ABSTRACT
The mammalian testis is a remarkable immunoprivileged site that protects male germ cells from detrimental immune responses. However, a large spectrum of microbial pathogens, including viruses, bacteria, and parasites, may infect the testis. To overcome its immunoprivileged status and enable local defense against microbial infection, the testis has established its own innate immune system. In addition to having immune cells residing in the interstitial spaces, the testis has tissue-specific cells well equipped with innate immune machinery. The testicular immune environment must be tightly regulated to maintain a homeostasis and disruption of testicular immune homeostasis may impair spermatogenesis and male fertility. Understanding the mechanisms underlying testicular immunoregulation aids the development of strategies for the prevention and treatment of immunological impairment of spermatogenesis. Recent studies have revealed that Tyro3, Axl, and Mer (TAM) receptor tyrosine kinases and pattern recognition receptors (PRRs) play important roles in the maintenance of the testicular immunoprivileged status and local innate immune responses against microbial infections. This chapter focuses on the mechanisms by which TAM receptors and PRRs regulate testicular immune homeostasis.
