Looking Beyond Respiratory Cultures: Microbiome-Cytokine Signatures of Bacterial Pneumonia and Tracheobronchitis in Lung Transplant Recipients.

Bacterial pneumonia and tracheobronchitis are diagnosed frequently following lung transplantation. The diseases share clinical signs of inflammation and are often difficult to differentiate based on culture results. Microbiome and host immune-response signatures that distinguish between pneumonia and tracheobronchitis are undefined. Using a retrospective study design, we selected 49 bronchoalveolar lavage fluid samples from 16 lung transplant recipients associated with pneumonia (n = 8), tracheobronchitis (n = 12) or colonization without respiratory infection (n = 29). We ensured an even distribution of Pseudomonas aeruginosa or Staphylococcus aureus culture-positive samples across the groups. Bayesian regression analysis identified non-culture-based signatures comprising 16S ribosomal RNA microbiome profiles, cytokine levels and clinical variables that characterized the three diagnoses. Relative to samples associated with colonization, those from pneumonia had significantly lower microbial diversity, decreased levels of several bacterial genera and prominent multifunctional cytokine responses. In contrast, tracheobronchitis was characterized by high microbial diversity and multifunctional cytokine responses that differed from those of pneumonia-colonization comparisons. The dissimilar microbiomes and cytokine responses underlying bacterial pneumonia and tracheobronchitis following lung transplantation suggest that the diseases result from different pathogenic processes. Microbiomes and cytokine responses had complementary features, suggesting that they are closely interconnected in the pathogenesis of both diseases.

Novel protective mechanism for interleukin-33 at the mucosal barrier during influenza-associated bacterial superinfection.

Influenza A is a highly contagious respiratory virus that causes seasonal epidemics and occasional worldwide pandemics. The primary cause of influenza-related mortality is bacterial superinfection. There are numerous mechanisms by which preceding influenza infection attenuates host defense, allowing for increased susceptibility to bacterial pneumonia. Herein, we demonstrate that influenza inhibits Staphylococcus aureus-induced production of interleukin-33 (IL-33). Restoration of IL-33 during influenza A and methicillin-resistant S. aureus superinfection enhanced bacterial clearance and improved mortality. Innate lymphoid Type 2 cells and alternatively activated macrophages are not required for IL-33-mediated protection during superinfection. We show that IL-33 treatment resulted in neutrophil recruitment to the lung, associated with improved bacterial clearance. These findings identify a novel role for IL-33 in antibacterial host defense at the mucosal barrier.

Central interleukin-1 receptors contribute to suppression of feeding after acute colitis in the rat.

Experimental colitis, induced in rats by intrarectal administration of trinitrobenzenesulfonic acid (TNB), results in a suppression of eating for 3 days. Because interleukin-1 (IL-1) is elevated within 24 h after TNB treatment, and because chronic administration of IL-1 leads to a pattern of anorexia similar to that seen after TNB, we evaluated the role of endogenous IL-1 in the anorexia observed in the TNB model. Human recombinant IL-1 receptor antagonist (rhIL-1ra) was administered chronically via osmotic minipump either peripherally or centrally after TNB treatment. Peripheral delivery of 40 micrograms/h rhIL-1ra significantly attenuated TNB-induced anorexia. However, 24 micrograms/h rhIL-1ra attenuated TNB-induced anorexia only when delivered centrally, not peripherally. These findings implicate central IL-1 receptors in the suppression of eating during acute experimental colitis but leave open a possible involvement of peripheral IL-1 receptors.

Exudative and absorptive permeability in different phases of an experimental colitis condition.

BACKGROUND: Increased intestinal 'permeability' in inflammatory bowel disease and in animal models of this disease has been reported. This study asks if permeability changes are bidirectional and parallel cellular inflammation. METHODS: In rats acute inflammatory cell infiltration (ICI) was induced in an excluded bowel loop by instillation of 4% acetic acid. Plasma exudation was investigated by intravenous infusion of 125I-albumin and determination of radioactivity in loop perfusates. Absorption was measured by placing 51Cr-ethylenediaminetetraacetic acid in the loop and counting total radioactivity appearing in urine over 24 h. RESULTS: Acute ICI was induced with acetic acid on day 4 but, as judged by ICI and histology, recovered by day 14. Acetic acid treatment resulted in increased absorption on day 4, which return to control levels by day 14. Acetic acid treatment resulted in increased plasma exudation on day 4, which remained increased on day 14. CONCLUSION: Absorption and exudation changes are not necessarily bidirectional, and ICI may not be required for significant and sustained plasma exudation to take place. We suggest that the exudative response reflects a 'functional inflammation' that may occur and be important also in the absence of the traditional indices of bowel inflammation.

On the suppression of food intake in experimental models of colitis in the rat.

We measured daily food intake and body weight in rats before and after the induction of colitis by intrarectal administration of either 2,4,6-trinitrobenzenesulfonic acid in ethyl alcohol (TNBE) or 4% acetic acid (AA). Administration of TNBE or AA induced inflammation in the distal colon, which was reflected by a significant increase in myeloperoxidase (MPO) activity in the colon. On days 1, 2, and 3 after induction of colitis by TNBE, food intake fell by 80, 70, and 50%, respectively, compared with pretreatment values; food intake returned to normal by day 4. Body weight fell within 24 h after induction of colitis and remained 10% less than control for at least 5 days. Colitis induced by AA produced a similar pattern and degree of decreased food intake and weight loss. Treatment with the 5'-lipoxygenase inhibitor MK-886 significantly reduced concentrations of leukotriene B4 in the colon of TNBE-treated rats but did not affect food intake. In contrast, the cyclooxygenase inhibitor indomethacin decreased prostaglandin E2 concentrations in the colon but also attenuated the suppression of feeding by 52 and 64% on the first 2 days after induction of colitis by TNBE. These results identify a specific prostaglandin-mediated suppression of feeding in the rat with acute colitis induced by TNBE and illustrate the utility of this model for studying mechanisms underlying anorexia associated with inflammation of the gastrointestinal tract.