Sex steroid modulation of thymic hormone production in thymus epithelial cell culture

The present study was carried out to determine the direct effect of sex hormones (SHs) on thymus epithelial cell (TEC) production/secretion of the thymic hormone thymosin alpha-1 (TMA1) by using the techniques of in situ hybridization and quantitative high-performance liquid chromatography. The results were as follows: (a) the TECs which stained positive for TMA1-mRNA tended to group together, and TMA1-mRNA expression was observed exclusively in their cytoplasm; (b) at doses over 3 × 10−9 M estradiol-17β(E2β) caused a progressive loss of the number of TMA1-mRNA-positive cells, whereas 5α-dihydrotestosterone (5α-DHT) did not affect the cell number at all; (c) the degree of TMA1-mRNA expression decreased significantly at increasing concentrations of E2 β over 3 × 10−12 M and 5α-DHT over 3 × 10−10 M; (d) the production of TMA1 by TECs was significantly inhibited by increasing concentrations of E2 β over 3 × 10−11 M and 5α-DHT over 3 × 10−10 M. The above results clearly indicate that SHs, especially E2 β, directly modulate TECs to produce the thymic hormone TMA1 probably through their receptor mechanism.