Divergent role of gamma interferon in a murine model of pulmonary versus systemic Klebsiella pneumoniae infection

BATF2 enhances proinflammatory cytokine responses in macrophages and improves early host defense against pulmonary Klebsiella pneumoniae infection

Basic leucine zipper transcription factor ATF-like 2 (BATF2) is a transcription factor that is emerging as an important regulator of the innate immune system. BATF2 is among the top upregulated genes in human alveolar macrophages treated with LPS, but the signaling pathways that induce BATF2 expression in response to Gram-negative stimuli are incompletely understood. In addition, the role of BATF2 in the host response to pulmonary infection with a Gram-negative pathogen like Klebsiella pneumoniae (Kp) is not known. We show that induction of Batf2 gene expression in macrophages in response to Kp in vitro requires TRIF and type I interferon (IFN) signaling, but not MyD88 signaling. Analysis of the impact of BATF2 deficiency on macrophage effector functions in vitro showed that BATF2 does not directly impact macrophage phagocytic uptake and intracellular killing of Kp. However, BATF2 markedly enhanced macrophage proinflammatory gene expression and Kp-induced cytokine responses. In vivo, Batf2 gene expression was elevated in lung tissue of wild-type (WT) mice 24 h after pulmonary Kp infection, and Kp-infected BATF2-deficient (Batf2-/-) mice displayed an increase in bacterial burden in the lung, spleen, and liver compared with WT mice. WT and Batf2-/- mice showed similar recruitment of leukocytes following infection, but in line with in vitro observations, proinflammatory cytokine levels in the alveolar space were reduced in Batf2-/- mice. Altogether, these results suggest that BATF2 enhances proinflammatory cytokine responses in macrophages in response to Kp and contributes to the early host defense against pulmonary Kp infection.NEW & NOTEWORTHY This study investigates the signaling pathways that mediate induction of BATF2 expression downstream of TLR4 and also the impact of BATF2 on the host defense against pulmonary Kp infection. We demonstrate that Kp-induced upregulation of BATF2 in macrophages requires TRIF and type I IFN signaling. We also show that BATF2 enhances Kp-induced macrophage cytokine responses and that BATF2 contributes to the early host defense against pulmonary Kp infection.

Type I interferons drive MAIT cell functions against bacterial pneumonia

Mucosal-associated invariant T (MAIT) cells are abundant in the lung and contribute to host defense against infections. During bacterial infections, MAIT cell activation has been proposed to require T cell receptor (TCR)-mediated recognition of antigens derived from the riboflavin synthesis pathway presented by the antigen-presenting molecule MR1. MAIT cells can also be activated by cytokines in an MR1-independent manner, yet the contribution of MR1-dependent vs. -independent signals to MAIT cell functions in vivo remains unclear. Here, we use Klebsiella pneumoniae as a model of bacterial pneumonia and demonstrate that MAIT cell activation is independent of MR1 and primarily driven by type I interferons (IFNs). During Klebsiella infection, type I IFNs stimulate activation of murine and human MAIT cells, induce a Th1/cytotoxic transcriptional program, and modulate MAIT cell location within the lungs. Consequently, adoptive transfer or boosting of pulmonary MAIT cells protect mice from Klebsiella infection, with protection being dependent on direct type I IFN signaling on MAIT cells. These findings reveal type I IFNs as new molecular targets to manipulate MAIT cell functions during bacterial infections.

Recurrent emergence of Klebsiella pneumoniae carbapenem resistance mediated by an inhibitory ompK36 mRNA secondary structure

Outer membrane porins in Gram-negative bacteria facilitate antibiotic influx. In Klebsiella pneumoniae, modifications in the porin OmpK36 are implicated in increasing resistance to carbapenems. An analysis of large K. pneumoniae genome collections, encompassing major healthcare-associated clones, revealed the recurrent emergence of a synonymous cytosine-to-thymine transition at position 25 (25c > t) in ompK36. We show that the 25c > t transition increases carbapenem resistance through depletion of OmpK36 from the outer membrane. The mutation attenuates K. pneumoniae in a murine pneumonia model, which accounts for its limited clonal expansion observed by phylogenetic analysis. However, in the context of carbapenem treatment, the 25c > t transition tips the balance toward treatment failure, thus accounting for its recurrent emergence. Mechanistically, the 25c > t transition mediates an intramolecular messenger RNA (mRNA) interaction between a uracil encoded by 25t and the first adenine within the Shine-Dalgarno sequence. This specific interaction leads to the formation of an RNA stem structure, which obscures the ribosomal binding site thus disrupting translation. While mutations reducing OmpK36 expression via transcriptional silencing are known, we uniquely demonstrate the repeated selection of a synonymous ompK36 mutation mediating translational suppression in response to antibiotic pressure.

Biofilm of Klebsiella pneumoniae minimize phagocytosis and cytokine expression by macrophage cell line

Infectious bacteria in biofilm mode are involved in many persistent infections. Owing to its importance in clinical settings, many in vitro and in vivo studies are being conducted to study the structural and functional properties of biofilms, their drug resistant mechanism and the s urvival mechanism of planktonic and biofilm cells. In this regard, there is not sufficient information on the interaction between Klebsiella biofilm and macrophages. In this study, we have attempted to unravel the interaction between Klebsiella biofilm and macrophages in terms of phagocytic response and cytokine expression. In vitro phagocytosis assays were performed for heat inactivated and live biofilms of K. pneumoniae, together with the expression analysis of TLR2, iNOS, inflammatory cytokines such as IL-β1, IFN-γ, IL-6, IL-12, IL-4, TNF-α and anti-inflammatory cytokine, IL-10. A phagocytic rate of an average of 15% was observed against both heat inactivated and live biofilms when LPS + IFN-γ activated macrophages were used. This was significantly higher than non-activated macrophages when tested against heat inactivated and live biofilms (average 8%). Heat-inactivated and live biofilms induced similar phagocytic responses and up-regulation of pro-inflammatory genes in macrophages, indirectly conveying that macrophage responses are to some extent dependent on the biofilm matrix.

A New Live Auxotrophic Vaccine Induces Cross-Protection against Klebsiella pneumoniae Infections in Mice

The development of a whole-cell vaccine from bacteria auxotrophic for D-amino acids present in the bacterial cell wall is considered a promising strategy for providing protection against bacterial infections. Here, we constructed a prototype vaccine, consisting of a glutamate racemase-deficient mutant, for preventing Klebsiella pneumoniae infections. The deletion mutant lacks the murI gene and requires exogenous addition of D-glutamate for growth. The results showed that the K. pneumoniae ΔmurI strain is attenuated and includes a favourable combination of antigens for inducing a robust immune response and conferring an adequate level of cross-protection against systemic infections caused by K. pneumoniae strains, including some hypervirulent serotypes with elevated production of capsule polysaccharide as well as multiresistant K. pneumoniae strains. The auxotroph also induced specific production of IL-17A and IFN-γ. The rapid elimination of the strain from the blood of mice without causing disease suggests a high level of safety for administration as a vaccine.

Exploring Klebsiella pneumoniae capsule polysaccharide proteins to design multiepitope subunit vaccine to fight against pneumonia

BACKGROUND

Klebsiella pneumoniae is an emerging human pathogen causing neonatal lung disease, catheter-associated infections, and nosocomial outbreaks with high fatality rates. Capsular polysaccharide (CPS) protein plays a major determinant in virulence and is considered as a promising target for vaccine development.

RESEARCH DESIGN AND METHODS

In this study, we used immunoinformatic approaches to design a multi-peptide vaccine against K. pneumonia. The epitopes were selected through several immune filters, such as antigenicity, conservancy, nontoxicity, non-allergenicity, binding affinity to HLA alleles, overlapping epitopes, and peptides having common epitopes.

RESULTS

Finally, a construct comprising 2 B-Cell, 8 CTL, 2 HTL epitopes, along with adjuvant, linkers was designed. Peptide-HLA interaction analysis showed strong binding of these epitopes with several common HLA molecules. The in silico immune simulation and population coverage analysis of the vaccine showed its potential to evoke strong immune responses.. Further, the interaction between vaccine and immune was evaluated by docking and simulation, revealing high affinity and complex stability. Codon adaptation and in silico cloning revealed higher expression of vaccine in E. coli K12 expression system.

CONCLUSIONS

Conclusively, the findings of the present study suggest that the designed novel multi-epitopic vaccine holds potential for further experimental validation against the pathogen.

