Klebsiella (K.) pneumoniae is a common cause of pneumonia-derived sepsis. Myeloid related protein 8 (MRP8, S100A8) and MRP14 (S100A9) are the most abundant cytoplasmic proteins in neutrophils. They can form MRP8/14 heterodimers that are released upon cell stress stimuli. MRP8/14 reportedly exerts antimicrobial activity, but in acute fulminant sepsis models MRP8/14 has been found to contribute to organ damage and death. We here determined the role of MRP8/14 in K. pneumoniae sepsis originating from the lungs, using an established model characterized by gradual growth of bacteria with subsequent dissemination. Infection resulted in gradually increasing MRP8/14 levels in lungs and plasma. Mrp14 deficient (mrp14−/−) mice, unable to form MRP8/14 heterodimers, showed enhanced bacterial dissemination accompanied by increased organ damage and a reduced survival. Mrp14−/− macrophages were reduced in their capacity to phagocytose Klebsiella. In addition, recombinant MRP8/14 heterodimers, but not MRP8 or MRP14 alone, prevented growth of Klebsiella in vitro through chelation of divalent cations. Neutrophil extracellular traps (NETs) prepared from wildtype but not from mrp14−/− neutrophils inhibited Klebsiella growth; in accordance, the capacity of human NETs to kill Klebsiella was strongly impaired by an anti-MRP14 antibody or the addition of zinc. These results identify MRP8/14 as key player in protective innate immunity during Klebsiella pneumonia.

The Stability and Workload Index for Transfer score is derived from information readily available at the time of ICU dismissal and acceptably predicts ICU readmission. It is not known if discharge decisions based on this prediction score will decrease the number of ICU readmissions and/or improve outcome.

IntroductionStaphylococcus (S.) aureus has emerged as an important cause of necrotizing pneumonia. Lung injury during S. aureus pneumonia may be enhanced by local release of damage associated molecular patterns such as high-mobility group box 1 (HMGB1). In the current study we sought to determine the functional role of HMGB1 and its receptors, toll-like receptor 4 (TLR4) and the receptor for advanced glycation end products (RAGE), in the injurious host response to S. aureus pneumonia.MethodsPneumonia was induced in wild type (Wt), TLR4 deficient (tlr4−/−) and RAGE deficient (rage−/−) mice by intranasal inoculation of 1 × 107 colony-forming units (CFU) of a USA300 S. aureus. In a separate set of experiments, Wt mice were injected intraperitoneally with a monoclonal anti-HMGB1 antibody or an isotype matched control antibody immediately before and every 24 hours after intranasal infection of S. aureus. Mice were sacrificed at 6, 24, 48 or 72 hours after infection for harvesting of blood and organs.ResultsS. aureus pneumonia was associated with HMGB1 release in the bronchoalveolar compartment peaking after 24 hours. Anti-HMGB1 attenuated lung pathology and protein leak and reduced interleukin-1β release 6 hours after infection, but not at later time points. RAGE deficiency more modestly attenuated lung pathology without influencing protein leak, while TLR4 deficiency did not impact on lung injury.ConclusionThese data suggest that HMGB1 and RAGE, but not TLR4, contribute to lung injury accompanying the early phase of S. aureus pneumonia.

