Role of toll-like receptors in the reproductive tract inflammation and male infertility

Male reproductive system is immunoprivileged and has special immune microenvironment to protect the testicular cells including the germ cells. A wide range of microorganisms are identified that can infect male reproductive tissues via hematogenous dissemination as well as male genitourinary tract, and severely impair reproductive functions. Testis is equipped with unique innate immune system to overcome its immunoprivileged state in case of testicular microbial infection. The testicular cells, mainly the Leydig cells, Sertoli cells and germ cells reportedly express components of innate immune system and their counteracting regulatory system. The innate immune responses are mostly mediated by pattern recognition receptors (PRRs), among which the toll-like receptors (TLRs) have crucial role in the testis. Various TLRs have been shown to express in the testicular cells, especially in Leydig and Sertoli cells and initiate appropriate innate immune responses. If the intricate balance of immune responsiveness and suppression in the testicular tissue is disrupted, it may result in inflammation which is an essential etiological factor of male infertility. Since the concept on the association of TLRs with male infertility is unclear, the present review article aims to synthesize a concise overview on the expression, functions and signalling pathways of testicular TLRs and their impact upon male fertility.