Pregnancy-associated plasma protein-A and placental protein 5 in human seminal plasma.

Human seminal plasma contains two glycoproteins which are physiochemically and immunologically indistinguishable from pregnancy-associated plasma protein-A and placental protein 5. Seminal concentrations of both glycoproteins did not correlate with clinical assessment of semen quality. Furthermore, analysis of split ejaculates indicated a nontesticular origin for both proteins, which are possibly secreted into the distal portions of the tract by the accessory glands (prostate gland and seminal vesicles). The physiological significance of these findings has yet to be determined. However, it is suggested that pregnancy-associated plasma protein-A, a known potent inhibitor of leukocyte elastase, protects the deposited sperm against proteolytic attack originating from the localized leukocyte reaction within the female reproductive tract, thus contributing towards sperm survival within this immunologically hostile environment and enabling fertilization to occur.