Suppression of lymphocyte mitogenesis by tamoxifen.

Tamoxifen (at 0.1-1 microM concentrations) inhibited significantly the response of rat spleen cells to phytohemagglutinin, concanavalin A, pokeweed mitogen and lipid A in a dose-dependent manner. To achieve this inhibition, it was sufficient to expose the lymphocytes for 4 h to tamoxifen prior to mitogenic stimulation. Estradiol did not have a consistent effect on lymphocyte mitogenesis under the same conditions and did not modify the suppressive effect of tamoxifen, even when the lymphocytes were treated first with estradiol followed by tamoxifen. It is suggested that the inhibitory effect of tamoxifen on these in vitro lymphocyte reactions is not mediated by the estrogen receptor.