When will functional thymic-gonadal axis be established ?

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This study was carried out to determine when functional 'thymusgonad' axis would be established using human fetal thymus. Thymus tissues regally obtained from 13 to 24 week old fetuses were used for (1) immunohistochemical staining of estrogen receptor (ER), serum thymic factor (FTS) and keratin, and (2) quantitation by ELISA of ER and FTS in the tissue.The findings were as follows ; (1) in 16 week old fetal thymus ER-stained cells appeared exclusively in the medullary area which were confirmed as epithelial cells by keratin-staining. They were also scattered in the cortical area. (2) at the same gestational week, predominantly FTS-stained cells were diffusely distributed throughout the medulla, with some scattered in the cortical area. Their structural features were similar to those of ER-stained cells.The present results may provide evidence for E regulation of development-growth of the fetal thymus at mid-pregnancy through its effect on the epithelial cells via a receptor mechanism that produces FTS to stimulate the proliferation, differentiation and/or selection of T cells.