Progesterone-induced Blocking Factor Increases the Frequency of Foxp3+CD4+CD25+ Regulatory T Cells in Human Peripheral Blood.

BACKGROUND: Pregnancy is a unique immunological state in which the semi-allogeneic fetus must be tolerated by the maternal immune system. Progesterone-induced blocking factor (PIBF) contributes to sustaining this immune balance through its regulatory effects, particularly those involving CD25⁺ T cells and maternal immune tolerance mechanisms. OBJECTIVE: To investigate whether PIBF influences the proportion of Foxp3+ cells among activated human peripheral CD4+ CD25+ T cells. METHODS: We isolated peripheral blood mononuclear cells (PBMCs) were isolated from 15 healthy women of reproductive-age, all sampled during the follicular phase of their menstrual cycles. The cells were stimulated with anti-CD3, anti-CD28 and IL-2 and cultured for 5 days in the presence or absence of PIBF at concentrations of 200 or 1000 ng/mL. The proportion of CD4+CD25+Foxp3+T cells was quantified by flow cytometry. RESULTS: Treatment with PIBF increased the percentage of CD4+CD25+Foxp3+ T cells compared with untreated controls (mean ± SE: control 2.7 ± 1.18%; PIBF 200 ng/mL 3.05 ± 1.06%, p = 0.008; PIBF 1000 ng/mL 3.50 ± 1.39%, p = 0.002). Although the increases were significant relative to the control group, no clear dose‑dependent trend was observed between the two PIBF concentrations. No adverse effects on cell viability were detected under the experimental conditions. CONCLUSION: In vitro treatment of activated human peripheral CD4+CD25+ T cells with PIBF increased the percentage of Foxp3+ cells, suggesting that PIBF may promote regulatory T cell phenotypes in the context of maternal-fetal tolerance.