A Phenotypic Analysis of Regulatory T Cells and Uterine NK Cells from First Trimester Pregnancies and Associations with HLA-G

Problem The prevalence of regulatory T cells and NK cells expressing activation and HLA-G receptors, and the influence of in vivo sHLA-G and mHLAG on HLA-G receptors expressed by NK cells in the uterine compartment is unclear. Method of study KIR2DL4 and/or ILT2 expression on regulatory T cells and NK cells from the placental bed and peripheral blood in first trimester was assessed using flow cytometry. Expression of mHLA-G on trophoblast cells and sHLA-G in 'uterine' and peripheral blood was determined with ELISA and flow cytometry, and specific associations with expression levels of cognate receptors or activation markers on immune cells were determined. Results In the placental bed, CD45RA surface expression on Tregs was similar to peripheral Tregs in pregnant women, but T cells with lower CD4 and CD8 expression were accumulated. HLA-G receptor expression was increased on NK cells from 'uterine blood'. Soluble HLA-G was significantly increased in 'uterine blood' compared with peripheral blood, but no correlation was found between sHLA-G and mHLA-G in the uterine compartment. A correlation was found between sHLA-G and the fraction of KIR2DL4-positive NK cells in the uterine compartment, and a tendency was observed between mHLA-G and the fraction of ILT2-positive NK cells in the uterine compartment. Conclusion The NK subset in the placental bed displays a unique phenotype that may be influenced by mHLA-G on trophoblast cells and locally accumulated sHLA-G in the uterus.