Human decidual natural killer cells express the receptor for and respond to the cytokine interleukin 15

The natural killer (NK) cells that are present in the uterine mucosa (decid ua) during early pregnancy have a distinctive phenotype, CD56(bright) CD16( -). These cells have previously been shown to proliferate and be activated by interleukin (IL)-2. However, IL-2 is absent from the decidua and placent a, and we have therefore investigated whether IL-15 is present in the uteru s and can act on decidual NK cells. Both IL-15 mRNA and protein were found in a variety of cells but particularly in decidual macrophages. IL-15 induc ed a proliferative response in decidual NK cells that was blocked by anti-I L-15 and was augmented by stem cell factor. The cytolytic activity of decid ual NK cells against K562 was augmented. Interestingly, in contrast to IL-2 , although activation with IL-15 resulted in some killing of JEG-3 chorioca rcinoma cells, normal trophoblast cells remained resistant to lysis. These findings suggest that IL-15 is a candidate cytokine responsible for NK cell proliferation in vivo in the progesterone-dominated secretory endometrium and early decidua.