Innate Lymphoid Cells and Natural Killer Cells in Bacterial Infections: Function, Dysregulation, and Therapeutic Targets

Infectious diseases represent one of the largest medical challenges worldwide. Bacterial infections, in particular, remain a pertinent health challenge and burden. Moreover, such infections increase over time due to the continuous use of various antibiotics without medical need, thus leading to several side effects and bacterial resistance. Our innate immune system represents our first line of defense against any foreign pathogens. This system comprises the innate lymphoid cells (ILCs), including natural killer (NK) cells that are critical players in establishing homeostasis and immunity against infections. ILCs are a group of functionally heterogenous but potent innate immune effector cells that constitute tissue-resident sentinels against intracellular and extracellular bacterial infections. Being a nascent subset of innate lymphocytes, their role in bacterial infections is not clearly understood. Furthermore, these pathogens have developed methods to evade the host immune system, and hence permit infection spread and tissue damage. In this review, we highlight the role of the different ILC populations in various bacterial infections and the possible ways of immune evasion. Additionally, potential immunotherapies to manipulate ILC responses will be briefly discussed.

From Klebsiella pneumoniae Colonization to Dissemination: An Overview of Studies Implementing Murine Models

Klebsiella pneumoniae is a Gram-negative pathogen responsible for community-acquired and nosocomial infections. The strains of this species belong to the opportunistic group, which is comprised of the multidrug-resistant strains, or the hypervirulent group, depending on their accessory genome, which determines bacterial pathogenicity and the host immune response. The aim of this survey is to present an overview of the murine models mimicking K. pneumoniae infectious processes (i.e., gastrointestinal colonization, urinary, pulmonary, and systemic infections), and the bacterial functions deployed to colonize and disseminate into the host. These in vivo approaches are pivotal to develop new therapeutics to limit K. pneumoniae infections via a modulation of the immune responses and/or microbiota.

Intestinal Infection Is Associated With Impaired Lung Innate Immunity to Secondary Respiratory Infection

Background

Pneumonia and diarrhea are among the leading causes of death worldwide, and epidemiological studies have demonstrated that diarrhea is associated with an increased risk of subsequent pneumonia. Our aim was to determine the impact of intestinal infection on innate immune responses in the lung.

Methods

Using a mouse model of intestinal infection by Salmonella enterica serovar Typhimurium (S. Typhimurium [ST]), we investigated associations between gastrointestinal infections and lung innate immune responses to bacterial (Klebsiella pneumoniae) challenge.

Results

We found alterations in frequencies of innate immune cells in the lungs of intestinally infected mice compared with uninfected mice. On subsequent challenge with K. pneumoniae, we found that mice with prior intestinal infection have higher lung bacterial burden and inflammation, increased neutrophil margination, and neutrophil extracellular traps, but lower overall numbers of neutrophils, compared with mice without prior intestinal infection. Total numbers of dendritic cells, innate-like T cells, and natural killer cells were not different between mice with and without prior intestinal infection.

Conclusions

Together, these results suggest that intestinal infection impacts lung innate immune responses, most notably neutrophil characteristics, potentially resulting in increased susceptibility to secondary pneumonia.

Efficacy and safety of intratracheal IFN-γ treatment to reverse stroke-induced susceptibility to pulmonary bacterial infections

Stroke-induced immunosuppression contributes to the development of stroke-associated pneumonia (SAP). Experiments in mice demonstrated that apoptosis of IFN-γ producing cells and reduced IFN-γ secretion resulted in impaired immune responses and the development of pneumonia after middle cerebral artery occlusion (MCAo). In the present study, we investigated the efficacy of intratracheal IFN-γ treatment to prevent SAP and demonstrated that modest benefits on pulmonary cytokine response in IFN-γ treated stroke mice did not prevent spontaneously developing infections and even slightly reduced bacterial clearance of aspirated pneumococci. Our results suggest that pulmonary IFN-γ treatment is not an effective preventive measure for SAP.

Regulation of Pulmonary Bacterial Immunity by Follistatin-Like Protein 1

Klebsiella pneumoniae is a common cause of antibiotic-resistant pneumonia. Follistatin-like protein 1 (FSTL-1) is highly expressed in the lung and is critical for lung homeostasis. The role of FSTL-1 in immunity to bacterial pneumonia is unknown. Wild-type (WT) and FSTL-1 hypomorphic (Hypo) mice were infected with Klebsiella pneumoniae to determine infectious burden, immune cell abundance, and cytokine production. FSTL-1 Hypo/TCRδ^-/- and FSTL-1 Hypo/IL17ra^-/- were also generated to assess the role of γδT17 cells in this model. FSTL-1 Hypo mice had reduced K. pneumoniae lung burden compared with that of WT controls. FSTL-1 Hypo mice had increased Il17a/interleukin-17A (IL-17A) and IL-17-dependent cytokine expression. FSTL-1 Hypo lungs also had increased IL-17A⁺ and TCRγδ⁺ cells. FSTL-1 Hypo/TCRδ^-/- displayed a lung burden similar to that of FSTL-1 Hypo and reduced lung burden compared with the TCRδ^-/- controls. However, FSTL-1 Hypo/TCRδ^-/- mice had greater bacterial dissemination than FSTL-1 Hypo mice, suggesting that gamma delta T (γδT) cells are dispensable for FSTL-1 Hypo control of pulmonary infection but are required for dissemination control. Confusing these observations, FSTL-1 Hypo/TCRδ^-/- lungs had an increased percentage of IL-17A-producing cells compared with that of TCRδ^-/- mice. Removal of IL-17A signaling in the FSTL-1 Hypo mouse resulted in an increased lung burden. These findings identify a novel role for FSTL-1 in innate lung immunity to bacterial infection, suggesting that FSTL-1 influences type-17 pulmonary bacterial immunity.

Innate Lymphoid Cells: Important Regulators of Host-Bacteria Interaction for Border Defense

Innate lymphoid cells (ILCs) are a recently discovered type of innate immune lymphocyte. They include three different groups classified by the nature of the transcription factors required for their development and by the cytokines they produce. ILCs mainly reside in tissues close to the mucosal barrier such as the respiratory and gastrointestinal tracts. Due to their close proximity to the mucosal surface, ILCs are exposed to a variety of both commensal and pathogenic bacteria. Under non-pathological conditions, ILCs have been shown to be important regulators for the maintenance of tissue homeostasis by mutual interactions with the microbiome. Besides these important functions at homeostasis, several studies have also provided emerging evidence that ILCs contribute to defense against pathogenic bacterial infection by responding rapidly to the pathogens as well as orchestrating other immune cells. In this review, we summarize recent advances in our understanding of the interactions of ILCs and bacteria, with special focus on the function of the different ILC subsets in bacterial infections.

Pulmonary Innate Immune Response Determines the Outcome of Inflammation During Pneumonia and Sepsis-Associated Acute Lung Injury

The lung is a primary organ for gas exchange in mammals that represents the largest epithelial surface in direct contact with the external environment. It also serves as a crucial immune organ, which harbors both innate and adaptive immune cells to induce a potent immune response. Due to its direct contact with the outer environment, the lung serves as a primary target organ for many airborne pathogens, toxicants (aerosols), and allergens causing pneumonia, acute respiratory distress syndrome (ARDS), and acute lung injury or inflammation (ALI). The current review describes the immunological mechanisms responsible for bacterial pneumonia and sepsis-induced ALI. It highlights the immunological differences for the severity of bacterial sepsis-induced ALI as compared to the pneumonia-associated ALI. The immune-based differences between the Gram-positive and Gram-negative bacteria-induced pneumonia show different mechanisms to induce ALI. The role of pulmonary epithelial cells (PECs), alveolar macrophages (AMs), innate lymphoid cells (ILCs), and different pattern-recognition receptors (PRRs, including Toll-like receptors (TLRs) and inflammasome proteins) in neutrophil infiltration and ALI induction have been described during pneumonia and sepsis-induced ALI. Also, the resolution of inflammation is frequently observed during ALI associated with pneumonia, whereas sepsis-associated ALI lacks it. Hence, the review mainly describes the different immune mechanisms responsible for pneumonia and sepsis-induced ALI. The differences in immune response depending on the causal pathogen (Gram-positive or Gram-negative bacteria) associated pneumonia or sepsis-induced ALI should be taken in mind specific immune-based therapeutics.

