Ultrastructure of Peyer's patches in the domestic fowl and turkey.

Peyer's patches in the fowl and turkey were indistinguishable at the ultrastructural level and were similar in many respects to those found in mammals. They were overlaid by a lymphoepithelium containing undifferentiated intestinal epithelial cells with a well developed microvillous border, follicle associated epithelial (FAE) or M cells with short blunt microvilli, lymphocytes and plasma cells. FAE cells had a lightly stained cytoplasm with vacuoles and vesicles. They were similar to mammalian FAE cells. The lymphoid aggregates of Peyer's patches consisted of small and large lymphocytes, lymphoblasts and plasma cells. Macrophages and globule leucocytes were seen among the lymphoid cells.