FAE) of rat small intestine. The most frequent adherence of the various morphological types of bacteria to the epithelial membranes was found at the apex of the FAE. The attachment sites were deeply invaginated, and their bottoms were deformed into a sharp cone shape. Four layers with different electron densities were formed just beneath the apical membranes by microfilaments which surrounded the invaginations. The electron density of each layer was gradually decreased as being apart from the invaginations. The extremities of some bacteria in the invaginations were deformed into sharpened shapes. The cell walls of the extremities of the bacteria were occasionally dissolved in the invaginations, and their cytoplasms were slightly swollen with low electron densities. In some invaginations, the attached bacteria were eliminated to leave their fragments such as filamentous debris and a part of cell walls. Finally these remnants disappeared completely. When the bacterial colonies existed in the middle region of the FAE, the attachment of bacteria resulted in the engulfment of bacteria by M cells. The degenerated bacteria whose cytoplasmic matrices were separated into high electron dense materials and cleared materials were occasionally engulfed by ordinary microvillous columnar epithelial cells or goblet cells throughout the FAE. These findings suggest that the epithelial cells reject the attachment of live indigenous bacteria and that the M cells absorb indigenous bacteria in rat Peyer's patches. KEY WORDS: epithelial apoptosis, indigenous bacteria, M cell, Peyer's patch, ultrastructure.

Immunohistochemical and Histoplanimetrical Study on the Spatial Relationship between the Settlement of Indigenous Bacteria and the Secretion of Bactericidal Peptides in Rat Alimentary Tract

“…Therefore, the stable settlement of indigenous bacteria is considered to be maintained by the delicate balance of the proliferation rate of indigenous bacteria over the exfoliation rate of effete apoptotic epithelial cells [20,21]. In addition, the indigenous bacteria closely attached to the epithelial cell membranes are eliminated by physical and chemical elimination by epithelial cells themselves [10,11]. The proliferation and settlement of indigenous bacteria are regulated by several other factors, as well, such as the thickness of the mucous layer, digestive enzymes, pH in the milieu, the secretion of several bactericidal substances and so on [5,9].…”

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

“…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 short time, the indigenous bacteria which adhere to epithelial cells incessantly proliferate and are in turn expelled by the physical and chemical activities of villous columnar epithelial cells [17,18]. From these findings, the lowest migration speed of the epithelial cells, that is, the longest "stay" of the adhered indigenous bacteria on the epithelial surface, might intensify the settlement of indigenous bacteria on the mucosal epithelium.…”

“…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.…”

“…The numbers of indigenous bacteria are generally maintained in the alimentary tract under a physiological condition [32], whereas the numbers are sometimes changed under the effects from foods and the environmental stress [42] or the invasion of pathogenic bacteria [12]. It has been considered that the settlement and proliferation of intestinal indigenous bacteria are complicatedly regulated by non-specific host defense mechanisms, such as motility by various contractile histological elements, the physical barrier of a thick mucous layer, the secretion of bactericidal substances, the chemical and physical elimination system of villous columnar epithelial cells themselves and the rapid replacement of their cells [17][18][19]27].…”

“…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.…”