In human endometrium, cytokines and growth factors that vary periodically during the menstrual cycles have been suggested to play various roles in uterine function. In the present study, differential gene expression in human endometrium between the proliferative and the secretory phases was investigated by using a human cDNA expression array system. Human interleukin (IL)-15 was identified as an up-regulated transcription product during the secretory phase, in comparison with the proliferative phase, and therefore its expression in human uterus was examined by Northern blot analysis. In human endometrium, expression of IL-15 mRNA significantly increased during the secretory phase compared with the proliferative phase (P < 0.01). The most abundant expression of IL-15 mRNA during the menstrual cycle was observed in the midsecretory phase. In the first trimester pregnancy, the expression of IL-15 mRNA in the decidua was significantly higher than that in the chorionic villi (P < 0.01). By using an in-vitro decidualization with human endometrial stromal cells, it was demonstrated that the expression of IL-15 mRNA is up-regulated during progesterone-induced decidualization. These results suggest that IL-15 plays a role in uterine function during pregnancy, as well as during the menstrual cycle.
