PROBLEM: Human seminal plasma is known to exhibit immunosuppressive activity in seminal plasma.
PURPOSE: The purpose was to characterize immunosuppressive proteins in seminal plasma.
METHOD: Gel filtration fractions of 100 to >440 kDa were identified that inhibited DNA synthesis and killing activity of interleukin-2 stimulated lymphocytes.
RESULTS: The fractions exhibiting immunosuppression also inhibited DNA synthesis in a mink lung cell bioassay commonly used to measure the activity for transforming growth factor β (TGF-β). The negative growth activity was diminished by aTGF-β neutralizing monoclonal antibody. TGF-β was further detected in the active fractions by Western immunoblot.
CONCLUSIONS: These results identified TGF-β as an immunosuppressive protein in human seminal plasma and may provide insight into the role of immunosuppression played by seminal plasma, such as in reproduction and neoplasia.