A Porcine Ex Vivo Lung Perfusion Model To Investigate Bacterial Pathogenesis

The implementation of infection models that approximate human disease is essential to understand infections and for testing new therapies before they enter into clinical stages. Rodents are used in most preclinical studies, although the differences between mice and humans have fueled the conclusion that murine studies are unreliable predictors of human outcomes. In this study, we have developed a whole-lung porcine model of infection using the ex vivo lung perfusion (EVLP) system established to recondition human lungs for transplant. As a proof of principle, we provide evidence demonstrating that infection of the porcine EVLP with the human pathogen Klebsiella pneumoniae recapitulates the known features of Klebsiella-triggered pneumonia. Moreover, our data revealed that the porcine EVLP model is useful to reveal features of the virulence of K. pneumoniae, including the manipulation of immune cells. Together, the findings of this study support the utility of the EVLP model using pig lungs as a surrogate host for assessing respiratory infections.

The use of animal infection models is essential to understand microbial pathogenesis and to develop and test treatments. Insects and two-dimensional (2D) and 3D tissue models are increasingly being used as surrogates for mammalian models. However, there are concerns about whether these models recapitulate the complexity of host-pathogen interactions. In this study, we developed the ex vivo lung perfusion (EVLP) model of infection using porcine lungs to investigate Klebsiella pneumoniae-triggered pneumonia as a model of respiratory infections. The porcine EVLP model recapitulates features of K. pneumoniae-induced pneumonia lung injury. This model is also useful to assess the pathogenic potential of K. pneumoniae, as we observed that the attenuated Klebsiella capsule mutant strain caused less pathological tissue damage with a concomitant decrease in the bacterial burden compared to that in lungs infected with the wild type. The porcine EVLP model allows assessment of inflammatory responses following infection; similar to the case with the mouse pneumonia model, we observed an increase of il-10 in the lungs infected with the wild type and an increase of ifn-γ in lungs infected with the capsule mutant. This model also allows monitoring of phenotypes at the single-cell level. Wild-type K. pneumoniae skews macrophages toward an M2-like state. In vitro experiments probing pig bone marrow-derived macrophages uncovered the role for the M2 transcriptional factor STAT6 and that Klebsiella-induced il-10 expression is controlled by p38 and extracellular signal-regulated kinase (ERK). Klebsiella-induced macrophage polarization is dependent on the capsule. Together, the findings of this study support the utility of the EVLP model using pig lungs as a platform to investigate the infection biology of respiratory pathogens.

Prekallikrein inhibits innate immune signaling in the lung and impairs host defense during pneumosepsis in mice

Prekallikrein (PKK, also known as Fletcher factor and encoded by the gene KLKB1 in humans) is a component of the contact system. Activation of the contact system has been implicated in lethality in fulminant sepsis models. Pneumonia is the most frequent cause of sepsis. We sought to determine the role of PKK in host defense during pneumosepsis. To this end, mice were infected with the common human pathogen Klebsiella pneumoniae via the airways, causing an initially localized infection of the lungs with subsequent bacterial dissemination and sepsis. Mice were treated with a selective PKK‐directed antisense oligonucleotide (ASO) or a scrambled control ASO for 3 weeks prior to infection. Host response readouts were determined at 12 or 36 h post‐infection, including genome‐wide messenger RNA profiling of lungs, or mice were followed for survival. PKK ASO treatment inhibited constitutive hepatic Klkb1 mRNA expression by >80% and almost completely abolished plasma PKK activity. Klkb1 mRNA could not be detected in lungs. Pneumonia was associated with a progressive decline in PKK expression in mice treated with control ASO. PKK ASO administration was associated with a delayed mortality, reduced bacterial burdens, and diminished distant organ injury. While PKK depletion did not influence lung pathology or neutrophil recruitment, it was associated with an upregulation of multiple innate immune signaling pathways in the lungs already prior to infection. Activation of the contact system could not be detected, either during infection in vivo or at the surface of Klebsiella in vitro. These data suggest that circulating PKK confines pro‐inflammatory signaling in the lung by a mechanism that does not involve contact system activation, which in the case of respiratory tract infection may impede early protective innate immunity. © 2019 Authors. Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Immunoinformatics-Aided Design and Evaluation of a Potential Multi-Epitope Vaccine against Klebsiella Pneumoniae

Klebsiella pneumoniae is an opportunistic gram-negative bacterium that causes nosocomial infection in healthcare settings. Despite the high morbidity and mortality rate associated with these bacterial infections, no effective vaccine is available to counter the pathogen. In this study, the pangenome of a total of 222 available complete genomes of K. pneumoniae was explored to obtain the core proteome. A reverse vaccinology strategy was applied to the core proteins to identify four antigenic proteins. These proteins were then subjected to epitope mapping and prioritization steps to shortlist nine B-cell derived T-cell epitopes which were linked together using GPGPG linkers. An adjuvant (Cholera Toxin B) was also added at the N-terminal of the vaccine construct to improve its immunogenicity and a stabilized multi-epitope protein structure was obtained using molecular dynamics simulation. The designed vaccine exhibited sustainable and strong bonding interactions with Toll-like receptor 2 and Toll-like receptor 4. In silico reverse translation and codon optimization also confirmed its high expression in E. coli K12 strain. The computer-aided analyses performed in this study imply that the designed multi-epitope vaccine can elicit specific immune responses against K. pneumoniae. However, wet lab validation is necessary to further verify the effectiveness of this proposed vaccine candidate.

Klebsiella pneumoniae infection biology: living to counteract host defences

Klebsiella species cause a wide range of diseases including pneumonia, urinary tract infections (UTIs), bloodstream infections and sepsis. These infections are particularly a problem among neonates, elderly and immunocompromised individuals. Klebsiella is also responsible for a significant number of community-acquired infections. A defining feature of these infections is their morbidity and mortality, and the Klebsiella strains associated with them are considered hypervirulent. The increasing isolation of multidrug-resistant strains has significantly narrowed, or in some settings completely removed, the therapeutic options for the treatment of Klebsiella infections. Not surprisingly, this pathogen has then been singled out as an 'urgent threat to human health' by several organisations. This review summarises the tremendous progress that has been made to uncover the sophisticated immune evasion strategies of K. pneumoniae. The co-evolution of Klebsiella in response to the challenge of an activated immune has made Klebsiella a formidable pathogen exploiting stealth strategies and actively suppressing innate immune defences to overcome host responses to survive in the tissues. A better understanding of Klebsiella immune evasion strategies in the context of the host-pathogen interactions is pivotal to develop new therapeutics, which can be based on antagonising the anti-immune strategies of this pathogen.

The Effects of IFN-λ on Epithelial Barrier Function Contribute to Klebsiella pneumoniae ST258 Pneumonia

IFN-λ and IL-22, cytokines that share the coreceptor IL-10RB, are both induced over the course of Klebsiella pneumoniae ST258 (KP35) pneumonia. IL-22 is known to protect mucosal barriers, whereas the effects of IFN-λ on the mucosa are not established. We postulated that IFN-λ plays a role in regulating the airway epithelial barrier to facilitate cellular trafficking to the site of infection. In response to IFN-λ, the transmigration of neutrophils across a polarized monolayer of airway epithelial cells was increased, consistent with diminished epithelial integrity. KP35 infection increased epithelial permeability, and pretreatment with IFN-λ amplified this effect and facilitated bacterial transmigration. These effects of IFN-λ were confirmed in vivo, in that mice lacking the receptor for IFN-λ (Ifnlr1-/-) were protected from bacteremia in a murine model of KP35 pneumonia. Conversely, the integrity of the epithelial barrier was protected by IL-22, with subsequent impairment of neutrophil and bacterial transmigration in vitro. Maximal expression of IL-22 in vivo was observed later in the course of infection than IFN-λ production, with high levels of IL-22 produced by recruited immune cells at 48 hours, consistent with a role in epithelial barrier recovery. The divergent and opposing expression of these two related cytokines suggests a regulated interaction in the host response to KP35 infection. A major physiological effect of IFN-λ signaling is a decrease in epithelial barrier integrity, which facilitates immune cell recruitment but also enables K. pneumoniae invasion.

