Twenty-six week-old BDF1 mice were gonadectomized and grafted with thymus from irradiated (8.5 Gy) newborn, 6-week-old, or 26-week-old mice. One month later, grafted thymuses were recovered and examined in terms of thymocyte numbers, subpopulations and proliferative responses to Concananavlin A (Con A). The growth of the irradiated thymus was significantly higher in gonadectomized (Gx) than in sham-operated (Sham) mice and the magnitude of thymic growth was apparently age-dependent, as it was greater for newborns than for older mice. Con A response of thymocytes was also significantly higher in Gx mice than in Sham mice, and the magnitude of the response declined with advancing age of the thymus donors. Flow cytometric analysis revealed that a significant increase in the percentage of CD4+CD8- was observed in thymus grafts showing high Con A responses. However, this effect of Gx on the thymus graft was dependent on age of the thymus donor. Namely, newborn thymus grafts could grow equally well in both Gx and Sham recipients, whereas thymus grafts from 6- and 26-week-old mice could grow well only in Gx, but not in Sham recipients. The number of thymocytes was comparable in thymus grafts from 6- and 26-week-old mice, but the proliferative response to Con A was higher in the former than in the latter graft. Collectively, Gx appeared to promote immigration of thymocyte precursors into the thymus and to enhance proliferation and differentiation of thymocytes towards CD4+CD8- T cells, in an age-related manner. © 1995.

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