title: Appearance and development of lymphoid cells in the chicken (Gallus gallus) caecal tonsil.
abstract: We have analyzed by electron microscopy, immunohistochemistry, and flow cytometry the development of chicken caecal tonsil, the largest lymphoid organ of avian gut-associated lymphoid tissue (GALT).
  
  
  
  White Leghorn chickens of different ages obtained from a local supplier were routinely processed by transmission electron microscopy. For both immunohistochemistry and flow cytometry, we tested a battery of specific monoclonal antibodies (mAbs) to chicken cell markers on caecal cryosections or cell suspensions, respectively.
  
  
  
  A rudimentary caecal tonsil occurs at the end of incubation. The organ grows just after birth, reaching the adult condition 4 days later. Firstly (4 days to 2 weeks), it contains predominantly T lymphocytes, principally TcR alphabeta+ and CD4+ cells, which occupy largely the named caecal diffuse lymphoid tissue. In adult tonsils (6-week-old chickens) however, B lymphocytes, mainly expressing either IgM or IgA, predominate. They occur in both the subepithelial zone and the germinal centers, in which there are also a few T cells. After 2 weeks the CD8+ lymphocytes gradually become more numerous than CD4+ cells. In the tonsillar epithelium CD8+TcRgammadelta+ T cells, CD8+TcRgammadelta-alphabeta-, presumably NK cells, and a few B lymphocytes are the main cell subpopulations.
  
  
  
  Chicken caecum grows fast after hatching. The diffuse lymphoid tissue largely contains TcR alphabeta CD4+ or CD8+ cells. CD8+ cells of caecal epithelium represent gammadelta T cells or NK cells. B lymphocytes which occur in the subepithelial zone, germinal centers, and, in few numbers, the caecal epithelium predominantly express either IgM or IgA.
authors.affiliation: Department of Cell Biology, Faculty of Biology, Complutense University, Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Gómez Del Moral
authors.forename: J
authors.initials: J
authors.lastname: Fonfría
authors.forename: A
authors.initials: A
authors.lastname: Varas
authors.forename: E
authors.initials: E
authors.lastname: Jiménez
authors.forename: J
authors.initials: J
authors.lastname: Moreno
authors.forename: A G
authors.initials: AG
authors.lastname: Zapata
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology; D002432:Cecum / Q000166:cytology / Q000196:embryology / Q000254:growth & development* / Q000276:immunology; D002642:Chick Embryo / Q000166:cytology; D002645:Chickens / Q000254:growth & development* / Q000276:immunology; D005434:Flow Cytometry; D007124:Immunoenzyme Techniques; D007136:Immunoglobulins / Q000032:analysis; D008221:Lymphoid Tissue / Q000166:cytology / Q000196:embryology / Q000254:growth & development* / Q000276:immunology; D008854:Microscopy, Electron; D011948:Receptors, Antigen, T-Cell; D016176:T-Lymphocyte Subsets / Q000166:cytology* / Q000276:immunology
chemical_list: D007136:Immunoglobulins; D011948:Receptors, Antigen, T-Cell