Stimulation of lung innate immunity protects against lethal pneumococcal pneumonia in mice

The RNA receptor RIG-I binding synthetic oligodeoxynucleotide promotes pneumonia survival

Pneumonia is a worldwide threat to public health, demanding novel preventative and therapeutic strategies. The lung epithelium is a critical environmental interface that functions as a physical barrier to pathogen invasion while also actively sensing and responding to pathogens. We have reported that stimulating lung epithelial cells with a combination therapeutic consisting of a diacylated lipopeptide and a synthetic CpG oligodeoxynucleotide (ODN) induces synergistic pneumonia protection against a wide range of pathogens. We report here that mice deficient in TLR9, the previously described receptor for ODN, still displayed partial ODN-induced protection. This prompted us to seek an alternate ODN receptor, and we discovered by mass spectroscopy that the RNA sensor RIG-I could also bind DNA-like ODN. ODN binding by RIG-I resulted in MAVS-dependent pneumonia-protective signaling events. While RIG-I is essential to native defenses against viral infections, we report that therapeutic RIG-I activation with ODN promoted pathogen killing and host survival following both viral and bacterial challenges. These data indicate that maximal ODN-induced pneumonia protection requires activation of both the TLR9/MyD88 and RIG-I/MAVS signaling pathways. These findings not only identify what we believe to be a novel pattern recognition receptor for DNA-like molecules, but reveal a potential therapeutic strategy to protect susceptible individuals against lethal pneumonias during periods of peak vulnerability.

Alveolar epithelial cells shape lipopolysaccharide-induced inflammatory responses and reprogramming of alveolar macrophages

Alveolar macrophages (AMs) are sentinels in the airways, where they sense and respond to invading microbes and other stimuli. Unlike macrophages in other locations, AMs can remain responsive to Gram-negative lipopolysaccharides (LPS) after they have responded to LPS in vivo (they do not develop "endotoxin tolerance"), suggesting that the alveolar microenvironment may influence their responses. Although alveolar epithelial cells (AECs) normally limit AMs' innate responses, preventing inflammation induced by harmless antigens in the lung, how AECs influence the innate responses of AMs to infectious agents has been uncertain. Here we report that (1) after exposure to aspirated (intranasal instillation) LPS, AMs increase their responses to TLR agonists and elevate their phagocytic and bactericidal activities in mice; (2) Aspirated LPS pre-exposure increases host resistance to pulmonary infection caused by Gram-negative bacteria and the protection effect lasts for at least 35 days; (3) LPS stimulation of AECs both increases AMs' innate immune responses and prevents AMs from developing tolerance in vitro; (4) Upon LPS stimulation, AMs secreted TNF-α induces AECs to release GM-CSF, which potentiates AMs' response. These experiments have revealed a previously unappreciated role that AECs may play in boosting the innate responses of AMs and promoting resistance to pulmonary infections.

Antimicrobial mitochondrial reactive oxygen species induction by lung epithelial immunometabolic modulation

Pneumonia is a worldwide threat, making discovery of novel means to combat lower respiratory tract infection an urgent need. Manipulating the lungs' intrinsic host defenses by therapeutic delivery of certain pathogen-associated molecular patterns protects mice against pneumonia in a reactive oxygen species (ROS)-dependent manner. Here we show that antimicrobial ROS are induced from lung epithelial cells by interactions of CpG oligodeoxynucleotides (ODN) with mitochondrial voltage-dependent anion channel 1 (VDAC1). The ODN-VDAC1 interaction alters cellular ATP/ADP/AMP localization, increases delivery of electrons to the electron transport chain (ETC), increases mitochondrial membrane potential (ΔΨm), differentially modulates ETC complex activities and consequently results in leak of electrons from ETC complex III and superoxide formation. The ODN-induced mitochondrial ROS yield protective antibacterial effects. Together, these studies identify a therapeutic metabolic manipulation strategy to broadly protect against pneumonia without reliance on antibiotics.

Mechanical bacterial lysate enhances antimicrobial barrier mechanisms in human airway epithelial cells

Polyvalent mechanical bacterial lysate is effective in the prevention of respiratory tract infections, although its mechanism of action is not entirely elucidated. Because epithelial cells constitute the frontline defense against infections, we investigated the molecular mechanisms of innate response exerted by bronchial epithelial cells in the presence of polyvalent mechanical bacterial lysate. By using primary human bronchial epithelial cells, we observed that polyvalent mechanical bacterial lysate was able to increase the expression of cellular adhesion molecules such as ICAM-1 and E-cadherin, as well as the expression of amphiregulin, a growth factor able to support human bronchial epithelial cell proliferation. Remarkably, polyvalent mechanical bacterial lysate promoted in human bronchial epithelial cells the de novo expression of human β-defensin-2, a major antimicrobial peptide, conferring them a direct antimicrobial activity. Moreover, polyvalent mechanical bacterial lysate-stimulated human bronchial epithelial cells provided signals for increased IL-22 production by innate lymphoid cells via IL-23, which could further contribute to the release of antimicrobial peptides by epithelial cells. In agreement with these in vitro data, the concentration of both IL-23 and antimicrobial peptides (human β-defensin-2 and LL-37) increased in the saliva of healthy volunteers after sublingual administration of polyvalent mechanical bacterial lysate. Altogether, these results indicate that polyvalent mechanical bacterial lysate administration might support mucosal barrier integrity and promote mechanisms of antimicrobial activity in airway epithelial cells.

Antimicrobial mitochondrial reactive oxygen species induction by lung epithelial metabolic reprogramming

Pneumonia is a worldwide threat, making discovery of novel means to combat lower respiratory tract infections an urgent need. We have previously shown that manipulating the lungs' intrinsic host defenses by therapeutic delivery of a unique dyad of pathogen-associated molecular patterns protects mice against pneumonia in a reactive oxygen species (ROS)-dependent manner. Here we show that antimicrobial ROS are induced from lung epithelial cells by interactions of CpG oligodeoxynucleotides (ODNs) with mitochondrial voltage-dependent anion channel 1 (VDAC1) without dependence on Toll-like receptor 9 (TLR9). The ODN-VDAC1 interaction alters cellular ATP/ADP/AMP localization, increases delivery of electrons to the electron transport chain (ETC), enhances mitochondrial membrane potential (Δ Ψm ), and differentially modulates ETC complex activities. These combined effects promote leak of electrons from ETC complex III, resulting in superoxide formation. The ODN-induced mitochondrial ROS yield protective antibacterial effects. Together, these studies identify a therapeutic metabolic manipulation strategy that has the potential to broadly protect patients against pneumonia during periods of peak vulnerability without reliance on currently available antibiotics.

Author Summary

Pneumonia is a major cause of death worldwide. Increasing antibiotic resistance and expanding immunocompromised populations continue to enhance the clinical urgency to find new strategies to prevent and treat pneumonia. We have identified a novel inhaled therapeutic that stimulates lung epithelial defenses to protect mice against pneumonia in a manner that depends on production of reactive oxygen species (ROS). Here, we report that the induction of protective ROS from lung epithelial mitochondria occurs following the interaction of one component of the treatment, an oligodeoxynucleotide, with the mitochondrial voltage-dependent anion channel 1. This interaction alters energy transfer between the mitochondria and the cytosol, resulting in metabolic reprogramming that drives more electrons into the electron transport chain, then causes electrons to leak from the electron transport chain to form protective ROS. While antioxidant therapies are endorsed in many other disease states, we present here an example of therapeutic induction of ROS that is associated with broad protection against pneumonia without reliance on administration of antibiotics.

