Interleukin-8 expression and modulation in human preovulatory follicles and ovarian cells

Abstract

Just before the time of ovulation, the number of neutrophils increases markedly in the thecal layer of the leading follicle. A preovulatory rise in chemotactic activity for neutrophils in human follicular fluid has also been detected. We hypothesized that interleukin-8 (IL-8), a neutrophil chemoattractant/activating factor and a potent angiogenic agent, may be an important modulator of leukocyte chemotaxis in ovulatory function. In this regard we investigated the expression and modulation of IL-8 in human follicular fluid samples from patients undergoing in vitro fertilization- embryo transfer therapy and in ovarian stromal and granulosa-lutein cell cultures. The concentration of IL-8 in pre-hCG follicular fluid samples (n = 4) was 16 ± 12 (mean ± SEM) pg/ml, and that in post-hCG samples (n = 101) was 262 ± 45 pg/ml (P = 0.001). In post-hCG samples, the concentration of IL-8 in an individual follicle correlated with the size of that follicle (r = 0.61; P = 0.02). We also observed a correlation between serum IL-8 levels (22 ± 3 pg/ml) and follicular fluid levels(303 ± 143 pg/ml), with a 14-fold gradient (r = 0.71; P = 0.01) in 11 patients tested for both. IL-8 messenger RNA (mRNA) and the protein were expressed constitutively in ovarian stromal cell cultures, and the level was increased by IL-1α and tumor necrosis factor-α in a time- and concentration-dependent manner. hCG and LH induced higher levels of IL-8 mRNA expression and protein production. Granulosa- lutein cells also expressed IL-8 mRNA and protein, and the levels were increased by IL-1α and tumor necrosis factor-α. Importantly, progesterone suppressed both basal and IL-1α-stimulated IL-8 expression in stromal and granulosa-lutein cell types. In summary, we found that IL-8 levels are elevated in periovulatory follicular fluid, and both granulosa-lutein and ovarian stromal cells express the mRNA and produce the protein. The modulation of IL-8 in these cell cultures by steroid and trophic hormones suggests that IL-8 may play an important role in the physiology of ovulation, such as timely follicular rupture and neovascularization of the corpus luteum.