Sexually transmitted diseases (STDs) are a major worldwide health problem that compromise reproductive fecundity as well as cut short the lives of millions of men, women and children. 1,2 Despite extensive efforts, only limited success has been achieved in dealing with STDs, including herpes simplex virus type 2 (HSV-2), Chlamydia trachomatis, group B streptococcus and human immunode®ciency virus [(HIV), the causative agent of acquired immune-de®ciency syndrome (AIDS)], 3 which collectively devastate both adults and newborns. It is now well recognized that the heterosexual transmission of HIV, which is reponsible for 70±80% of the new cases identi®ed in the last 2 years, is the major route of infection worldwide. 4,5 With the identi®cation of HIV in semen and cervical secretions, 6±8 AIDS is now the major life-threatening STD. 9,10 As strategies are developed to prevent and effectively treat this growing global health problem, understanding the immune system in the female reproductive tract and the way it is regulated by the endocrine system has particular importance.The adaptive and innate immune systems are the two key branches that determine host protection throughout the female reproductive tract and at other mucosal surfaces, including the respiratory, gastrointestinal and urinary tracts. Adaptive immunity encompasses the recognition and response to antigens with resultant protection that is gradual, very speci®c and mediated through antibodies and/or T cells. In contrast, innate immune responses use non-speci®c mechanisms that are inherent, rapid and mediated by germline-encoded receptors. 11