Does immunity regulate ejaculate quality and fertility in humans?

The production of high-quality ejaculates may represent significant costs during male reproduction. Spermatozoa are perceived as nonself by the immune system and are exposed to immunological attacks in the male reproductive tract. Autoimmunity to spermatozoa results in the production of antisperm antibodies that reduce sperm quality and hence fertility. Thus, males are dependent on the testis being an immunoprivileged site to reduce immunological reactions against their own sperm, and immunoprivilege is obtained by the blood-testis barrier and by hormonal immunosuppression. A meta-analysis on the effects of immunosuppressive corticosteroid treatment of male infertility revealed that treatment reduced the level of antisperm antibodies, improved sperm motility and sperm count, and increased conception rate. These results emphasize the importance of immunosuppression and the associated pathogenicity from infectious organisms as important costs for the production of high-quality ejaculates.