Marilen Benner

CHAPTER 2 32 The decidual immune environment is marked by a tolerance signature The fetal-maternal interface is the major site where maternal immune cells come into contact with cells of fetal origin. Treg are important for regulation of the decidual immune environment and pregnancy success (19). DPMC contained significantly more CD4 + CD25 high CD127 - Treg than MMC (9.5%±3.5% versus 5.2%±1.9%) (Figure 3b). We further subdivided Treg based on expression of CD45RA andCD25 (36). DPMCcontained significantlymoreCD4 + CD25 high CD45RA - activated and differentiated Treg than MMC (8.4%±5.9% versus 2.4%±1.6%), while the percentage of CD4 + CD25 + CD45RA + naive Treg did not differ significantly (1.3%±1.2% versus 1.9%±1.3%) (Figure 3c). Treg percentages in MMC did not differ from PBMC, but DPMC contained significantly less naive Treg compared to PBMC (1.3%±1.2% versus 3.4%±2.0%). This suggests, that different from the pre-implantation endometrium, the human decidual environment is marked by a immune signature that includes the activation and differentiation of Treg. Figure 3. Distribution of regulatory T cells. (A) Representative staining of CD25, CD127, and CD45RA on CD4+ T cells from peripheral blood (PBMC, n=17), menstrual blood (MMC, n=16), and term decidua (DPMC, n=12). (B) Percentage of CD25highCD127- Treg within CD4+ T cells in PBMC, MMC, and DPMC. (C) Distribution of naive Treg (CD45RA+CD25+) and differentiated Treg (CD45RACD25++) in CD4+ T cells. **p < 0.01, and ***p < 0.001 (lines indicate mean, non-parametric Kruskal-Wallis with Dunns post-hoc test).