Morphological study of antigen-sampling structures in the rat large intestine

Abstract

Organized lymphoid tissue in the rat colon exists as clusters (colonic lymphoid patches) of intramucosal and submucosal follicles in the proximal, mid, and distal colon, interspersed by solitary follicles. The follicular lymphoid cells of colonic lymphoid patches are separated from the gut lumen by a highly specialized lymphoepithelium which lacks mature goblet cells. Cells of this epithelium are of two types: those characterized by an electron-dense cytoplasm, large numbers of apical vesicles and lysosomes, and prolonged extensions of the apical cytoplasm forming thin partitions between the gut lumen and underlying intercellular spaces; and cells with a less electron-dense cytoplasm, distorted mitochondria, and little endoplasmic reticulum. Both cell types bear normal microvilli and have numerous lateral membrane processes which penetrate large intercellular spaces. A ferritin-India ink label infused into the colonic lumen was preferentialfy adsorbed onto the surface of this follicle-associated epithelium. Indigenous colonic bacteria were observed penetrating the superficial cytoplasm of the electron-dense cells where they were enclosed in lysosomes and digested. An antigen-sampling role is proposed for the colonic lymphoid patch epithelium.

Ultrastructural and cytoarchitectural features of lymphoreticular organs in the colon and rectum of adult BALB/c mice

“…In many species, colonic lymphoid tissue is organized as both solitary follicles and lymphoglandular complexes. Solitary follicles are scattered along the colon and rectum in the lamina propria and face the colonic lumen separated only by a follicle epithelium (Szakal et al, 1980;Deasy et al, 1983;Bland and Britton, 1984;Liebler et al, 1988a;Morfitt and Pohlenz, 1989). In lymphoglandular complexes, lymphoid follicles are largely below the muscularis mucosae, with crypts near the colonic lumen extending down through the muscularis mucosae and branching into numerous smaller diverticula in lymphoid tissue (Atkins and Schofield, 1972).…”

“…In all species examined including humans, specialized follicle epithelium either covers the surface of domes rising to the luminal surface or lines pits and diverticula, passing through the muscularis mucosae (Deasy et al, 1983;Bland and Britton, 1984;Liebler et al, 1988a;Morfitt and Pohlenz, 1989;Langman and Roland, 1986;O'Leary and Sweeney, 1986;Jacob et al, 1987). This follicle epithelium contains cells compatible with M cells, characterized by sparse irregular microvilli with few or no filaments, apical membrane with vesicular and tubular invaginations, abundant vesicles, and absence of organelles in the apical cytoplasm (Liebler et al, 198813;Morfitt and Pohlenz, 1989;Jacob et al, 1987).…”

Identification of the Site of Uptake of the E. coli Heat‐labile Enterotoxin, LTB

“…In comparison to the binding of LTB to the villous epithelial cells, the binding and internalization of LTB to the cells overlying the lymphoid follicles is more reminiscent of the mode of entry postulated for absorption of most soluble antigens [8,9]. The uptake of LTB following its binding to the epithelial cells of the villous or the lymphoid follicles, appears to be much more efficient than the traditional antigen sampling method postulated for most orally administered antigens, as at no time was any fluorescence found associated with either the villous epithelial cells, or the cells overlying the lympboid follicles, following oral administration of comparable doses of the soluble antigen, FITC-BSA or LTB co-administered with the GMi-ganglioside.…”

“…The immunity induced by this regime has at best been poor, short-term and often confined to the mucosal immune system. The small amount of antigen which is actually absorbed is believed to be taken up by M cells of the Peyer's patches via a non-specific, antigen sampling mechanism [8][9][10].…”

“…Following absorption of the antigen, by the M cells, it crosses these cells and is presented to the underlying IgAproducing B cells within the dome of the Peyer's patch, or alternatively stimulates the IgG suppressor T cells, resident in the marginal area of the lymphoid follicle [II. 12], which subsequently suppress the production of a systemic IgG response, thereby resulting in systemic tolerance [8,9,13,14].…”