Neutrophil infiltration of the chorioamnion-decidua tissue at the maternal-fetal interface (chorioamnionitis) is a leading cause of prematurity, fetal inflammation, and perinatal mortality. We induced chorioamnionitis in preterm rhesus macaques by intraamniotic injection of LPS. Here, we show that, during chorioamnionitis, the amnion upregulated phospho-IRAK1-expressed neutrophil chemoattractants CXCL8 and CSF3 in an IL-1-dependent manner. IL-1R blockade decreased chorio-decidua neutrophil accumulation, neutrophil activation, and IL-6 and prostaglandin E2 concentrations in the amniotic fluid. Neutrophils accumulating in the chorio-decidua had increased survival mediated by BCL2A1, and IL-1R blockade also decreased BCL2A1+ chorio-decidua neutrophils. Readouts for inflammation in a cohort of women with preterm delivery and chorioamnionitis were similar to findings in the rhesus macaques. IL-1 is a potential therapeutic target for chorioamnionitis and associated morbidities.

Chorioamnionitis is associated with preterm labor and fetal inflammatory response syndrome (FIRS), causing fetal organ injury and morbidity particularly in extremely premature infants. However, the effects of inflammation on the fetal immune system remain poorly understood, due to the difficulty of studying immune development in infants. Therefore, we used the model of intra-amniotic (IA) LPS administered at ~80% gestation in rhesus monkeys to cause chorioamnionitis and FIRS that is similar in human pathology. Importantly, the frequency of IL-17+ and IL-22+ CD4+ T-cells increased in the spleen of LPS-exposed fetuses, while Treg frequency decreased. These changes persisted for at least 48h. Notably, Th17 cytokines were predominantly expressed by FoxP3+CD4+ T-cells and not by their FoxP3− counterparts. Bi-functional IL17+FoxP3+ exhibited a phenotype of inflammatory Treg (RORcHigh/+, HeliosLow/−, IL-2+, IFNγ+ and IL-8+) compared to typical FoxP3+ cells. Diminished splenic Treg frequency in LPS-exposed fetuses was associated with inadequate Treg generation in the thymus. Mechanistically, the emergence of inflammatory Treg was largely dependent on IL-1 signaling. However, blockage of IL-1R signaling did not abolish the deleterious effects of LPS on Treg frequency in the thymus or spleen. Collectively, we demonstrate that a prenatal inflammatory environment leads to inadequate Treg generation in the thymus with a switch of splenic Treg towards an inflammatory phenotype. Both processes likely contribute to the pathogenesis of chorioamnionitis. Approaches to manipulate Treg numbers and function could thus be useful therapeutically to alleviate FIRS in preterm infants.

Accumulation of activated neutrophils at the feto-maternal interface is a defining hallmark of intrauterine inflammation (IUI) that might trigger an excessive immune response during pregnancy. Mechanisms responsible of this massive neutrophil recruitment are poorly investigated. We have previously showed that intraamniotic injection of LPS in rhesus macaques induced a neutrophil predominant inflammatory response similar to that seen in human IUI. Here, we demonstrate that anti-TNF antibody (Adalimumab) inhibited ∼80% of genes induced by LPS involved in inflammatory signaling and innate immunity in chorio-decidua neutrophils. Consistent with the gene expression data, TNF-blockade decreased LPS-induced neutrophil accumulation and activation at the feto-maternal interface. We also observed a reduction in IL-6 and other pro-inflammatory cytokines but not prostaglandins concentrations in the amniotic fluid. Moreover, TNF-blockade decreased mRNA expression of inflammatory cytokines in the chorio-decidua but not in the uterus, suggesting that inhibition of TNF-signaling decreased the inflammation in a tissue-specific manner within the uterine compartment. Taken together, our results demonstrate a predominant role for TNF-signaling in modulating the neutrophilic infiltration at the feto-maternal interface during IUI and suggest that blockade of TNF-signaling could be considered as a therapeutic approach for IUI, the major leading cause of preterm birth.