In pregnancy, the decidua is infiltrated by leukocytes promoting fetal development without causing immunological rejection. Murine regulatory T (Treg) cells are known to be important immune regulators at this site. The aim of the study was to characterize the phenotype and origin of Treg cells and determine the quantitative relationship between Treg, T-helper type 1 (TH1), TH2, and TH17 cells in first-trimester human decidua. Blood and decidual CD4 T cells from 18 healthy first-trimester pregnant women were analyzed for expression of Treg-cell markers (CD25, FOXP3, CD127, CTLA4, and human leukocyte antigen-DR [HLA-DR]), chemokine receptors (CCR4, CCR6, and CXCR3), and the proliferation antigen MKI67 by six-color flow cytometry. Treg cells were significantly enriched in decidua and displayed a more homogenous suppressive phenotype with more frequent expression of FOXP3, HLA-DR, and CTLA4 than in blood. More decidual Treg cells expressed MKI67, possibly explaining their enrichment at the fetal-maternal interface. Using chemokine receptor expression profiles of CCR4, CCR6, and CXCR3 as markers for TH1, TH2, and TH17 cells, we showed that TH17 cells were nearly absent in decidua, whereas TH2-cell frequencies were similar in blood and decidua. CCR6 TH1 cells, reported to secrete high levels of interferon gamma (IFNG), were fewer, whereas the moderately IFNG-secreting CCR6− TH1 cells were more frequent in decidua compared with blood. Our results point toward local expansion of Treg cells and low occurrence of TH17 cells. Furthermore, local, moderate TH1 activity seems to be a part of normal early pregnancy, consistent with a mild inflammatory environment controlled by Treg cells.
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Vol. 82 • No. 4