Immunological and dermatological impact of progesterone

C21 steroids and especially progesterone are involved in various physiological processes besides reproduction. Langerhans cells are becoming a major topic in immunology and, from this point, it is of high interest that progesterone is able to increase the number of Langerhans cells in different epithelial cells. This has an impact for a gender specificity of HIV1 infection, and also for the high premenstrual incidence of sexually transmitted diseases. Matrix metalloproteinase activity is of high physiological importance for tissue regeneration; progesterone suppresses the expression of some members of the matrix metalloproteinase super-family and reduces the collagenolytic activity. These effects can be observed during pregnancy, but are not only apparent on the myometrium; the suppressing effect of progesterone on matrix metalloproteinases can also be observed in the skin. The dermatological aspect of this observation is discussed.