The elevation of the proinflammatory chemoattractant cytokine levels in ectopic and eutopic endometrium of endometriosis implies an inflammatory basis for this disease. The relationship between endothelial cells and leukocytes is likely to be important in the regulation of inflammatory mediators of endometriosis. The aim of this study was to describe the temporal and spatial expression of IL-8 in human endometrial endothelial cells (HEEC) in vivo and to compare the in vitro regulation of IL-8 expression by sex steroids in HEEC from women with or without endometriosis. Eutopic endometrial tissues and endometriosis implants were grouped according to menstrual cycle phase and examined by immunohistochemistry for IL-8 expression. Endothelial cells of endometriotic implants expressed higher IL-8 immunoreactivity compared with endothelial cells of eutopic endometrium from women with or without endometriosis (P < 0.02). For in vitro studies, HEEC were isolated from women with or without endometriosis and grown to preconfluence. The purity of cultured HEEC (90-95%) was confirmed by immunocytochemistry using endothelium-specific markers, CD31 and CD146. The effects of estradiol (5 x 10(-8) m), progesterone (10(-7) m), or both on IL-8 mRNA and protein levels were analyzed by RT-PCR and ELISA, respectively. Sex steroids reduced the expression of IL-8 mRNA and protein in HEEC from women without endometriosis. In contrast, both estradiol and progesterone stimulated IL-8 mRNA and protein expression in HEEC from women with endometriosis. We postulate that the stimulation of chemokine expression by sex steroids in HEEC of women with endometriosis may play a role in the inflammatory aspect of this disease.