Mechanisms of testicular immune privilege

Toll-like receptor 3-initiated antiviral responses in mouse male germ cells in vitro

The testis is an immunoprivileged site where local cell-initiated innate immunity plays a crucial role in antimicrobial responses. Toll-like receptors (TLRs) mediate innate immune responses in testicular somatic cells. Although several TLRs are expressed in some stages of male germ cells, the potential role of TLRs in triggering antimicrobial responses in the germ cells has yet to be exclusively studied. The current study demonstrates that TLR3 is constitutively expressed in spermatogonia and spermatocytes and can be activated by a synthetic double-strained RNA analog, polyinosinic-polycytidylic acid. TLR3 activation in these male germ cells up-regulates the expression of proinflammatory cytokines, such as interleukin IL1B, IL6, and tumor necrosis factor alpha, through activation of nuclear factor kappa B; it also induces production of type 1 interferons (IFNA and IFNB) through the activation of IFN regulatory factor 3. In addition, TLR3 activation increases the production of two major antiviral proteins, namely, double-stranded RNA-activated protein kinase and MX1 protein, by germ cells. Data in this article describe an antiviral response of male germ cells through the activation of TLR3 in vitro.