Membrane progesterone receptors in human regulatory T cells: a reality in pregnancy.

<bold>Objective: </bold>To provide evidence of the existence of membrane progesterone receptor alpha (mPRα) on regulatory T cells (Treg) in peripheral blood during pregnancy, postulating a possible explanation for the effect of progesterone on preterm birth.<bold>Design: </bold>Cross-sectional study.<bold>Setting: </bold>Tertiary Obstetric Department in a University Hospital.<bold>Population: </bold>Healthy pregnant women.<bold>Methods: </bold>Treg cells from peripheral blood samples were studied by flow cytometry using multiple monoclonal antibody expression.<bold>Main Outcome Measures: </bold>Evaluate the number and percentage of CD4(+) CD25(high) CD127(low) , the number and percentage of Treg cells among the total CD4(+) T cells, and the percentage and mean fluorescence intensity (MFI) of mPRα in that population, using several gating strategies.<bold>Results: </bold>43 peripheral blood samples were collected from healthy women during pregnancy, whose median gestational age was 28.7 ± 7.1 (16-40) weeks. The percentage of CD4(+) in the total lymphocytes was 43% (32-51) and the percentage of CD4(+) CD25(high) CD127(low) was 4.8% (1.6-5.9), with only 45% (16-72) of those cells expressing the intracellular marker FoxP3 (Treg cell pool). We confirmed the existence of mPRα in that specific population because 8.0% (2.02-33) of the Treg cells were marked with the specific monoclonal antibody, with an mPRα(+) MFI of 719 (590-1471).<bold>Conclusions: </bold>This research shows that Treg cells express mPRα during pregnancy, which might play an important role in immune modulation by progesterone. [ABSTRACT FROM AUTHOR]