Natural killer cell-intrinsic type I IFN signaling controls Klebsiella pneumoniae growth during lung infection

Klebsiella pneumoniae is a significant cause of nosocomial pneumonia and an alarming pathogen owing to the recent isolation of multidrug resistant strains. Understanding of immune responses orchestrating K. pneumoniae clearance by the host is of utmost importance. Here we show that type I interferon (IFN) signaling protects against lung infection with K. pneumoniae by launching bacterial growth-controlling interactions between alveolar macrophages and natural killer (NK) cells. Type I IFNs are important but disparate and incompletely understood regulators of defense against bacterial infections. Type I IFN receptor 1 (Ifnar1)-deficient mice infected with K. pneumoniae failed to activate NK cell-derived IFN-γ production. IFN-γ was required for bactericidal action and the production of the NK cell response-amplifying IL-12 and CXCL10 by alveolar macrophages. Bacterial clearance and NK cell IFN-γ were rescued in Ifnar1-deficient hosts by Ifnar1-proficient NK cells. Consistently, type I IFN signaling in myeloid cells including alveolar macrophages, monocytes and neutrophils was dispensable for host defense and IFN-γ activation. The failure of Ifnar1-deficient hosts to initiate a defense-promoting crosstalk between alveolar macrophages and NK cell was circumvented by administration of exogenous IFN-γ which restored endogenous IFN-γ production and restricted bacterial growth. These data identify NK cell-intrinsic type I IFN signaling as essential driver of K. pneumoniae clearance, and reveal specific targets for future therapeutic exploitations.

Comparison of Diabetic and Non-diabetic Human Leukocytic Responses to Different Capsule Types of Klebsiella pneumoniae Responsible for Causing Pyogenic Liver Abscess

The major risk factor for Klebsiella liver abscess (KLA) is type 2 diabetes mellitus (DM), but the immunological mechanisms involved in the increased susceptibility are poorly defined. We investigated the responses of neutrophils and peripheral blood mononuclear cells (PBMCs) to hypervirulent Klebsiella pneumoniae (hvKP), the causative agent of KLA. DNA and myeloperoxidase levels were elevated in the plasma of KLA patients compared to uninfected individuals indicating neutrophil activation, but diabetic status had no effect on these neutrophil extracellular trap (NET) biomarkers in both subject groups. Clinical hvKP isolates universally stimulated KLA patient neutrophils to produce NETs ex vivo, regardless of host diabetic status. Ability of representative capsule types (K1, K2, and non-K1/K2 strains) to survive intra- and extra-cellular killing by type 2 DM and healthy neutrophils was subsequently examined. Key findings were: (1) type 2 DM and healthy neutrophils exhibited comparable total, phagocytic, and NETs killing against hvKP, (2) phagocytic and NETs killing were equally effective against hvKP, and (3) hypermucoviscous K1 and K2 strains were more resistant to total, phagocytic, and NETs killing compared to the non-mucoviscous, non-K1/K2 strain. The cytokine response and intracellular killing ability of type 2 DM as well as healthy PBMCs upon encounter with the different capsule types was also examined. Notably, the IL-12–IFNγ axis and its downstream chemokines MIG, IP-10, and RANTES were produced at slightly lower levels by type 2 DM PBMCs than healthy PBMCs in response to representative K1 and non-K1/K2 strains. Furthermore, type 2 DM PBMCs have a mild defect in its ability to control hvKP replication relative to healthy PBMCs. In summary, our work demonstrates that type 2 DM does not overtly impact neutrophil intra- and extra-cellular killing of hvKP, but may influence cytokine/chemokine production and intracellular killing by PBMCs.

IL-36γ is a crucial proximal component of protective type-1-mediated lung mucosal immunity in Gram-positive and -negative bacterial pneumonia

Interleukin-36γ (IL-36γ) is a member of novel IL-1-like proinflammatory cytokine family that are highly expressed in epithelial tissues and several myeloid-derived cell types. Little is known about the role of the IL-36 family in mucosal immunity, including lung anti-bacterial responses. We used murine models of IL-36γ deficiency to assess the contribution of IL-36γ in the lung during experimental pneumonia. Induction of IL-36γ was observed in the lung in response to Streptococcus pneumoniae (Sp) infection, and mature IL-36γ protein was secreted primarily in microparticles. IL-36γ-deficient mice challenged with Sp demonstrated increased mortality, decreased lung bacterial clearance and increased bacterial dissemination, in association with reduced local expression of type-1 cytokines, and impaired lung macrophage M1 polarization. IL-36γ directly stimulated type-1 cytokine induction from dendritic cells in vitro in a MyD88-dependent manner. Similar protective effects of IL-36γ were observed in a Gram-negative pneumonia model (Klebsiella pneumoniae). Intrapulmonary delivery of IL-36γ-containing microparticles reconstituted immunity in IL-36γ^-/- mice. Enhanced expression of IL-36γ was also observed in plasma and bronchoalveolar lavage fluid of patients with acute respiratory distress syndrome because of pneumonia. These studies indicate that IL-36γ assumes a vital proximal role in the lung innate mucosal immunity during bacterial pneumonia by driving protective type-1 responses and classical macrophage activation.

Acyloxyacyl hydrolase promotes the resolution of lipopolysaccharide-induced acute lung injury

Pulmonary infection is the most common risk factor for acute lung injury (ALI). Innate immune responses induced by Microbe-Associated Molecular Pattern (MAMP) molecules are essential for lung defense but can lead to tissue injury. Little is known about how MAMP molecules are degraded in the lung or how MAMP degradation/inactivation helps prevent or ameliorate the harmful inflammation that produces ALI. Acyloxyacyl hydrolase (AOAH) is a host lipase that inactivates Gram-negative bacterial endotoxin (lipopolysaccharide, or LPS). We report here that alveolar macrophages increase AOAH expression upon exposure to LPS and that Aoah+/+ mice recover more rapidly than do Aoah-/- mice from ALI induced by nasally instilled LPS or Klebsiella pneumoniae. Aoah-/- mouse lungs had more prolonged leukocyte infiltration, greater pro- and anti-inflammatory cytokine expression, and longer-lasting alveolar barrier damage. We also describe evidence that the persistently bioactive LPS in Aoah-/- alveoli can stimulate alveolar macrophages directly and epithelial cells indirectly to produce chemoattractants that recruit neutrophils to the lung and may prevent their clearance. Distinct from the prolonged tolerance observed in LPS-exposed Aoah-/- peritoneal macrophages, alveolar macrophages that lacked AOAH maintained or increased their responses to bioactive LPS and sustained inflammation. Inactivation of LPS by AOAH is a previously unappreciated mechanism for promoting resolution of pulmonary inflammation/injury induced by Gram-negative bacterial infection.

Acquired resistance to innate immune clearance promotes Klebsiella pneumoniae ST258 pulmonary infection

Adaptive changes in the genome of a locally predominant clinical isolate of the multidrug-resistant Klebsiella pneumoniae ST258 (KP35) were identified and help to explain the selection of this strain as a successful pulmonary pathogen. The acquisition of 4 new ortholog groups, including an arginine transporter, enabled KP35 to outcompete related ST258 strains lacking these genes. KP35 infection elicited a monocytic response, dominated by Ly6C^hi monocytic myeloid-derived suppressor cells that lacked phagocytic capabilities, expressed IL-10, arginase, and antiinflammatory surface markers. In comparison with other K. pneumoniae strains, KP35 induced global changes in the phagocytic response identified with proteomics, including evasion of Ca²⁺ and calpain activation necessary for phagocytic killing, confirmed in functional studies with neutrophils. This comprehensive analysis of an ST258 K. pneumoniae isolate reveals ongoing genetic adaptation to host microenvironments and innate immune clearance mechanisms that complements its repertoire of antimicrobial resistance genes and facilitates persistence in the lung.

RSV-specific anti-viral immunity is disrupted by chronic ethanol consumption

Alcohol-use disorders (AUD) persist in the United States and are heavily associated with an increased susceptibility to respiratory viral infections. Respiratory syncytial virus (RSV) in particular has received attention as a viral pathogen commonly detected in children and immune-compromised populations (elderly, asthmatics), yet more recently was recognized as an important viral pathogen in young adults. Our study evaluated the exacerbation of RSV-associated illness in mice that chronically consumed alcohol for 6 weeks prior to infection. Prior studies showed that lung viral titers remained elevated in these animals, leading to a hypothesis that T-cell activation and immune specificity were deficient in controlling viral spread and replication in the lungs. Herein, we confirm a reduction in RSV-specific IFNγ production by CD8 T cells and a depolarization of Th1 (CD4+IFNγ+) and Th2 (CD4+IL-4+) T cells at day 5 after RSV infection. Furthermore, over the course of viral infection (day 1 to day 7 after RSV infection), we detected a delayed influx of neutrophils, monocytes/macrophages, and lymphocytes into the lungs. Taken together, the data show that both the early and late adaptive immunity to RSV infection are altered by chronic ethanol consumption. Future studies will determine the interactions between the innate and adaptive immune systems to delineate therapeutic targets for individuals with AUD often hospitalized by respiratory infection.

