The recovery of spleen-seeking and lymph-node-seeking thymus subpopulations following cortisol administration

The administration of cortisol acetate depleted the population of spleen-seeking thymus cells to a greater extent than the population of lymph node-seeking thymus cells. While the proportion of lymph node-seeking thymus cells was increased following cortisol administration to about five times that found in the normal thymus, the number of lymph node-seeking cells in the atrophied thymus was reduced to about one-fifth of the number present in the thymus of untreated mice. Cortisol administration completely eliminated the small proportion of TL-positive cells present among the lymph node-seeking population, and drastically reduced the proportion of TL-positive spleen-seeking cells. The rate of recovery of the number of spleen-seeking thymus cells was much more rapid than that of the lymph node-seeking cells. The number of spleen-seeking cells increased significantly within 12 days after the administration of cortisol, and full recovery was evident by day 20. In contrast, the number of lymph node-seeking cells started to increase only 18 days after cortisol administration, and reached the level found in the normal thymus about 8 days later. The recovery of TL-positive lymph node-seeking cells paralleled the recovery of the TL-negative lymph node-seeking population rather than that of the TL-positive spleen-seeking population. Possible developmental interrelations between the spleen-seeking and lymph node-seeking populations of thymus cells are discussed.