Interleukin-6 secretion in vitro is up-regulated in ectopic and eutopic endometrial stromal cells from women with endometriosis

An in vitro model developed to compare human endometrial and endometriosis stromal cells was used to examine basal and stimulated expression of interleukin (IL-6). Stromal cells isolated from normal endometrium (NE) exhibited the lowest level of IL-6 secretion (84 pg/10⁶ cells-48 h), whereas those cells isolated from endometriosis implants (EI) secreted the highest concentration of this inflammatory cytokine (46,264 pg/10⁶ cells · 48 h; P < 0.01). Eutopic endometrial stromal cells from women with endometriosis (EE) expressed an intermediate concentration of IL-6 (831 pg/10⁶ cells · 48 h). Stimulation of the various cultures with IL-1β dramatically augmented stromal cell production of IL-6. The mean concentrations of stimulated IL-6 secretion were 16,257, 37,800, and 264,290 pg/10⁶ cells · 48 h for NE, EE, and EI cells, respectively (P < 0.03). Exposure of the cell cultures to 10 nmol/L estradiol had little direct effect on IL-6 production. The results indicate that endometrial stromal cells isolated from tissues of women with and without endometriosis express IL-6 under basal and cytokine-stimulated conditions. Differential responsiveness among the three cell sources indicates that NE, EE, and EI cells have intrinsic quantitative differences in cytokine regulation.