Delineation between T and B suppressive molecules from human seminal plasma: II. Spermine is the major suppressor of T-lymphocytes in vitro.

The nature of the human semen T-suppressor was investigated in vitro on human lymphocyte proliferations induced by phytohemagglutinin (PHA) or by alloantigens. Purification by ion-exchange chromatography, followed by butanol extraction, showed this factor to be present only in the polyamine-containing fractions. The purified product, obtained by preparative thin-layer electrophoresis, contained almost exclusively spermine and exhibited the same suppressive activity as this polyamine. Human T-lymphocyte suppression occurred in the presence of fetal calf serum, but it did not occur in a serum-free medium. No suppression was observed after preincubation of the fetal calf serum with hydroxylamine, a spermine oxidase inhibitor, whereas a nondialyzable fraction, from normal human serum, decreased the suppression. The semen factor did not act by direct cytotoxicity, as there was no effect of preincubation and suppression could be induced only within the first 6 hr of mitogen activation. These data demonstrate that the in vitro T-suppressive activity of semen can be assigned mainly to spermine and show that in vivo this suppression must require locally the presence of a spermine oxidase or related enzyme.