AGE-RELATED-CHANGES IN THE SECRETORY DENDRITIC CELLS OF THE PIGEON BURSA OF FABRICIUS - AN IMMUNOHISTOCHEMICAL AND ULTRASTRUCTURAL-STUDY

The present study was undertaken to determine, by means of immunohisto chemical techniques, image analysis and ultrastructural methods, wheth er the secretory-dendritic cells (SDC) of the pigeon bursa of Fabriciu s undergo changes from hatching to the involutive stage (120 days) of the organ. A monoclonal antibody against vimentin (VIM) was used to la bel SDC. VIM-like immunoreactivity (VIM-L, IR) was observed labelling dendritic cell profiles in all age groups. These cells are primarily l ocalized within the medulla and at the cortico-medullary border of the lymphoid follicles. At hatching VIM-L, IR was present mainly in the c ell bodies, whereas during post-hatching bursal growth (7 to 75 days) it was also present in the cell processes. Conversely, the involutive period examined (90-120 days) was characterized by a progressive decre ase of VIM-I, IR in the SDC processes. Quantitative studies confirmed the immunohistochemical findings. At the ultrastructural level, there was a progressive increase from 0 to 90 days of age in both the number and size of secretory granules and break-down bodies, as well as in t he length of the SDC processes. The involutive stage showed the revers e phenomena. The present results demonstrate that the SDC of the pigeo n bursa of Fabricius undergo age-related changes parallel with that of the organ. The possible involvement of SDC in the maintenance of the bursal microenvironment and their role in the maturation of lymphoid l ine cells is discussed.