Changes in the expression of Toll-like receptors in the chicken testis during sexual maturation and Salmonella infection

Rooster infertility is a major concern in the poultry industry and chicken male reproductive organs are the infectious tissues of various pathogenic microorganisms. Protection of the chicken male reproductive organs from pathogens is therefore an essential aspect of reproductive physiology. Recently Toll-like receptors (TLRs) have been identified as one of the key components of innate immunity in vertebrate species and have been reported to be expressed in the reproductive organs in various female species, including the chicken. However, mechanisms of antimicrobial protection of male reproductive organs mediated by TLRs are poorly understood. The objectives of this study were to determine the expression profile of the entire family of the ten chicken TLR genes in the chicken testis, to investigate whether sexual maturation affects their testicular mRNA abundance and to determine the changes in their expression levels in response to Salmonella enteritidis (SE) infection. RNA was extracted from the testis of healthy pre-pubertal, sexually mature and aged birds, and from sexually mature SE infected birds. RT-PCR analysis revealed that all TLRs, apart from TLR1-1 (TLR6), were expressed in the chicken testis. Quantitative real-time PCR analysis revealed that the testicular mRNA abundance of certain TLRs was developmentally regulated with respect to sexual maturation, while SE infection resulted in a significant induction of TLR2-1, 4, 5, 15 and 21 in the testis of sexually mature birds compared, to healthy birds of the same age. These findings provide strong evidence to suggest a key role of TLRs in the innate immune responses of chicken testis against Salmonella colonization.