Prostaglandins in primate semen: biasing the immune system to benefit spermatozoa and virus?

The levels of prostaglandins in human semen are many orders of magnitude higher than those found elsewhere in the body and semen contains 19-hydroxy PGE which has not been found in other tissues. The reason for the presence of these prostaglandins is now becoming apparent with the demonstration of powerful effects of PGE and 19-hydroxy PGE on the balance of cytokines (stimulating IL-10 and inhibiting IL-12) released by antigen presenting cells. The effects of the seminal prostaglandins will be two-fold. First, there will be cAMP mediated direct effect on T cells, inhibiting clonal proliferation, inhibiting natural killer cell function and biasing the CD4 cells to a T-helper-2 pattern of cytokine production away from one that would favour a cell-mediated response. Second, and perhaps the major effect, is at the level of the antigen presenting cell that will reinforce the direct effects and induce a tolerance of antigens that are presented together with the IL-10, or PGE. Such tolerance might be necessary for the survival of the spermatozoa under adverse conditions, for instance, in the presence of infection Viruses and other invading organisms would also benefit from this switch in cytokines and the inhibition of the cell-mediated defences. Particular concerns are human immunodeficiency virus (HIV) and human papilloma virus (HPV) which can be transmitted in semen. Not only will the initial immune response be affected, but also repeated exposure to semen will reduce immunesurveillance and the removal of virally infected cells.