Viral PB1-F2 and host IFN-γ guide ILC2 and T cell activity during influenza virus infection.

Functional plasticity of innate lymphoid cells (ILCs) and T cells is regulated by host environmental cues, but the influence of pathogen-derived virulence factors has not been described. We now report the interplay between host interferon (IFN)-γ and viral PB1-F2 virulence protein in regulating the functions of ILC2s and T cells that lead to recovery from influenza virus infection of mice. In the absence of IFN-γ, lung ILC2s from mice challenged with the A/California/04/2009 (CA04) H1N1 virus, containing nonfunctional viral PB1-F2, initiated a robust IL-5 response, which also led to improved tissue integrity and increased survival. Conversely, challenge with Puerto Rico/8/1934 (PR8) H1N1 virus expressing fully functional PB1-F2, suppressed IL-5+ ILC2 responses, and induced a dominant IL-13+ CD8 T cell response, regardless of host IFN-γ expression. IFN-γ-deficient mice had increased survival and improved tissue integrity following challenge with lethal doses of CA04, but not PR8 virus, and increased resistance was dependent on the presence of IFN-γR+ ILC2s. Reverse-engineered influenza viruses differing in functional PB1-F2 activity induced ILC2 and T cell phenotypes similar to the PB1-F2 donor strains, demonstrating the potent role of viral PB1-F2 in host resistance. These results show the ability of a pathogen virulence factor together with host IFN-γ to regulate protective pulmonary immunity during influenza infection.

Sequential targeting of interferon pathways for increased host resistance to bacterial superinfection during influenza.

Bacterial co-infections represent a major clinical complication of influenza. Host-derived interferon (IFN) increases susceptibility to bacterial infections following influenza, but the relative roles of type-I versus type-II IFN remain poorly understood. We have used novel mouse models of co-infection in which colonizing pneumococci were inoculated into the upper respiratory tract; subsequent sublethal influenza virus infection caused the bacteria to enter the lungs and mediate lethal disease. Compared to wild-type mice or mice deficient in only one pathway, mice lacking both IFN pathways demonstrated the least amount of lung tissue damage and mortality following pneumococcal-influenza virus superinfection. Therapeutic neutralization of both type-I and type-II IFN pathways similarly provided optimal protection to co-infected wild-type mice. The most effective treatment regimen was staggered neutralization of the type-I IFN pathway early during co-infection combined with later neutralization of type-II IFN, which was consistent with the expression and reported activities of these IFNs during superinfection. These results are the first to directly compare the activities of type-I and type-II IFN during superinfection and provide new insights into potential host-directed targets for treatment of secondary bacterial infections during influenza.

Prevention of Influenza Virus-Induced Immunopathology by TGF-ß Produced during Allergic Asthma.

Asthma is believed to be a risk factor for influenza infection, however little experimental evidence exists to directly demonstrate the impact of asthma on susceptibility to influenza infection. Using a mouse model, we now report that asthmatic mice are actually significantly more resistant to a lethal influenza virus challenge. Notably, the observed increased resistance was not attributable to enhanced viral clearance, but instead, was due to reduced lung inflammation. Asthmatic mice exhibited a significantly reduced cytokine storm, as well as reduced total protein levels and cytotoxicity in the airways, indicators of decreased tissue injury. Further, asthmatic mice had significantly increased levels of TGF-ß1 and the heightened resistance of asthmatic mice was abrogated in the absence of TGF-ß receptor II. We conclude that a transient increase in TGF-ß expression following acute asthma can induce protection against influenza-induced immunopathology.

Limited Efficacy of Antibacterial Vaccination Against Secondary Serotype 3 Pneumococcal Pneumonia Following Influenza Infection.

BACKGROUND: Secondary bacterial infections following influenza represent a major cause of mortality in the human population, which, in turn, has led to a call for stockpiling of bacterial vaccines for pandemic preparedness. METHODS: To investigate the efficacy of bacterial vaccination for protection against secondary pneumococcal infection, mice were immunized with pneumococcal capsular polysaccharide conjugate vaccine, and then sequentially coinfected 5 weeks later with PR8 influenza virus and A66.1 Streptococcus pneumoniae. RESULTS: In the absence of influenza virus exposure, vaccination with polysaccharide conjugate vaccine was highly effective, as indicated by 100% survival from lethal pneumococcal pneumonia and 10 000-fold greater efficiency in clearance of bacteria from the lung compared to unvaccinated mice. Enhanced clearance after vaccination was dependent upon Fc receptor (FcR) expression. However, following influenza, <40% of vaccinated mice survived bacterial coinfection and FcR-dependent clearance of antibody-opsonized bacteria reduced bacterial levels in the lungs only 5-10 fold. No differences in lung myeloid cell numbers or in FcR cell surface expression were observed following influenza. CONCLUSIONS: The results show that induction of antibacterial humoral immunity is only partially effective in protection against secondary bacterial infections that occur following influenza, and suggest that additional therapeutic strategies to overcome defective antibacterial immunity should be explored.

