Testicular immune tolerance and viral infections

Testes are anatomically and functionally designed to prevent immune reactions against allogenic sperm antigens. On the other side, the immune tolerance properties of the testes aid some viruses concealing from the systemic immune defense. Although testes possess their unique antiviral response, which is counteracted by immunosuppressive mechanisms to ascertain unaltered testicular functions, high viral load and uncontrolled progression of infections breach the testicular immune homeostasis, eliciting inflammatory reactions. This may disintegrate the testicular physical barriers that seclude the sperm antigens from systemic immune cells. This leads to autoimmune responses, thereby affecting testicular functions and the development of various pathological conditions that perturb fertility. Viral infections may have long-lasting effects by possible transmission of virus-mediated mutations to subsequent generations. Since the testicular responses to viral infections are only partially explained, the present chapter aims to provide a concise understanding of the testicular immune tolerance that renders testes to be a safe harbor for viruses. In addition, the chapter discusses the mechanism of testicular antiviral responses in order to encourage research to combat viral persistence in the testes and thereby to prevent re-emergence of viral infection as well as sexual transmission of the viruses through the semen.