Klebsiella pneumoniae: Going on the Offense with a Strong Defense

Klebsiella pneumoniae causes a wide range of infections, including pneumonias, urinary tract infections, bacteremias, and liver abscesses. Historically, K. pneumoniae has caused serious infection primarily in immunocompromised individuals, but the recent emergence and spread of hypervirulent strains have broadened the number of people susceptible to infections to include those who are healthy and immunosufficient. Furthermore, K. pneumoniae strains have become increasingly resistant to antibiotics, rendering infection by these strains very challenging to treat. The emergence of hypervirulent and antibiotic-resistant strains has driven a number of recent studies. Work has described the worldwide spread of one drug-resistant strain and a host defense axis, interleukin-17 (IL-17), that is important for controlling infection. Four factors, capsule, lipopolysaccharide, fimbriae, and siderophores, have been well studied and are important for virulence in at least one infection model. Several other factors have been less well characterized but are also important in at least one infection model. However, there is a significant amount of heterogeneity in K. pneumoniae strains, and not every factor plays the same critical role in all virulent Klebsiella strains. Recent studies have identified additional K. pneumoniae virulence factors and led to more insights about factors important for the growth of this pathogen at a variety of tissue sites. Many of these genes encode proteins that function in metabolism and the regulation of transcription. However, much work is left to be done in characterizing these newly discovered factors, understanding how infections differ between healthy and immunocompromised patients, and identifying attractive bacterial or host targets for treating these infections.

Innate Immune Signaling Activated by MDR Bacteria in the Airway

Health care-associated bacterial pneumonias due to multiple-drug resistant (MDR) pathogens are an important public health problem and are major causes of morbidity and mortality worldwide. In addition to antimicrobial resistance, these organisms have adapted to the milieu of the human airway and have acquired resistance to the innate immune clearance mechanisms that normally prevent pneumonia. Given the limited efficacy of antibiotics, bacterial clearance from the airway requires an effective immune response. Understanding how specific airway pathogens initiate and regulate innate immune signaling, and whether this response is excessive, leading to host-induced pathology may guide future immunomodulatory therapy. We will focus on three of the most important causes of health care-associated pneumonia, Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae, and review the mechanisms through which an inappropriate or damaging innate immune response is stimulated, as well as describe how airway pathogens cause persistent infection by evading immune activation.

Pseudomonas aeruginosa: breaking down barriers

Many bacterial pathogens have evolved ingenious ways to escape from the lung during pneumonia to cause bacteremia. Unfortunately, the clinical consequences of this spread to the bloodstream are frequently dire. It is therefore important to understand the molecular mechanisms used by pathogens to breach the lung barrier. We have recently shown that Pseudomonas aeruginosa, one of the leading causes of hospital-acquired pneumonia, utilizes the type III secretion system effector ExoS to intoxicate pulmonary epithelial cells. Injection of these cells leads to localized disruption of the pulmonary-vascular barrier and dissemination of P. aeruginosa to the bloodstream. We put these data in the context of previous studies to provide a holistic model of P. aeruginosa dissemination from the lung. Finally, we compare P. aeruginosa dissemination to that of other bacteria to highlight the complexity of bacterial pneumonia. Although respiratory pathogens use distinct and intricate strategies to escape from the lungs, a thorough understanding of these processes can lay the foundation for new therapeutic approaches for bacterial pneumonia.

TIR-Domain-Containing Adaptor-Inducing Interferon-β (TRIF) Mediates Antibacterial Defense during Gram-Negative Pneumonia by Inducing Interferon-x03B3

Klebsiella pneumoniae is an important cause of Gram-negative pneumonia and sepsis. Mice deficient for TIR-domain-containing adaptor-inducing interferon-β (TRIF) demonstrate enhanced bacterial growth and dissemination during Klebsiella pneumonia. We show here that the impaired antibacterial defense of TRIF mutant mice is associated with absent interferon (IFN)-x03B3; production in the lungs. IFN-x03B3; production by splenocytes in response to K. pneumoniae in vitro was critically dependent on Toll-like receptor 4 (TLR4), the common TLR adaptor myeloid differentiation primary response gene (MyD88) and TRIF. Reconstitution of TRIF mutant mice with recombinant IFN-x03B3; via the airways reduced bacterial loads in lungs and distant body sites to levels measured in wild-type mice, and partially restored pulmonary cytokine levels. The IFN-x03B3;-induced, improved, enhanced antibacterial response in TRIF mutant mice occurred at the expense of increased hepatocellular injury. These data indicate that TRIF mediates antibacterial defense during Gram-negative pneumonia, at least in part, by inducing IFN-x03B3; at the primary site of infection.

Alcohol's Effects on Lung Health and Immunity

It has long been known that people with alcohol use disorder (AUD) not only may develop physical dependence but also may experience devastating long-term health problems. The most common and identifiable alcohol-associated health problems include liver cirrhosis, pancreatitis, cardiomyopathies, neuropathies, and dementia. However, the lung also is adversely affected by alcohol abuse, a fact often overlooked by clinicians and the public. Individuals with AUD are more likely to develop pneumonia, tuberculosis (TB), respiratory syncytial virus (RSV) infection, and acute respiratory distress syndrome (ARDS). Increased susceptibility to these and other pulmonary infections is caused by impaired immune responses in people with AUD. The key immune cells involved in combating pulmonary conditions such as pneumonia, TB, RSV infection, and ARDS are neutrophils, lymphocytes, alveolar macrophages, and the cells responsible for innate immune responses. Researchers are only now beginning to understand how alcohol affects these cells and how these effects contribute to the pathophysiology of pulmonary diseases in people with AUD.

Vaccine approaches for multidrug resistant Gram negative infections

Multidrug resistant (MDR) Gram negative bacterial infections are increasing in frequency and are associated with significant financial costs, morbidity and mortality. Current antibiotic therapies are associated with unacceptably poor clinical outcomes and toxicity. Unfortunately, the development of novel antimicrobials is stagnant leaving a significant clinical need for alternative treatments of MDR Gram negative rod infections. Recent preclinical studies have identified Th17 cells as critical mediators of broadly protective adaptive immunity, including protection against MDR infections. Studies of Th17 eliciting antigens, adjuvants and routes of immunization have identified potential vaccine strategies that may confer long-lived adaptive immunity against MDR Gram negative bacterial infections.

Conventional NK cells can produce IL-22 and promote host defense in Klebsiella pneumoniae pneumonia

It was reported that host defense against pulmonary Klebsiella pneumoniae infection requires IL-22, which was proposed to be of T cell origin. Supporting a role for IL-22, we found that Il22(-/-) mice had decreased survival compared with wild-type mice after intratracheal infection with K. pneumoniae. Surprisingly, however, Rag2(-/-) mice did not differ from wild-type mice in survival or levels of IL-22 in the lungs postinfection with K. pneumoniae. In contrast, K. pneumoniae-infected Rag2(-/-)Il2rg(-/-) mice failed to produce IL-22. These data suggested a possible role for NK cells or other innate lymphoid cells in host defense and production of IL-22. Unlike NK cell-like innate lymphoid cells that produce IL-22 and display a surface phenotype of NK1.1(-)NKp46(+)CCR6(+), lung NK cells showed the conventional phenotype, NK1.1(+)NKp46(+)CCR6(-). Mice depleted of NK cells using anti-asialo GM1 showed decreased survival and higher lung bacterial counts, as well as increased dissemination of K. pneumoniae to blood and liver, compared with control-treated mice. NK cell depletion also led to decreased production of IL-22 in the lung. Within 1 d postinfection, although there was no increase in the number of lung NK cells, a subset of lung NK cells became competent to produce IL-22, and such cells were found in both wild-type and Rag2(-/-) mice. Our data suggest that, during pulmonary infection of mice with K. pneumoniae, conventional NK cells are required for optimal host defense, which includes the production of IL-22.

Activation of IFN-γ/STAT/IRF-1 in hepatic responses to Klebsiella pneumoniae infection

BACKGROUND

Klebsiella pneumoniae-caused liver abscess (KLA) has become a health problem in Taiwan and is continually reported in other countries. Diabetes mellitus, the most common metabolic disorder, underlies half of the KLA patients in Taiwan. The clinical impact of KLA has been well-documented. Nevertheless, the molecular basis regarding how K. pneumoniae causes liver infection, particularly in diabetic individuals, remains unclear.

