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

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.