Epithelial immunomodulation by aerosolized Toll-like receptor agonists prevents allergic inflammation in airway mucosa in mice

Allergic asthma is a chronic inflammatory respiratory disease associated with eosinophilic infiltration, increased mucus production, airway hyperresponsiveness, and airway remodeling. Epidemiologic data reveal that the prevalence of allergic sensitization and associated diseases has increased in the twentieth century. This has been hypothesized to be partly due to reduced contact with microbial organisms (the hygiene hypothesis) in industrialized society. Airway epithelial cells, once considered a static physical barrier between the body and the external world, are now widely recognized as immunologically active cells that can initiate, maintain, and restrain inflammatory responses, such as those that mediate allergic disease. Airway epithelial cells can sense allergens via expression of myriad Toll-like receptors (TLRs) and other pattern-recognition receptors. We sought to determine whether the innate immune response stimulated by a combination of Pam2CSK4 ("Pam2", TLR2/6 ligand) and a class C oligodeoxynucleotide ODN362 ("ODN", TLR9 ligand), when delivered together by aerosol ("Pam2ODN"), can modulate the allergic immune response to allergens. Treatment with Pam2ODN 7 days before sensitization to House Dust Mite (HDM) extract resulted in a strong reduction in eosinophilic and lymphocytic inflammation. This Pam2ODN immunomodulatory effect was also seen using Ovalbumin (OVA) and A. oryzae (Ao) mouse models. The immunomodulatory effect was observed as much as 30 days before sensitization to HDM, but ineffective just 2 days after sensitization, suggesting that Pam2ODN immunomodulation lowers the allergic responsiveness of the lung, and reduces the likelihood of inappropriate sensitization to aeroallergens. Furthermore, Pam2 and ODN cooperated synergistically suggesting that this treatment is superior to any single agonist in the setting of allergen immunotherapy.

The effect of aerosolized bacterial lysate on experimentally induced Mannheimia haemolytica pneumonia in calves

Bovine respiratory disease (BRD) often occurs during specific periods of increased susceptibility when stress, viral infection, or reduced air quality are thought to suppress respiratory defences. The innate immune system is rapidly responsive and broadly protective and could be a target for preventing BRD during these periods of increased susceptibility. This study tested the hypothesis that stimulation of pulmonary innate immune responses by aerosol delivery of a lysate of killed Escherichia coli and Staphylococcus aureus bacteria would protect calves against Mannheimia haemolytica pneumonia. Ten clean-catch colostrum-deprived Holstein calves were randomly assigned to receive either aerosolized bacterial lysate or saline 24 hours before M. haemolytica challenge. Effects of this treatment on clinical, hematologic, microbiologic, and pathologic outcomes were assessed. Compared to controls, lysate-treated calves had lower serum haptoglobin and blood leukocyte and neutrophil concentrations following M. haemolytica challenge. There were no differences in temperature, heart and respiratory rates, clinical scores, ultrasound lesions, or number of M. haemolytica in the nasal cavity or lung. Thus, treatment with bacterial lysate prior to M. haemolytica challenge appeared to ameliorate early measures of inflammation but did not provide sufficient protection to substantially alter the course of disease.

Krueppel-Like Factor 4 Expression in Phagocytes Regulates Early Inflammatory Response and Disease Severity in Pneumococcal Pneumonia

The transcription factor Krueppel-like factor (KLF) 4 fosters the pro-inflammatory immune response in macrophages and polymorphonuclear neutrophils (PMNs) when stimulated with Streptococcus pneumoniae, the main causative pathogen of community-acquired pneumonia (CAP). Here, we investigated the impact of KLF4 expression in myeloid cells such as macrophages and PMNs on inflammatory response and disease severity in a pneumococcal pneumonia mouse model and in patients admitted to hospital with CAP. We found that mice with a myeloid-specific knockout of KLF4 mount an insufficient early immune response with reduced levels of pro-inflammatory cytokines and increased levels of the anti-inflammatory cytokine interleukin (IL) 10 in bronchoalveolar lavage fluid and plasma and an impaired bacterial clearance from the lungs 24 hours after infection with S. pneumoniae. This results in higher rates of bacteremia, increased lung tissue damage, more severe symptoms of infection and reduced survival. Higher KLF4 gene expression levels in the peripheral blood of patients with CAP at hospital admission correlate with a favourable clinical presentation (lower sequential organ failure assessment (SOFA) score), lower serum levels of IL-10 at admission, shorter hospital stay and lower mortality or requirement of intensive care unit treatment within 28 days after admission. Thus, KLF4 in myeloid cells such as macrophages and PMNs is an important regulator of the early pro-inflammatory immune response and, therefore, a potentially interesting target for therapeutic interventions in pneumococcal pneumonia.

Acceptability of a Sublingual Drug Formulation for Respiratory Tract Infections in Children Aged 3 to 5 Years

In pediatrics, acceptability has emerged as a key factor for compliance, and consequently for treatment safety and efficacy. Polyvalent mechanical bacterial lysate (PMBL) in 50-mg sublingual tablets is indicated in children and adults for the prophylaxis of recurrent respiratory tract infections. This medication may be prescribed in children over 3 years of age; the appropriateness of this sublingual formulation should thus be demonstrated amongst young children. Using a multivariate approach integrating the many aspects of acceptability, standardized observer reports were collected for medication intake over the course of treatment (days 1, 2, and 10) in 37 patients aged 3 to 5 years, and then analyzed in an intelligible model: the acceptability reference framework. According to this multidimensional model, 50-mg PMBL sublingual tablets were classified as "positively accepted" in children aged 3 to 5 years on all three days of evaluation. As the acceptability evaluation should be relative, we demonstrated that there was no significant difference between the acceptability of these sublingual tablets and a score reflecting the average acceptability of oral/buccal medicines in preschoolers. These results highlight that sublingual formulations could be appropriate for use in preschoolers.

Host-directed therapy in foals can enhance functional innate immunity and reduce severity of Rhodococcus equi pneumonia

Pneumonia caused by the intracellular bacterium Rhodococcus equi is an important cause of disease and death in immunocompromised hosts, especially foals. Antibiotics are the standard of care for treating R. equi pneumonia in foals, and adjunctive therapies are needed. We tested whether nebulization with TLR agonists (PUL-042) in foals would improve innate immunity and reduce the severity and duration of pneumonia following R. equi infection. Neonatal foals (n = 48) were nebulized with either PUL-042 or vehicle, and their lung cells infected ex vivo. PUL-042 increased inflammatory cytokines in BAL fluid and alveolar macrophages after ex vivo infection with R. equi. Then, the in vivo effects of PUL-042 on clinical signs of pneumonia were examined in 22 additional foals after intrabronchial challenge with R. equi. Foals infected and nebulized with PUL-042 or vehicle alone had a shorter duration of clinical signs of pneumonia and smaller pulmonary lesions when compared to non-nebulized foals. Our results demonstrate that host-directed therapy can enhance neonatal immune responses against respiratory pathogens and reduce the duration and severity of R. equi pneumonia.

Live attenuated Bordetella pertussis vaccine candidate BPZE1 transiently protects against lethal pneumococcal disease in mice

BPZE1 is a live attenuated vaccine against infection by Bordetella pertussis, the causative agent of whooping cough. It was previously shown that BPZE1 provides heterologous protection in mouse models of disease caused by unrelated pathogens, such as influenza virus and respiratory syncytial virus. Protection was also observed in mouse models of asthma and contact dermatitis. In this study, we demonstrate that BPZE1 also displays protection against an unrelated bacterial pathogen in a mouse model of invasive pneumococcal disease mediated by Streptococcus pneumoniae. While a single administration of BPZE1 provided no protection, two doses of 10⁶ colony-forming units of BPZE1 given in a three-week interval protected against mortality, lung colonization and dissemination in both BALB/c and C57BL/6 mice. Unlike for the previously reported influenza challenge model, protection was short-lived, and waned within days after booster vaccination. Formaldehyde-killed BPZE1 protected only when administered following a live prime, indicating that priming requires live BPZE1 for protection. Protection against mortality was directly linked to substantially decreased bacterial dissemination in the blood and was lost in MyD88 knock-out mice, demonstrating the role of the innate immune system in the mechanism of protection. This is the first report on a heterologous protective effect of the live BPZE1 vaccine candidate against an unrelated bacterial infection.

The Role of Innate Immunity in Pulmonary Infections

Innate immunity forms a protective line of defense in the early stages of pulmonary infection. The primary cellular players of the innate immunity against respiratory infections are alveolar macrophages (AMs), dendritic cells (DCs), neutrophils, natural killer (NK) cells, and innate lymphoid cells (ILCs). They recognize conserved structures of microorganisms through membrane-bound and intracellular receptors to initiate appropriate responses. In this review, we focus on the prominent roles of innate immune cells and summarize transmembrane and cytosolic pattern recognition receptor (PRR) signaling recognition mechanisms during pulmonary microbial infections. Understanding the mechanisms of PRR signal recognition during pulmonary pathogen infections will help us to understand pulmonary immunopathology and lay a foundation for the development of effective therapies to treat and/or prevent pulmonary infections.

