Expression of mRNAs for interleukin-4, interleukin-6 and their receptors in porcine corpus luteum during the estrous cycle

There is increasing evidence that inflammatory cytokines regulate corpus luteum (CL) function in many species. The purpose of the present study was to determine whether interleukin (IL)-4 and IL-6 are expressed in the porcine CL, and whether these cytokines influence porcine luteal steroidogenesis. The gene expressions of IL-4, IL-6 and their specific receptors were determined in the CL of Chinese Meishan pigs during the estrous cycle. Moreover, the effects of these cytokines on progesterone (P₄), estradiol-17β (E₂) and prostaglandin (PG) F2α secretion by cultured luteal cells were investigated. IL-4 and IL-6 mRNAs were detected in the CL at all luteal stages. Furthermore, mRNAs of the receptors for IL-4 and IL-6 were clearly expressed in the CL throughout the estrous cycle. Real-time PCR analysis revealed that IL-6 receptor (IL-6R) mRNA expression was higher in the regressed CL (days 19-21 after ovulation) than in the CL at other stages (P < 0.01). Exposure of cultured luteal cells obtained from mid-stage CL (days 8-11) to IL-6 (1-100 ng/ml), it inhibited P₄ and E₂ secretion by the cells (P < 0.05). Although IL-4 (1-100 ng/ml) did not significantly alter P₄ secretion, it inhibited E₂ secretion by the cells (P < 0.05). Neither IL-4 nor IL-6 had any effect on PGF2α secretion by the cells. These results suggest that IL-4 and IL-6 are locally produced in the porcine CL, and that they inhibit steroid production from luteal cells via their specific receptors. Collectively, both IL-4 and IL-6 may play roles in regulating porcine CL function throughout the estrous cycle.