Introduction: In pregnancy, maternal T-cells express less inflammatory cytokines and this is regulated via suppression of the transcription factor NF-κB (p65). Fas activation can induce degradation of p65. Placental exosomes are present in maternal plasma and are FasL+. We have shown that pregnant plasma can induce p65 suppression in T-cells from non-pregnant women. In this study we aim to determine whether the suppression of inflammatory cytokine production in T-cells in pregnancy is mediated via Fas/FasL interactions and whether the source of FasL is placentally derived.
Methods/Results: Using flow cytometry Fas expression was shown to increase in circulating T-cells during pregnancy relative to non-pregnant controls. Jurkat T-cells express high levels of Fas and stimulation with PMA and ionomycin (P/I) results in an increased production of IFNγ and IL-2 mRNA. In contrast, activation of Fas using the Fas activating antibody CH11 prior to P/I stimulation resulted in suppressed p65 expression and an inability to induce IFNγ and IL-2. Fas expression on Jurkat T-cells was reduced by ~50% using Fas siRNAs. Reduced Fas expression resulted in an inability of these cells to respond to CH11. Levels of p65 remained high which resulted in transfected cells producing IFNγ and IL-2 mRNA in response to P/I stimulation. The source of p65 suppression is placental, we isolated exosomes from maternal plasma by ultracentrifugation and subsequent purification on a sucrose gradient and demonstrated that only fractions containing FasL+ exosomes were able to suppress p65 in Jurkat T-cells.
Conclusion: Our data suggest that Fas/FasL interactions regulate the level of p65 expression in maternal T-cells throughout pregnancy, and ultimately inflammatory cytokine production. The amount of Fas expressed on maternal T-cells and the abundance of FasL placental exosomes in maternal circulation will dictate the ability of T-cells to alter the cytokine environment to a favorable one for pregnancy success.