DIFFERENTIAL-EFFECTS OF GONADECTOMY ON THE THYMOCYTE PHENOTYPIC PROFILE IN MALE AND FEMALE RATS

As an organ responsible for generation of T-cell repertoire the thymus occupies a central position in establishment of mature immune respons e. To assess the potential role of the gonadal steroids in development and maintenance of immunological sexual dimorphism, the effects of go nadectomy pre- and postpuberty on the thymocyte profile of male and fe male rats were examined. Rats aged 30 days or 75 days were gonadectomi zed; 30 days later the thymic cellularity was estimated and the expres sion of the cell surface antigens (CD4 and CD8) and the T-cell recepto r (TCR) alpha beta was analyzed by now cytometry. Regardless of age at surgery, the thymus weight and total thymocyte yield were greater in sham-operated males than females; this sexual dimorphism in thymic cel lularity persisted after gonadectomy. Sexual dimorphism in the composi tion of thymocyte subsets was also evident in sham-operated rats, with males expressing a higher percentage of CD4-8- cells, and remained af ter gonadectomy of adult rats. In male rats, gonadectomy at day 75 inc reased the percentage of CD4+8- single-positive and TCR alpha beta + c ells. In contrast, in females, ovariectomy decreased the percentages o f CD4+8- single-positive, CD4-CD8- double-negative, and TCR alpha beta + cells and increased the percentage of CD4+CD8+ double-positive cell s. In the immature rats gonadectomy increased the percentages of CD4+8 - single-positive and TCR alpha beta + thymocytes and decreased the pe rcentages of double-positive and double-negative cells in males, while in the female it increased the percentage of CD4+8- single-positive t hymocytes. Gonadectomy at that age abolished the sexual dimorphism in the expression of accessory molecules (i.e., CD4/CD8), but facilitated gender-specific expression of TCR alpha beta. In conclusion, the resu lts suggest that the gonadal steroids are more important for the devel opment than for the maintenance of the sexual dimorphism in the thymoc yte composition.