The self-sustaining capacity of lymphoid cells in the irradiated thymus

The self-sustaining capacity of thymus lymphoid cells was studied in mice exposed to sublethal doses of X-rays. During exposure various parts of the organism were protected by lead shielding. When the thymus was protected and the rest of the organism exposed to radiation an initial cellular depletion of the thymus not exceeding 70 per cent was followed by a complete cellular regeneration of the organ within 3 weeks. This regeneration was shown to proceed without any cellular support from the bone marrow. When the thymus was included in the radiation field and/or damaged by cortisone treatment resulting in a depopulation exceeding 70 per cent, no or only partial regeneration occurred. The results indicate that the cell population in the thymus of mice can be self-sustaining for at least 3 weeks.