Human semen inhibits T rosette formation through an opiate mediated mechanism.

Seminal plasma contains high levels of opioid peptides and both seminal plasma and endogenous opioids can influence the immune system. In order to investigate whether these two findings can be related, semen was collected from 7 normal subjects, and assayed for beta-endorphin content and for its in vitro ability to inhibit the total T rosette formation of human lymphocytes in the presence or in the absence of 10(-6) M naloxone, an universal opiate antagonist. The results were as follows: 1) immunoreactive beta-endorphin content in seminal plasma was 4 to 12 times higher than the peripheral plasma levels detected in the same subjects (76.1 +/- 42.1 SD vs 10.5 +/- 2.0 SD pg/ml); 2) increasing concentrations of seminal plasma (1%, 5%, and 10%) in RPMI 1640 significantly depressed the T rosette formation ability of lymphocytes; and 3) the simultaneous addition to the incubation mixture of 10(-6) M naloxone prevented the phenomenon, while naloxone per se was ineffective. The possibility that endogenous opioids may play a role in the immunomodulatory action of human semen is suggested.