Immunosuppressive activity of bovine seminal plasma on bovine lymphocytes in vitro

Pooled seminal plasma obtained from six bulls was tested for its immunosuppressive activities in vitro on blastogenesis of bovine lymphocytes. Lymphocyte stimulation assay and mixed lymphocyte reaction were used as test procedures. Concanavalin A and phytohemagglutinin were utilized in the lymphocyte stimulation assays as nonspecific stimuli. Tritiated thymidine uptake by the lymphocytes was measured after incubation for 5 d with seminal plasma. Undiluted seminal plasma was cytotoxic to lymphocytes up to and at 1/100 dilution but not at 1/400. Undiluted seminal plasma was immunosuppressive at a 1/400 dilution. Lyophilization of seminal plasma without prior dialysis resulted in loss of immunosuppressive activity. After dialysis and lyophilization, the reconstituted seminal plasma suppressed thymidine uptake by Concanavalin A and phytohemagglutinin-stimulated bovine lymphocytes while being noncytotoxic. This paper documents that bovine seminal plasma is immunosuppressive and also cytotoxic to the bovine cells that generate an immune response.