Allergic Lung Inflammation Reduces Tissue Invasion and Enhances Survival from Pulmonary Pneumococcal Infection in Mice, Which Correlates with Increased Expression of Transforming Growth Factor ß1 and SiglecF(low) Alveolar Macrophages.

Asthma is generally thought to confer an increased risk for invasive pneumococcal disease (IPD) in humans. However, recent reports suggest that mortality rates from IPD are unaffected in patients with asthma and that chronic obstructive pulmonary disease (COPD), a condition similar to asthma, protects against the development of complicated pneumonia. To clarify the effects of asthma on the subsequent susceptibility to pneumococcal infection, ovalbumin (OVA)-induced allergic lung inflammation (ALI) was induced in mice followed by intranasal infection with A66.1 serotype 3 Streptococcus pneumoniae. Surprisingly, mice with ALI were significantly more resistant to lethal infection than non-ALI mice. The heightened resistance observed following ALI correlated with enhanced early clearance of pneumococci from the lung, decreased bacterial invasion from the airway into the lung tissue, a blunted inflammatory cytokine and neutrophil response to infection, and enhanced expression of transforming growth factor ß1 (TGF-ß1). Neutrophil depletion prior to infection had no effect on enhanced early bacterial clearance or resistance to IPD in mice with ALI. Although eosinophils recruited into the lung during ALI appeared to be capable of phagocytizing bacteria, neutralization of interleukin-5 (IL-5) to inhibit eosinophil recruitment likewise had no effect on early clearance or survival following infection. However, enhanced resistance was associated with an increase in levels of clodronate-sensitive, phagocytic SiglecF(low) alveolar macrophages within the airways following ALI. These findings suggest that, while the risk of developing IPD may actually be decreased in patients with acute asthma, additional clinical data are needed to better understand the risk of IPD in patients with different asthma phenotypes.

Differing effects of interleukin-10 on cutaneous and pulmonary Francisella tularensis live vaccine strain infection.

We investigated the role of interleukin-10 (IL-10) in cutaneous and pulmonary infection with Francisella tularensis. We found that after intradermal challenge of mice with the live vaccine strain (LVS) of F. tularensis, splenic IL-10 levels increased rapidly and reached a peak 5 days after infection. However, IL-10 expression after infection was detrimental, since IL-10(-/-) mice showed increased bacterial clearance and were resistant to an infectious dose (>10(6) CFU/mouse) that was uniformly lethal for IL-10(+/+) mice. Furthermore, IL-10(+/+) mice treated with neutralizing anti-IL-10R monoclonal antibody were able to survive lethal cutaneous LVS challenge. The presence of IL-10 appeared to restrain the expression of IL-17, since high levels of splenic IL-17 were observed after intradermal LVS infection only in IL-10(-/-) mice. Furthermore, treatment with neutralizing anti-IL-17R antibody ablated the enhanced survival observed in IL-10(-/-) mice. However, neutralization of IL-10 activity in IL-17R(-/-) mice failed to provide protection. Thus, IL-10 suppresses a protective IL-17 response that is necessary for resistance to cutaneous LVS infection. Surprisingly, however, IL-10(-/-) mice were significantly more susceptible to pulmonary infection with LVS. Finally, although IL-10 is a critical and novel regulator of immunity to F. tularensis LVS infection, its effects were masked during infection with the highly virulent SchuS4 strain. Taken together, these findings suggest that differentially regulating expression of the IL-10 pathway in various tissues could ultimately have prophylactic and therapeutic benefits for protection against tularemia.

Lack of immunogenicity of xenogeneic DNA from porcine biomaterials.

