Effects of sexual maturation and Salmonella infection on the expression of Toll-like receptors in the chicken vagina

Toll-like receptors (TLRs) are a critical component of the innate immune response in many vertebrates, including avian species. The recent findings of chicken TLRs (cTLRs) expression in ovarian follicles and in the chicken ovary in vivo, as well as the changes in their expression in response to lipopolysaccharide or Salmonella enteritidis (SE) infection, have broad implications for reproductive physiology and for the prevention of transmission of zoonotic diseases to humans through the consumption of contaminated poultry eggs. Because the main route of egg contamination is from infection of the oviduct and mainly from the vagina, the aim of this study was to investigate the expression of the ten cTLRs identified to date in the chicken oviduct in vivo, to determine whether sexual maturation affects their mRNA abundance and to investigate whether SE infection alters the expression of TLRs in the chicken vagina. RNA was extracted from the vagina of healthy prepubertal, sexually mature and aged birds, and from sexually mature and aged SE infected birds. RT-PCR analysis revealed that all types of cTLRs apart from TLR1-1 were expressed in the vagina of sexually mature birds. Quantitative real-time PCR analysis revealed that the mRNA abundance of TLR2-1, 2-2 and 4 differ with respect to sexual maturation in the chicken vagina. SE infection resulted in a significant induction of TLR5 and 15 in the vagina of sexually mature birds, and in a significant induction of TLR2-1, 4 and 15 in the vagina of aged birds, while a significant down-regulation was observed for TLR7 in the vagina of sexually mature birds. These findings suggest that a TLR mediated immune response mechanism exists in the chicken vagina, playing a crucial role in preventing microbial pathogens from being incorporated into newly forming eggs.