Differential Effects of Male and Female Gonadal Hormones on the Intrathymic T cell Maturation

The study was undertaken to further elucidate a role of gonadal hormones in maintenance of normal thymocyte maturation and sexual dimorphism in the intrathymic T-cell development. Rats of both sexes were gonadectomized or sham-gonadectomized (controls) at age of 2 and 6 months, and 30 days later the thymus size, cellularity and thymocyte composition were evaluated. In both control and gonadectomized rats, in spite of age, sexual dimorphism in the thymus size and cellularity was found. Gonadectomy in 2-month-old rats of both sexes increased the thymus cellularity, volumes of both cortex and medulla and thymus size (to a less extent in males), while in 6-month-old rats, in this respect, it was effective only in females. In ovariectomized (OVX) rats the increase in volume of cortex was more marked in younger rats, while that of medulla did not differ between rats of different age. It seems obvious that in both groups of OVX rats the volume of medullary non-lymphoid component was enlarged (the increase in medullary volume was more pronounced than that in its cellularity). Unlikely, in rats orchidectomized (ORX) at age of 2 months the volume of this component was either decreased or unaltered (the increase in the volume of medulla was less conspicuous than that in the number of medullary thymocytes). In control and gonadectomized rats of both ages, sexual dimorphism in the composition of thymocyte subsets was also observed. Gonadectomy in 2-month-old rats affected distinct stages of thymocyte maturation in male (increased the relative proportions of CD4+8+TCRαβ(low) cells and their CD4–8+TCRαβ(low) precursors and decreased those of the most mature CD4+8-TCRαβ(high) and CD4–8+TCRαβ(high) cells) and female rats (decreased only the percentage of the least mature CD4–8-TCRαβ-cells). In older rats only ovariectomy had impact on the relative proportion of thymocytes decreasing, besides the relative proportion of CD4–8-TCRαβ(-) cells, those of CD4–8+TCRαβ(-), CD4–8+TCRαβ(low), positively selected CD4+8+TCRαβ(high) and the most mature CD4+8-TCRαβ(high), CD4–8+TCRαβ(high) cells and exerting an opposite effect on the percentages of CD4+8+TCRαβ(-) and CD4+8+TCRαβ(low) cells. Thus, results showed sex- and age-dependent changes in sensitivity of both the developing thymocytes and non-lymphoid cells to long-lasting gonadal deprivation.