METHODOLOGY/PRINCIPLE FINDINGS

Auto-bioluminescence-expressing K. pneumoniae was inoculated into diabetic mice and age-match naïve control. With the use of in vivo imaging system, translocation of the bioluminescence-expressing K. pneumoniae from intestine to extraintestinal organs, mainly the liver, was noted in 80% of the diabetic mice, whereas the same bacteria causes extraintestinal infections in only 31% of naïve mice. Besides increased morbidity, the severity of hepatic tissue injury was also enhanced in the K. pneumoniae-infected diabetic mice. Upon K. pneumoniae infection, IFN-γ production was significantly evoked in the liver. To mediate IFN-γ signal, STAT (signal transducers and activators of transcription) 1 and 3 were activated in hepatocytes, and so was the expression of IRF (interferon regulatory factor)-1. Moreover, accumulation of neutrophils which was triggered by prolonged production of IL-1β and MIP-2, and significant increases in the level of active caspase 3 and phospho-eIF2α, were exclusively revealed in the K. pneumoniae-infected diabetic mice.

CONCLUSION

The activation of IFN-γ/STAT/IRF-1 signaling demonstrated by this work emphasizes the role of IFN-γ for mediating the hepatic response to K. pneumoniae infection.

Alcoholic lung injury: metabolic, biochemical and immunological aspects

Chronic alcohol abuse is a systemic disorder and a risk factor for acute respiratory distress syndrome (ARDS) and chronic obstructive pulmonary disease (COPD). A significant amount of ingested alcohol reaches airway passages in the lungs and can be metabolized via oxidative and non-oxidative pathways. About 90% of the ingested alcohol is metabolized via hepatic alcohol dehydrogenase (ADH)-catalyzed oxidative pathway. Alcohol can also be metabolized by cytochrome P450 2E1 (CYP2E1), particularly during chronic alcohol abuse. Both the oxidative pathways, however, are associated with oxidative stress due to the formation of acetaldehyde and/or reactive oxygen species (ROS). Alcohol ingestion is also known to cause endoplasmic reticulum (ER) stress, which can be mediated by oxidative and/or non-oxidative metabolites of ethanol. An acute as well as chronic alcohol ingestions impair protective antioxidants, oxidize reduced glutathione (GSH, cellular antioxidant against ROS and oxidative stress), and suppress innate and adaptive immunity in the lungs. Oxidative stress and suppressed immunity in the lungs of chronic alcohol abusers collectively are considered to be major risk factors for infection and development of pneumonia, and such diseases as ARDS and COPD. Prior human and experimental studies attempted to identify common mechanisms by which alcohol abuse directly causes toxicity to alveolar epithelium and respiratory tract, particularly lungs. In this review, the metabolic basis of lung injury, oxidative and ER stress and immunosuppression in experimental models and alcoholic patients, as well as potential immunomodulatory therapeutic strategies for improving host defenses against alcohol-induced pulmonary infections are discussed.

CD8+ T cells and risk for bacterial pneumonia and all-cause mortality among HIV-infected women

BACKGROUND

Bacterial pneumonia risk is disproportionately high among those infected with HIV. This risk is present across all CD4(+) T-cell levels (TCLs), suggesting that additional factors govern susceptibility. This study examines CD8(+) TCLs and risk for HIV-associated bacterial pneumonia and all-cause mortality.

METHODS

Demographic, clinical, and laboratory data were obtained for 885 HIV-infected women enrolled in the HIV Epidemiologic Research Study (HERS). Bacterial pneumonia cases were identified using clinical, microbiological, and radiographic criteria. CD8(+) TCLs were assessed at 6-month intervals. Statistical methods included Cox proportional hazards regression modeling and covariate-adjusted survival estimates.

RESULTS

Relative to a referent CD8(+) TCL of 401-800 cells per cubic millimeter, risk for bacterial pneumonia was significantly higher when CD8(+) TCLs were <400 (hazard ratio 1.65, P = 0.017, 95% confidence interval 1.10 to 2.49), after adjusting for age, CD4(+) TCL, viral load, and antiretroviral use. There was also a significantly higher risk of death when CD8(+) TCLs were ≤400 cells per cubic millimeter (hazard ratio 1.45, P = 0.04, 95% confidence interval 1.02 to 2.06). Covariate-adjusted survival estimates revealed shorter time to pneumonia and death in this CD8(+) TCL category, and the overall associations of the categorized CD8(+) TCL with bacterial pneumonia and all-cause mortality were each statistically significant (P = 0.017 and P < 0.0001, respectively).

CONCLUSIONS

CD8(+) TCL ≤400 cells per cubic millimeter was associated with increased risk for pneumonia and all-cause mortality in HIV-infected women in the HERS cohort, suggesting that CD8(+) TCL could serve as an adjunctive biomarker of pneumonia risk and mortality in HIV-infected individuals.

Marking and quantifying IL-17A-producing cells in vivo

Interleukin (IL)-17A plays an important role in host defense against a variety of pathogens and may also contribute to the pathogenesis of autoimmune diseases. However, precise identification and quantification of the cells that produce this cytokine in vivo have not been performed. We generated novel IL-17A reporter mice to investigate expression of IL-17A during Klebsiella pneumoniae infection and during experimental autoimmune encephalomyelitis, conditions previously demonstrated to potently induce IL-17A production. In both settings, the majority of IL-17A was produced by non-CD4(+) T cells, particularly γδ T cells, but also invariant NKT cells and other CD4(-)CD3ε(+) cells. As measured in dual-reporter mice, IFN-γ-producing Th1 cells greatly outnumbered IL-17A-producing Th17 cells throughout both challenges. Production of IL-17A by cells from unchallenged mice or by non-T cells under any condition was not evident. Administration of IL-1β and/or IL-23 elicited rapid production of IL-17A by γδ T cells, invariant NKT cells and other CD4(-)CD3ε(+) cells in vivo, demonstrating that these cells are poised for rapid cytokine production and likely comprise the major sources of this cytokine during acute immunologic challenges.

Assessment of hypermucoviscosity as a virulence factor for experimental Klebsiella pneumoniae infections: comparative virulence analysis with hypermucoviscosity-negative strain

Background

Klebsiella pneumoniae displaying the hypermucoviscosity (HV) phenotype are considered more virulent than HV-negative strains. Nevertheless, the emergence of tissue-abscesses-associated HV-negative isolates motivated us to re-evaluate the role of HV-phenotype.

Results

Instead of genetically manipulating the HV-phenotype of K. pneumoniae, we selected two clinically isolated K1 strains, 1112 (HV-positive) and 1084 (HV-negative), to avoid possible interference from defects in the capsule. These well-encapsulated strains with similar genetic backgrounds were used for comparative analysis of bacterial virulence in a pneumoniae or a liver abscess model generated in either naïve or diabetic mice. In the pneumonia model, the HV-positive strain 1112 proliferated to higher loads in the lungs and blood of naïve mice, but was less prone to disseminate into the blood of diabetic mice compared to the HV-negative strain 1084. In the liver abscess model, 1084 was as potent as 1112 in inducing liver abscesses in both the naïve and diabetic mice. The 1084-infected diabetic mice were more inclined to develop bacteremia and had a higher mortality rate than those infected by 1112. A mini-Tn5 mutant of 1112, isolated due to its loss of HV-phenotype, was avirulent to mice.

Conclusion

These results indicate that the HV-phenotype is required for the virulence of the clinically isolated HV-positive strain 1112. The superior ability of the HV-negative stain 1084 over 1112 to cause bacteremia in diabetic mice suggests that factors other than the HV phenotype were required for the systemic dissemination of K. pneumoniae in an immunocompromised setting.

The IκB family member Bcl-3 coordinates the pulmonary defense against Klebsiella pneumoniae infection

Bcl-3 is an atypical member of the IκB family that has the potential to positively or negatively modulate nuclear NF-κB activity in a context-dependent manner. Bcl-3's biologic impact is complex and includes roles in tumorigenesis and diverse immune responses, including innate immunity. Bcl-3 may mediate LPS tolerance, suppressing cytokine production, but it also seems to contribute to defense against select systemic bacterial challenges. However, the potential role of Bcl-3 in organ-specific host defense against bacteria has not been addressed. In this study, we investigated the relevance of Bcl-3 in a lung challenge with the Gram-negative pathogen Klebsiella pneumoniae. In contrast to wild-type mice, Bcl-3-deficient mice exhibited significantly increased susceptibility toward K. pneumoniae pneumonia. The mutant mice showed increased lung damage marked by neutrophilic alveolar consolidation, and they failed to clear bacteria in lungs, which correlated with increased bacteremic dissemination. Loss of Bcl-3 incurred a dramatic cytokine imbalance in the lungs, which was characterized by higher levels of IL-10 and a near total absence of IFN-γ. Moreover, Bcl-3-deficient mice displayed increased lung production of the neutrophil-attracting chemokines CXCL-1 and CXCL-2. Alveolar macrophages and neutrophils are important to antibacterial lung defense. In vitro stimulation of Bcl-3-deficient alveolar macrophages with LPS or heat-killed K. pneumoniae recapitulated the increase in IL-10 production, and Bcl-3-deficient neutrophils were impaired in intracellular bacterial killing. These findings suggest that Bcl-3 is critically involved in lung defense against Gram-negative bacteria, modulating functions of several cells to facilitate efficient clearance of bacteria.

