A potent myeloid response is rapidly activated in the lungs of premature Rhesus macaques exposed to intra-uterine inflammation

Abstract

Intrauterine inflammation/infection (IUI), which is present in up to 40% of premature births, leads to elevated levels of pro-inflammatory mediators and microbial products within the amniotic fluid, which come in close contact to fetal mucosae. Yet, knowledge on the fetal mucosal responses to IUI exposure remains limited. To address these questions, we used a non-human primate model of IUI, in which pregnant Rhesus macaques received intra-amniotic (IA) LPS, compared with IA saline.We found that IA LPS exposure induced a robust and rapid inflammation of the fetal lung, but not the intestine. This inflammatory response was characterized by high levels of pro-inflammatory cytokines in the lung and the alveolar wash, and a potent myeloid cell response, dominated by neutrophils and monocytes/macrophages. scRNAseq analyses of fetal lungs showed that the infiltrating (neutrophils and inflammatory monocytes) and the resident (alveolar and interstitial macrophages) myeloid cells exhibited transcriptional profiles consistent with exposure to TLR ligands, as well as to cytokines, notably IL-1 and TNFα. However, blocking IL-1 signaling or TNFα, alone or simultaneously by administering inhibitors intra-amniotically and subcutaneously to the dam only partially blunted fetal lung inflammation.Together, our novel data indicate that the fetal innate immune system can mount a rapid multi-factorial mucosal innate response to IUI, responding both to direct signaling by bacterial products and to indirect cytokine-mediated pathways of activation. These data thus provide more mechanistic insights into the association between IUI exposure and the post-natal lung morbidities of the premature infant.

Inflammatory blockade prevents injury to the developing pulmonary gas exchange surface in preterm primates

“…These results demonstrate that the combination of IL1 and TNF blockade is sufficient to prevent severe lung injury in experimental chorioamnionitis, despite continued cellular recruitment of immune cells and significant levels of inflammatory cytokines in the BAL 41 . We therefore hypothesized that blockade may reduce inflammatory activation of resident stromal and immune cells in the lung, preventing secondary injury to lung structure.…”

“…In order to model fetal chorioamnionitis, we treated Rhesus fetuses at GD130 with intra-amniotic injection of endotoxin/lipopolysaccharide (LPS), an injury that has been shown to mimic the inflammation present during chorioamnionitis in prenatal mouse, rabbit, pig, and sheep 32,33,39,40 , as well as Rhesus macaque in prior studies from our group 33,39,40 . LPS robustly induced IL1b, TNFa, and IL-6 after 16h in both lung tissue and alveolar wash in Rhesus 39,41 and led to rapid infiltration and activation of neutrophils and myeloid cells in the fetal Rhesus lung 41 . A detailed evaluation of the inflammatory state of the chorioamnionitis lung in Rhesus macaques is reported seperately 41 .…”

“…LPS robustly induced IL1b, TNFa, and IL-6 after 16h in both lung tissue and alveolar wash in Rhesus 39,41 and led to rapid infiltration and activation of neutrophils and myeloid cells in the fetal Rhesus lung 41 . A detailed evaluation of the inflammatory state of the chorioamnionitis lung in Rhesus macaques is reported seperately 41 . Here, we evaluated the hypothesis that this inflammatory milieu would directly impair the developmental progression of the Rhesus lung.…”

“…We treated pregnant Rhesus dams with anakinra (100mg, Kineret, SOBI), a potent IL1 receptor antagonist, and adalimumab (40mg, Humira, AbbVie Inc), an anti-TNF monoclonal antibody, by subcutaneous injection 3h prior to LPS exposure, and by intraamniotic injection (anakinra 50mg and adalimumab 40mg) 1h prior to LPS treatment (Figure 4A). This combination blockade did not reduce either myeloid or neutrophil accumulation in the lung compared to LPS, but modestly reduced inflammatory cytokine levels in the BAL of treated animals and the expression of TLR, IL1, and TNF response pathways in several immune lineages (finding detailed in 41 ). Despite these modest changes, inflammatory blockade provided remarkable protection to lung alveoli (Figure 4B-S).…”

“…Fetal immunity is carefully balanced to provide protection from pathogens while also allowing development of tolerance and colonization of microbiota. Extensive data from human studies, and our companion report on Rhesus immune development 41 , shows that chorioamnionitis disrupts this immune development 32,33 . Clinical chorioamnionitis is typically treated with antimicrobials, which also have unintended but significant impacts on immune development 82,83 .…”