Potential effects of vaccinations on the prevention of COVID-19: rationale, clinical evidence, risks, and public health considerations

Introduction Coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus (SARS-CoV-2), has quickly spread around the world. Areas covered This review will discuss the available immunologic and clinical evidence to support the benefit of the influenza, pneumococcal, and tuberculosis vaccines in the context of COVID-19 as well as to provide an overview on the COVID-19-specific vaccines that are in the development pipeline. In addition, implications for vaccination strategies from a public health perspective will be discussed. Expert opinion Some vaccines are being considered for their potentially beneficial role in preventing or improving the prognosis of COVID-19: influenza, pneumococcal and tuberculosis vaccines. These vaccines may have either direct effect on COVID-19 via different types of immune responses or indirect effects by reducing the burden of viral and bacterial respiratory diseases on individual patients and national healthcare system and by facilitating differential diagnoses with other viral/bacterial respiratory disease. On the other hand, a large number of candidate vaccines against SARS-CoV-2 are currently in the pipeline and undergoing phase I, II, and III clinical studies. As SARS-CoV-2 vaccines are expected to be marketed through accelerated regulatory pathways, vaccinovigilance as well as planning of a successful vaccination campaign will play a major role in protecting public health.

IL-6 Deficiency Exacerbates Allergic Asthma and Abrogates the Protective Effect of Allergic Inflammation against Streptococcus pneumoniae Pathogenesis

Allergic asthma (AA) is characterized as a Th2-biased airway inflammation that can develop lung inflammation and remodeling of the respiratory tract. Streptococcus pneumoniae is a major respiratory pathogen, causing noninvasive (otitis media and pneumonia) and invasive diseases (sepsis) in humans. We sought to determine the role of IL-6 in the regulation of lung inflammation in murine AA caused by Aspergillus fumigatus as well as its consequence on the regulation of airway barrier integrity and S. pneumoniae disease. In an AA model, IL-6 deficiency led to increased lung inflammation, eosinophil recruitment, tissue pathology, and collagen deposition. Additionally, IL-6-deficient asthmatic mice exhibited reduced goblet cell hyperplasia and increased TGF-β production. These key changes in the lungs of IL-6-deficient asthmatic mice resulted in dysregulated tight junction proteins and increased lung permeability. Whereas the host response to AA protected against S. pneumoniae lung disease, the IL-6 deficiency abrogated the protective effect of allergic inflammation against S. pneumoniae pathogenesis. Consistent with in vivo data, IL-6 knockdown by small interfering RNA or the blockade of IL-6R signaling exacerbated the TGF-β-induced dysregulation of tight junction proteins, E-cadherin and N-cadherin expression, and STAT3 phosphorylation in MLE-12 epithelial cells. Our findings demonstrate a previously unrecognized role of host IL-6 response in the regulation of lung inflammation during AA and the control of S. pneumoniae bacterial disease. A better understanding of the interactions between lung inflammation and barrier framework could lead to the development of therapies to control asthma inflammation and preserve barrier integrity.

Pulmonary and systemic responses to aerosolized lysate of Staphylococcus aureus and Escherichia coli in calves

Background

Constitutive and inducible defenses protect the respiratory tract from bacterial infection. The objective of this study was to characterize the response to an aerosolized lysate of killed bacteria, as a basis for studying the regulation and in vivo effects of these inducible innate immune responses.

Results

Bacterial lysate consisting of heat-killed and sonicated Staphylococcus aureus and Escherichia coli was aerosolized to 6 calves and systemic and pulmonary innate immune and inflammatory responses were measured in the first 24 h relative to baseline. Evaluated parameters included clinical parameters (body temperature and heart and respiratory rates), blood acute phase proteins and leukocyte counts, and leukocytes and proteins in bronchoalveolar lavage fluid. Mild clinical signs with increased heart rates and rectal temperatures developed following administration of the lysate, with resolution by 24 h. Serum haptoglobin and plasma fibrinogen concentrations were elevated at 24 h relative to baseline. Bronchoalveolar lavage fluid (BALF) had increased cellularity and increased proportion of neutrophils, as well as higher concentrations of interleukin (IL)-8, IL-10 and total protein at 24 h relative to baseline. Mass spectrometry identified 965 unique proteins in BALF: 19 proteins were increased and 26 proteins were decreased relative to baseline. The upregulated proteins included those involved in innate immunity including activation of complement, neutrophils and platelets. At postmortem examination, calves receiving higher doses of lysate had areas of lobular consolidation and interlobular edema. Histologically, neutrophils were present within bronchioles and to a lesser extent within alveoli. Calves receiving highest doses of lysate had patchy areas of neutrophils, hemorrhage and hyaline membranes within alveoli.

Conclusions

Aerosolization of bacterial lysate stimulated an innate immune response in lungs and airways, with alveolar damage observed at higher doses. Such a stimulus could be of value for investigating the effects of inducible innate immune responses on occurrence of disease, or for evaluating how stress, drugs or genetics affect these dynamic responses of the respiratory tract.

Broad-spectrum suppression of bacterial pneumonia by aminoglycoside-propagated Acinetobacter baumannii

Antimicrobial resistance is increasing in pathogenic bacteria. Yet, the effect of antibiotic exposure on resistant bacteria has been underexplored and may affect pathogenesis. Here we describe the discovery that propagation of the human pathogen Acinetobacter baumannii in an aminoglycoside antibiotic results in alterations to the bacterium that interact with lung innate immunity resulting in enhanced bacterial clearance. Co-inoculation of mice with A. baumannii grown in the presence and absence of the aminoglycoside, kanamycin, induces enhanced clearance of a non-kanamycin-propagated strain. This finding can be replicated when kanamycin-propagated A. baumannii is killed prior to co-inoculation of mice, indicating the enhanced bacterial clearance results from interactions with innate host defenses in the lung. Infection with kanamycin-propagated A. baumannii alters the kinetics of phagocyte recruitment to the lung and reduces pro- and anti-inflammatory cytokine and chemokine production in the lung and blood. This culminates in reduced histopathologic evidence of lung injury during infection despite enhanced bacterial clearance. Further, the antibacterial response induced by killed aminoglycoside-propagated A. baumannii enhances the clearance of multiple clinically relevant Gram-negative pathogens from the lungs of infected mice. Together, these findings exemplify cooperation between antibiotics and the host immune system that affords protection against multiple antibiotic-resistant bacterial pathogens. Further, these findings highlight the potential for the development of a broad-spectrum therapeutic that exploits a similar mechanism to that described here and acts as an innate immunity modulator.

Inducible epithelial resistance against acute Sendai virus infection prevents chronic asthma-like lung disease in mice

BACKGROUND AND PURPOSE

Respiratory viral infections play central roles in the initiation, exacerbation and progression of asthma in humans. An acute paramyxoviral infection in mice can cause a chronic lung disease that resembles human asthma. We sought to determine whether reduction of Sendai virus lung burden in mice by stimulating innate immunity with aerosolized Toll-like receptor (TLR) agonists could attenuate the severity of chronic asthma-like lung disease.

EXPERIMENTAL APPROACH

Mice were treated by aerosol with 1-μM oligodeoxynucleotide (ODN) M362, an agonist of the TLR9 homodimer, and 4-μM Pam2CSK4 (Pam2), an agonist of the TLR2/6 heterodimer, within a few days before or after Sendai virus challenge.

KEY RESULTS

Treatment with ODN/Pam2 caused ~75% reduction in lung Sendai virus burden 5 days after challenge. The reduction in acute lung virus burden was associated with marked reductions 49 days after viral challenge in eosinophilic and lymphocytic lung inflammation, airway mucous metaplasia, lumenal mucus occlusion and hyperresponsiveness to methacholine. Mechanistically, ODN/Pam2 treatment attenuated the chronic asthma phenotype by suppressing IL-33 production by type 2 pneumocytes, both by reducing the severity of acute infection and by down-regulating Type 2 (allergic) inflammation.

CONCLUSION AND IMPLICATIONS

These data suggest that treatment of susceptible human hosts with aerosolized ODN and Pam2 at the time of a respiratory viral infection might attenuate the severity of the acute infection and reduce initiation, exacerbation and progression of asthma.