Comparative effects of carbapenems on bacterial load and host immune response in a Klebsiella pneumoniae murine pneumonia model

Doripenem is a carbapenem with potent broad-spectrum activity against Gram-negative pathogens, including antibiotic-resistant Enterobacteriaceae. As the incidence of extended-spectrum β-lactamase (ESBL)-producing Gram-negative bacilli is increasing, it was of interest to examine the in vivo comparative efficacy of doripenem, imipenem, and meropenem against a Klebsiella pneumoniae isolate expressing the TEM-26 ESBL enzyme. In a murine lethal lower respiratory infection model, doripenem reduced the Klebsiella lung burden by 2 log(10) CFU/g lung tissue over the first 48 h of the infection. Treatment of mice with meropenem or imipenem yielded reductions of approximately 1.5 log(10) CFU/g during this time period. Seven days postinfection, Klebsiella titers in the lungs of treated mice decreased an additional 2 log(10) CFU/g relative to those in the lungs of untreated control animals. Lipopolysaccharide (LPS) endotoxin release assays indicated that 6 h postinfection, meropenem- and imipenem-treated animals had 10-fold more endotoxin in lung homogenates and sera than doripenem-treated mice. Following doripenem treatment, the maximum endotoxin release postinfection (6 h) was 53,000 endotoxin units (EU)/ml, which was 2.7- and 6-fold lower than imipenem or meropenem-treated animals, respectively. While the levels of several proinflammatory cytokines increased in both the lungs and sera following intranasal K. pneumoniae inoculation, doripenem treatment, but not meropenem or imipenem treatment, resulted in significantly increased interleukin 6 levels in lung homogenates relative to those in lung homogenates of untreated controls, which may contribute to enhanced neutrophil killing of bacteria in the lung. Histological examination of tissue sections indicated less overall inflammation and tissue damage in doripenem-treated mice, consistent with improved antibacterial efficacy, reduced LPS endotoxin release, and the observed cytokine induction profile.

Clinical disease caused by Klebsiella in 2 unrelated patients with interleukin 12 receptor beta1 deficiency

Patients with interleukin 12 (IL-12)p40 or IL-12 receptor β1 (IL12Rβ1) deficiencies are prone to develop infections caused by mycobacteria and salmonella; other infections have only been rarely observed. In this report we describe 2 unrelated patients with complete autosomal recessive IL12Rβ1 deficiency who suffered from sepsis attributable to Klebsiella pneumoniae. A Mexican boy suffered from disseminated bacille Calmette-Guérin disease and infections caused by K pneumoniae and Candida albicans and had a fatal outcome. A Turkish girl living in France suffered from disseminated Nocardia nova infection and K pneumoniae sepsis. Therefore, Klebsiella infections should be considered in patients with IL12Rβ1 deficiency. Conversely, IL12Rβ1 deficiency should be considered in patients with unexplained klebsiellosis.

Interleukin-1 deficiency in combination with macrophage depletion increases susceptibility to Pseudomonas aeruginosa bacteremia

We evaluated the role of IL-1 during Pseudomonas aeruginosa bacteremia by intravenously injecting P. aeruginosa strain D4 into IL-1-deficient and WT mice. The two strains showed equivalent mortality rates. However, when the mice were pretreated with cyclophosphamide, bacteremia-induced mortality was significantly greater in the IL-1-deficient mice than in the WT mice (P < 0.01). We then investigated the role of neutrophils and macrophages in protecting IL-1-deficient mice from bacteremia by administering anti-Gr-1 antibody or liposomes containing dichloromethylene diphosphonate, respectively. After P. aeruginosa inoculation survival was significantly lower in the macrophage-depleted IL-1-deficient mice than in the WT mice. In contrast, neutrophil depletion did not have this effect. Compared to the macrophage-depleted WT mice, the macrophage-depleted IL-1-deficient bacteremic mice had higher bacterial counts in various organs 48 and 72 hr post-infection. They also had lower TNF-alpha, IL-6, and INF-gamma concentrations in their livers during the early phase of sepsis. Thus, IL-1 deficiency becomes disadvantageous during P. aeruginosa bacteremia when it is accompanied by immunosuppression, particularly when macrophage functions are seriously impaired.

Alcohol use disorder and perioperative immune dysfunction

The anesthesiological sequelae of long-term alcohol abuse include a three to fivefold increased risk of postoperative infection, prolonged intensive care unit stays and longer hospital stays. The cause of the higher infection rates is an altered immune response in long-term alcoholic patients. Preoperatively, the T helper cells 1 to T helper cells 2 ratio is depressed in long-term alcoholic patients and remains suppressed after surgery. The lower preoperative T helper cells 1 to T helper cells 2 ratio is predictive of later onset of infections. Postoperatively, the cytotoxic lymphocyte (Tc1/Tc2) ratio is decreased in long-term alcoholic patients and remains depressed for 5 days. The interleukin (IL)-6/IL-10 ratio and the lipopolysaccharide-stimulated interferon gamma/IL-10 ratio in whole blood cells are decreased after surgery in long-term alcoholic patients. Depressed Tc1/Tc2, IL-6/IL-10 and lipopolysaccharide-stimulated interferon gamma/IL-10 ratios in the postoperative period are predictive of subsequent postoperative infections. Perioperative interventions should aim to minimize dysregulation of the immune system.

Beta2-microglobulin-dependent bacterial clearance and survival during murine Klebsiella pneumoniae bacteremia

Klebsiella pneumoniae is a leading cause of both community-acquired and nosocomial gram-negative bacterial pneumonia. A significant clinical complication of Klebsiella pulmonary infections is peripheral blood dissemination, resulting in a systemic infection concurrent with the localized pulmonary infection. We report here on the critical importance of beta(2)-microglobulin expression during murine K. pneumoniae bacteremia. Beta(2)-microglobulin knockout mice displayed significantly increased mortality upon intravenous inoculation that correlated with increased bacterial burden in the blood, liver, and spleen. As beta(2)-microglobulin knockout mice lack both CD8(+) T cells and invariant NK T cells, mouse models specifically deficient in either cell population were examined to see if this would account for the increased mortality noted in beta(2)-microglobulin knockout mice. Surprisingly, neither CD8 T-cell-deficient (TAP-1 knockout; in vivo anti-CD8 antibody treatment) nor invariant NK (iNK) T-cell-deficient (CD1d knockout, J alpha281 knockout) mice were more susceptible to K. pneumoniae bacteremia. Combined, these studies clearly indicate the importance of a beta(2)-microglobulin-dependent but CD8 T-cell- and iNK T-cell-independent mechanism critical for survival during K. pneumoniae bacteremia.

Host and microbiota factors that control Klebsiella pneumoniae mucosal colonization in mice

Klebsiella pneumoniae is both an opportunistic pathogen and a commensal organism. We have previously reported that K. pneumoniae strain IA565 (KpIA565) is non-pathogenic in a murine model of acute pneumonia. In this study, KpIA565 was inoculated into wild-type mice and found to stably colonize and persist in the nasal cavity and gastrointestinal tract of mice for up to 3weeks post-inoculation. Intranasal inoculation of wild-type or germ-free mice with KpIA565 resulted in similar bacterial levels in the nasal cavity, suggesting KpIA565 nasal colonization is independent of normal nasal microbiota. In contrast, KpIA565 gastrointestinal tract colonization was significantly higher in germ-free mice than in wild-type mice, indicating that members of the endogenous microbiota regulate KpIA565 colonization. In the presence of non-specific dextran sodium sulfate-induced inflammation, KpIA565 gastrointestinal tract colonization was significantly higher when compared to non-DSS treated mice. Interestingly, KpIA565 colonization was unaffected by Citrobacter rodentium-induced gastrointestinal tract inflammation. However, gastrointestinal tract colonization with K. pneumoniae strain IA565 had no impact on the inflammatory histopathology in either colitis model. This study is the first to identify and describe mechanisms influencing the growth and behavior of a murine commensal strain of K. pneumoniae.

