NF‐κB‐regulated suppression of T‐bet in T cells represses Th1 immune responses in pregnancy

The molecular mechanisms that suppress Th1 immune responses in pregnancy are unknown. We assessed the expression of the Th1 cytokine transcription factor T‐bet. We isolated PBMC and T cells from non‐pregnant and pregnant women and demonstrated that T‐bet is specifically down‐regulated in pregnancy under basal and stimulated conditions. Low levels of T‐bet protein were detected in the nuclear fraction of unstimulated PBMC from non‐pregnant, but not pregnant women. Nuclear levels of T‐bet increased in response to PMA/ionomycin in PBMC from non‐pregnant, but not pregnant women. T‐bet expression was greater in whole cell lysates of stimulated CD3+ T cells from non‐pregnant relative to pregnant women. NF‐κB is specifically down‐regulated in T cells in pregnant women, resulting in suppressed expression of Th1 cytokines IL‐2, IFN‐γ and TNF‐α. In this study, down‐regulation of NF‐κB also resulted in diminished expression of T‐bet. PMA induces NF‐κB translocation, T‐bet expression and IL‐2, IFN‐γ and TNF‐α production. Conversely, pre‐incubation with SN50, and NF‐κB oligodeoxyribonucleotide decoys suppressed PMA‐induced NF‐κB translocation and gene transcription, respectively, resulting in diminished T‐bet expression and Th1 cytokine production. Therefore, maintenance of the cytokine environment for pregnancy success is mediated via strict regulation of Th1 immune responses, more specifically through control of NF‐κB and T‐bet transcription.