Progesterone-induced blocking factor (PIBF) influences the expression of membrane progesterone receptors (mPRs) on peripheral CD4⁺ T lymphocyte cells in normal fertile females

Purpose: Progesterone-induced blocking factor (PIBF) is a protein secreted by lymphocytes exposed to progesterone (P4). P4 and PIBF have immunomodulatory effects on peripheral CD4⁺ T cells during normal pregnancy. Membrane progesterone receptors (mPRs) may correlate with the immunomodulatory properties of P4 on T cells. Variation in expression of mPRs may influence P4 regulatory performance during pregnancy. On the other hand, PIBF increases in pregnant normal women compared to women who have experienced abortion. The present study aimed to determine whether PIBF, in addition to having a direct influence on the immune system, can affect P4 performance through its effect on mPR expression. Such novel research findings demonstrate the importance of PIBF in the maintenance of pregnancy.

Methods: Isolated peripheral blood mononuclear cells (PBMCs) from 30 healthy women were stimulated with the mitogen phytohemagglutinin (PHA). Cells were either exposed to various concentrations of PIBF or had no exposure at all in a culture medium at 37 °C for 3 days. The mean fluorescence intensity (MFI) of mPRα and mPRβ was evaluated using polyclonal and monoclonal antibodies on CD4⁺ T cells.

Results: PIBF was able to significantly increase mPR expression on the surface of peripheral CD4⁺ T cells (p ≤ 0.05).

Conclusion: This study characterized the effects of PIBF on mPR expression on peripheral CD4⁺ T cells of healthy fertile women. Thus, a decrease in PIBF concentration during abnormal pregnancy can modulate mPR expression and regulatory performance of P4 on T cells. Future research into this issue is likely to open up a new understanding of the etiology of abortion.