Animal Models of Pneumococcal pneumonia

Streptococcus pneumoniae remains the most common bacterial pathogen causing lower respiratory tract infections and is a leading cause of morbidity and mortality worldwide, especially in children and the elderly. Another important aspect related to pneumococcal infections is the persistent rate of penicillin and macrolide resistance. Therefore, animal models have been developed to better understand the pathogenesis of pneumococcal disease and test new therapeutic agents and vaccines. This narrative review will focus on the characteristics of the different animal pneumococcal pneumonia models. The assessment of the different animal models will include considerations regarding pneumococcal strains, microbiology properties, procedures used for bacterial inoculation, pathogenesis, clinical characteristics, diagnosis, treatment, and preventive approaches.

One-hit wonder: Late after burn injury, granulocytes can clear one bacterial infection but cannot control a subsequent infection

OBJECTIVE

Burn injury induces an acute hyperactive immune response followed by a chronic immune dysregulation that leaves those afflicted susceptible to multiple secondary infections. Many murine models are able to recapitulate the acute immune response to burn injury, yet few models are able to recapitulate long-term immune suppression and thus chronic susceptibility to bacterial infections seen in burn patients. This has hindered the field, making evaluation of the mechanisms responsible for these susceptibilities difficult to study. Herein we describe a novel mouse model of burn injury that promotes chronic immune suppression allowing for susceptibility to primary and secondary infections and thus allows for the evaluation of associated mechanisms.

METHODS

C57Bl/6 mice receiving a full-thickness contact burn were infected with Pseudomonas aeruginosa 14 days (primary infection) and/or 17 days (secondary infection) after burn or sham injury. The survival, pulmonary and systemic bacterial load as well as frequency and function of innate immune cells (neutrophils and macrophages) were evaluated.

RESULTS

Following secondary infection, burn mice were less effective in clearance of bacteria compared to sham injured or burn mice following a primary infection. Following secondary infection both neutrophils and macrophages recruited to the airways exhibited reduced production of anti-bacterial reactive oxygen and nitrogen species and the pro-inflammatory cytokineIL-12 while macrophages demonstrated increased expression of the anti-inflammatory cytokine interleukin-10 compared to those from sham burned mice and/or burn mice receiving a primary infection. In addition the BALF from these mice contained significantly higher level so of the anti-inflammatory cytokine IL-4 compared to those from sham burned mice and/or burn mice receiving a primary infection.

CONCLUSIONS

Burn-mediated protection from infection is transient, with a secondary infection inducing immune protection to collapse. Repeated infection leads to increased neutrophil and macrophage numbers in the lungs late after burn injury, with diminished innate immune cell function and an increased anti-inflammatory cytokine environment.

Integrative Physiology of Pneumonia

Pneumonia is a type of acute lower respiratory infection that is common and severe. The outcome of lower respiratory infection is determined by the degrees to which immunity is protective and inflammation is damaging. Intercellular and interorgan signaling networks coordinate these actions to fight infection and protect the tissue. Cells residing in the lung initiate and steer these responses, with additional immunity effectors recruited from the bloodstream. Responses of extrapulmonary tissues, including the liver, bone marrow, and others, are essential to resistance and resilience. Responses in the lung and extrapulmonary organs can also be counterproductive and drive acute and chronic comorbidities after respiratory infection. This review discusses cell-specific and organ-specific roles in the integrated physiological response to acute lung infection, and the mechanisms by which intercellular and interorgan signaling contribute to host defense and healthy respiratory physiology or to acute lung injury, chronic pulmonary disease, and adverse extrapulmonary sequelae. Pneumonia should no longer be perceived as simply an acute infection of the lung. Pneumonia susceptibility reflects ongoing and poorly understood chronic conditions, and pneumonia results in diverse and often persistent deleterious consequences for multiple physiological systems.

Host-pathogen kinetics during influenza infection and coinfection: insights from predictive modeling

Influenza virus infections are a leading cause of morbidity and mortality worldwide. This is due in part to the continual emergence of new viral variants and to synergistic interactions with other viruses and bacteria. There is a lack of understanding about how host responses work to control the infection and how other pathogens capitalize on the altered immune state. The complexity of multi-pathogen infections makes dissecting contributing mechanisms, which may be non-linear and occur on different time scales, challenging. Fortunately, mathematical models have been able to uncover infection control mechanisms, establish regulatory feedbacks, connect mechanisms across time scales, and determine the processes that dictate different disease outcomes. These models have tested existing hypotheses and generated new hypotheses, some of which have been subsequently tested and validated in the laboratory. They have been particularly a key in studying influenza-bacteria coinfections and will be undoubtedly be useful in examining the interplay between influenza virus and other viruses. Here, I review recent advances in modeling influenza-related infections, the novel biological insight that has been gained through modeling, the importance of model-driven experimental design, and future directions of the field.

Allergic Asthma Favors Brucella Growth in the Lungs of Infected Mice

Allergic asthma is a chronic Th2 inflammatory disease of the lower airways affecting a growing number of people worldwide. The impact of infections and microbiota composition on allergic asthma has been investigated frequently. Until now, however, there have been few attempts to investigate the impact of asthma on the control of infectious microorganisms and the underlying mechanisms. In this work, we characterize the consequences of allergic asthma on intranasal (i.n.) infection by Brucella bacteria in mice. We observed that i.n. sensitization with extracts of the house dust mite Dermatophagoides farinae or the mold Alternaria alternata (Alt) significantly increased the number of Brucella melitensis, Brucella suis, and Brucella abortus in the lungs of infected mice. Microscopic analysis showed dense aggregates of infected cells composed mainly of alveolar macrophages (CD11c+ F4/80+ MHCII+) surrounded by neutrophils (Ly-6G+). Asthma-induced Brucella susceptibility appears to be dependent on CD4+ T cells, the IL-4/STAT6 signaling pathway and IL-10, and is maintained in IL-12- and IFN-γR-deficient mice. The effects of the Alt sensitization protocol were also tested on Streptococcus pneumoniae and Mycobacterium tuberculosis pulmonary infections. Surprisingly, we observed that Alt sensitization strongly increases the survival of S. pneumoniae infected mice by a T cell and STAT6 independent signaling pathway. In contrast, the course of M. tuberculosis infection is not affected in the lungs of sensitized mice. Our work demonstrates that the impact of the same allergic sensitization protocol can be neutral, negative, or positive with regard to the resistance of mice to bacterial infection, depending on the bacterial species.

Mycobacterium tuberculosis Invasion of the Human Lung: First Contact

Early immune responses to Mycobacterium tuberculosis (Mtb) invasion of the human lung play a decisive role in the outcome of infection, leading to either rapid clearance of the pathogen or stable infection. Despite their critical impact on health and disease, these early host-pathogen interactions at the primary site of infection are still poorly understood. In vitro studies cannot fully reflect the complexity of the lung architecture and its impact on host-pathogen interactions, while animal models have their own limitations. In this study, we have investigated the initial responses in human lung tissue explants to Mtb infection, focusing primarily on gene expression patterns in different tissue-resident cell types. As first cell types confronted with pathogens invading the lung, alveolar macrophages, and epithelial cells displayed rapid proinflammatory chemokine and cytokine responses to Mtb infection. Other tissue-resident innate cells like gamma/delta T cells, mucosal associated invariant T cells, and natural killer cells showed partially similar but weaker responses, with a high degree of variability across different donors. Finally, we investigated the responses of tissue-resident innate lymphoid cells to the inflammatory milieu induced by Mtb infection. Our infection model provides a unique approach toward host-pathogen interactions at the natural port of Mtb entry and site of its implantation, i.e., the human lung. Our data provide a first detailed insight into the early responses of different relevant pulmonary cells in the alveolar microenvironment to contact with Mtb. These results can form the basis for the identification of host markers that orchestrate early host defense and provide resistance or susceptibility to stable Mtb infection.

Interleukin 1α (IL-1α) Promotes Pathogenic Immature Myeloid Cells and IL-1β Favors Protective Mature Myeloid Cells During Acute Lung Infection

Bacterial pneumonia is a common risk factor for acute lung injury and sepsis-mediated death, but the mechanisms underlying the overt inflammation and accompanying pathology are unclear. Infiltration of immature myeloid cells and necrotizing inflammation mediate severe pathology and death during pulmonary infection with Francisella tularensis. However, eliciting mature myeloid cells provides protection. Yet, the host factors responsible for this pathologic immature myeloid cell response are unknown. Here, we report that while the influx of both mature and immature myeloid cells is strictly MyD88 dependent, the interleukin 1 (IL-1) receptor mediates an important dual function via its ligands IL-1α and IL-1β. Although IL-1β favors the appearance of bacteria-clearing mature myeloid cells, IL-1α contributes to lung infiltration by ineffective and pathologic immature myeloid cells. Finally, IL-1α and IL-1β are not the sole factors involved, but myeloid cell responses during acute pneumonia were largely unaffected by lung levels of interleukin 10, interleukin 17, CXCL1, granulocyte colony-stimulating factor, and granulocyte-macrophage colony-stimulating factor.

