DIFFERENTIAL-EFFECTS OF GONADECTOMY ON THYMIC STROMAL CELLS IN PROMOTING T-CELL DIFFERENTIATION IN MICE

Twenty-six week-old BDF1 mice were gonadectomized and grafted with thy mus from irradiated (8.5 Gy) newborn, 6-week-old, or 26-week-old mice. One month later, grafted thymuses were recovered and examined in term s of thymocyte numbers, subpopulations and proliferative responses to Concananavlin A (Con A). The growth of the irradiated thymus was signi ficantly higher in gonadectomized (Gx) than in sham-operated (Sham) mi ce and the magnitude of thymic growth was apparently age-dependent, as it was greater for newborns than for older mice. Con A response of th ymocytes was also significantly higher in Gx mice than in Sham mice, a nd the magnitude of the response declined with advancing age of the th ymus donors. Flow cytometric analysis revealed that a significant incr ease in the percentage of CD4(+)CD8(-) was observed in thymus grafts s howing 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, wherea s thymus grafts from 6- and 26-week-old mice could grow well only in G x, 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. C ollectively, Gx appeared to promote immigration of thymocyte precursor s into the thymus and to enhance proliferation and differentiation of thymocytes towards CD4+ CD8(-) T cells, in an age-related manner.