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.