Interleukin-18 system messenger RNA and protein expression in human endometrium during the menstrual cycle

Objective: To investigate the IL-18 system, including IL-18, IL-18 receptor (IL-18R), IL-18 binding protein (IL-18BP), and IL-18 precursor (proIL-18), mRNA and protein expression in human endometrium during the menstrual cycle. Design: Controlled study. Setting: Clinical and academic research setting in a university medical center. Patient(s): Human endometrium was obtained from surgical specimens of normal cycling women undergoing hysterectomy for benign reasons. Intervention(s): A total of 24 human endometrium samples were obtained at proliferative and secretory phase from surgical specimens of normal cycling women undergoing hysterectomy. Quantitative competitive polymerase chain reaction (QC PCR) and immunohistochemistry were performed. Main Outcome Measure(s): The differences of IL-18 system mRNA and the ratio of antagonist to agonist in both proliferative and secretory phases of endometrium were analyzed. Result(s): Our results showed a complete IL-18 system, including mRNA expression and protein production in both proliferative and secretory phases of the endometrium. The QC PCR demonstrated that both IL-18 and IL-18R decreased and IL-18BP increased mRNA expression in human endometrium in secretory phase compared with proliferative phase. A positive correlation of IL-18 and IL-18R in human endometrium was demonstrated in proliferative phase but not in secretory phase. In addition, there is a significantly higher ratio of IL-18BP to IL-18 mRNA levels in secretory endometrium compared with proliferative phase endometrium (P<.05). Conclusion(s): The expression and ratio of IL-18 antagonist to agonist may be responsible for embryo implantation.