Background: Endometriosis is a complex disease associated with a wide range of immune responses, including pain, adhesion, exudation of peritoneal fluid, elevation of cytokine levels and generation of autoantibodies. Interleukin (IL)-18 is a strong pleiotropic cytokine known to be involved in various immune diseases. The aim of this study is to elucidate the role of IL-18 in the pathogenesis of endometriosis.
Methods: IL-18 and IL-1beta concentrations were measured in the peritoneal fluid and sera of 39 endometriosis patients and 15 control women. Expression of IL-18 and IL-18 receptor alpha-chain (IL-18Ralpha) was analysed in endometriotic tissues immunohistochemically. The effects of IL-18 on cyclooxygenase (COX)-II gene expression were analysed in peritoneal fluid monocytes and endometriotic cells of endometriosis patients.
Results: IL-18 concentrations in the peritoneal fluid of endometriosis patients averaged 592.57 +/- 108.27 pg/ml, significantly higher than 260.50 +/- 55.88 pg/ml in non-endometriotic samples. IL-18 concentrations in the serum did not differ significantly between endometriosis and control patients. Similarly, no significant differences were observed in IL-1beta concentrations in either the peritoneal fluid or the serum. IL-18 and IL-18Ralpha were expressed in endometriotic tissues. IL-18Ralpha expression was also observed in cells infiltrating into the inflammatory area of the endometriosis patients. COX-II was induced in peritoneal fluid monocytes and in endometriotic cells in response to IL-18 stimulation.
Conclusions: The elevation of IL-18 in the peritoneal fluid of endometriosis patients and the induction of COX-II in peritoneal monocytes by IL-18 suggest that IL-18 plays a pathogenic role in endometriosis.