Effects of Antenatal Colonization with Ureaplasma urealyticum on Pulmonary Disease in the Immature Baboon

Abstract

Current nonhuman models for bronchopulmonary dysplasia have not included perinatal infection. We studied the effects of antenatal Ureaplasma urealyticum (Uu) infection in the 125-d immature baboon. Ten 125-d gestation (term = 185 d) baboon dams were delivered after intra-amniotic inoculation with Uu. Serial blood and tracheal aspirate samples were analyzed for Uu colony-forming units, IL-6, IL-8, and cell counts. Physiologic parameters were serially recorded. Lung histology was examined after 14 d of ventilation and compared with unexposed controls. All Uu-exposed animals had >4 × 102 CFU in tracheal aspirate at 24 h. Four of nine Uu animals remained heavily colonized [(+) Uu] at necropsy (>6 × 103). Five animals had negative or low tracheal colony-forming units. All Uu animals had significant increases for white blood cells, IL-6, and IL-8 in amniotic and fetal lung fluid. Compared with controls, (+) Uu animals had significantly higher fraction of inspired oxygen, airway pressures, oxygenation index, and ventilation efficiency index between 48 and 240 h and had significantly elevated tracheal IL-6 and IL-8 concentrations between 72 and 240 h. Compared with controls (-) Uu animals had significantly better oxygenation index and ventilation efficiency index scores between 48 and 144 h. Lung histopathology in both Uu groups showed more severe bronchiolitis and interstitial pneumonitis compared with controls. Two patterns of disease were observed after Uu perinatal infection. Persistent colonization manifested a picture consistent with acute pneumonitis, worse lung function from 2 to 10 d, and prolonged elevated tracheal cytokines. Colonized animals that subsequently cleared Uu from the lung demonstrated early improved lung function compared with unexposed controls yet still manifested mixed bronchiolitis and interstitial pneumonitis at necropsy. Inherent immune system responses may determine outcome of perinatal Ureaplasma colonization.