Interleukin-2 Receptor/p55(Tac)-Inducing Activity in Porcine Follicular Fluids*

Very recently, it has been reported that interleukin-1 (IL-1) has an inhibitory effect on progesterone production by porcine granulosa cells in vitro. In the present study we investigated the presence of IL-1 or IL-1-like activity in porcine ovarian follicular fluids (FF) as the first step in elucidating the physiological role of IL-1 in follicular growth and maturation. Since IL-1 and IL-1-like substances have interleukin-2 receptor (IL-2R)/p55(Tac)-inducing activity (TIA), we determined the TIA in the FF by means of a highly sensitive TIA assay using flow cytometry. TIA was significantly higher (P less than 0.01) in the FF of small follicles than in those of medium-sized and large follicles. A significant negative correlation (P less than 0.05) was apparent between TIA and 17 beta-estradiol concentration in the FF. The conditioned media of porcine granulosa cells also showed TIA. Of these conditioned media, those from small follicles exhibited higher TIA than those from medium-sized and large follicles. TIA in the conditioned media decreased rapidly as the culture period was extended. Sex steroids such as 17 beta-estradiol, progesterone, testosterone, and androstenedione had no effect on IL-2R/p55(Tac) induction. These results indicate that porcine granulosa cells produce the IL-2R/p55(Tac)-inducing factor, the activity of which decreases in association with the maturation of the follicles. Because of the heterogeneity of IL-2R-inducing factors, the relationship between TIA in the FF and IL-1 should be elucidated. We discuss the possibility that this factor may play a role in follicular maturation and that enhancement of IL-2R/p55(Tac) expression by this factor may contribute to the local defense mechanism in ovarian follicles.