Klebsiella species is the second most commonly isolated gram-negative organism in sepsis and a frequent causative pathogen in pneumonia. The receptor for advanced glycation end products (RAGE) is expressed on different cell types and plays a key role in diverse inflammatory responses. We here aimed to investigate the role of RAGE in the host response to Klebsiella (K.) pneumoniae pneumonia and intransally inoculated rage gene deficient (RAGE-/-) and normal wild-type (Wt) mice with K. pneumoniae. Klebsiella pneumonia resulted in an increased pulmonary expression of RAGE. Furthermore, the high-affinity RAGE ligand high mobility group box-1 was upregulated during K. pneumoniae pneumonia. RAGE deficiency impaired host defense as reflected by a worsened survival, increased bacterial outgrowth and dissemination in RAGE-/- mice. RAGE-/- neutrophils showed a diminished phagocytosing capacity of live K. pneumoniae in vitro. Relative to Wt mice, RAGE-/- mice demonstrated similar lung inflammation, and slightly elevated—if any—cytokine and chemokine levels and unchanged hepatocellular injury. In addition, RAGE-/- mice displayed an unaltered response to intranasally instilled Klebsiella lipopolysaccharide (LPS) with respect to pulmonary cell recruitment and local release of cytokines and chemokines. These data suggest that (endogenous) RAGE protects against K. pneumoniae pneumonia. Also, they demonstrate that RAGE contributes to an effective antibacterial defense during K. pneumoniae pneumonia, at least partly via its participation in the phagocytic properties of professional granulocytes. Additionally, our results indicate that RAGE is not essential for the induction of a local and systemic inflammatory response to either intact Klebsiella or Klebsiella LPS.

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Staphylococcus aureus has evolved as an important cause of pneumonia in both hospital and community settings. Staphylococcal lung infection can lead to overwhelming pulmonary inflammation. During infection, neutrophils release complexes of myeloid-related protein (MRP)8 and MRP14 (MRP8/ 14). MRP8/14 has been shown to exert pro-inflammatory and chemotactic activity, and to assist in the killing of S. aureus. In the current study we sought to determine the role of MRP8/14 in the host response during S. aureus pneumonia.Pneumonia was induced in wildtype and MRP14-deficient mice (mice unable to form MRP8/14) by intranasal inoculation of 1×10 7 CFU of S. aureus USA300. Mice were sacrificed at 6, 24, 48 or 72 h after infection for analyses.S. aureus pneumonia was associated with a strong rise in MRP8/14 in bronchoalveolar lavage fluid and lung tissue. Surprisingly, MRP14 deficiency had a limited effect on bacterial clearance and was associated with increased cytokine levels in bronchoalveolar lavage fluid and aggravated lung histopathology. MRP14 deficiency in addition was associated with a diminished transmigration of neutrophils into bronchoalveolar lavage fluid at late time-points after infection together with reduced release of nucleosomes.MRP8/14 serves in an unexpected protective role for the lung in staphylococcal pneumonia. @ERSpublications MRP8/14 unexpectedly protects against excessive pulmonary inflammation in murine staphylococcal pneumonia http://ow.ly/IwYt6

BackgroundNeutrophil extracellular traps (NETs) are a central player in the host response to bacteria: neutrophils release extracellular DNA (nucleosomes) and neutrophil elastase to entrap and kill bacteria. We studied the role of NETs in Burkholderia pseudomallei infection (melioidosis), an important cause of Gram-negative sepsis in Southeast Asia.MethodsIn a prospective observational study, circulating nucleosomes and neutrophil elastase were assayed in 44 patients with Gram-negative sepsis caused by B. pseudomallei (melioidosis) and 82 controls. Functional assays included human neutrophil stimulation and killing assays and a murine model of B. pseudomallei infection in which NET function was compromised using DNase. Specified pathogen-free 8- to 12-week-old C57BL/6 mice were sacrificed post-infection to assess bacterial loads, inflammation, and pathology.ResultsNucleosome and neutrophil elastase levels were markedly elevated in patients compared to controls. NETs killed B. pseudomallei effectively, and neutrophils stimulated with B. pseudomallei showed increased elastase and DNA release in a time- and dose-dependent matter. In mice, NET disruption with intravenous DNase administration resulted in decreased nucleosome levels. Although DNase treatment of mice resulted in diminished liver inflammation, no differences were observed in bacterial dissemination or systemic inflammation.ConclusionB. pseudomallei is a potent inducer of NETosis which was reflected by greatly increased levels of NET-related components in melioidosis patients. Although NETs exhibited antibacterial activity against B. pseudomallei, NET formation did not protect against bacterial dissemination and inflammation during B. pseudomallei-induced sepsis.Electronic supplementary materialThe online version of this article (doi:10.1186/s40635-014-0021-2) contains supplementary material, which is available to authorized users.