Ultrastructural and immunocytochemical study on bursal follicle medulla cells in Gallus domesticus.

The use of the monoclonal anti-cytokeratin 6 and 18 antibody Dako CK 1 revealed a marked positivity of reticulo-epithelial cells (REp). Aspecific esterase testing, light microscopy, and electron microscopy were used in order to obtain a comparison between the morphology of the lymphoid follicle medulla and the picture obtained by using the monoclonal antibody CK 1. Results showed that the bursal follicle medulla can be divided into 2 areas: an esterase-positive, cytokeratin-negative centre-medulla, and a more peripheral cytokeratin-positive, esterase-negative area. These 2 regions appear to be separated by a boundary composed of flattened REp cells. Desmosomes were also observed not only among their processes, but also between the latter and the side of the cortico-medullar boundary epithelium which is external with respect to the basal membrane.