Novel strategies for targeting innate immune responses to influenza

Diverse roles of lung macrophages in the immune response to influenza A virus

Influenza viruses are one of the major causes of human respiratory infections and the newly emerging and re-emerging strains of influenza virus are the cause of seasonal epidemics and occasional pandemics, resulting in a huge threat to global public health systems. As one of the early immune cells can rapidly recognize and respond to influenza viruses in the respiratory, lung macrophages play an important role in controlling the severity of influenza disease by limiting viral replication, modulating the local inflammatory response, and initiating subsequent adaptive immune responses. However, influenza virus reproduction in macrophages is both strain- and macrophage type-dependent, and ineffective replication of some viral strains in mouse macrophages has been observed. This review discusses the function of lung macrophages in influenza virus infection in order to better understand the pathogenesis of the influenza virus.

Novel neuroendocrine role of γ-aminobutyric acid and gastrin-releasing peptide in the host response to influenza infection

Gastrin-releasing peptide (GRP), an evolutionarily conserved neuropeptide, significantly contributes to influenza-induced lethality and inflammation in rodent models. Because GRP is produced by pulmonary neuroendocrine cells (PNECs) in response to γ-aminobutyric acid (GABA), we hypothesized that influenza infection promotes GABA release from PNECs that activate GABAB receptors on PNECs to secrete GRP. Oxidative stress was increased in the lungs of influenza A/PR/8/34 (PR8)-infected mice, as well as serum glutamate decarboxylase 1, the enzyme that converts L-glutamic acid into GABA. The therapeutic administration of saclofen, a GABAB receptor antagonist, protected PR8-infected mice, reduced lung proinflammatory gene expression of C-C chemokine receptor type 2 (Ccr2), cluster of differentiation 68 (Cd68), and Toll like receptor 4 (Tlr4) and decreased the levels of GRP and high-mobility group box 1 (HMGB1) in sera. Conversely, baclofen, a GABAB receptor agonist, significantly increased the lethality and inflammatory responses. The GRP antagonist, NSC77427, as well as the GABAB antagonist, saclofen, blunted the PR8-induced monocyte infiltration into the lung. Together, these data provide the first report of neuroregulatory control of influenza-induced disease.

Zonulin as a Potential Therapeutic Target in Microbiota-Gut-Brain Axis Disorders: Encouraging Results and Emerging Questions

The relationship between dysbiosis and central nervous diseases has been proved in the last 10 years. Microbial alterations cause increased intestinal permeability, and the penetration of bacterial fragment and toxins induces local and systemic inflammatory processes, affecting distant organs, including the brain. Therefore, the integrity of the intestinal epithelial barrier plays a central role in the microbiota-gut-brain axis. In this review, we discuss recent findings on zonulin, an important tight junction regulator of intestinal epithelial cells, which is assumed to play a key role in maintaining of the blood-brain barrier function. In addition to focusing on the effect of microbiome on intestinal zonulin release, we also summarize potential pharmaceutical approaches to modulate zonulin-associated pathways with larazotide acetate and other zonulin receptor agonists or antagonists. The present review also addresses the emerging issues, including the use of misleading nomenclature or the unsolved questions about the exact protein sequence of zonulin.

Healthy adults supplemented with a nutraceutical formulation containing Aloe vera gel, rosemary and Poria cocos enhances the effect of influenza vaccination in a randomized, triple-blind, placebo-controlled trial

