Regulation of the immune response to Candida albicans by monocytes and progesterone

Recurrent vaginal infections caused by Candida albicans are associated with decreased cell-mediated immune responses. We report that circulating progesterone levels and variations between persons in the activity of their monocytes are two of the factors that influence the extent of lymphocyte proliferation in response to C. albicans. With the use of peripheral blood mononuclear cells from five men and four women, removal of the monocytes increased the lymphocyte response to C. albicans antigens in eight persons. The percentage increase in proliferation was inversely proportional to the proliferative response observed when the monocytes were present, suggesting that differences existed between persons in the ability of their monocytes to down regulate the response. An approximate 50% decrease in C. albicans-induced lymphocyte proliferation was observed in the presence of luteal-phase levels (25 ng/ml), as opposed to proliferative-phase levels (0.15 ng/ml) of progesterone. Monocyte removal obviated the ability of 25 ng/ml progesterone to inhibit this response, suggesting that progesterone inhibited lymphocyte proliferation through a monocyte-dependent mechanism. Thus fluctuations in a woman's monocyte activity in response to genetic, hormonal, or environmental factors may influence her ability to mount an effective cell-mediated immune response to C. albicans.