Up-regulated mRNA expression of Toll-like receptor (TLR)-2 and -4 in bovine oviductal cells after treatment with estradiol or progesterone indicates a stimulatory effect of steroid hormones on the immune system in the reproductive tract

Abstract

Female reproductive epithelial cells produce a variety of substances that promote reproduction and immune defense. These cells secrete peptide mediators that regulate the traffic and activity of immune cells. Several factors are supposed to be involved in these processes, e.g. Toll-like receptors (TLR) which mediate the induction and secretion of chemokines after recognizing pathogens. The aim of the present study was to investigate the mRNA expression of TLR-2 and TLR-4 in cultured bovine oviductal cells after treatment with steroid hormones as well as in different regions of the bovine oviduct during the estrous cycle in vivo. Bovine oviducts from the slaughterhouse were classified into four phases: pre-ovulatory, post-ovulatory, early or late luteal phase. Oviductal epithelial cells (>60%) were harvested by flushing separately the ampulla and the isthmus. Furthermore, primary cell culture was carried out with attached oviductal cells after 4 days. Then, the cells were treated with 10 pg/ml estradiol or 10 ng/ml progesterone for up to 6h, respectively. Total RNA was extracted from oviductal cells and real-time RT-PCR was performed. Treatment of cultured oviductal cells with estradiol or progesterone resulted in a significant 5–8 fold higher expression of TLR-2 and TLR-4 after 4h or 6h. Analysis of oviductal cells in vivo revealed a significant lower mRNA expression of TLR-2 during the pre-ovulatory phase compared with the post-ovulatory phase. Interestingly, a higher local TLR-2 expression was noted after ovulation in the isthmus than in the ampulla. In contrast, TLR-4 expression seems to be unregulated without regional differences during the whole estrous cycle in vivo. These results showed that TLR-2 and TLR-4 were expressed in the bovine oviduct. Especially, the regulated expression of TLR-2 and the stimulation by steroid hormones suggests that this receptor is important for an oviductal immune response. Such results support the hypothesis that steroid hormones have an impact on the immune system in reproductive tissues.