Prolactin receptors on human lymphocytes and their modulation by cyclosporine

Prolactin receptors have been identified for the first time on human peripheral blood lymphocytes. These receptors are present on T- and B-cells as well as monocytes. The specific binding of [¹²⁵I]prolactin to these cells can be selectively enhanced at certain concentrations and blocked by higher concentrations of cyclosporine, a known immunosuppressive agent which inhibits the mitogenesis of T-cells. Prolactin also induces ornithine decarboxylase, a key growth regulatory enzyme, in lymphocytes. Therefore, we suggest that the lymphocyte prolactin receptor may be involved in regulating lymphocyte function, and that one of the actions of cyclosporine is to block this rather ubiquitously occurring receptor.