Human seminal plasma suppresses lymphocyte responses in vitro in serum-free medium

The in vitro immunosuppressive properties of human seminal plasma have been re-investigated in serum-free medium in view of recent suggestions that the previously observed effects might be dependent on the presence of exogenous serum co-factors present in the culture media. The present studies reveal that low concentrations of seminal plasma can inhibit the ability of peripheral blood leukocytes to lyse K562 target cells in the absence of fetal calf or new-born calf serum. These inhibitory effects could be achieved by pre-incubating the effector cells in seminal plasma at 37 degrees C prior to use in the natural killer cell assay or by incorporating it into the assay system. Additional studies revealed that human seminal plasma could also inhibit the proliferative response of peripheral blood lymphocytes to phytohaemagglutinin in serum-free HB103 medium. These effects were most marked and consistent if the seminal plasma was present throughout the period of culture. Overall, these studies indicate that the previously reported suppressive effects of human seminal plasma in these systems cannot be entirely attributable to cytotoxic factors generated by exogenous serum components.