The study objective was to examine the role of a formulation, UP360, containing rosemary and Poria cocos extracts and Aloe vera gel powder, in healthy adults on supporting immune function with influenza vaccination. A 56-day randomized, triple-blind, placebo-controlled, parallel study consisted of a 28-day pre-vaccination period, an influenza vaccination on Day 28 and a 28-day post-vaccination period. Men and women ages 40-80 who had not yet been vaccinated for the flu were randomized to UP360 or Placebo (n = 25/group). At baseline, Days 28 and 56, blood lymphocyte populations, immunoglobulins (Ig), and cytokines were measured, and quality of life (QoL) questionnaires administered. The Wisconsin Upper Respiratory Symptom Survey (WURSS)-24 was completed daily by participants to measure incidence of upper respiratory tract infection (URTIs). In the post-vaccination period, TCR gamma-delta (γδ+) cells, known as γδ T cells, increased with UP360 supplementation compared to Placebo (p < 0.001). The UP360 group had a 15.6% increase in influenza B-specific IgG levels in the post-vaccination period (p = 0.0006). UP360 significantly increased the amount of circulating glutathione peroxidase (GSH-Px) from baseline at Day 28 (p = 0.0214), an enzyme that is important for neutralizing free radicals. While UP360 supplementation initially decreased levels of anti-inflammatory cytokine IL-1RA in the pre-vaccination period, IL-1RA levels were increased in the post-vaccination period (p ≤ 0.0482). Levels of IL-7 increased from baseline at Day 56 with UP360 supplementation (p = 0.0458). Despite these changes in immune markers, there were no differences in URTI symptoms or QoL between UP360 and Placebo. These results suggest UP360 supplementation was beneficial in eliciting a healthy, robust immune response in the context of vaccination. No changes in subjective measures of URTI illness or QoL demonstrated that participants' QoL was not negatively impacted by UP360 supplementation. There were no differences in clinical chemistry, vitals or adverse events confirming the good safety profile of UP360. The trial was registered on the International Clinical Trials Registry Platform (ISRCTN15838713).

Enhanced activity of NLRP3 inflammasome and its proinflammatory effect in influenza A viral pneumonia

Aim: The aim of this study was to investigate the activity of NLRP3 inflammasome and its effect on inducing severe pneumonia 1 week after influenza A virus (IAV) infection. Materials & methods: The expression levels of NLRP3, caspase-1 and IL-1β were assessed in murine macrophages stimulated with IAV. And the severity of viral pneumonia in mice was explored. Results & conclusion: The data showed that although the expression of NLRP3 diverged, activity of NLRP3 inflammasome was enhanced 1 week after IAV infection, and more severe viral pneumonia was associated with IL-1β in serum. It infers that enhanced activity of NLRP3 inflammasome induces augmented expression of IL-1β and severe pneumonia in a NLRP3-independent way, 1 week after IAV infection.

Evidence for Interplay Between the Renin-Angiotensin System and Toll-Like Receptor 4 Signaling Pathways in the Induction of Virus-Induced Acute Lung Injury

Dedication: This article is dedicated to Howard Young, an exceptional scientist who has provided outstanding mentorship to many postbaccalaureates, graduate students, and postdoctoral fellows during his career. Howard has been a colleague to many and was never tired of learning new things. He has brought "thinking out of the box" to the level of an art form and has always provided thoughtful and constructive suggestions to those who have sought his counsel. I am personally greatly indebted to Howard for his guidance in molecular biology over the past 30 years, and hope that we will continue to share a passion for learning and mentoring others for years to come. Thank you, Howard! -Stephanie N. Vogel The SARS-CoV-2 pandemic has led to an unprecedented explosion in studies that have sought to identify key mechanisms that underlie the ravaging aspects of this disease on individuals. SARS-CoV-2 virus gains access to cells by (1) binding of the viral spike (S) protein to cell-associated angiotensin-converting enzyme 2 (ACE2), a key receptor in the renin-angiotensin system (RAS), followed by (2) cleavage of S protein by a cellular serine protease ("S protein priming") to facilitate viral entry. Dysregulation of the RAS system has been implicated in the spectrum of clinical symptoms associated with SARS-CoV-2, including hypercytokinemia, elevated markers of endothelial injury and thrombosis, and both localized and systemic inflammation. However, the underlying mechanisms have yet to be fully delineated.

