APPEARANCE AND DEVELOPMENT OF LYMPHOID-CELLS IN THE CHICKEN (GALLUS-GALLUS) CECAL TONSIL

Background: We have analyzed by electron microscopy, immunohistochemis try, and flow cytometry the development of chicken caecal tonsil, the largest lymphoid organ of avian gut-associated lymphoid tissue (GALT). Methods: White Leghorn chickens of different ages obtained from a loc al supplier were routinely processed by transmission electron microsco py. For both immunohistochemistry and flow cytometry, we tested a batt ery of specific monoclonal antibodies (mAbs) to chicken cell markers o n caecal cryosections or cell suspensions, respectively, Results: A ru dimentary caecal tonsil occurs at the end of incubation. The organ gro ws just after birth, reaching the adult condition 4 days later, Firstl y (4 days to 2 weeks), it contains predominantly T lymphocytes, princi pally TcR alpha beta(+) and CD4(+) cells, which occupy largely the nam ed caecal diffuse lymphoid tissue. In adult tonsils (8-week-old chicke ns) however, B lymphocytes, mainly expressing either IgM or IgA, predo minate. They occur in both the subepithelial zone and the germinal cen ters, in which there are also a few T cells, After 2 weeks the CD8(+) lymphocytes gradually become more numerous than CD4(+) cells, In the t onsillar epithelium CD8(+)TcR gamma delta(+) T cells, CD8(+)TcR gamma delta(-) alpha beta(-), presumably NK cells, and a few B lymphocytes a re the main cell subpopulations. Conclusions: Chicken caecum grows fas t after hatching, The diffuse lymphoid tissue largely contains TcR alp ha beta CD4(+) or CD8(+) cells, CD8(+) cells of caecal epithelium repr esent gamma delta T cells or NK cells, B lymphocytes which occur in th e subepithelial zone, germinal centers, and, in few numbers, the caeca l epithelium predominantly express either IgM or IgA, (C) 1998 Wiley-L iss, Inc.