Cells In Follicle-associated Epithelium Research Articles

Carbonic anhydrase--a marker for particles shed from the epithelium to the lymphoid follicles of the ileal Peyer's patch in goat kids and lambs.

Carbonic anhydrase (CA) was found to be a marker for 50 nanometer membrane-bounded particles shed from the lateral cell border of follicle-associated epithelial cells (FAE) in the ileal Peyer's patch (PP) of pre- and post-natal lambs and goat kids. The CA-positive particles seemed to filter into the underlying lymphoid tissue where they formed part of the matrix embedding the cells of the follicle centre.

The follicle-associated epithelium of the ileal Peyer's patch in ruminants is distinguished by its shedding of 50 nm particles.

Significant differences were found between the follicle-associated epithelial cells (FAE) covering the domes of the jejunal and ileal Peyer's patches (PP) in calves. Whereas the FAE of the jejunal PP had scattered membraneous (M) cells among absorptive epithelial cells, the FAE of the ileal PP constituted a homogeneous population of cells different from both absorptive cells and M cells. The FAE of the ileal PP had short microvilli or folds, cytoplasmic vesicles and vacuoles containing acid phosphatase. Fifty nanometer membrane-bounded particles were found in lacunae extending from the lateral cell border. These particles appeared to have been shed from the FAE. Finger-like projections, rich in microfilaments, extended into the lacunae. M cells had short, sparse microvilli, many vesicles, few lysosomal structures, and they enfolded groups of mononuclear leucocytes. Transcytosis of macromolecular tracers occurred in both M cells and in the FAE of the ileal PP, though the uptake was greater in the latter. The 50 nm particles were also found between cells in the lymphoid tissue underneath the FAE of the ileal PP. The FAE of PP in pre- and post-natal lambs from 115 days of gestation and onwards, and goat kids, showed similar structural features.

Transport of membrane-bound macromolecules by M cells in follicle-associated epithelium of rabbit Peyer's patch.

M cells in Peyer's patch epithelium conduct transepithelial transport of luminal antigens to cells of the mucosal immune system. To determine the distribution of specific lectin-binding sites on luminal membranes of living M cells and to follow the transport route of membrane-bound molecules, lectin-ferritin conjugates and cationized ferritin were applied to rabbit Peyer's patch mucosa in vivo and in vitro. The degree to which binding enhances transport was estimated by comparing quantitatively the transport of an adherent probe, wheat germ agglutinin-ferritin, to that of a nonadherent BSA-colloidal gold probe. When applied to fixed tissue, the lectins tested bound equally well to M cells and columnar absorptive cells. On living mucosa, however, ferritin conjugates of wheat germ agglutinin and Ricinus communis agglutinins I and II bound more avidly to M cells. Absorptive cells conducted little uptake and no detectable transepithelial transport. Lectins on M cell membranes were endocytosed from coated pits, rapidly transported in a complex system of tubulocisternae and vesicles, and remained adherent to M cell basolateral membranes. Cationized ferritin adhered to anionic sites and was similarly transported, but was released as free clusters at M cell basolateral surfaces. When applied simultaneously to Peyer's patch mucosa, wheat germ agglutinin-ferritin was transported about 50 times more efficiently than was bovine serum albumin-colloidal gold.

The role of epithelial cells in gut-associated immune reactivity.

Epithelial cells and their products are essential participants in both initial and final stages of reactivity to foreign materials in the gut lumen. Follicle-associated epithelial cells, called "M"-cells by others, more efficiently transport antigens from the lumen than do columnar absorptive cells. Epithelial cells degrade antigens intracellularly. The presence of Ia-like antigens on epithelial cells of the gastrointestinal tract and thymus suggests a role in antigen presentation. Actively phagocytic macrophages are present within the epithelium of Peyer's patches and appendix, providing antigen degradation and presentation. Follicle-associated epithelial cells transport materials from lamina propria into intestinal lumen. Therefore, FAE cells are capable of bidirectional transport. Plasma cells are located within and immediately beneath the epithelium of Peyer's patches and appendix, where defects in the basal lamina indicate diminished capability for molecular selection. Transmission of antibodies into the lumen would modulate further antigen uptake and provide for interaction with organisms.

The behavior of bursal lymphoid follicle-associated cells after treatment with testosterone.

Administration of androgens produces damage in lymphoid tissue and in the bursa of Fabricius. After IM administration of 5 mg of testosterone propionate (TP) beginning at hatching and continued during the following 4 days, a significant reduction in the bursal weights is observed. Histologically, an increase in the connective tissue is observed and cystic formations are also found. In all cysts examined, there is continuity of the cystic lumen with the free surface. The follicle-associated epithelial (FAE) cells are on the bottom of the pseudocysts and form a separation between the pseudocystic cavity and the lymphoid tissue which is still further inwards. These cells do not lose their esterase activity, even though they are often flattened. Furthermore, they disappear in the pseudocysts deprived of lymphoid tissue. A new hypothesis is advanced that the FAE cells originate from the mesenchyme with differentiation in the histiocytic line.

Functional histology of appendix.

The appendix is a prominent example of gut associated lymphoepithelial tissue, whose function is to react to the wide variety of antigens present in the gastrointestinal tract. It is composed of a large number of repeating units, the lymphoid follicles, each of which is divided into an apical dome, a large basal nodule with a germinal center, and laterally extending thymus dependent areas. The dome epithelium consists mainly of columnar absorptive cells and of specialized follicle associated epithelial (FAE) cells which are efficient at transporting material from the lumen to the underlying lymphoid tissue, and may also transport macromolecules from the lymphoid follicle into the lumen. The dome epithelium normally has large numbers of lymphocytes within it, as well as smaller numbers of macrophages and plasma cells. Macrophages, and perhaps FAE cells, are capable of processing and presenting antigens to reactive lymphocytes. Lymphocyte proliferation and differentiation in response to antigenic stimulation begins in the lymphoid follicles, but most of the lymphocytes leave by the lymphatics, migrate through lymph nodes and spleen, frequently to complete differentiation into IgA-secreting plasma cells in the lamina propria of mucosal surfaces. Normal function of appendix probably helps suppress potentially destructive humoral antibody responses while promoting local immunity.

Differentiation of epithelium, lymphocytes, granulocytes, and erythrocytes in bursa of fabricius transplanted to chorioallantoic membrane

Early B cell differentiation in chickens occurs within the specialized microenvironment provided by epithelium in the bursa of Fabricius. It has been unclear to what extent continued association of this epithelium with the gut lumen and its contents is necessary for normal differentiation. Bursa was transplanted from chick embryos of 10 to 12 days incubation onto the chorioallantoic membrane of hosts of comparable ages. Implants were harvested 5 to 7 days later and studied by light and electron microscopy. Epithelial cells differentiated into both the mucous type and the specialized type previously described as follicle-associated epithelium (FAE). FAE cells were capable of taking up ferritin by micropinocytosis. Lymphoid cells migrated into epithelium through intervals in the basal lamina. Differentiative stages of granulocytes and erythrocytes were found in connective tissue subjacent to epithelium. Differentiation of specialized epithelium, early B cell differentiation, and transient granulopoiesis and erythropoiesis associated with the bursa appear not to depend upon continued physical association with the gastrointestinal tract.