Seminal plasma suppression of human lymphocyte responses in vitro requires the presence of bovine serum factors.

The effect of bovine sera on the ability of human seminal plasma (SP) to suppress lymphocyte responses was investigated. Marked suppression of natural cell-mediated cytotoxicity (NCMC) against K562 targets was observed when effectors were pretreated for 1 h with SP (1:50 dilution) in the presence of 10% newborn calf serum (NBCS). Some suppression of natural cytotoxicity was observed when the effectors were treated with SP in the presence of 10% fetal calf serum (FCS) and this suppression was greater if the length of pretreatment with SP was increased to 20 h. Suppression of NCMC did not occur, or was considerably less, when the effectors were treated with SP in the presence of 10% autologous human plasma or in HB103 serum-free medium. The effect of bovine sera on suppression of T lymphocyte response to mitogen was also examined. Pre-treatment of lymphocytes with SP (1:50 dilution) for 1 h in the presence of 10% NBCS was sufficient to abrogate completely the stimulatory effect of PHA. In the presence of 10% FCS it was necessary for SP to be present throughout the assay for suppression to occur. In HB103 medium, stimulation was only slightly decreased below control values when SP was present throughout the assay, but suppression was considerably less than that obtained upon addition of NBCS or FCS to the culture medium. These findings imply that suppression of lymphocyte activity by SP is dependent on the presence of exogenous serum co-factors and in the light of this finding, the clinical relevance of SP suppression may require re-examination.