The thymus and tail regenerative capacity in Xenopus laevis tadpoles

A morphofunctional analysis of the thymus from differently aged Xenopus laevis tadpoles during regenerationof the tail is reported. In stage 50 larvae, competent to regenerate, the appendage cut provoked thymicstructural modifications that affected the medullary microenvironment cells and changes in TNF-immunoreactivity. Mucocyte-like cells, multicellular epithelial cysts, myoid cells and cells immunoreactiveto TNF- increased in number. Increased numbers of lymphocytes were also found in regeneratingareas and, at the end of regeneration, thymic structural and immunocytochemical patterns were restoredto control levels. The observed cellular responses and the induction of molecules critical for thymus constitutiveprocesses suggest a stimulation of thymic function after tail amputation. In older larvae, whosecapacity to form a new complete and correctly patterned tail was reduced, thymic morphological changeswere more severe and may persist throughout the regeneration process with a significant reduction inorgan size. In these larvae the histological patterns and the marked thymic decrease may be related tothe events occurring during regeneration, i.e. the higher inflammatory response and the reduced tailregenerative potential.