Prolactin receptor expression by rat NK cells

We have recently begun investigating the effects of prolactin (PRL) on the function, or growth and differentiation of rat NK cells. Initially, we sought to determine the expression of a receptor for PRL (PRLr) on rat NK cells and to determine the effects of interleukin 2 (IL-2) on its expression. By a combination of reverse transcription/polymerase chain reaction (RT/PCR) and Southern blotting, we were able to identify a PRLr specific transcript using RNA isolated from highly purified, IL-2-activated NK (A-NK) cells. Using primers specific for unique portions of the major forms of PRLr transcripts in liver and ovary, it was determined that the NK cell PRLr has some homology with the major form of transcript for PRLr found in rat liver. By flow cytometric and ¹²⁵I-PRL binding analyses, we determined that A-NK cells expressed detectable levels of PRLr internally. Surface PRLr was not detectable by flow cytometry on freshly isolated NK cells from normal rats, and incubation of NK cells with rIL-2 did not induce detectable surface PRLr. Similarly, incubation of NK cells with PRL was not found to induce expression of the alpha chain of the IL-2 receptor (IL2rα; CD25) on NK cells or other lymphoid cells. However, we were able to detect surface expression of PRLr on NK cells from bromocriptine-treated rats. Taken together, these data indicate that both cultured and freshly isolated populations of NK cell express PRLr.