Marilen Benner

CHAPTER 8 230 meets the eye. The endometrium forms the basis for all immune adaptations occurring upon initiation of pregnancy. If dysregulated, complications like pregnancy loss, PE, and IUGR can arise. Pregnancy is accompanied by a general increase in a memory phenotype of T cells and B cells, and shifts in their respective subsets. Both key players of adaptive immunity influence the local immune environment, through direct suppressive effects, or cytokine secretion. Ultimately, reproductive immunology demands complex regulatory mechanisms allowing for trophoblast invasion, whilst maintaining reactivity towards infectious threats. We showed that Treg and B cells contribute to this intricate balance. Local differentiation or modification equips uterine immune cells for their pregnancy-specific regulatory tasks. Natural colonization by a uterine microbiome can influence these delicate interactions needed for implantation, progression of pregnancy, and development of a healthy child. M i c r o b i o m e E n d o m e t r i u m U t e r i n e i m m u n i t y H o r m o n e s F e m a l e c y c l e Receptive window Infertility, implantation failure, miscarriage, preeclampsia Fertility & healthy pregnancy Figure 1. Interacting mechanisms direct uterine health. Only correctly orchestrated conditions allow for conception and healthy pregnancy. The presented data underline the extraordinary characteristics of uterine immune cells, in absence of, or during, pregnancy. These investigations are challenging to model in vitro when using readily accessible sources of lymphocytes. No cell lines are available that are identical to