IL-15 expression at human endometrium and decidua

A large number of natural killer (NK) cells appear in human uterine mucosa during the secretory phase and first trimester pregnancy. We investigated t he expression of interleukin (IL)-15, a possible stimulator for these NK ce lls, in human endometrium and first trimester decidua. Semiquantitative rev erse transcriptase-polymerase chain reaction revealed that IL-15 mRNA expre ssion was stronger during the secretory phase and first trimester pregnancy than during the proliferative phase. Immunohistochemistry revealed that im munoreactivity for anti-IL-15 was higher during the secretory phase than it was during the proliferative phase. This was prominent in the perivascular stromal cells around invading spiral arteries during the mid- to late-secr etory phase. In first trimester decidua, endothelial cells were also staine d as strongly as stromal cells. A membrane-bound IL-15 molecule was detecte d on the surface of first trimester decidual cells by flow cytometry. Proge sterone stimulated the release of soluble IL-15 in the supernatant of cultu red decidual cells. These results suggest that IL-15 expression in human ut erine mucosa corresponds to the fluctuation of uterine NK cells and that it s production is hormonally controlled, especially by progesterone.