The Effects of Pregnancy on the Pulmonary Immune Response in a Mouse Model of LPS-Induced Acute Lung Injury.

OBJECTIVE: This study evaluated the effect of pregnancy on the pulmonary innate immune response in a mouse model of acute lung injury (ALI) using nebulized lipopolysaccharide (LPS). STUDY DESIGN: Pregnant (day 14) C57BL/6NCRL mice and nonpregnant controls received nebulized LPS for 15 minutes. Twenty-four hours later, mice were euthanized for tissue harvest. Analysis included blood and bronchoalveolar lavage fluid (BALF) differential cell counts, whole-lung inflammatory cytokine transcription levels by reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR), and whole-lung vascular cell adhesion molecule 1 (VCAM-1), intercellular adhesion molecule 1 (ICAM-1), and BALF albumin by western blot. Mature bone marrow neutrophils from uninjured pregnant and nonpregnant mice were examined for chemotactic response using a Boyden chamber and for cytokine response to LPS by RT-qPCR. RESULTS: In LPS-induced ALI, pregnant mice had higher BALF total cell (p < 0.001) and neutrophil counts (p < 0.001) as well as higher peripheral blood neutrophils (p < 0.01) than nonpregnant mice, but a similar increase (as compared with unexposed mice) in airspace albumin levels. Whole-lung expression of interleukin 6, tumor necrosis factor-α (TNF-α), and keratinocyte chemoattractant (CXCL1) was also similar. In vitro, marrow-derived neutrophils from pregnant and nonpregnant mice had similar chemotaxis to CXCL1 and N-formylmethionine-leucyl-phenylalanine, but neutrophils from pregnant mice expressed lower levels of TNF (p < 0.001) and CXCL1 (p < 0.01) after LPS stimulation. In uninjured mice, VCAM-1 was higher in lungs from pregnant versus nonpregnant mice (p < 0.05). CONCLUSION: In this model, pregnancy is associated with an augmented lung neutrophil response to ALI without increased capillary leak or whole-lung cytokine levels relative to the nonpregnant state. This may stem from increased peripheral blood neutrophil response and intrinsically increased expression of pulmonary vascular endothelial adhesion molecules. Differences in lung innate cell homeostasis may affect the response to inflammatory stimuli and explain severe lung disease in respiratory infection during pregnancy. KEY POINTS: · Inhalation of LPS in midgestation versus virgin mice is associated with increased neutrophilia.. · This occurs without a comparative increase in cytokine expression.. · This may be explained by pregnancy-enhanced pre-exposure expression of VCAM-1 and ICAM-1..

Storage conditions of high-fat diets affect pulmonary inflammation.

Obesity alters the risks and outcomes of inflammatory lung diseases. It is important to accurately recapitulate the obese state in animal models to understand these effects on the pathogenesis of disease. Diet-induced obesity is a commonly used model of obesity, but when applied to other disease models like acute respiratory distress syndrome, pneumonia, and asthma, it yields widely divergent. We hypothesized high-fat chow storage conditions would affect lipid oxidation and inflammatory response in the lungs of lipopolysaccharide (LPS)-challenged mice. For 6 weeks, C57BL/6crl mice were fed either a 10% (low-fat diet, LFD) or 60% (high-fat diet, HFD) stored at room temperature (RT, 23°C) for up to 7, 14, 21, or 42 days. Mice were treated with nebulized LPS to induce lung inflammation, and neutrophil levels in bronchoalveolar lavage were determined 24 h later. Lipid oxidation (malondialdehyde, MDA) was assayed by thiobarbituric acid reactive substances in chow and mouse plasma. Concentrations of MDA in chow and plasma rose in proportion to the duration of RT chow storage. Mice fed a HFD stored <2 weeks at RT had an attenuated response 24 h after LPS compared with mice fed an LFD. This effect was reversed after 2 weeks of chow storage at RT. Chow stored above freezing underwent lipid oxidation associated with significant alterations in the LPS-induced pulmonary inflammatory response. Our data show that storage conditions affect lipid peroxidation, which in turn affects pulmonary inflammatory responses in a mouse model of disease. It also suggests changes in the microbiome, although not significantly different suggests decreased variety and richness of bacteria in the gut, a large aspect of the immune system. Dietary composition and storage of chow may also affect pulmonary inflammation and the gut microbiome in humans.

Pulmonary Surfactant Promotes Virulence Gene Expression and Biofilm Formation in Klebsiella pneumoniae.

The interactions between Klebsiella pneumoniae and the host environment at the site of infection are largely unknown. Pulmonary surfactant serves as an initial point of contact for inhaled bacteria entering the lung and is thought to contain molecular cues that aid colonization and pathogenesis. To gain insight into this ecological transition, we characterized the transcriptional response of K. pneumoniae MGH 78578 to purified pulmonary surfactant. This work revealed changes within the K. pneumoniae transcriptome that likely contribute to host colonization, adaptation, and virulence in vivo Notable transcripts expressed under these conditions include genes involved in capsule synthesis, lipopolysaccharide modification, antibiotic resistance, biofilm formation, and metabolism. In addition, we tested the contributions of other surfactant-induced transcripts to K. pneumoniae survival using engineered isogenic KPPR1 deletion strains in a murine model of acute pneumonia. In these infection studies, we identified the MdtJI polyamine efflux pump and the ProU glycine betaine ABC transporter to be significant mediators of K. pneumoniae survival within the lung and confirmed previous evidence for the importance of de novo leucine synthesis to bacterial survival during infection. Finally, we determined that pulmonary surfactant promoted type 3 fimbria-mediated biofilm formation in K. pneumoniae and identified two surfactant constituents, phosphatidylcholine and cholesterol, that drive this response. This study provides novel insight into the interactions occurring between K. pneumoniae and the host at an important infection site and demonstrates the utility of purified lung surfactant preparations for dissecting host-lung pathogen interactions in vitro.

Hyperleptinemia is associated with impaired pulmonary host defense.

We have previously reported that obesity attenuates pulmonary inflammation in both patients with acute respiratory distress syndrome (ARDS) and in mouse models of the disease. We hypothesized that obesity-associated hyperleptinemia, and not body mass per se, drives attenuation of the pulmonary inflammatory response and that this e_ect could also impair the host response to pneumonia. We examined the correlation between circulating leptin levels and risk, severity, and outcome of pneumonia in 2 patient cohorts (NHANES III and ARDSNet-ALVEOLI) and in mouse models of diet-induced obesity and lean hyperleptinemia. Plasma leptin levels in ambulatory subjects (NHANES) correlated positively with annual risk of respiratory infection independent of BMI. In patients with severe pneumonia resulting in ARDS (ARDSNet-ALVEOLI), plasma leptin levels were found to correlate positively with subsequent mortality. In obese mice with pneumonia, plasma leptin levels were associated with pneumonia severity, and in obese mice with sterile lung injury, leptin levels were inversely related to bronchoalveolar lavage neutrophilia, as well as to plasma IL-6 and G-CSF levels. These results were recapitulated in lean mice with experimentally induced hyperleptinemia. Our findings suggest that the association between obesity and elevated risk of pulmonary infection may be driven by hyperleptinemia.