Menstrual cycle-specific inhibition of the proliferation of endometrial stromal cells by interleukin 6 and its soluble receptor

OBJECTIVE: This study investigated the possible roles of interleukin 6 and soluble interleukin 6 receptor in the growth of endometrial and endometriotic cells. STUDY DESIGN: Endometrial and endometriotic stromal cells were collected from the uterus or from ovarian chocolate cysts. We examined the effects of interleukin 6, soluble interleukin 6 receptor, and a combination of both factors on the proliferation of endometrial and endometriotic stromal cells. The action of sex steroids on the interleukin 6 regulation of the growth of stromal cells was also evaluated. The gene expressions of interleukin 6 receptor and glycoprotein 130 were examined in endometrial and endometriotic cells by reverse transcription-polymerase chain reaction. RESULTS: Interleukin 6 had no effect on the growth of stromal cells in tissue from the proliferative phase. In contrast, the addition of concentrations of >/=100 pg/mL interleukin 6 induced significant inhibition of stromal cell proliferation in tissue from the secretory phase. Similarly, the addition of soluble interleukin 6 receptor caused significant suppression in the growth of endometrial stromal cells in tissue from the secretory phase but not the proliferative phase. On the other hand, stromal cells of endometriotic tissues were resistant to interleukin 6, showing no inhibitory response. Although the combination treatment did not affect the proliferation of stromal cells of the proliferative phase and of endometriotic tissues, 10 pg/mL interleukin 6 inhibited proliferation of stromal cells of the secretory phase in the presence of 1 ng/mL soluble interleukin 6 receptor. Treatment with estradiol and progesterone for 10 days newly induced the inhibitory response to interleukin 6 in the endometrial cells from the proliferative phase. Expressions of transcripts of interleukin 6 receptor and glycoprotein 130 were observed in the endometrial cells from the proliferative and secretory phases and in endometriotic cells. CONCLUSIONS: Interleukin 6 may play a central role in regulation of the growth of endometrial cells as a mediator of endocrine action. Endometriotic cells may behave differently from their normal counterparts in terms of the inhibitory regulation exerted by interleukin 6.