Background: Clinically useful biomaterials are derived from xenogeneic extracellular matrices, but extensive processes often used to remove all residual DNA are detrimental to their proper biological function. We hypothesized that deliberate and repeated injection of DNA extracted from clinically implantable, xenogeneic extracellular matrices might elicit an immune response in a well-established murine model that could ultimately lead to altered extracellular matrix remodeling. Methods: DNA was purified from unprocessed porcine extracellular matrices and processed extracellular matrices before sterilization (aseptic) and after sterilization. Groups of 10 mice were injected with these 3 purified DNAs and 3 controls: (1) DNA from E. coli; (2) DNA from unprocessed porcine extracellular matrices combined with interleukin-12 and methylated bovine serum albumin and emulsified in incomplete Freund's adjuvant; and (3) buffered saline. Immunizations occurred every 2 weeks for a total of 3 injections. Local cytokines and systemic anti-DNA antibodies were quantified 3 and 7 days after final injection. Results: The DNA extracted from unprocessed, aseptic, or sterilized porcine extracellular matrices failed to elicit a rejection response, and only with significant, proinflammatory adjuvant activation could such a response be seen. Without the adjuvants, biomaterial-derived DNA resulted in a mild accommodation cytokine response locally and no systemic anti-DNA antibody expression even at doses approximately 100-fold larger than would be clinically likely via extracellular matrix implantation. Conclusion: The immunological safety of porcine extracellular matrix biomaterials appears not to be related to DNA residues present. Such biomaterials need not be extensively processed, likely leading to detrimental changes in their bioactivity, solely in an effort to remove the mammalian DNA.

Lethal synergy between SARS-CoV-2 and Streptococcus pneumoniae in hACE2 mice and protective efficacy of vaccination.

Secondary infections are frequent complications of viral respiratory infections, but the potential consequence of SARS-CoV-2 coinfection with common pulmonary pathogens is poorly understood. We report that coinfection of human ACE2-transgenic mice with sublethal doses of SARS-CoV-2 and Streptococcus pneumoniae results in synergistic lung inflammation and lethality. Mortality was observed regardless of whether SARS-CoV-2 challenge occurred before or after establishment of sublethal pneumococcal infection. Increased bacterial levels following coinfection were associated with alveolar macrophage depletion, and treatment with murine GM-CSF reduced numbers of lung bacteria and pathology and partially protected from death. However, therapeutic targeting of IFNs, an approach that is effective against influenza coinfections, failed to increase survival. Combined vaccination against both SARS-CoV-2 and pneumococci resulted in 100% protection against subsequent coinfection. The results indicate that when seasonal respiratory infections return to prepandemic levels, they could lead to an increased incidence of lethal COVID-19 superinfections, especially among the unvaccinated population.

Direct role for the Rpd3 complex in transcriptional induction of the anaerobic DAN/TIR genes in yeast.

Saccharomyces cerevisiae adapts to hypoxia by expressing a large group of "anaerobic" genes. Among these, the eight DAN/TIR genes are regulated by the repressors Rox1 and Mot3 and the activator Upc2/Mox4. In attempting to identify factors recruited by the DNA binding repressor Mot3 to enhance repression of the DAN/TIR genes, we found that the histone deacetylase and global repressor complex, Rpd3-Sin3-Sap30, was not required for repression. Strikingly, the complex was instead required for activation. In addition, the histone H3 and H4 amino termini, which are targets of Rpd3, were also required for DAN1 expression. Epistasis tests demonstrated that the Rpd3 complex is not required in the absence of the repressor Mot3. Furthermore, the Rpd3 complex was required for normal function and stable binding of the activator Upc2 at the DAN1 promoter. Moreover, the Swi/Snf chromatin remodeling complex was strongly required for activation of DAN1, and chromatin immunoprecipitation analysis showed an Rpd3-dependent reduction in DAN1 promoter-associated nucleosomes upon induction. Taken together, these data provide evidence that during anaerobiosis, the Rpd3 complex acts at the DAN1 promoter to antagonize the chromatin-mediated repression caused by Mot3 and Rox1 and that chromatin remodeling by Swi/Snf is necessary for normal expression.

SON DNA-binding protein mediates macrophage autophagy and responses to intracellular infection.

Intracellular pathogens affect diverse host cellular defence and metabolic pathways. Here, we used infection with Francisella tularensis to identify SON DNA-binding protein as a central determinant of macrophage activities. RNAi knockdown of SON increases survival of human macrophages following F. tularensis infection or inflammasome stimulation. SON is required for macrophage autophagy, interferon response factor 3 expression, type I interferon response and inflammasome-associated readouts. SON knockdown has gene- and stimulus-specific effects on inflammatory gene expression. SON is required for accurate splicing and expression of GBF1, a key mediator of cis-Golgi structure and function. Chemical GBF1 inhibition has similar effects to SON knockdown, suggesting that SON controls macrophage functions at least in part by controlling Golgi-associated processes.