Lung epithelial cells: therapeutically inducible effectors of antimicrobial defense

Lung epithelial cells are increasingly recognized to be active effectors of microbial defense, contributing to both innate and adaptive immune function in the lower respiratory tract. As immune sentinels, lung epithelial cells detect diverse pathogens through an ample repertoire of membrane-bound, endosomal, and cytosolic pattern-recognition receptors (PRRs). The highly plastic epithelial barrier responds to detected threats via modulation of paracellular flux, intercellular communications, mucin production, and periciliary fluid composition. Epithelial PRR stimulation also induces production of cytokines that recruit and sculpt leukocyte-mediated responses, and promotes epithelial generation of antimicrobial effector molecules that are directly microbicidal. The epithelium can alternately enhance tolerance to pathogens, preventing tissue damage through PRR-induced inhibitory signals, opsonization of pathogen-associated molecular patterns, and attenuation of injurious leukocyte responses. The inducibility of these protective responses has prompted attempts to therapeutically harness epithelial defense mechanisms to protect against pneumonias. Recent reports describe successful strategies for manipulation of epithelial defenses to protect against a wide range of respiratory pathogens. The lung epithelium is capable of both significant antimicrobial responses that reduce pathogen burdens and tolerance mechanisms that attenuate immunopathology. This manuscript reviews inducible lung epithelial defense mechanisms that offer opportunities for therapeutic manipulation to protect vulnerable populations against pneumonia.

NLRP3 Inflammasome Mediates Dormant Neutrophil Recruitment following Sterile Lung Injury and Protects against Subsequent Bacterial Pneumonia in Mice

Sterile lung injury is an important clinical problem that complicates the course of severely ill patients. Interruption of blood flow, namely ischemia-reperfusion (IR), initiates a sterile inflammatory response in the lung that is believed to be maladaptive. The rationale for this study was to elucidate the molecular basis for lung IR inflammation and whether it is maladaptive or beneficial. Using a mouse model of lung IR, we demonstrate that sequential blocking of inflammasomes [specifically, NOD-, LRR-, and pyrin domain-containing 3 (NLRP3)], inflammatory caspases, and interleukin (IL)-1β, all resulted in an attenuated inflammatory response. IL-1β production appeared to predominantly originate in conjunction with alveolar type 2 epithelial cells. Lung IR injury recruited unactivated or dormant neutrophils producing less reactive oxygen species thereby challenging the notion that recruited neutrophils are terminally activated. However, lung IR inflammation was able to limit or reduce the bacterial burden from subsequent experimentally induced pneumonia. Notably, inflammasome-deficient mice were unable to alter this bacterial burden following IR. Thus, we conclude that the NLRP3 inflammasome, through IL-1β production, regulates lung IR inflammation, which includes recruitment of dormant neutrophils. The sterile IR inflammatory response appears to serve an important function in inducing resistance to subsequent bacterial pneumonia and may constitute a critical part of early host responses to infection in trauma.

β2-Adrenoceptor signaling in airway epithelial cells promotes eosinophilic inflammation, mucous metaplasia, and airway contractility

The mostly widely used bronchodilators in asthma therapy are β₂-adrenoreceptor (β₂AR) agonists, but their chronic use causes paradoxical adverse effects. We have previously determined that β₂AR activation is required for expression of the asthma phenotype in mice, but the cell types involved are unknown. We now demonstrate that β₂AR signaling in the airway epithelium is sufficient to mediate key features of the asthmatic responses to IL-13 in murine models. Our data show that inhibition of β₂AR signaling with an aerosolized antagonist attenuates airway hyperresponsiveness (AHR), eosinophilic inflammation, and mucus-production responses to IL-13, whereas treatment with an aerosolized agonist worsens these phenotypes, suggesting that β₂AR signaling on resident lung cells modulates the asthma phenotype. Labeling with a fluorescent β₂AR ligand shows the receptors are highly expressed in airway epithelium. In β₂AR^-/- mice, transgenic expression of β₂ARs only in airway epithelium is sufficient to rescue IL-13-induced AHR, inflammation, and mucus production, and transgenic overexpression in WT mice exacerbates these phenotypes. Knockout of β-arrestin-2 (βarr-2^-/-) attenuates the asthma phenotype as in β₂AR^-/- mice. In contrast to eosinophilic inflammation, neutrophilic inflammation was not promoted by β₂AR signaling. Together, these results suggest β₂ARs on airway epithelial cells promote the asthma phenotype and that the proinflammatory pathway downstream of the β₂AR involves βarr-2. These results identify β₂AR signaling in the airway epithelium as capable of controlling integrated responses to IL-13 and affecting the function of other cell types such as airway smooth muscle cells.

Chronic lung inflammation primes humoral immunity and augments antipneumococcal resistance

Airway epithelial cells (AECs) display remarkable plasticity in response to infectious stimuli and their functional adaptations are critical for antimicrobial immunity. However, the roles of AECs and humoral mediators to host defense in non-communicable lung inflammation remain elusive. We dissected pulmonary defense against Streptococcus pneumoniae in hosts with pre-existing inflammatory conditions (SPC-HAxTCR-HA mice). Lung tissue transcriptomics and bronchoalveolar lavage fluid (BALF) proteomics revealed an induction of humoral defense mechanisms in inflamed lungs. Accordingly, besides antibacterial proteins and complement components being overrepresented in inflamed lungs, elevated polymeric immunoglobulin receptor (pIgR)-expression in AECs correlated with increased secretory immunoglobulin (SIg) transport. Consequently, opsonization assays revealed augmented pneumococcal coverage by SIgs present in the BALF of SPC-HAxTCR-HA mice, which was associated with enhanced antipneumococcal resistance. These findings emphasize the immunologic potential of AECs as well as their central role in providing antibacterial protection and put forward pIgR as potential target for therapeutic manipulation in infection-prone individuals.

Do antiepileptic drugs increase the risk of infectious diseases? A meta-analysis of placebo-controlled studies

AIMS

Experimental studies show that some antiepileptic drugs (AEDs) may modify natural immune defences, thus influencing the risk of developing infectious diseases. The aim of this meta-analysis was to explore whether AEDs as a class of drugs or singularly may increase risk of infectious diseases.

METHODS

A meta-analysis of all randomized, double-blind, placebo-controlled trials (RCTs) investigating any AED in any condition was performed. All terms that could be coded in the System Organ Classes (SOCs) of infections and infestations using the Medical Dictionary for Regulatory Activities were recorded. Additional subanalyses were performed also pooling together AEDs sharing similar mechanisms of action.

RESULTS

Two hundreds and sixty-nine double-blind, placebo-controlled studies were identified and, among them, 127 RCTs with 16 AEDs (brivaracetam, gabapentin, lacosamide, levetiracetam, lamotrigine, oxcarbazepine, perampanel, pregabalin, phenytoin, remacemide, retigabine, rufinamide, tiagabine, topiramate, valproate, zonisamide) reported at least one of 19 symptoms or diseases that could be included in the Medical Dictionary for Regulatory Activities SOC term infections and infestations. These terms were singularly recorded and then pooled together in the SOC term infection and infestation. Topiramate was significantly associated with an increased risk of infection (risk difference = 0.04; 95% confidence interval = 0.01/0.06), while oxcarbazepine was significantly associated with a lower risk (-0.005; -0.09/-0.01). Risk difference of all studies with all AEDs showed a slight, but significantly increased risk of infection (0.01; 0.00/0.002). Levetiracetam and brivaracetam RCTs, when pooled together, were associated with a significantly increased risk of infection (0.03; 0.01/0.05).

CONCLUSIONS

Some AEDs are associated with a mild increased risk of infection.