Thiocarbazate building blocks enable the construction of azapeptides for rapid development of therapeutic candidates

Peptides, polymers of amino acids, comprise a vital and expanding therapeutic approach. Their rapid degradation by proteases, however, represents a major limitation to their therapeutic utility and chemical modifications to native peptides have been employed to mitigate this weakness. Herein, we describe functionalized thiocarbazate scaffolds as precursors of aza-amino acids, that, upon activation, can be integrated in a peptide sequence to generate azapeptides using conventional peptide synthetic methods. This methodology facilitates peptide editing-replacing targeted amino acid(s) with aza-amino acid(s) within a peptide-to form azapeptides with preferred therapeutic characteristics (extending half-life/bioavailability, while at the same time typically preserving structural features and biological activities). We demonstrate the convenience of this azapeptide synthesis platform in two well-studied peptides with short half-lives: FSSE/P5779, a tetrapeptide inhibitor of HMGB1/MD-2/TLR4 complex formation, and bradykinin, a nine-residue vasoactive peptide. This bench-stable thiocarbazate platform offers a robust and universal approach to optimize peptide-based therapeutics.

Protection against influenza-induced Acute Lung Injury (ALI) by enhanced induction of M2a macrophages: possible role of PPARγ/RXR ligands in IL-4-induced M2a macrophage differentiation

Many respiratory viruses cause lung damage that may evolve into acute lung injury (ALI), a cytokine storm, acute respiratory distress syndrome, and ultimately, death. Peroxisome proliferator activated receptor gamma (PPARγ), a member of the nuclear hormone receptor (NHR) family of transcription factors, regulates transcription by forming heterodimers with another NHR family member, Retinoid X Receptor (RXR). Each component of the heterodimer binds specific ligands that modify transcriptional capacity of the entire heterodimer by recruiting different co-activators/co-repressors. However, the role of PPARγ/RXR ligands in the context of influenza infection is not well understood. PPARγ is associated with macrophage differentiation to an anti-inflammatory M2 state. We show that mice lacking the IL-4Rα receptor, required for M2a macrophage differentiation, are more susceptible to mouse-adapted influenza (A/PR/8/34; "PR8")-induced lethality. Mice lacking Ptgs2, that encodes COX-2, a key proinflammatory M1 macrophage mediator, are more resistant. Blocking the receptor for COX-2-induced Prostaglandin E2 (PGE2) was also protective. Treatment with pioglitazone (PGZ), a PPARγ ligand, increased survival from PR8 infection, decreased M1 macrophage gene expression, and increased PPARγ mRNA in lungs. Conversely, conditional knockout mice expressing PPARγ-deficient macrophages were significantly more sensitive to PR8-induced lethality. These findings were extended in cotton rats: PGZ blunted lung inflammation and M1 cytokine gene expression after challenge with non-adapted human influenza. To study mechanisms by which PPARγ/RXR transcription factors induce canonical M2a genes, WT mouse macrophages were treated with IL-4 in the absence or presence of rosiglitazone (RGZ; PPARγ ligand), LG100754 (LG; RXR ligand), or both. IL-4 dose-dependently induced M2a genes Arg1, Mrc1, Chil3, and Retnla. Treatment of macrophages with IL-4 and RGZ and/or LG differentially affected induction of Arg1 and Mrc1 vs. Chil3 and Retnla gene expression. In PPARγ-deficient macrophages, IL-4 alone failed to induce Arg1 and Mrc1 gene expression; however, concurrent treatment with LG or RGZ + LG enhanced IL-4-induced Arg1 and Mrc1 expression, but to a lower level than in WT macrophages, findings confirmed in the murine alveolar macrophage cell line, MH-S. These findings support a model in which PPARγ/RXR heterodimers control IL-4-induced M2a differentiation, and suggest that PPARγ/RXR agonists should be considered as important tools for clinical intervention against influenza-induced ALI.

HMGB1: A Potential Target of Nervus Vagus Stimulation in Pediatric SARS-CoV-2-Induced ALI/ARDS

From the start of pandemics, children were described as the ones who were less affected by SARS-Cov-2 or COVID-19, which was mild in most of the cases. However, with the growing vaccination rate of the adult population, children became more exposed to the virus and more cases of severe SARS-CoV-2-induced ARDS are being diagnosed with the disabling consequences or lethal outcomes associated with the cytokine storm. Thus, we do hypothesize that some of the children could benefit from nervus vagus stimulation during COVID-19 ARDS through the inhibition of HMGB1 release and interaction with the receptor, resulting in decreased neutrophil accumulation, oxidative stress, and coagulopathy as well as lung vascular permeability. Moreover, stimulation through alpha-7 nicotinic acetylcholine receptors could boost macrophage phagocytosis and increase the clearance of DAMPs and PAMPs. Further rise of FGF10 could contribute to lung stem cell proliferation and potential regeneration of the injured lung. However, this stimulation should be very specific, timely, and of proper duration, as it could lead to such adverse effects as increased viral spread and systemic infection, especially in small children or infants due to specific pediatric immunity state and anatomical features of the respiratory system.

