The thymus and skin wound healing in Xenopus laevis adults.

The capacity to heal wounds without scars is generally lost during the development in vertebrates. To explore the involvement of cells of the adaptive immune system in a scar-like tissue based repair, we studied the thymus in 15-month-old Xenopus after skin incisional wounding. After injury, the organ size significantly increased and marked changes in structure and TNF-α immunoreactivity were detected in the medullary microenvironment when the granulation tissue was present in the repair area. Most of the lymphocytes present in this wound connective tissue were found to be immunoreactive to specific T cell markers. Thymic mucocyte-like cells and epithelial cysts increased in number, the myoid cells acquired a faster turnover and associated in large clusters, blood vessels were dilated and corpuscles similar to mammalian Hassall's bodies were formed in medulla. A higher number of stronger medullary TNF-α immunoreactive cells, i.e., dendritic, epithelial, granular basophilic and myoid cells were also induced after wounding. With progression of healing the thymus gradually returned to histochemical patterns of controls. Our results suggest that during the scar-based skin repair of Xenopus adults the activity of the thymus may be stimulated and associated with the T lymphocyte infiltration observed into injured granulation tissue.