Ultrastructural study on microfold cells and microvillus cells in the follicle-associated epithelium over Peyer's Patches in albino rat

Microfold cells [M cells] act as gateways to the mucosal immune system. The aim of the study was to perform a detailed ultrastructural study on M cells and microvillus enterocytes in the follicle-associated epithelium that covers the dome region of the ileal Peyer's patches in the albino rat to understand the relationship between the two types of cells, the origin of M cells, and their possible mechanism in sampling of the luminal antigens. The follicle-associated epithelium over the Peyer's patches in 10 adult albino rats was studied carefully under transmission electron microscope with a special attention to M cells and microvillus enterocytes. M cells were characterized by pale cytoplasm and either paucity or lack of apical microvilli beside intracytoplasmic pockets harboring migrating lymphocytes. In the microvilli-lacking areas, however, bundles of microvillus filaments occasionally remained in the apical cytoplasm and small vesicles and tubules were found at the apical poles of M cells. Microvillus cells had apical brush borders composed of long, regular, and densely packed microvilli; however, a wide range of diversity of the apical surface morphology was noted. Sometimes, transitional epithelial cells from microvillus to M cells were observed as columnar cells, which had microvilli of moderate height in their apical border with appearance of bare areas, in addition to other cells, which had a microfolded profile that bore few stout and short microvilli. Pale cytoplasmic extensions of dendritic morphology were seen extending among the epithelial cells covering the Peyer's patches. The M cells were differentiated from the intestinal enterocytes by distinctive ultrastructural features. The observed transitional epithelial cells might indicate that the M cells probably originated from the microvillus enterocytes. The M cells transport the antigens from the intestinal lumen to the lymphocytes in the intraepithelial pockets for induction of mucosal-associated immune response

Histological and ultrastructural studies of the marsupial Didelphis albiventris Peyer's patches

Differing from the studied Eutheria the white belly opossum Peyer"s patches do not present a conspicous dome. M cells are located in the inmer layer of bilaminal invaginations formed at the bottom of the villi. A great variation in the morphology of M cells was observed. The enterocytes located at the epithelial inner layer may present endocytic vesicles, and the microvilli are shorter tha the microvilli of enterocytes lining the small intestine. As these morphological aspects have been described to exist in the enterocytes of the lancet opossum small intstine it was surmised that the opossum Peyer's patches special epithelium could represent the persistence in adult animals of a cellular pattern established before the intestinal maturation had occurred