The state of persistent estrus on Natural Killer (NK) cell activity in C57/B6 mouse strain

Estrogen has been found to suppress cell-mediated immunity in mice. Work in vitro with rat cells has indicated that estrogen suppresses the activity of NK cells. Persistent estrus in the mouse is inducible by constant light and results in constantly elevated circulating estrogen. In this study, female and male mice were then assigned to either constant light or cycling light/dark condition for 8 weeks. At the end of week 8, the animals were sacrificed when the control females were in proestrus. Cardiac blood was collected and assayed for estrogen concentration. Spleens were collected and a standard ⁵¹Cr-release cytotoxicity assay was run. The females in constant light, when compared to males in constant light or females and males in cycling light, had lower NK cell activity and higher lymphocyte count. These results suggest that persistent estrus does not affect lymphocyte count, though it does suppress NK cell activity. These results give insight into the effects of a changing endocrine environment, such as menstrual cycles and menopause, on immune function in humans.