The upper and lower respiratory tract microbiome in severe aspiration pneumonia.

Uncertainty persists whether anaerobic bacteria represent important pathogens in aspiration pneumonia. In a nested case-control study of mechanically ventilated patients classified as macro-aspiration pneumonia (MAsP, n = 56), non-macro-aspiration pneumonia (NonMAsP, n = 91), and uninfected controls (n = 11), we profiled upper (URT) and lower respiratory tract (LRT) microbiota with bacterial 16S rRNA gene sequencing, measured plasma host-response biomarkers, analyzed bacterial communities by diversity and oxygen requirements, and performed unsupervised clustering with Dirichlet Multinomial Models (DMM). MAsP and NonMAsP patients had indistinguishable microbiota profiles by alpha diversity and oxygen requirements with similar host-response profiles and 60-day survival. Unsupervised DMM clusters revealed distinct bacterial clusters in the URT and LRT, with low-diversity clusters enriched for facultative anaerobes and typical pathogens, associated with higher plasma levels of SPD and sCD14 and worse 60-day survival. The predictive inter-patient variability in these bacterial profiles highlights the importance of microbiome study in patient sub-phenotyping and precision medicine approaches for severe pneumonia.

Surfactant Protein D Influences Mortality During Abdominal Sepsis by Facilitating Escherichia coli Colonization in the Gut.

Determine the role of surfactant protein D (SPD) in sepsis. DESIGN: Murine in vivo study. SETTING: Research laboratory at an academic medical center. PATIENTS: SPD knockout (SPD-/-) and wild-type (SPD+/+) mice. INTERVENTIONS: SPD-/- and SPD+/+ mice were subjected to cecal ligation and puncture (CLP). After CLP, Escherichia coli bacteremia was assessed in both groups. Cecal contents from both groups were cultured to assess for colonization by E. coli. To control for parental effects on the microbiome, SPD-/- and SPD+/+ mice were bred from heterozygous parents, and levels of E. coli in their ceca were measured. Gut segments were harvested from mice, and SPD protein expression was measured by Western blot. SPD-/- mice were gavaged with green fluorescent protein, expressing E. coli and recombinant SPD (rSPD). MEASUREMENTS AND MAIN RESULTS: SPD-/- mice had decreased mortality and decreased E. coli bacteremia compared with SPD+/+ mice following CLP. At baseline, SPD-/- mice had decreased E. coli in their cecal flora. When SPD-/- and SPD+/+ mice were bred from heterozygous parents and then separated after weaning, less E. coli was cultured from the ceca of SPD-/- mice. E. coli gut colonization was increased by gavage of rSPD in SPD-/- mice. The source of enteric SPD in SPD+/+ mice was the gallbladder. CONCLUSIONS: Enteral SPD exacerbates mortality after CLP by facilitating colonization of the mouse gut with E. coli.

mTORC1 is a mechanosensor that regulates surfactant function and lung compliance during ventilator-induced lung injury.

The acute respiratory distress syndrome (ARDS) is a highly lethal condition that impairs lung function and causes respiratory failure. Mechanical ventilation (MV) maintains gas exchange in patients with ARDS but exposes lung cells to physical forces that exacerbate injury. Our data demonstrate that mTOR complex 1 (mTORC1) is a mechanosensor in lung epithelial cells and that activation of this pathway during MV impairs lung function. We found that mTORC1 is activated in lung epithelial cells following volutrauma and atelectrauma in mice and humanized in vitro models of the lung microenvironment. mTORC1 is also activated in lung tissue of mechanically ventilated patients with ARDS. Deletion of Tsc2, a negative regulator of mTORC1, in epithelial cells impairs lung compliance during MV. Conversely, treatment with rapamycin at the time MV is initiated improves lung compliance without altering lung inflammation or barrier permeability. mTORC1 inhibition mitigates physiologic lung injury by preventing surfactant dysfunction during MV. Our data demonstrate that, in contrast to canonical mTORC1 activation under favorable growth conditions, activation of mTORC1 during MV exacerbates lung injury and inhibition of this pathway may be a novel therapeutic target to mitigate ventilator-induced lung injury during ARDS.

Post-sepsis immunosuppression depends on NKT cell regulation of mTOR/IFN-γ in NK cells.

As treatment of the early, inflammatory phase of sepsis improves, post-sepsis immunosuppression and secondary infection have increased in importance. How early inflammation drives immunosuppression remains unclear. Although IFN-γ typically helps microbial clearance, we found that increased plasma IFN-γ in early clinical sepsis was associated with the later development of secondary Candida infection. Consistent with this observation, we found that exogenous IFN-γ suppressed macrophage phagocytosis of zymosan in vivo, and antibody blockade of IFN-γ after endotoxemia improved survival of secondary candidemia. Transcriptomic analysis of innate lymphocytes during endotoxemia suggested that NKT cells drove IFN-γ production by NK cells via mTORC1. Activation of invariant NKT (iNKT) cells with glycolipid antigen drove immunosuppression. Deletion of iNKT cells in Cd1d-/- mice or inhibition of mTOR by rapamycin reduced immunosuppression and susceptibility to secondary Candida infection. Thus, although rapamycin is typically an immunosuppressive medication, in the context of sepsis, rapamycin has the opposite effect. These results implicated an NKT cell/mTOR/IFN-γ axis in immunosuppression following endotoxemia or sepsis. In summary, in vivo iNKT cells activated mTORC1 in NK cells to produce IFN-γ, which worsened macrophage phagocytosis, clearance of secondary Candida infection, and mortality.