Marilen Benner

CHAPTER 6 164 Endometrium Uterine cavity PSA Bacteroides Antimicrobial peptides APC naive T cell Treg cell Th17 cell NK cell PRR Niche competition with pathogenic species Defense against pathogens IL-10 Induction of cell types and cytokines needed for fertility Tissue adaptation, vascularization Endometrium suited for blastocyst implantation and healthy placentation Commensal colonization of the uterus Figure 2. Uterine microbiota may contribute to healthy endometrium physiology. Upon pathogen recognition receptor (PRR) stimulation, epithelial cells release soluble factors such as cytokines affecting local lymphocyte populations. If bacteria are naturally present in the uterus, similar interaction with host cells as seen in mucosa of the gut can be envisioned. Local lymphocytes e.g. antigen presenting cells (APCs) could sense microbes by probing through the epithelia or upon barrier breach initiating a signaling cascade. Presence of commensals might alter the mucosal T cell balance and the involved cytokines can have an effect on the local immune environment. Cells important for healthy implantation and placentation such as uterine natural killer (NK) cells are potentially affected. Therefore colonization might have an impact on important initial steps of endometrial physiology. APC, antigen presenting cell; IL-10, interleukin 10; NK cell, natural killer cell; PSA, Polysaccharide A; PRR, pattern recognition receptor; Th17, T helper 17 cells; Treg, regulatory T cell.