Kelleher, M. A. | bioRxiv Science

bioRxiv2026

Choriodecidual Ureaplasma parvum infection induces fetal lung inflammation prior to intra-amniotic infection in a nonhuman primate model

Preterm birth before 28 weeks remains a leading cause of neonatal mortality and long-term morbidity. Intrauterine infection-driven chorioamnionitis is strongly associated with preterm labor, fetal inflammatory response syndrome, and neonatal lung disease. Ureaplasma species are among the most common organisms isolated in chorioamnionitis and are frequently detected in the placenta, amniotic fluid, and respiratory tract of preterm infants. Clinical and experimental data implicate Ureaplasma exposure in early lung inflammation, impaired alveolar development, and bronchopulmonary dysplasia (BPD), yet the pathogenic events preceding microbial invasion of the amniotic cavity or fetal tissues remain poorly defined. To characterize early intrauterine and fetal lung inflammatory responses to localized choriodecidual U. parvum infection, we used a chronically catheterized pregnant rhesus macaque (Macaca mulatta) model. Time-mated animals underwent surgical placement of maternal, amniotic, and choriodecidual catheters and were inoculated with low-passage U. parvum serovar 1 or vehicle control at approximately 117 days gestational age. Placenta, fetal membranes, fetal plasma, and fetal lungs were assessed by qRT-PCR, multiplex cytokine assays, immunoblotting, immunohistochemistry, and trichrome staining to evaluate inflammatory signaling, inflammasome activation, prostaglandin pathways, immune cell infiltration, fibrosis, and lung maturation markers. Choriodecidual infection was confirmed in all inoculated animals. Amniotic fluid remained culture-and PCR-negative, and fetal lungs were largely free of detectable bacterial DNA. Despite the absence of intra-amniotic infection, fetal lung cytokine profiling revealed broad pro-inflammatory activation, with elevated GM-CSF, IL-1{beta}, IL-6, IL-8, MIP-1/{beta}, MCP-1, VEGF and reduced IL-10 contrasting with a modest systemic response limited to elevated plasma IL-18. Fetal lungs showed increased immune cell infiltration, upregulation of NLRP3, PYCARD, and CASP1, and activation of SAPK/JNK and NF-{kappa}B signaling. Histopathology demonstrated increased alveolar macrophages and intra-alveolar neutrophils with minimal fibrosis. Surfactant gene expression was altered (increased SFTPA, decreased SFTPB), and elevated -SMA indicated early myofibroblast activation. Localized choriodecidual U. parvum infection induces fetal lung inflammation prior to detectable intra-amniotic infection, demonstrating that direct infection of the amniotic fluid or fetal lung is not required for the initiation of fetal pulmonary inflammation. These findings suggest that subclinical ascending infection may initiate fetal lung injury and increase susceptibility to postnatal respiratory morbidity associated with preterm birth.

physiology↗

bioRxiv2023

Fetal Membrane Inflammasome Activation by Choriodecidual Ureaplasma parvum Infection without Intra-Amniotic Infection in an NHP Model

Intrauterine infection is a significant cause of preterm labor and neonatal morbidity and mortality. Ureaplasma parvum is the micro-organism most commonly isolated from cases of preterm birth and preterm premature rupture of membranes (pPROM). However, the mechanisms during the early stages of ascending reproductive tract infection that initiate maternal-fetal inflammatory pathways, preterm birth and pPROM remain poorly understood. To examine inflammation in fetal (chorioamnionic) membranes in response to Ureaplasma parvum infection, we utilized a novel in vivo non-human primate model of early choriodecidual infection. Eight chronically catheterized pregnant rhesus macaques underwent maternal-fetal catheterization surgery at 105-112 days gestation and choriodecidual inoculation with Ureaplasma parvum (105cfu/mL of a low passaged clinical isolate, serovar 1; n=4) or saline/sterile media (Controls; n=4) starting at 115-119 days gestation, repeated every 5 days until scheduled cesarean-section at 136-140d gestation (term=167d). The average inoculation to delivery interval was 21 days and Ureaplasma infection of the amniotic fluid was undetectable by culture and PCR in all animals. Inflammatory mediators in amniotic fluid (AF) were assessed by Luminex, ELISA and multiplex assays. RNA was extracted from the chorion and amnionic membranes for single gene analysis (qRT-PCR) and protein expression was determined by Western blot and immunohistochemistry. Our NHP model of choriodecidual Ureaplasma infection, representing an early-stage ascending reproductive tract infection without microbial invasion of the amniotic cavity, resulted in increased fetal membrane protein and gene expression of MMP-9 and PTGS2, but did not result in preterm labor (no increase in uterine contractility) or increased concentrations of amniotic fluid pro-inflammatory cytokines (IL-1{beta}, IL-6, IL-8, IL-18, TNF-). However, membrane expression of inflammasome sensor molecules, NLRP3, NLRC4, AIM2 and NOD2, and the adaptor protein ASC (PYCARD) gene expression were significantly increased in the Ureaplasma group when compared to non-infected controls. Gene expression of IL-1{beta}, IL-18, the IL-18R1 receptor, CASPASE-1 and pro-CASPASE-1 protein were also increased in the fetal membranes with Ureaplasma infection. Downstream inflammatory signaling genes MYD88 was also significantly upregulated in both the amnion and chorion, along with a significant increase in NFKB in the chorion. These results demonstrate that even at the early stages of ascending reproductive tract Ureaplasma infection, activation of inflammasome complexes and pathways associated with degradation of chorioamnionic membrane integrity are present. This study therefore provides experimental evidence for the importance of the early stages of ascending Ureaplasma infection in initiating processes of pPROM and preterm labor. These findings have implications for the identification of intrauterine inflammation before microbes are detectable in the amniotic fluid (sterile inflammation) and the timing of potential treatments for preterm labor and fetal injury caused by intrauterine infection.

physiology↗