Molecular alterations in human milk in simulated maternal nasal mucosal infection with live attenuated influenza vaccination

Breastfeeding protects against mucosal infections in infants. The underlying mechanisms through which immunity develops in human milk following maternal infection with mucosal pathogens are not well understood. We simulated nasal mucosal influenza infection through live attenuated influenza vaccination (LAIV) and compared immune responses in milk to inactivated influenza vaccination (IIV). Transcriptomic analysis was performed on RNA extracted from human milk cells to evaluate differentially expressed genes and pathways on days 1 and 7 post-vaccination. Both LAIV and IIV vaccines induced influenza-specific IgA that persisted for at least 6 months. Regulation of type I interferon production, toll-like receptor, and pattern recognition receptor signaling pathways were highly upregulated in milk on day 1 following LAIV but not IIV at any time point. Upregulation of innate immunity in human milk may provide timely protection against mucosal infections until antigen-specific immunity develops in the human milk-fed infant.

Identification of Nifurtimox and Chrysin as Anti-Influenza Virus Agents by Clinical Transcriptome Signature Reversion

The rapid development in the field of transcriptomics provides remarkable biomedical insights for drug discovery. In this study, a transcriptome signature reversal approach was conducted to identify the agents against influenza A virus (IAV) infection through dissecting gene expression changes in response to disease or compounds’ perturbations. Two compounds, nifurtimox and chrysin, were identified by a modified Kolmogorov–Smirnov test statistic based on the transcriptional signatures from 81 IAV-infected patients and the gene expression profiles of 1309 compounds. Their activities were verified in vitro with half maximal effective concentrations (EC₅₀s) from 9.1 to 19.1 μM against H1N1 or H3N2. It also suggested that the two compounds interfered with multiple sessions in IAV infection by reversing the expression of 28 IAV informative genes. Through network-based analysis of the 28 reversed IAV informative genes, a strong synergistic effect of the two compounds was revealed, which was confirmed in vitro. By using the transcriptome signature reversion (TSR) on clinical datasets, this study provides an efficient scheme for the discovery of drugs targeting multiple host factors regarding clinical signs and symptoms, which may also confer an opportunity for decelerating drug-resistant variant emergence.

Involvement and therapeutic implications of airway epithelial barrier dysfunction in type 2 inflammation of asthma

Type 2 inflammation is a complex immune response and primary mechanism for several common allergic diseases including allergic rhinitis, allergic asthma, atopic dermatitis, and chronic rhinosinusitis with nasal polyps. It is the predominant type of immune response against helminths to prevent their tissue infiltration and induce their expulsion. Recent studies suggest that epithelial barrier dysfunction contributes to the development of type 2 inflammation in asthma, which may partly explain the increasing prevalence of asthma in China and around the globe. The epithelial barrier hypothesis has recently been proposed and has received great interest from the scientific community. The development of leaky epithelial barriers leads to microbial dysbiosis and the translocation of bacteria to inter- and sub-epithelial areas and the development of epithelial tissue inflammation. Accordingly, preventing the impairment and promoting the restoration of a deteriorated airway epithelial barrier represents a promising strategy for the treatment of asthma. This review introduces the interaction between type 2 inflammation and the airway epithelial barrier in asthma, the structure and molecular composition of the airway epithelial barrier, and the assessment of epithelial barrier integrity. The role of airway epithelial barrier disruption in the pathogenesis of asthma will be discussed. In addition, the possible mechanisms underlying the airway epithelial barrier dysfunction induced by allergens and environmental pollutants, and current treatments to restore the airway epithelial barrier are reviewed.