Allergic Airway Disease Prevents Lethal Synergy of Influenza A Virus-Streptococcus pneumoniae Coinfection.

Fatal outcomes following influenza infection are often associated with secondary bacterial infections. Allergic airway disease (AAD) is known to influence severe complications from respiratory infections, and yet the mechanistic effect of AAD on influenza virus-Streptococcus pneumoniae coinfection has not been investigated previously. We examined the impact of AAD on host susceptibility to viral-bacterial coinfections. We report that AAD improved survival during coinfection when viral-bacterial challenge occurred 1 week after AAD. Counterintuitively, mice with AAD had significantly deceased proinflammatory responses during infection. Specifically, both CD4+ and CD8+ T cell interferon gamma (IFN-γ) responses were suppressed following AAD. Resistance to coinfection was also associated with strong transforming growth factor ß1 (TGF-ß1) expression and increased bacterial clearance. Treatment of AAD mice with IFN-γ or genetic deletion of TGF-ß receptor II expression reversed the protective effects of AAD. Using a novel triple-challenge model system, we show for the first time that AAD can provide protection against influenza virus-S. pneumoniae coinfection through the production of TGF-ß that suppresses the influenza virus-induced IFN-γ response, thereby preserving antibacterial immunity.IMPORTANCE Asthma has become one of the most common chronic diseases and has been identified as a risk factor for developing influenza. However, the impact of asthma on postinfluenza secondary bacterial infection is currently not known. Here, we developed a novel triple-challenge model of allergic airway disease, primary influenza infection, and secondary Streptococcus pneumoniae infection to investigate the impact of asthma on susceptibility to viral-bacterial coinfections. We report for the first time that mice recovering from acute allergic airway disease are highly resistant to influenza-pneumococcal coinfection and that this resistance is due to inhibition of influenza virus-mediated impairment of bacterial clearance. Further characterization of allergic airway disease-associated resistance against postinfluenza secondary bacterial infection may aid in the development of prophylactic and/or therapeutic treatment against coinfection.

Evaluation of Pneumococcal Surface Protein A as a Vaccine Antigen against Secondary Streptococcus pneumoniae Challenge during Influenza A Infection.

Secondary bacterial pneumonia is responsible for significant morbidity and mortality during seasonal and pandemic influenza. Due to the unpredictability of influenza A virus evolution and the time-consuming process of manufacturing strain-specific influenza vaccines, recent efforts have been focused on developing anti-Streptococcus pneumoniae immunity to prevent influenza-related illness and death. Bacterial vaccination to prevent viral-bacterial synergistic interaction during co-infection is a promising concept that needs further investigation. Here, we show that immunization with pneumococcal surface protein A (PspA) fully protects mice against low-dose, but not high-dose, secondary bacterial challenge using a murine model of influenza A virus-S. pneumoniae co-infection. We further show that immunization with PspA is more broadly protective than the pneumococcal conjugate vaccine (Prevnar). These results demonstrate that PspA is a promising vaccine target that can provide protection against a physiologically relevant dose of S. pneumoniae following influenza infection.

Defective anti-polysaccharide IgG vaccine responses in IgA deficient mice.

We report that IgA-/- mice exhibit specific defects in IgG antibody responses to various polysaccharide vaccines (Francisella tularensis LPS and Pneumovax), but not protein vaccines such as Fluzone. This defect further included responses to polysaccharide-protein conjugate vaccines (Prevnar and Haemophilus influenzae type b-tetanus toxoid vaccine). In agreement with these findings, IgA-/- mice were protected from pathogen challenge with protein- but not polysaccharide-based vaccines. Interestingly, after immunization with live bacteria, IgA+/+ and IgA-/- mice were both resistant to lethal challenge and their IgG anti-polysaccharide antibody responses were comparable. Immunization with live bacteria, but not purified polysaccharide, induced production of serum B cell-activating factor (BAFF), a cytokine important for IgG class switching; supplementing IgA-/- cell cultures with BAFF enhanced in vitro polyclonal IgG production. Taken together, these findings show that IgA deficiency impairs IgG class switching following vaccination with polysaccharide antigens and that live bacterial immunization can overcome this defect. Since IgA deficient patients also often show defects in antibody responses following immunization with polysaccharide vaccines, our findings could have relevance to the clinical management of this population.

Alarmin function of galectin-9 in murine respiratory tularemia.

