Progesterone inhibits glucocorticoid-induced murine thymocyte apoptosis

Sex and sex hormones modulate immune development and responses. A primary t arget of their effects is the structure and cellularity of the thymus; ther efore, we examined the effects of sex and sex steroids on thymocyte apoptos is. We demonstrate initially that male DBA mice have a significantly higher percentage of glucocorticoid-induced apoptotic thymocytes (46.1 +/- 3.8%) than their female counterparts (31.6 +/- 3.1%; P = 0.012). We postulated th at this gender difference was due to differential modulation of glucocortic oid-induced apoptosis by sex hormones such as estrogen, testosterone or pro gesterone. Both estrogen and testosterone increased in vitro thymocyte apop tosis. In contrast, progesterone not only inhibited spontaneous in vitro th ymocyte apoptosis, but also prevented in vitro glucocorticoid-induced apopt osis. Progesterone administration also suppressed glucocorticoid-induced in vivo thymocyte apoptosis. These results suggest that anti-apoptotic effect s of progesterone may influence T cell development and subsequent immune re sponses. (C) 2000 International Society for Immunopharmacology. Published b y Elsevier Science Ltd. All rights reserved.