A Critical, Nonlinear Threshold Dictates Bacterial Invasion and Initial Kinetics During Influenza

Secondary bacterial infections increase morbidity and mortality of influenza A virus (IAV) infections. Bacteria are able to invade due to virus-induced depletion of alveolar macrophages (AMs), but this is not the only contributing factor. By analyzing a kinetic model, we uncovered a nonlinear initial dose threshold that is dependent on the amount of virus-induced AM depletion. The threshold separates the growth and clearance phenotypes such that bacteria decline for dose-AM depletion combinations below the threshold, stay constant near the threshold, and increase above the threshold. In addition, the distance from the threshold correlates to the growth rate. Because AM depletion changes throughout an IAV infection, the dose requirement for bacterial invasion also changes accordingly. Using the threshold, we found that the dose requirement drops dramatically during the first 7d of IAV infection. We then validated these analytical predictions by infecting mice with doses below or above the predicted threshold over the course of IAV infection. These results identify the nonlinear way in which two independent factors work together to support successful post-influenza bacterial invasion. They provide insight into coinfection timing, the heterogeneity in outcome, the probability of acquiring a coinfection, and the use of new therapeutic strategies to combat viral-bacterial coinfections.

Inducible epithelial resistance protects mice against leukemia-associated pneumonia

Despite widespread infection prevention efforts, pneumonia remains the leading cause of death among patients with acute leukemia, due to complex disease- and treatment-dependent immune defects. We have reported that a single inhaled treatment with a synergistic combination of Toll-like receptor 2/6 (TLR 2/6) and TLR9 agonists (Pam2-ODN) induces protective mucosal defenses in mice against a broad range of pathogens. As Pam2-ODN-induced protection persists despite depletion of several leukocyte populations, we tested whether it could prevent pneumonia in a mouse model of acute myeloid leukemia (AML) remission induction therapy. Pam2-ODN prevented death due to pneumonia caused by Pseudomonas aeruginosa, Streptococcus pneumoniae, and Aspergillus fumigatus when mice were heavily engrafted with leukemia cells, had severe chemotherapy-induced neutropenia or both. Pam2-ODN also extended survival of pneumonia in NSG mice engrafted with primary human AML cells. Protection was associated with rapid pathogen killing in the lungs at the time of infection and with reduced pathogen burdens at distant sites at the end of observation. Pathogen killing was inducible directly from isolated lung epithelial cells and was not abrogated by the presence of leukemia cells or cytotoxic agents. Pam2-ODN had no discernible effect on replication rate, total tumor population, or killing by chemotherapy of mouse or human leukemia cells, either in vitro or in vivo. Taken together, we report that therapeutic stimulation of lung epithelial defenses robustly protects against otherwise lethal pneumonias despite the profound immune dysfunction associated with acute leukemia and its treatment. These findings may suggest an opportunity to protect this population during periods of peak vulnerability.

IL-22 Defect During Streptococcus pneumoniae Infection Triggers Exacerbation of Chronic Obstructive Pulmonary Disease

Progression of chronic obstructive pulmonary disease (COPD) is linked to episodes of exacerbations caused by bacterial infections due to Streptococcus pneumoniae. Our objective was to identify during COPD, factors of susceptibility to bacterial infections among cytokine network and their role in COPD exacerbations. S. pneumoniae was used to sub-lethally challenge mice chronically exposed to air or cigarette smoke (CS) and to stimulate peripheral blood mononuclear cells (PBMC) from non-smokers, smokers and COPD patients. The immune response and the cytokine production were evaluated. Delayed clearance of the bacteria and stronger lung inflammation observed in infected CS-exposed mice were associated with an altered production of IL-17 and IL-22 by innate immune cells. This defect was related to a reduced production of IL-1β and IL-23 by antigen presenting cells. Importantly, supplementation with recombinant IL-22 restored bacterial clearance in CS-exposed mice and limited lung alteration. In contrast with non-smokers, blood NK and NKT cells from COPD patients failed to increase IL-17 and IL-22 levels in response to S. pneumoniae, in association with a defect in IL-1β and IL-23 secretion. This study identified IL-17 and IL-22 as susceptibility factors in COPD exacerbation. Therefore targeting such cytokines could represent a potent strategy to control COPD exacerbation.

Pneumonia in the neutropenic cancer patient

PURPOSE OF REVIEW

Pneumonia is the leading cause of death among neutropenic cancer patients, particularly those with acute leukaemia. Even with empiric therapy, case fatality rates of neutropenic pneumonias remain unacceptably high. However, recent advances in the management of neutropenic pneumonia offer hope for improved outcomes in the cancer setting. This review summarizes recent literature regarding the clinical presentation, microbiologic trends, diagnostic advances and therapeutic recommendations for cancer-related neutropenic pneumonia.

RECENT FINDINGS

Although neutropenic patients acquire pathogens both in community and nosocomial settings, patients' obligate healthcare exposures result in the frequent identification of multidrug-resistant bacterial organisms on conventional culture-based assessment of respiratory secretions. Modern molecular techniques, including expanded use of galactomannan testing, have further facilitated identification of fungal pathogens, allowing for aggressive interventions that appear to improve patient outcomes. Multiple interested societies have issued updated guidelines for antibiotic therapy of suspected neutropenic pneumonia. The benefit of antibiotic medications may be further enhanced by agents that promote host responses to infection.

SUMMARY

Neutropenic cancer patients have numerous potential causes for pulmonary infiltrates and clinical deterioration, with lower respiratory tract infections among the most deadly. Early clinical suspicion, diagnosis and intervention for neutropenic pneumonia provide cancer patients' best hope for survival.

Morphine compromises bronchial epithelial TLR2/IL17R signaling crosstalk, necessary for lung IL17 homeostasis

Opportunistic lung infection and inflammation is a hallmark of chronic recreational/clinical use of morphine. We show that early induction of IL17 from the bronchial epithelium, following pathogenic encounter is a protective response, which contributes to pathogenic clearance and currently attributed to TLR2 activation in immune cells. Concurrent activation of TLR2 and IL17R in bronchial epithelium results in the sequestration of MyD88 (TLR2 adapter) by Act1/CIKS (IL17R adapter), thereby turning off TLR2 signaling to restore homeostasis. Morphine inhibits the early IL17 release and interaction between Act1 and MyD88, leading to decreased pathogenic clearance and sustained inflammation. Hence, we propose that therapeutically targeting either TLR2 or IL17 in bronchial epithelia, in the context of morphine, can restore inflammatory homeostasis.

Importance of bacterial replication and alveolar macrophage-independent clearance mechanisms during early lung infection with Streptococcus pneumoniae

Although the importance of alveolar macrophages for host immunity during early Streptococcus pneumoniae lung infection is well established, the contribution and relative importance of other innate immunity mechanisms and of bacterial factors are less clear. We have used a murine model of S. pneumoniae early lung infection with wild-type, unencapsulated, and para-amino benzoic acid auxotroph mutant TIGR4 strains to assess the effects of inoculum size, bacterial replication, capsule, and alveolar macrophage-dependent and -independent clearance mechanisms on bacterial persistence within the lungs. Alveolar macrophage-dependent and -independent (calculated indirectly) clearance half-lives and bacterial replication doubling times were estimated using a mathematical model. In this model, after infection with a high-dose inoculum of encapsulated S. pneumoniae, alveolar macrophage-independent clearance mechanisms were dominant, with a clearance half-life of 24 min compared to 135 min for alveolar macrophage-dependent clearance. In addition, after a high-dose inoculum, successful lung infection required rapid bacterial replication, with an estimated S. pneumoniae doubling time of 16 min. The capsule had wide effects on early lung clearance mechanisms, with reduced half-lives of 14 min for alveolar macrophage-independent and 31 min for alveolar macrophage-dependent clearance of unencapsulated bacteria. In contrast, with a lower-dose inoculum, the bacterial doubling time increased to 56 min and the S. pneumoniae alveolar macrophage-dependent clearance half-life improved to 42 min and was largely unaffected by the capsule. These data demonstrate the large effects of bacterial factors (inoculum size, the capsule, and rapid replication) and alveolar macrophage-independent clearance mechanisms during early lung infection with S. pneumoniae.

