Intercellular spaces in the lymph nodule associated epithelium of the rabbit Peyer's patch and appendix.

Abstract

Summary. Intercellular spaces in the epithelium of the rabbit Peyer's patch and appendix were examined by scanning and transmission electron microscopy to elucidate their threedimensional structure and their relationship to the reticular spaces in the underlying lymph nodule.Two types of intercellular spaces were distinguished: regularly arranged tubular channels and irregularly winding tunnels. The tubular channels were observed around normal enterocytes on the villi or internodular folds and apical portions of nodule domes. The channel spaces were lined with a successive arrangement of belt-like intercrestal surfaces of prismatic enterocytes and variously sized processes on the crests. The processes adjoining opposed crests formed a ladder-like structure or pectinate septa between neighboring channels.The irregularly winding tunnels were formed among processes of irregularly shaped cells corresponding to FAE cells (BOCKMAN and COOPER, 1973) or M cells (OWEN and JONES, 1974) in the nodule associated epithelium. In the appendix, the tunnels were frequently organized into two-storey spaces, the adlumenal and basal spaces, which were incompletely separated by cytoplasmic processes. These tunnels continued by pores in the basement membrane to the reticular spaces in the underlying lymph nodules. Furthermore, the tunnels and the basement membrane pores constantly contained single or grouped free cells or their processes.The findings in the present study suggest that the tubular channels are intraepithelial compartments for the absorption of nutrients and fluid, and the irregular tunnels are an intraepithelial network of spaces for the housing of lymphoid cells coming from the underlying lymph nodule. The Peyer's patch and appendix are important constituents of the gut associated lymphoid tissue. In both organs, the lumenal portions of the lymph nodules bulge into the intestinal lumen and closely associate with the overlying epithelium.The nodule or follicle associated epithelium (FAE) is thought to play a mediating role in conveying immunological information from the intestinal lumen to the underlying lymphatic tissue (BOCKMAN et al., 1983). For this mediation function, specialized cells have been proposed, which are morphologically distinguishable from common enterocytes.

M cells in the rabbit palatine tonsil: the distribution, spatial arrangement and membrane subdomains as defined by confocal lectin histochemistry

“…This formation is similar to that described for M cells in the simple epithelium of the Peyer's patch domes (Owen and Jones 1974;Gebert et al 1996). However, thin section and scanning electron microscopy revealed that, in the rabbit Peyer's patch, the M cells leave openings to one or more of their lateral sides through which clusters of lymphocytes communicate with each other and form a continuous intraepithelial compartment (Ogawa and Miyoshi 1985;Regoli et al 1995). In contrast, the present findings demonstrate that the tonsillar M cells almost entirely engulf the non-epithelial cells and leave open only narrow tunnels at the base of one of their lateral aspects.…”

Structural specializations for antigen uptake and processing in the digestive tract

“…The follicle-associated epithelium forms the antigen-receiving surface of mucosal lymphoid nodules and serves a function equivalent to the afferent lymphatics in lymph nodes and spleen [24,41]. The spaces in the follicle epithelium beneath M cells are sites of constant migration of lymphoid cells into and out of the epithelium [40]. Over villi the basal lamina forms a continuous sheet of non-cellular matrix which separates the epithelium and the lamina propria.…”

Organization of the reticular network of rabbit Peyer's patches

“…Differentiated M cells (Owen and Jones, 1974; Bockman and Cooper, 19731, which are characterized by attenuated cytoplasmic processes embracing lymphocytes and other mononuclear cells, are responsible for transporting antigens (Owen, 1977;Owen and Nemanic, 1978;Wolf et al, 1981;Bhalla and Owen, 1982;Bye et al, 1984;Owen et al, 1986;Bass et al, 1988). The basal laminae of the dome epithelia possess numerous pores through which lymphocytes andlor other free cells migrate (Ogawa and Miyoshi, 1985;McClugage et al, 1986). Recent immunohistochemical studies have shown that each compartment of the patches is defined by typical localization of lymphocyte subsets and accessory cells such as macrophages and dendritic cells and also by its different functions (Ermak and Owen, 1986; reviewed by Pabst, 1987).…”