Mechanisms of testicular immune privilege

The testis exhibits a distinctive form of immune privilege to protect the germ cells from the host immuneattack. The property of testicular immune privilege was originally attributed to the blood-testis barrier in theseminiferous epithelium, which sequesters antigens. Recent studies have uncovered several levels of immune controlbesides the blood-testis barrier involved in the privilege of the testis, including the mechanisms of immune tolerance,reduced immune activation, localized active immunosuppression and antigen-specific immunoregulation. The somaticcells of the testis, especially Sertoli cells, play a key role in regulating the testicular immune privileged status. Theconstitutive expression of anti-inflammatory factors in the testis by somatic cells is essential for local immunosuppression.Growing evidence shows that androgens orchestrate the inhibition of proinflammatory factors and shift cytokinebalance toward a tolerogenic environment. Disruption of these protective mechanisms, which may be caused by trauma,infection and genetic factors, can lead to orchitis and infertility. This review article highlights the unique immuneenvironment of the testis, particularly focuses on the regulation of testicular immune privilege.

Testicular defense systems： immune privilege and innate immunity

The mammalian testis possesses a special immunological environment because of its properties of remarkable immune privilege and effective local innate immunity. Testicular immune privilege protects immunogenic germ cells from systemic immune attack, and local innate immunity is important in preventing testicular microbial infections. The breakdown of local testicular immune homeostasis may lead to orchitis, an etiological factor of male infertility. The mechanisms underlying testicular immune privilege have been investigated for a long time. Increasing evidence shows that both a local immunosuppressive milieu and systemic immune tolerance are involved in maintaining testicular immune privilege status. The mechanisms underlying testicular innate immunity are emerging based on the investigation of the pattern recognition receptor-mediated innate immune response in testicular cells. This review summarizes our current understanding of testicular defense mechanisms and identifies topics that merit further investigation.