Ultrastructural Study on the Differentiation and the Fate of M cells in Follicle-Associated Epithelium of Rat Peyer's Patch

Abstract

ABSTRACT. The differentiation process of immature microvillous epithelial cells to M cells and the fate of M cells in the follicle-associated epithelium (FAE) of the mucosa-associated lymphoid tissues are still unclear. In this study, the differentiation process and the fate of M cells were clarified in rat Peyer's patches under a transmission electron microscope. Almost all immature epithelial cells were found to possess long, slender microvilli, which gradually shortened, thickened and dispersed as the immature epithelial cells migrated away from the crypt orifices. These morphological changes started in the centers and moved to the peripheries of the apical surfaces of epithelial cells, accompanied by the protrusion of apical cytoplasm out of the terminal web. During these changes, the bundles of microfilaments of microvilli never shortened, and both small vesicles in the apical cytoplasm and tiny invaginations of the apical membranes were found. The intraepithelial migrating cells gradually accumulated to form typical intraepithelial pockets. In all FAE, there was no morphological sign of cell death in M cells. The rearrangement of microfilament bundles, the reconstruction of microvilli and the disappearance of pockets resulted in the transformation of M cells into microvillous epithelial cells. These serial ultrastructural changes suggest that M cells are a temporal and transitional cell type caused by the active engulfment of luminal substances and that when the engulfment ceases, the M cells transform into mature microvillous epithelial cells.

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

“…Several possible sugars that are specific for indigenous bacterial lectins, are expressed restrictedly on the lateapoptotic epithelial cells of the most luminal sites of mucosa in the rat jejuno-ileum [3] and through the rat alimentary tract [28]. In the small intestine, the apices of both the intestinal villi and the domes of mucosal lymphatic follicles are unstable sites where apoptotic epithelial cells are incessantly shed into the intestinal lumen [18,19]. The lifespan and migration speed of columnar epithelial cells are crucial factors in the regulation of the settlement of indigenous bacteria in the rat small and large intestine.…”

Immunohistochemical Study on the Secretory Host Defense System of Bactericidal Peptides in Rat Digestive Organs

“…Several possible sugars specific for indigenous bacterial lectins are expressed strictly on late-apoptotic epithelial cells of the most luminal sites in rat jejuno-ileum [5] and whole alimentary tract [39]. The most luminal sites of both the intestinal villi and the domes of mucosal lymphatic follicles are also shedding sites of effete epithelial cells at the late apoptotic stage [27,28]. Therefore, the stable settlement of indigenous bacteria is considered to be maintained by the delicate balance of the proliferation rate of indigenous bacteria in relation to the exfoliation rate of effete apoptotic epithelial cells.…”

Unique Microanatomy of Ileal Peyer's Patches of the One Humped Camel (Camelus dromedarius) is not Age‐Dependent

“…However, M cells show different morphological characteristics in various species (Owen, 1977;Bye et al, 1984;Madara et al, 1984;Sicinski et al, 1986;Gebert and Hach, 1993;Gebert and Bartels, 1995). There are different morphologies of M cells in calves (Liebler et al, 1988(Liebler et al, , 1991 and in rats (Onishi et al, 2007). M cells play an important role in transporting particulate, microbial and soluble antigenic substances from the lumen to the subepithelial immunocompetent cells, thereby initiating mucosal immune responses (Gebert et al, 1996).…”