INVOLUTION AND CYSTIC TRANSFORMATION OF THE THYMUS IN THE BOTTLE-NOSED-DOLPHIN, TURSIOPS-TRUNCATUS

The thymus glands of 10 bottlenose dolphins, Tursiops truncatus, colle cted along the Texas Gulf coast were examined using standard histologi c and immunocytochemical methods. The thymus gland of Tursiops persist s into adult life, represented by medulla and progressively thinning c ortex. A network of epithelial cells, including Hassal bodies, is demo nstrable using polyclonal anti-cytokeratin antibody. The network conde nses, with loss of lymphoid cells as involution progresses. Cysts aris e within the condensed network. These cysts, found in eight of 10 anim als, increase in number and size with increasing body size. Body size tends to reflect age. Thymic cysts typically have an irregular shape w hen small but tend to become spherical as they enlarge. They may be li ned by squamous epithelium of variable thickness. Eventually, the cyst s become macroscopic and filled with a colloidlike material and may la rgely replace the thymus, which may be identified by noncystic remnant s adjacent to the cysts.