Oxytocin both increases proliferative response of peripheral blood lymphomonocytes to phytohemagglutinin and reverses immunosuppressive estrogen activity

It has been shown that the neurohypophyseal peptide oxytocin is present in the human thymus and in vitro it can mimic interleukin (IL)-2 action in the induction of interferon-gamma production. In the present study, we tested the capacity of oxytocin to modulate the response of peripheral blood mononuclear cells (PBMCs) to phytohemagglutinin (PHA) and its ability to change the membrane expression of IL-2 receptor CD25 and the CD95 activation marker. Furthermore, whether oxytocin was able to reverse the inhibition of PBMC blastic response and CD25 expression induced by estradiol benzoate (E(2)B) was studied. Fifteen healthy women were studied with a mean age of 33.8 years, no previous pregnancies, all in the early follicular phase of the cycle with normal values of circulating estrogens. The addition of oxytocin (1x10(-10) M, 1x10(-11) M, 1x10(-12) M) significantly increased the PBMC blastic response to PHA as well as the expression of both CD25 and CD95. These results were due to interaction of oxytocin with its specific receptor since the addition of an oxytocin antagonist completely reversed the oxytocin activity. In contrast, E(2)B induced a marked decrease of PHA-stimulated PBMC cell cycle progression and CD25 expression: the inhibitory effect of E(2)B was significantly counteracted by low concentrations of oxytocin. The present results support the hypothesis that neuropeptides may act as a link in the network between the immune and the neuroendocrine systems.