Identification of an immunosuppressive protein in bovine seminal plasma with activity against bovine lymphocytes

Seminal plasma was determined to have immunosuppressive activities in vitro on Concanavalin A-induced blastogenesis of bovine lymphocytes. This immunosuppressive activity was isolated and characterized using a pool of seminal plasma from five bulls. The immunosuppressive activity was associated with seminal plasma proteins of less than 50,000 daltons and also with those of approximately 150,000 daltons. The 150,000-dalton proteins were precipitable at 33% saturation with ammonium sulfate and with an antibody to a Sephadex G-200 chromatographic fraction of seminal plasma. The immunosuppressive activity of the less than 50,000 dalton proteins was lost upon chromatography on Sephadex G-25. This suggests that interaction of several components of low molecular weight might be necessary for this inhibitory activity to be expressed.