Comparison of innate immune agonists for induction of tracheal antimicrobial peptide gene expression in tracheal epithelial cells of cattle

Bovine respiratory disease is a complex of bacterial and viral infections of economic and welfare importance to the beef industry. Although tracheal antimicrobial peptide (TAP) has microbicidal activity against bacterial pathogens causing bovine respiratory disease, risk factors for bovine respiratory disease including BVDV and stress (glucocorticoids) have been shown to inhibit the induced expression of this gene. Lipopolysaccharide is known to stimulate TAP gene expression, but the maximum effect is only observed after 16 h of stimulation. The present study investigated other agonists of TAP gene expression in primary cultures of bovine tracheal epithelial cells. PCR analysis of unstimulated tracheal epithelial cells, tracheal tissue and lung tissue each showed mRNA expression for Toll-like receptors (TLRs) 1–10. Quantitative RT-PCR analysis showed that Pam3CSK4 (an agonist of TLR1/2) and interleukin (IL)-17A significantly induced TAP gene expression in tracheal epithelial cells after only 4–8 h of stimulation. Flagellin (a TLR5 agonist), lipopolysaccharide and interferon-α also had stimulatory effects, but little or no response was found with class B CpG ODN 2007 (TLR9 agonist) or lipoteichoic acid (TLR2 agonist). The use of combined agonists had little or no enhancing effect above that of single agonists. Thus, Pam3CSK4, IL-17A and lipopolysaccharide rapidly and significantly induce TAP gene expression, suggesting that these stimulatory pathways may be of value for enhancing innate immunity in feedlot cattle at times of susceptibility to disease.

Pneumonia during remission induction chemotherapy in patients with acute leukemia

BACKGROUND

Pneumonia is a major cause of death during induction chemotherapy for acute leukemia. The purpose of this study was to quantify the incidence, risk factors, and outcomes of pneumonia in patients with acute leukemia.

METHODS

We conducted a retrospective cohort study of 801 patients with acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), or acute lymphocytic leukemia (ALL) who underwent induction chemotherapy.

MEASUREMENTS AND MAIN RESULTS

Pneumonia was present at induction start in 85 patients (11%). Of the 716 remaining patients, 148 (21%) developed pneumonia. The incidence rate of pneumonia was higher in MDS and AML than in ALL (0.013 vs. 0.008 vs. 0.003 pneumonias per day, respectively; P < 0.001). In multivariate analysis, age greater than or equal to 60 years, AML, low platelet count, low albumin level, neutropenia, and neutrophil count greater than 7,300 were risk factors. The case fatality rate of pneumonia was 17% (40 of 233). Competing risk analysis demonstrated that in the absence of pneumonia, death was rare: 28-day mortality was 6.2% for all patients but only 1.26% in those without pneumonia. Compared with patients without pneumonia, patients with pneumonia had more intensive care unit days, longer hospital stays, and 49% higher costs (P < 0.001).

CONCLUSIONS

Pneumonia after induction chemotherapy for acute leukemia continues to be common, and it is the most important determinant of early mortality after induction chemotherapy. Given the high incidence, morbidity, mortality, and cost of pneumonia, interventions aimed at prevention are warranted in patients with acute leukemia.

Activation of lung toll-like receptors does not exacerbate sickness responses to lipopolysaccharide in mice

Pneumonia represents a leading cause of death. Recently, a novel treatment strategy for pneumonia has involved enhancing the host pulmonary innate immune response by pre-exposure to aerosolized toll-like receptor (TLR)9 and TLR2/6 agonists, known as O/P. O/P inhalation in mice has been demonstrated to stimulate innate lung immunity, and thus increase survival against subsequent pneumonia infection while producing barely detectable increases in systemic cytokines. Here, we examined the safety of O/P treatment when used in mice that are inflamed systemically. Swiss-Webster mice were treated with two doses of aerosolized O/P (1× or 8×) vs phosphate buffered saline (PBS) either immediately before intraperitoneal injection of 0.1mg/kg lipopolysaccharide (LPS) or PBS (equivolume) or 2h after. Sickness responses (reduced body weight, food intake, activity and social interaction) were examined at 2 and 5.5h post-treatment. Immediately following behavioral testing, mice were euthanized, perfused with PBS, and brains, spleens, livers and lungs snap frozen for assessment of pro-inflammatory cytokine mRNAs. While O/P treatment alone increased lung IL-1β, IFNγ and TNF-α, no such effects were observed in the brain, spleen or liver. Furthermore, there was no evidence that O/P treatment administered before or after LPS had any synergizing effect to potentiate the cytokine response to LPS in any compartment measured. Supportive of these findings were the measures of sickness behaviors that did not show any increased sickness response in O/P-treated mice exposed to LPS, suggestive that the cytokine signal produced in the lungs from O/P inhalation did not propagate to the brain and synergize with LPS-induced neuroinflammation. These findings support the safety of the use of O/P inhalation as a preventative measure against pneumonia and demonstrate a unique ability of the lungs to compartmentalize pulmonary inflammation and limit propagation of the cytokine signal to the brain.

B cells are not essential for Lactobacillus-mediated protection against lethal pneumovirus infection

We have shown previously that priming of respiratory mucosa with live Lactobacillus species promotes robust and prolonged survival from an otherwise lethal infection with pneumonia virus of mice, a property known as heterologous immunity. Lactobacillus priming results in a moderate reduction in virus recovery and a dramatic reduction in virus-induced proinflammatory cytokine production; the precise mechanisms underlying these findings remain to be elucidated. Because B cells have been shown to promote heterologous immunity against respiratory virus pathogens under similar conditions, in this study we explore the role of B cells in Lactobacillus-mediated protection against acute pneumovirus infection. We found that Lactobacillus-primed mice feature elevated levels of airway Igs IgG, IgA, and IgM and lung tissues with dense, B cell (B220(+))-enriched peribronchial and perivascular infiltrates with germinal centers consistent with descriptions of BALT. No B cells were detected in lung tissue of Lactobacillus-primed B cell deficient μMT mice or Jh mice, and Lactobacillus-primed μMT mice had no characteristic infiltrates or airway Igs. Nonetheless, we observed diminished virus recovery and profound suppression of virus-induced proinflammatory cytokines CCL2, IFN-γ, and CXCL10 in both wild-type and Lactobacillus-primed μMT mice. Furthermore, Lactobacillus plantarum-primed, B cell-deficient μMT and Jh mice were fully protected from an otherwise lethal pneumonia virus of mice infection, as were their respective wild-types. We conclude that B cells are dispensable for Lactobacillus-mediated heterologous immunity and were not crucial for promoting survival in response to an otherwise lethal pneumovirus infection.

TLR Agonists as Modulators of the Innate Immune Response and Their Potential as Agents Against Infectious Disease

Immunotherapies that can either activate or suppress innate immune responses are being investigated as treatments against infectious diseases and the pathology they can cause. The objective of these therapies is to elicit protective immune responses thereby limiting the harm inflicted by the pathogen. The Toll-like receptor (TLR) signaling pathway plays critical roles in numerous host immune defenses and has been identified as an immunotherapeutic target against the consequences of infectious challenge. This review focuses on some of the recent advances being made in the development of TLR-ligands as potential prophylactic and/or therapeutic agents.

Safety, tolerability, and biomarkers of the treatment of mice with aerosolized Toll-like receptor ligands

We have previously discovered a synergistically therapeutic combination of two Toll-like receptor ligands, an oligodeoxynucleotide (ODN) and Pam2CSK4. Aerosolization of these ligands stimulates innate immunity within the lungs to prevent pneumonia from bacterial and viral pathogens. Here we examined the safety and tolerability of this treatment in mice, and characterized the expression of biomarkers of innate immune activation. We found that neutrophils appeared in lung lavage fluid 4 h after treatment, reached a peak at 48 h, and resolved by 7 days. The peak of neutrophil influx was accompanied by a small increase in lung permeability. Despite the abundance of neutrophils in lung lavage fluid, only rare neutrophils were visible histopathologically in the interstitium surrounding bronchi and veins and none were visible in alveolar airspaces. The cytokines interleukin 6 (IL-6), tumour necrosis factor, and Chemokine (C-X-C motif) ligand 2 rose several hundred-fold in lung lavage fluid 4 h after treatment in a dose-dependent and synergistic manner, providing useful biomarkers of lung activation. IL-6 rose fivefold in serum with delayed kinetics compared to its rise in lavage fluid, and might serve as a systemic biomarker of immune activation of the lungs. The dose–response relationship of lavage fluid cytokines was preserved in mice that underwent myeloablative treatment with cytosine arabinoside to model the treatment of hematologic malignancy. There were no overt signs of distress in mice treated with ODN/Pam2CSK4 in doses up to eightfold the therapeutic dose, and no changes in temperature, respiratory rate, or behavioral signs of sickness including sugar water preference, food disappearance, cage exploration or social interaction, though there was a small degree of transient weight loss. We conclude that treatment with aerosolized ODN/Pam2CSK4 is well tolerated in mice, and that innate immune activation of the lungs can be monitored by the measurement of inflammatory cytokines in lung lavage fluid and serum.

