Testisimmune privilege - Assumptions versus facts.

The testis has long enjoyed a reputation as an immunologically privileged site based on its ability to protect auto-antigenic germ cells and provide an optimal environment for the extended survival of transplanted allo- or xeno-grafts. Exploration of the role of anatomical, physiological, immunological and cellular components in testis immune privilege revealed that the tolerogenic environment of the testis is a result of the immunomodulatory factors expressed or secreted by testicular cells (mainly Sertoli cells, peritubular myoid cells, Leydig cells, and resident macrophages). The blood-testis barrier/Sertoli cell barrier, is also important to seclude advanced germ cells but its requirement in testis immune privilege needs further investigation. Testicular immune privilege is not permanent, as an effective immune response can be mounted against transplanted tissue, and bacterial/viral infections in the testis can be effectively eliminated. Overall, the cellular components control the fate of the immune response and can shift the response from immunodestructive to immunoprotective, resulting in immune privilege.