Abstract
BACKGROUND: The testis is specific in that it produces haploid germ cells of which autoantigens newly appear long after the neonatal immune tolerance. Under normal condition, these autoantigens are protected by the blood-testis barrier formed by Sertoli cells. Thus, the testis is an immunologically privileged site where haploid cells are protected from autoimmune attack. METHODS: The immunological microenvironment in the testis was experimentally investigated using mice and rats. MAIN FINDINGS: Not only the blood-testis barrier but also various immuno-suppressive factors are involved in the immune-privileged testis. Indeed, germ cells transplanted into the xenogeneic seminiferous tubules could proliferate and differentiate with no aid of artificial immunosuppression. On the other hand, autoimmune orchitis could be experimentally produced by various methods of immunization with syngeneic or xenogeneic germ cell antigens. CONCLUSION: Our results indicate that the testis is immunologically privileged but also immunologically fragile organ. Therefore, the dual nature is critical for immunoregulation of testicular function.