Age/sex dependent and non-monotonous dose-response effect of diethylstilbestrol on the immune functions in mice

High amounts of estrogens are known to suppress immune functions in both human and animal models. Our supportive data is that the immune functions were activated by gonadectomy in young adults mice. However, recent reports indicate that estrogen is required for the normal development of thymus. These findings lead us to an assumption that sex hormone status induces much more complex effects on immune functions depending on the host age/sex and dose ranges. Here, low doses of DES (diet containing 0.4 or 4.0 microg/kg diet) were given for 2 months to young adult and aged C57BL/6 mice, and thymic and splenic parameters including flow-cytometric subpopulation analyses, mitogenic responses and NK activity were monitored. This study revealed that the low dose effects of exogenous estrogen are strongly dependent on the age and sex of the recipients and many parameters show non-monotonous dose response effect. In conclusion, effect of exogenous estrogens on immune functions should be assessed for all age and sex, and in expectation of non-monotonous dose-response relationship.