Cellular and molecular dynamics in the lungs of neonatal and juvenile mice in response to E. coli

Bacterial pneumonias cause significantly higher morbidity and mortality in neonates compared to other age groups. To understand the immune mechanisms that underlie these age-related differences, we employed a mouse model of E. coli pneumonia to examine cellular and molecular dynamics in immune responsiveness in neonates (PND 3-5) and juveniles (PND 12-18) at 24, 48, and 72 hours. Cytokine gene expression from whole lung extracts was quantified using qRT-PCR. E. coli challenge resulted in rapid and significant increases in neutrophils, monocytes, and yδT cells and significant decreases in dendritic cells and alveolar macrophages for both neonates and juveniles. Juveniles had significant increases in interstitial macrophages and recruited monocytes that were not observed in neonatal lungs. Expression of IFNγ-responsive genes were positively correlated with the levels and dynamics of MHCII-expressing innate cells in neonatal and juvenile lungs. Several facets of the responses of wild-type neonates was recapitulated in juvenile MHCII ^-/- juveniles. Employing a pre-clinical model of E. coli pneumonia, we identified significant differences in the early cellular and molecular dynamics in the lungs that likely contribute to the elevated susceptibility of neonates to bacterial pneumonia and could represent targets for intervention to improve respiratory outcomes and survivability of neonates.