Inhibition of cell proliferation by basic proteins from bull seminal plasma

The fraction of basic proteins has been shown to suppress the concanavalin A-induced proliferation of bovine lymphocytes effectively in a dose-dependent manner. The inhibitory effect was observed within a concentration range where the fraction of basic proteins was not cytotoxic. By separating the basic proteins, only two proteins, seminal ribonuclease and seminal antimicrobial protein were found to be active in inhibition of lymphocyte proliferation. Both proteins appear to function differently. At a concentration of 56 micrograms/ml, where both proteins inhibited DNA synthesis, seminal ribonuclease also inhibited RNA synthesis by greater than 50% whereas seminal antimicrobial protein had no effect on RNA synthesis. It was furthermore observed that the suppressive effect of the basic proteins was independent of the mitogenic stimulus and proliferation of both, T- as well as B-lymphocytes was inhibited by those proteins.