title: Ultrastructural study on the differentiation and the fate of M cells in follicle-associated epithelium of rat Peyer's patch.
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.
authors.affiliation: Department of Bioresource and Agrobiosciences, Graduate School of Science and Technology, Kobe University, Kobe, Japan.
authors.forename: Sachiko
authors.initials: S
authors.lastname: Onishi
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Yokoyama
authors.forename: Keigi
authors.initials: K
authors.lastname: Chin
authors.forename: Midori
authors.initials: M
authors.lastname: Yuji
authors.forename: Tetsurou
authors.initials: T
authors.lastname: Inamoto
authors.forename: Wang-Mei
authors.initials: WM
authors.lastname: Qi
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Warita
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Hoshi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kitagawa
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D004847:Epithelial Cells / Q000648:ultrastructure*; D008297:Male; D046529:Microscopy, Electron, Transmission; D008871:Microvilli / Q000648:ultrastructure*; D010581:Peyer's Patches / Q000166:cytology*; D051381:Rats; D017208:Rats, Wistar