Cyclic di-GMP stimulates protective innate immunity in bacterial pneumonia

Innate immunity is the primary mechanism by which extracellular bacterial pathogens are effectively cleared from the lung. We have previously shown that cyclic di-GMP (c-di-GMP [c-diguanylate]) is a novel small molecule immunomodulator and immunostimulatory agent that triggers protective host innate immune responses. Using a murine model of bacterial pneumonia, we show that local intranasal (i.n.) or systemic subcutaneous (s.c.) administration of c-di-GMP prior to intratracheal (i.t.) challenge with Klebsiella pneumoniae stimulates protective immunity against infection. Specifically, i.n. or s.c. administration of c-di-GMP 48 and 24 h prior to i.t. K. pneumoniae challenge resulted in significantly increased survival. Pretreatment with c-di-GMP resulted in a 5-fold reduction in bacterial CFU in the lung (P < 0.05) and an impressive >1,000-fold decrease in CFU in the blood (P < 0.01). c-di-GMP administration stimulated a robust innate response to bacterial challenge, characterized by enhanced accumulation of neutrophils and alphabeta T cells, as well as activated NK and alphabeta T lymphocytes, which was associated with earlier and more vigorous expression of chemokines and type I cytokines. Moreover, lung macrophages recovered from Klebsiella-infected mice pretreated with c-di-GMP expressed greater quantities of inducible nitric oxide synthase and nitric oxide ex vivo than did macrophages isolated from infected mice pretreated with the control, c-GMP. These findings demonstrate that c-di-GMP delivered in either a compartmentalized or systemic fashion stimulates protective innate immunity in the lung and protects mice against bacterial invasion. We propose that the cyclic dinucleotide c-di-GMP may be used clinically as an effective immunomodulator, immune enhancer, and vaccine adjuvant to protect against respiratory infection and pneumonia in humans and animals.

Air pollution particles diminish bacterial clearance in the primed lungs of mice

Epidemiological studies reveal increased incidence of lung infection when air pollution particle levels are increased. We postulate that one risk factor for bacterial pneumonia, prior viral infection, can prime the lung for greater deleterious effects of particles via the interferon-gamma (IFN-gamma) characteristic of successful host anti-viral responses. To test this postulate, we developed a mouse model in which mice were treated with gamma-interferon aerosol, followed by exposure to concentrated ambient particles (CAPs) collected from urban air. The mice were then infected with Streptococcus pneumoniae and the effect of these treatments on the lung's innate immune response was evaluated. The combination of IFN-gamma priming and CAPs exposure enhanced lung inflammation, manifest as increased polymorphonuclear granulocyte (PMN) recruitment to the lung, and elevated expression of pro-inflammatory cytokine mRNAs. Combined priming and CAPs exposure resulted in impaired pulmonary bacterial clearance, as well as increased oxidant production and diminished bacterial uptake by alveolar macrophages (AMs) and PMNs. The data suggest that priming and CAPs exposure lead to an inflamed alveolar milieu where oxidant stress causes loss of antibacterial functions in AMs and recruited PMNs. The model reported here will allow further analysis of priming and CAPs exposure on lung sensitivity to infection.

Pneumococcal capsular polysaccharide vaccine-mediated protection against serotype 3 Streptococcus pneumoniae in immunodeficient mice

Pneumococcal capsular polysaccharide (PPS) vaccines are less immunogenic in immunocompromised than immunocompetent individuals. However, neither the efficacy of PPS vaccines in immunocompromised individuals nor the host cellular subsets required for vaccine efficacy against pneumococcal disease have been directly investigated. In this study, we vaccinated CD4-deficient (CD4(-/-)), CD8-deficient (CD8(-/-)), and secretory immunoglobulin M-deficient (sIgM(-/-)) mice and wild-type C57BL/6 (Wt) mice with a conjugate of PPS of serotype 3 and tetanus toxoid (PPS3-TT) and determined the antibody response and efficacy of vaccination against systemic and pulmonary challenge with serotype 3 pneumococcus in immunized and control mice. Our results showed that the isotype and predominant IgG subclass of the PPS3 response differed between immunodeficient mouse strains and between immunodeficient and Wt mice, with CD8(-/-) mice having the most robust response. Vaccination protected Wt, CD4(-/-), and sIgM(-/-) mice from death resulting from both systemic and pulmonary challenge, whereas CD8(-/-) mice were protected only from systemic and not from pulmonary challenge. Passive vaccination with PPS3-TT-induced sera from Wt, CD4(-/-), CD8(-/-), and sIgM(-/-) mice protected naïve Wt mice from death due to pulmonary challenge; however, CD8(-/-) mice were not protected by sera from Wt or CD8(-/-) mice. Our findings suggest that PPS-based vaccines can be effective in the setting of CD4 T-cell deficiency but that CD8 T cells could be required for vaccine-mediated protection against pulmonary challenge with serotype 3 pneumococcus.

Differential effects of ethanol on IFN-gamma- and TNF-alpha-producing splenic T lymphocytes in a murine model of gram-negative pneumonia

The incidence of bacterial pneumonia is increased in alcoholic patients. Alcohol consumption has been shown to impair cytokine production. Tumor necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma) are critical for host defense against Klebsiella pneumoniae (K. pneumoniae). In order to examine the influence of alcohol on the immune response to infection, we investigated the frequency of TNF-alpha and IFN-gamma produced by splenic T-lymphocytes in a murine model of gram-negative pneumonia initiated after 8 days of alcohol treatment. Thirty-two Balb/c mice were pretreated with ethanol (3 mg/g body weight) or saline intraperitoneally over 8 days. On day 7 half of each group was administered K. pneumoniae. Mice were sacrificed 24 hours later to excise lungs and liver for histological assessment and spleens for cell isolation. IFN-gamma- and TNF-alpha-producing CD4(+) and CD8(+) lymphocytes were determined by FACS analysis. In mice with Klebsiella infection, the percentages of IFN-gamma-producing CD4(+) (P < 0.01) and CD8(+) (P < 0.01) were significantly decreased, the percentages of TNF-alpha-producing CD4(+) (P = 0.01) and CD8(+) (P < 0.01) T cells were significantly elevated after alcohol treatment compared with mice with saline treatment. The histological assessment showed an aggravation of K. pneumoniae-induced pneumonia in alcohol-treated mice. Alcohol differentially affects IFN-gamma and TNF-alpha production in Klebsiella-infected mice. Both effects obviously led to a weakened immune response as seen by increased histological damage. This suggests a role of T cells in the increased susceptibility of the alcoholic host to nosocomial infection due to inadequate cytokine response.

Identification of Klebsiella pneumoniae genes uniquely expressed in a strain virulent using a murine model of bacterial pneumonia

Klebsiella pneumoniae is a gram-negative bacterium of significant clinical importance. This study examines the differential pulmonary host anti-bacterial responses towards two clinical isolates of K. pneumoniae. Intratracheal inoculation with 7 x 10(4)CFU of strain 43816 induced 100% mortality in C57BL/6J mice within 5 days post infection, whereas infection with 5 x 10(5)CFU of strain IA565 resulted in 100% survival. Infection with strain 43816 resulted in significant pulmonary and peripheral blood bacterial burden and induction of the chemokines MIP-2, KC and MCP-1 by 24h post infection. In contrast, IA565-infected mice displayed basal chemokine levels and no detectable bacteria by 24h post inoculation were isolated from lungs or peripheral blood. These data indicate an apparent lack of pathogenicity of strain IA565. Since little is known about Klebsiella-specific virulence genes, we have utilized PCR-based genomic DNA and cDNA suppressive subtractive hybridization and identified nine DNA sequences unique to the pathogenic strain of K. pneumoniae 43816. These sequences were highly homologous to enteric bacterial genes regulating iron uptake, fimbrial-mediated adhesion, energy production and conversion, transcriptional regulation, signal transduction, restriction endonuclease activity, and membrane transport.

Comparison of the host responses to wild-type and cpsB mutant Klebsiella pneumoniae infections

Previously, we established an intranasal mouse model of Klebsiella pneumoniae infection and validated its utility using a highly virulent wild-type strain and an avirulent capsular polysaccharide mutant. In the present study we compare the host responses to both infections by examining cytokine production, cellular infiltration, pulmonary histology, and intranasal immunization.