In vivo modulation of the splenocyte yield and composition by female sex steroid hormones.

The study was designed to shed more light on the controversial role of the two main ovarian steroid hormones (i.e. estradiol and progesterone) in shaping the size and phenotypic characteristics of the splenic lymphocyte pool. For this purpose ovariectomized adult rats (OVX) were treated for 14 subsequent days with either estradiol or progesterone (to attain physiological concentrations of the hormones). Afterwards, the splenocyte yield, and overall number of splenocytes bearing TCR alpha beta receptor, CD4 and CD8 coreceptor were evaluated. Fourteen-day-long ovarian hormone deprivation produced an increase in the splenic weight and splenocyte yield (on the account of a rise in the number of TCR alpha beta- cells), although the number of TCR alpha beta+ cells was reduced as a result of a decrease in the size of the CD4+ cell subpopulation. Replacement of either estradiol or progesterone prevented the increase in splenic weight and reduced the splenocyte yield to values significantly lower than that in sham-OVX rats. Both the treatments completely abolished the effect of ovariectomy on the size of TCR alpha beta- cell population, but had differential effects on that of TCR alpha beta+ cell population; estradiol did not affect its size, while progesterone caused a reduction on the account of a decrease in the numbers of both CD4+ and CD8+ cells. The results suggest that: a) estradiol and progesterone have similar effects on the size of the splenic B cell population and that replacement of either estradiol or progesterone can prevent the effects of ovariectomy on the size of this population and b) estradiol does not affect while progesterone reduces the size of splenic T cell population. Thus, replacement of none of them is able to compensate the removal of gonads.