Early decline of thymic effect on T cell differentiation.

Thymic lobes of B6C3F1 mice ranging in age from 1 day to 11 weeks were implanted under the kidney capsule of T cell deprived syngeneic young adult TXB mice, and the capacity of the thymus grafts to influence the maturation of T cells was assessed at 6 and 12 weeks after the implantation in terms of (a) regenerative activities of the grafted thymus, (2) splenic T cell dependent anti-SRBC response, and (c) mitogenic reactivity of spleen and lymph node cells to T cell specific mitogens. The results revealed that: (1) thymic tissues from 1 week old donors were most efficient in restoring the immune potential of adult TXB mice; (2) a decline in mitogenic reactivities of spleen and lymph node cells was observed in recipients of thymus grafts from donors of 1 month and older; and a decline of splenic helper T cell function was observed in recipients of thymus grafts from 11 weeks old donors. The significance of this early decline in the thymic effect on T cell differentiation is discussed.