SEX-DIFFERENCES IN THE PHENOTYPIC CHARACTERISTICS OF RAT THYMOCYTES

This study was undertaken to assess whether there is any difference in the process of intrathymic T cell differentiation that could account for sexual dimorphism in the immune response. To accomplish this aim t he relative proportion of four main thymocyte subsets delineated by ex pression of CD4 and CD8 surface markers was studied in rats of both se xes, using appropriate monoclonal antibodies and direct two-color flow cytometric analysis (FCA). Although the total yield of T cells extrac ted from thymuses did not differ between the sexes, in females was fou nd a decreased percentage of double positive (DP) CD4(+)/CD8(+) cells accompanied by a proportional increase in the percentage of single pos itive (SP) CD4(+)/CD8(-) cells. The results indicate that the balance of intrathymic T cell maturation in females is shifted in faor of the helper/inducer subset. Moreover this shift in balance might be, at lea st partly, responsible for the phenomenon termed immunological sexual dimorphism.