Role of the thymus in radiation-induced lung damage after bone marrow transplantation.

Pneumonitis developing after total-body irradiation and bone marrow transplantation can be a serious complication of this form of therapy. In this study, the incidence of lung damage in a murine syngeneic transplant model was found to be decreased by prior removal of the thymus, indicating that thymus-derived cells, even in the absence of complicating factors such as graft-versus-host disease and opportunistic pathogens, can contribute to radiation-induced lung damage. It is suggested that the increased damage is due to a syngeneic graft-versus-host reaction mediated by a regenerating lymphoid system. If this concept is correct, new strategies can be identified that might be employed in altering the incidence of this serious transplant-related complication.