Sepsis is a complex immune disorder that is characterized by systemic hyperinflammation. Alarmins, which are multifunctional endogenous factors, have been implicated in exacerbation of inflammation in many immune disorders including sepsis. Here we show that Galectin-9, a host endogenous ß-galactoside binding lectin, functions as an alarmin capable of mediating inflammatory response during sepsis resulting from pulmonary infection with Francisella novicida, a Gram negative bacterial pathogen. Our results show that this galectin is upregulated and is likely released during tissue damage in the lungs of F. novicida infected septic mice. In vitro, purified recombinant galectin-9 exacerbated F. novicida-induced production of the inflammatory mediators by macrophages and neutrophils. Concomitantly, Galectin-9 deficient (Gal-9-/-) mice exhibited improved lung pathology, reduced cell death and reduced leukocyte infiltration, particularly neutrophils, in their lungs. This positively correlated with overall improved survival of F. novicida infected Gal-9-/- mice as compared to their wild-type counterparts. Collectively, these findings suggest that galectin-9 functions as a novel alarmin by augmenting the inflammatory response in sepsis development during pulmonary F. novicida infection.

Differential display: a critical analysis.

Differential display (DD) is a well-established analytical tool for measuring gene expression that is still popular due to its documented success and ability to identify novel genes not yet available for analysis by more powerful microarray hybridization. For a comprehensive analysis of all mRNAs in a given cell, it is statistically predicted that at least 240 different DD primer combinations are required. This prediction, however, has never been empirically tested. Using far more primer combinations than that predicted to evaluate 90% of the mRNAs in a cell, plus other modifications, we identified and confirmed the induction of five mRNAs by hydrogen peroxide in HA-1 hamster cells. However, five other known oxidant-inducible mRNAs were not identified by DD. Filter microarray hybridization did not result in the identification of any additional species modulated twofold or greater but previous two-dimensional protein gel electrophoresis identified 15 induced protein species. We conclude that the current statistical prediction for comprehensive analysis of all the mRNAs in a given cell is inaccurate, at least in our hands, and further conclude that DD is a useful but less than comprehensive method for assessing changes in mRNA levels.

Antistaphylococcal nanocomposite films based on enzyme-nanotube conjugates.

Infection with antibiotic-resistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) is one of the primary causes of hospitalizations and deaths. To address this issue, we have designed antimicrobial coatings incorporating carbon nanotube-enzyme conjugates that are highly effective against antibiotic-resistant pathogens. Specifically, we incorporated conjugates of carbon nanotubes with lysostaphin, a cell wall degrading enzyme, into films to impart bactericidal properties against Staphylococcus aureus and Staphylococcus epidermidis. We fabricated and characterized nanocomposites containing different conjugate formulations and enzyme loadings. These enzyme-based composites were highly efficient in killing MRSA (>99% within 2 h) without release of the enzyme into solution. Additionally, these films were reusable and stable under dry storage conditions for a month. Such enzyme-based film formulations may be used to prevent growth of pathogenic and antibiotic-resistant microorganisms on various common surfaces in hospital settings. Polymer and paint films containing such antimicrobial conjugates, in particular, could be advantageous to prevent risk of staphylococcal-specific infection and biofouling.

Interleukin-12 promotes gamma interferon-dependent neutrophil recruitment in the lung and improves protection against respiratory Streptococcus pneumoniae infection.

The ability of exogenous interleukin-12 (IL-12) to elicit protective innate immune responses against the extracellular pathogen Streptococcus pneumoniae was tested by infecting BALB/c mice intranasally (i.n.) with S. pneumoniae after i.n. administration of IL-12. It was found that administration of IL-12 resulted in lower bacterial burdens in the infected mice and significantly improved survival rates. All IL-12-treated mice contained higher levels of pulmonary gamma interferon (IFN-gamma) after infection and significantly more neutrophils than infected mice not treated with IL-12. IFN-gamma was found to be essential for IL-12-induced resistance and for neutrophil influx into the lungs, and the observed changes correlated with increased levels of the IL-8 homologue keratinocyte-derived chemokine (KC). In addition, in vitro tumor necrosis factor alpha (TNF-alpha) production by alveolar macrophages stimulated with heat-killed pneumococci was enhanced by IFN-gamma, and TNF-alpha in turn could enhance production of KC by lung cells. Finally, IL-12-induced protection was dependent upon the presence of neutrophils and the KC receptor CXCR2. Taken together, the results indicate that exogenous IL-12 can improve innate defense in the lung against S. pneumoniae by inducing IFN-gamma production, which in turn enhances chemokine expression, and promotes pulmonary neutrophil recruitment into the infected lung. The findings show that IL-12 and IFN-gamma can mediate a protective effect against respiratory infection caused by extracellular bacterial pathogens.