Further characterization of M cells in gut-associated lymphoid tissues of the chicken

M cells are considered to be the most effective cells for the transport of antigens from the intestinal lumen into the gut-associated lymphoid tissue. M cells are characterized by their ultrastructural appearance, the selecti ve uptake of antigens, the binding of lectins, and the presence of underlyi ng lymphocytes. Little attention has been paid to the interaction of intrae pithelial leucocytes and M cells in chickens; therefore, we have investigat ed both cell types separately and using double immunocytochemical staining in cecal tonsils and Meckel's diverticulum. In the follicle-associated epit helium (FAE), cells were present that differ from their neighbors by short, irregular microvilli. Ferritin was absorbed by these putative M cells, but also by other epithelial cells: The lectins of Triticum vulgaris (WGA) and glycine max (SBA) showed a patchy staining of the FAE. The numbers of intr a-epithelial leucocytes (IEL) increased rapidly after hatch, reaching innum erable at 6 wk of age. Most IEL were T lymphocytes expressing CD8 and only about 30% of them were B lymphocytes. Nevertheless, double staining of M ce lls (WGA/SBA) and IEL showed that M cells were much fewer than IEL. These r esults indicate that M cells are not solely induced by the intra-epithelial localization of leucocytes. Because the phenotype of IEL reflected the con tent of the adjacent underlying lamina propria, IEL immigrate the FAE local ly and do not migrate along with the epithelial cells from the crypts. Ln c onclusion, M cells exist in the chicken, but their phenotype and function a re less well demarcated from neighbor epithelial cells than is seen in mamm als.