Reproductive Immunology – an Update

Pregnancy is one of the most challenging experiences for the immune system. It entails the confrontation and cooperation of maternal cells with allogeneic (sperm) and semi-allogeneic (fetal) cells and factors. On the one hand, it must actively acquire a specific tolerance towards the foreign cells and organism (the fetus) to avoid harming reactions, while recognizing the very same to support and control their development and growth. On the other hand, the immune system simultaneously may not reduce its capability to defend mother and fetus from microorganisms and pathogens. Almost all branches of the immune system are claimed to react and adapt in order to fulfill these complex duties. In this review, current knowledge concerning the most important cellular and soluble immunological components in the decidua is presented. Special regards are made to decidual NK, T and dendritic cells as well as to trophoblast cells, representing the fetal counterpart of most bilateral interactions. Furthermore, the role and functions of soluble factors, including HLA-G, PIBF, IDO and a variety of cytokines, are described.