Candida albicans airway exposure primes the lung innate immune response against Pseudomonas aeruginosa infection through innate lymphoid cell recruitment and interleukin-22-associated mucosal response

Pseudomonas aeruginosa and Candida albicans are two pathogens frequently encountered in the intensive care unit microbial community. We have demonstrated that C. albicans airway exposure protected against P. aeruginosa-induced lung injury. The goal of the present study was to characterize the cellular and molecular mechanisms associated with C. albicans-induced protection. Airway exposure by C. albicans led to the recruitment and activation of natural killer cells, innate lymphoid cells (ILCs), macrophages, and dendritic cells. This recruitment was associated with the secretion of interleukin-22 (IL-22), whose neutralization abolished C. albicans-induced protection. We identified, by flow cytometry, ILCs as the only cellular source of IL-22. Depletion of ILCs by anti-CD90.2 antibodies was associated with a decreased IL-22 secretion and impaired survival after P. aeruginosa challenge. Our results demonstrate that the production of IL-22, mainly by ILCs, is a major and inducible step in protection against P. aeruginosa-induced lung injury. This cytokine may represent a clinical target in Pseudomonas aeruginosa-induced lung injury.

Lung epithelial cells are essential effectors of inducible resistance to pneumonia

Infectious pneumonias are the leading cause of death worldwide, particularly among immunocompromised patients. Therapeutic stimulation of the lungs' intrinsic defenses with a unique combination of inhaled Toll-like receptor (TLR) agonists broadly protects mice against otherwise lethal pneumonias. As the survival benefit persists despite cytotoxic chemotherapy-related neutropenia, the cells required for protection were investigated. The inducibility of resistance was tested in mice with deficiencies of leukocyte lineages due to genetic deletions and in wild-type mice with leukocyte populations significantly reduced by antibodies or toxins. Surprisingly, these serial reductions in leukocyte lineages did not appreciably impair inducible resistance, but targeted disruption of TLR signaling in the lung epithelium resulted in complete abrogation of the protective effect. Isolated lung epithelial cells were also induced to kill pathogens in the absence of leukocytes. Proteomic and gene expression analyses of isolated epithelial cells and whole lungs revealed highly congruent antimicrobial responses. Taken together, these data indicate that lung epithelial cells are necessary and sufficient effectors of inducible resistance. These findings challenge conventional paradigms about the role of epithelia in antimicrobial defense and offer a novel potential intervention to protect patients with impaired leukocyte-mediated immunity from fatal pneumonias.

Co-colonization by Haemophilus influenzae with Streptococcus pneumoniae enhances pneumococcal-specific antibody response in young children

BACKGROUND

Streptococcus pneumoniae (Spn), Haemophilus influenzae (Hi) and Moraxella catarrhalis (Mcat) are common bacterial pathogens of respiratory infections and common commensal microbes in the human nasopharynx (NP). The effect of interactions among theses bacteria during co-colonization of the NP on the host immune response has not been evaluated. The objective of this study was to assess the impact of co-colonization by Hi or Mcat on the systemic antibody response to vaccine protein candidate antigens of Spn and similarly the impact of co-colonization by Spn and Mcat on antibody responses to Hi vaccine protein candidate antigens.

METHODS

Serum samples were collected from healthy children at 6, 9, 15, 18, and 24 months of age when they were colonized with Spn, Hi, Mcat or their combinations. Quantitative ELISA was used to determine serum IgA and IgG against three Spn antigens and three Hi antigens, and as well as whole cells of non-typeable (NT) Spn and Hi.

RESULTS

NP colonization by Spn increased serum IgA and IgG titers against Spn antigens PhtD, PcpA and PlyD and whole cells of NTSpn, and co-colonization of Hi or Mcat with Spn resulted in further increases of serum pneumococcal-specific antibody levels. NP colonization by Hi increased serum IgA and IgG titers against Hi antigens P6, Protein D and OMP26 and whole cells of NTHi, but co-colonization of Spn or Mcat with Hi did not result in further increase of serum NTHi-specific antibody levels.

CONCLUSION

Co-colonization of Hi or Mcat with Spn enhances serum antibody response to NTSpn whole cells and Spn vaccine candidate antigens PhtD, PcPA and PlyD1. Co-colonization appears to variably modulate pathogen species-specific host adaptive immune response.

Adjuvant immunotherapies as a novel approach to bacterial infections

The rapid emergence of multidrug-resistant pathogens, especially Gram-negative bacteria and mycobacteria, represents one of the major medical challenges of the 21st century. The gradual loss of effective classical antibiotics for many bacterial pathogens, combined with an increasing population density and mobility, urgently calls for the development of novel treatments. Here, we discuss the potential of adjuvant immunotherapies to selectively stimulate protective immune responses as a treatment option for bacterial infections. In order to elicit appropriate immune responses and to avoid unwanted inflammatory tissue damage, it is essential to identify ligands and receptor pathways that specifically control protective responses at the site of infection. We summarize existing data and discuss suitable candidate targets for future immunotherapies of infectious diseases.

Deletion of the gene encoding calcitonin and calcitonin gene-related peptide α does not affect the outcome of severe infection in mice

Procalcitonin (PCT) is expressed in nonthryoidal tissues of humans during severe infections. Serum PCT levels are measured to diagnose and guide therapy, and there is some evidence that PCT may also contribute to the pathogenesis of sepsis. We tested whether disruption of the gene encoding PCT in mice affected the course of sepsis. Mice with exons 2-5 of the gene encoding calcitonin/calcitonin gene-related polypeptide α (Calca) knocked out and congenic C57BL/6J control mice were challenged with aerosolized Streptococcus pneumoniae or Pseudomonas aeruginosa, or injected intraperitoneally with S. pneumoniae. There were no significant differences in the survival of knockout and control mice in the two pneumonia models, and no significant differences in weight loss, splenic bacterial counts, or blood leukocyte levels in the peritoneal sepsis model. To verify disruption of the Calca gene in knockout mice, the absence of calcitonin in the serum of knockout mice and its presence and inducibility in control mice were confirmed. To evaluate PCT expression in nonthyroidal tissues of control mice, transcripts were measured in multiple organs. PCT transcripts were not significantly expressed in liver or spleen of control mice challenged with aerosolized P. aeruginosa or intraperitoneal endotoxin, and were expressed in lung only at low levels, even though serum IL-6 rose 3,548-fold. We conclude that mice are not an ideal loss-of-function model to test the role of PCT in the pathogenesis of sepsis because of low nonendocrine PCT expression during infection and inflammation. Nonetheless, our studies demonstrate that nonendocrine PCT expression is not necessary for adverse outcomes from sepsis.

Toll-like receptor-2/6 and Toll-like receptor-9 agonists suppress viral replication but not airway hyperreactivity in guinea pigs

Respiratory virus infections cause airway hyperreactivity (AHR). Preventative strategies for virus-induced AHR remain limited. Toll-like receptors (TLRs) have been suggested as a therapeutic target because of their central role in triggering antiviral immune responses. Previous studies showed that concurrent treatment with TLR2/6 and TLR9 agonists reduced lethality and the microbial burden in murine models of bacterial and viral pneumonia. This study investigated the effects of TLR2/6 and TLR9 agonist pretreatment on parainfluenza virus pneumonia and virus-induced AHR in guinea pigs in vivo. Synthetic TLR2/6 lipopeptide agonist Pam₂CSK₄ and Class C oligodeoxynucleotide TLR9 agonist ODN2395, administered in combination 24 hours before virus infection, significantly reduced viral replication in the lung. Despite a fivefold reduction in viral titers, concurrent TLR2/6 and TLR9 agonist pretreatment did not prevent virus-induced AHR or virus-induced inhibitory M2 muscarinic receptor dysfunction. Interestingly, the TLR agonists independently caused non-M2-dependent AHR. These data confirm the therapeutic antiviral potential of TLR agonists, while suggesting that virus inhibition may be insufficient to prevent virus-induced airway pathophysiology. Furthermore, TLR agonists independently cause AHR, albeit through a distinctly different mechanism from that of parainfluenza virus.