Interleukin (IL)-1β regulation of IL-1β and IL-1 receptor antagonist expression in cultured human endometrial stromal cells

The interleukin (IL)-1 system is a major regulator of local cellular interactions during embryonic implantation. Because IL-1β and IL receptor antagonist (IL-1ra) are both expressed in human endometrium, we hypothesized that an appropriate ratio of IL-1β to IL-1ra might favor the process of embryo implantation. Therefore, we investigated IL-1 regulation of the quantitative ratio of IL-1β/IL-1ra messenger RNA (mRNA) expression in human endometrial stromal cells using quantitative competitive PCR, as well as intracellular protein expression after stromal cell solubilization. Confluent stromal cell cultures were stimulated with human IL-1β (0-1000 IU/mL) for 24 h. After 24 h, total RNA was extracted, reverse transcribed, and coamplified by PCR with a defined amount of internal standard. The quantitative ratio was determined by the density of target to the internal standard. After culture with IL-1β for 24 and 48 h, stromal cells were solubilized, and the intracellular protein levels of IL-1β and IL-1ra were measured by enzyme-linked immunosorbent assay. The IL-1β and IL-1ra mRNA were both up-regulated, and IL-1R tI mRNA was down-regulated, by IL-1β in a dose-dependent manner. The quantitative ratio of IL-1β to IL- 1ra mRNA was constant with the presence of increasing concentrations of IL-1β (1-1000 IU/mL). IL-1β and IL-1ra protein was not detected in conditioned media of cultures before addition of IL-1β. IL-1β and IL-1ra protein levels increased with increasing amounts of IL-1β after solubilization of stromal cells. The IL-1β was detectable after 12 h of culture, in comparison with IL-1ra, which was detectable after 24 h of IL-1β stimulation. These results suggest that IL-1 may play a crucial role in embryo-maternal interaction by regulating stromal cell expression of IL-1β and IL-1ra, resulting in an appropriate ratio during the process of embryonic implantation.