Gut-associated lymphoid tissue in the chicken. I. Morphology, ontogeny, and some functional characteristics of Peyer's patches.

Lymphoid aggregates with many of the characteristics of mammalian Peyer's patches (PP) were identified in the chicken intestine. These chicken PP could not be seen with the naked eye at the time of hatching, but by 10 days of age, 1 or 2 PP were identified in 50% of the birds. Up to 16 wk of age, the numbers of PP increased to a maximum of 5 per animal and they were widely scattered in the intestine, apart from one that was regularly found about 5 to 10 cm anterior to the ileocecal junction. As the birds aged, the number of PP declined so that in older birds (58 wk) only a single PP was evident near the ileocecal junction. Chicken PP possess: a distinct lymphoepithelium with M cells and strong pinocytotic activity; follicles and a subepithelium zone and central zone similar to those of the cecal tonsil (CT). Studies with in ovo hormonal bursectomy and age-associated involution of PP suggested that the subepithelial zone is a B-dependent area and the central zone a T, or thymus-dependent region. These observations extend our knowledge of gut-associated lymphoid tissue (GALT) in the bird to include the bursa of Fabricius, CT, PP, and aggregates in the urodeum and proctodeum. They raise issues about the roles of chicken PP that may aid our understanding of the functions of mammalian GALT.