Transcriptional profiling of Toll-like receptors in chicken embryos and in the ovary during sexual maturation and in response to Salmonella enteritidis infection

One of the key members of the innate immune system in many vertebrate species is the family of Toll-like receptors (TLRs). These molecules, which initiate the innate immune response and mount an anti-microbial response in both vertebrates and invertebrates, have recently been identified in the chicken genome. The recent findings of chicken TLRs (cTLRs) expression in ovarian follicles during follicular growth and in response to lipopolysaccharide (LPS) infection are very important for reproductive physiology due to the transovarian transmission of Salmonella enteritidis (SE) in laying hens. The aim of this study was to investigate the expression of the ten cTLRs identified to date, in the chicken ovary in vivo and embryos during early embryonic development, to investigate whether sexual maturation affects their ovarian mRNA abundance and to investigate the transcriptional changes of TLRs in the chicken ovary in response to SE infection. RNA was extracted from embryos from day 3 to day 10 of embryonic development as well as from the ovaries of healthy prepubertal, sexually mature and aged birds, and from sexually mature and aged SE infected birds. RT-PCR analysis revealed that all TLRs apart from TLRs 1–1 and 2–2 were expressed in the ovary of sexually mature chickens, while all TLRs apart from TLR1–1 were expressed in the chicken embryos during embryonic development. Quantitative real-time PCR analysis revealed that the ovarian mRNA abundance of TLRs differ with respect to sexual maturation. SE infection resulted in a significant induction of TLR4, and 15 in the ovary of sexual mature birds, and in a significant induction of TLR15 in the ovary of aged birds, while a significant down-regulation was observed for TLR3 in the ovary of aged birds. These findings suggest that a TLR-mediated immune response mechanism exists in the chicken ovary.