Peyer's Patches: These are lymphoid follicles similar in many ways to lymph nodes, located in the mucosa and extending into the submucosa of the small intestine, especially the ileum. In adults, B lymphocytes predominate in Peyer's patches. Smaller lymphoid nodules can be found throughout the intestinal tract.
In the image of canine ileum below, three lymphoid follicles of a Peyer's patch can be seen. The muscularis is at the top left, and mucosal epithelium in the bottom right.
Intraepithelial lymphocytes: These are lymphocytes that are positioned in the basolateral spaces between lumenal epithelial cells, beneath the tight junctions (they are "inside" the epithelium, but not inside epithelial cells as the name may incorrectly suggest).
- Nagler-Anderson C: Man the barrier! Strategic defences in the intestinal mucosa. Nat Rev Immunol 1:59-67, 2001.
- Neutra MR, Frey A, Kraehenbuhl JP: Epithelial M cells: Gateways for mucosal infection and immunization. Cell 86:345, 1996.