Studies of hyperthymic mice. I. The influence of multiple thymus grafts on the size of the peripheral T cell pool and immunological performance.

Following the implantation of syngeneic chromosomally marked thymuses under the kidney capsule of normal adult mice, donor T cells were found in the blood and other lymphoid organs. The mice were found to have increased numbers of Thy.1-positive cells in spleen and lymph nodes, increased peripheral blood lymphocyte levels and also augmented immune responses to sheep erythrocytes. The contribution made by an individual graft to the donor T cell pool was independent of the number of thymuses grafted as was the growth of the grafts themselves. The results reaffirm that there is no homeostatic feedback control of thymus growth in adult mice.