Evidence for Immunosuppressive Effects of Human Semenogelin, a Major Protein of Seminal Plasma

Semenogelin (Sg) is secreted from the seminal vesicle and constitutes a major gel-forming protein in semen. Sg plays an important role for inhibiting sperm motility. Human seminal plasma has immunosuppressive effects on human peripheral blood lymphocytes (PBL). Here, we studied whether human Sg exerted immunosuppressive effects on human lymphocyte functions in vitro. We found that Sg reduced proliferation of PBL induced by phytohaemagglutinin (PHA) and anti-CD3 antibody. AntiSg antibody reversed the immunosuppressive effect, indicating that Sg was responsible for the effect. IL-2 secretion and IL2 mRNA expression in PHA-activated PBL were reduced by Sg. However, Sg had no effect on IL-2 receptor expression of PHAactivated PBL. Immunoglobulin production induced by pokeweed mitogen was inhibited by Sg. Collectively, Sg has suppressive effects on T cell-mediated immune responses and immunoglobulin production. Sg is associated with immunosuppressive effects on sperm in female reproductive tract at fertilization by reducing anti-sperm immune responses.