Is human testis an immune privileged tissue?

The expression of Fas L has been shown to be responsible for immune privilege of rodent testes. Immune privilege of human testis has been assumed based on the rodent data, but has never been demonstrated. In this study, we examined the expression of Fas L, Fas, bcl-2 and bcl-X_L in human testes (n = 5, age range from newborn to 85 years, obtained fresh from organ donors and orchidectomy specimens for cancer management) using Western Blot and RT-PCR. Both human, rat and mouse testes do not express Fas, bcl-2 and bcl-X_L. In contrast to rodent testes, Fas L is not expressed constitutively in human testes and is not induced following co-culture with mouse splenic mononuclear cells. In vitro co-culture of isolated mouse Sertoli cell suspension with human Jurkat cells (human Fas positive cell line) for 18-24 hours results in significant apoptosis of Jurkat cells. Co-culture of human Sertoli cell suspension with Jurkat cells however does not induce apoptosis. In vivo transplantation of human testes pieces under the kidney capsule of Fas L defective gld, Fas defective Ipr and normal C57/B6 strains of mice results in complete rejection of the transplanted tissue. In contrast, B6 nude recipients demonstrate normal architecture. We conclude that Fas L is not expressed in human testis. Fas L mediated apoptosis does not appear to play a role in immune privilege of human testis and human testis does not appear to be immune privileged.