F. Sanchezrefusta et al., AGE-RELATED-CHANGES IN THE MEDULLARY RETICULAR EPITHELIAL-CELLS OF THE PIGEON BURSA OF FABRICIUS, The Anatomical record, 246(4), 1996, pp. 473-480
Background: The medulla of the avian bursal lymphoid follicles contain
s heterogeneous cell populations, including the so called medullary re
ticular epithelial cells (REC). These cells may contribute to the burs
al microenvironment for B-lymphocyte differentiation and maturation. T
he bursa of Fabricius undergoes well-characterized posthatching develo
pmental changes, but the age-related changes of the medullary REC have
not been studied. The present study approaches this topic by analyzin
g hallmarks of epithelial cells: the occurrence of cytokeratin-type in
termediate filaments and of desmosomes and desmoplakins in pigeon medu
llary REC. Methods: The bursae of Fabricius of male king pigeons (Colu
mba livia L.) Morini's strain were examined at different ages (from ha
tching to 120 days after hatching) by light microscopic immunohistoche
mistry for pan-cytokeratins and desmoplakins and by transmission elect
ron microscopy. The area occupied by medullary cytokeratin-immunoreact
ive cells was evaluated with quantitative image analysis. Results: At
hatching, cytokeratin immunoreactivity was not detected in the bursal
lymphoid follicles. During the posthatching growth period of the organ
(7-75 days), there was a progressive and significant increase in the
area occupied by cytokeratin-immunoreactive medullary REC, in the inte
rmediate filaments filling the cytoplasm of REC, and in the number of
desmosomes. Conversely, during the regressive period analyzed (90-120
days), the density of cytokeratin-positive cells progressively decreas
ed, although they retained their ultrastructural characteristics. The
evaluation of desmoplakin immunoreactivity paralleled that of cytokera
tin. Conclusion: The present results demonstrate that the medullary RE
C of the pigeon bursa of Fabricius undergoes age dependent changes par
allel with that involving the whole organ. The possible contribution o
f medullary REC to the bursal microenvironment is discussed.