Development of Peyer's patch and cecal tonsil in gut-associated lymphoid tissues in the chicken embryo

It is well known that chicken B cells develop in the bursa of Fabricius (BF), which is categorized as gut-associated lymphoid tissue (GALT). Chicken GALT also includes Peyer's patch (PP) and cecal tonsil (CT). The relationship between these tissues in GALT during B cell development is currently unknown. In this study, we conducted comparative examination of PP, CT and BF development during embryogenesis using immunohistochemical staining. On day 13 of embryogenesis (E13), accumulation of MHC class II+ cells was observed in the intestine. Thereafter, Bu-1(+) cells and IgM(+) cells appeared, and their number continuously increased at the same sites where MHC class II+ cells were present. Similar results were obtained in the CT. The locations of embryonic PP were limited to two sites; near the Meckel's diverticulum and the ileocecal junction. Anlage of bursal follicles first appeared at E13 and developed thereafter. Immigration of Bu-1(+) cells to bursal follicles began at E13, and the number of Bu-1(+) cell subsequently increased. When the follicle of BF was eliminated from the embryo by treatment with testosterone, development of PP and CT were observed. We concluded therefore that the development of PP and CT start during late embryogenesis at the same time as the follicle of BF, and that appearance of surface IgM(+) cells in PP and CT is independent form the development of the follicle of BF.