Thymic hormone containing cells--IX. Steroids in vitro modulate thymulin secretion by human and murine thymic epithelial cells.

We investigated the in vitro effects (kinetics and dose-response) of adrenal and sexual steroid hormones on the secretion of thymulin, a thymic hormone, by human thymic epithelial cells in primary cultures as well as in a rat epithelial cell line. We demonstrated that all steroids tested, in a range of physiological doses, stimulated thymulin production to various extents. Progesterone and estradiol, however, were revealed to be the most efficient. Specific steroid antagonists abrogated the steroid-induced stimulation of thymulin production. These findings confirm our previous in vivo results and demonstrate that steroid hormones can act directly on thymic epithelial cells to modulate their endocrine production.