The identification of factors in seminal plasma responsible for suppression of natural killer cell activity

We have identified two components of human seminal plasma which suppress natural killer (NK) cell activity in vitro. Dialysis and gel filtration experiments have shown both components to be of low molecular weight. The first will suppress NK cells following a short period of pretreatment, but this suppression is dependent upon the presence of bovine serum in the medium and is directly related to a loss of cell viability as measured by trypan blue dye exclusion. We suggest that this molecule is a polyamine. The second factor will not suppress NK activity following pretreatment of lymphocytes, but is a potent suppressor when added for the duration of the assay. This suppression is completely bovine serum independent, unrelated to toxicity and appears to be mediated by prostaglandin E2. The relevance of these results to a clinical situation is discussed.