Molecular pathways involved in COVID-19 and potential pathway-based therapeutic targets

Deciphering the molecular downstream consequences of severe acute respiratory syndrome coronavirus (SARS-CoV)- 2 infection is important for a greater understanding of the disease and treatment planning. Furthermore, greater understanding of the underlying mechanisms of diagnostic and therapeutic strategies can help in the development of vaccines and drugs against COVID-19. At present, the molecular mechanisms of SARS-CoV-2 in the host cells are not sufficiently comprehended. Some of the mechanisms are proposed considering the existing similarities between SARS-CoV-2 and the other members of the β-CoVs, and others are explained based on studies advanced in the structure and function of SARS-CoV-2. In this review, we endeavored to map the possible mechanisms of the host response following SARS-CoV-2 infection and surveyed current research conducted by in vitro, in vivo and human observations, as well as existing suggestions. We addressed the specific signaling events that can cause cytokine storm and demonstrated three forms of cell death signaling following virus infection, including apoptosis, pyroptosis, and necroptosis. Given the elicited signaling pathways, we introduced possible pathway-based therapeutic targets; ADAM17 was especially highlighted as one of the most important elements of several signaling pathways involved in the immunopathogenesis of COVID-19. We also provided the possible drug candidates against these targets. Moreover, the cytokine-cytokine receptor interaction pathway was found as one of the important cross-talk pathways through a pathway-pathway interaction analysis for SARS-CoV-2 infection.

TLRs in COVID-19: How they drive immunopathology and the rationale for modulation

COVID-19 is both a viral illness and a disease of immunopathology. Proximal events within the innate immune system drive the balance between deleterious inflammation and viral clearance. We hypothesize that a divergence between the generation of excessive inflammation through over activation of the TLR associated myeloid differentiation primary response (MyD88) pathway relative to the TIR-domain-containing adaptor-inducing IFN-β (TRIF) pathway plays a key role in COVID-19 severity. Both viral elements and damage associated host molecules act as TLR ligands in this process. In this review, we detail the mechanism for this imbalance in COVID-19 based on available evidence, and we discuss how modulation of critical elements may be important in reducing severity of disease.

A Nonlethal Murine Flame Burn Model Leads to a Transient Reduction in Host Defenses and Enhanced Susceptibility to Lethal Pseudomonas aeruginosa Infection

Of the 486,000 burn injuries that required medical treatment in the United States in 2016, 40,000 people were hospitalized, with >3,000 fatalities. After burn injury, humans are at increased risk of sepsis and mortality from infections caused by Pseudomonas aeruginosa, an opportunistic pathogen. We hypothesize that systemic events were initiated from the burn that increased the host's susceptibility to P. aeruginosa. A nonlethal 10% total body surface area (TBSA), full-thickness flame burn was performed in CD-1 mice without and with subsequent P. aeruginosa (strain M2) infection. The 50% lethal dose for subcutaneous infection with P. aeruginosa M2 at the burn site immediately after the burn decreased by 6 log, with mortality occurring between 18 and 26 h, compared with P. aeruginosa-infected mice without burn injury. Bacteria in distal organs were detected by 18 h, concurrent with the onset of clinical symptoms. Serum proinflammatory cytokines (interleukin-6 [IL-6], IL-1β, gamma interferon, and tumor necrosis factor alpha) and the anti-inflammatory cytokine IL-10 were first detected at 12 h postburn with infection and continued to increase until death. Directly after burn alone, serum levels of HMGB1, a danger-associated molecular pattern and TLR4 agonist, transiently increased to 50 ng/ml before returning to 20 ng/ml. Burn with P. aeruginosa infection increased serum HMGB1 concentrations >10-fold (250 ng/ml) at the time of death. This HMGB1-rich serum stimulated TLR4-mediated NF-κB activation in a TLR4 reporter cell line. Treatment of infected burned mice with P5779, a peptide inhibitor of HMGB1, increased the mean survival from 23 to 42 h (P < 0.0001). We conclude that the high level of serum HMGB1, which preceded the increase in proinflammatory cytokines, is associated with postburn mortality.

Competing Bioaerosols May Influence the Seasonality of Influenza-Like Illnesses, including COVID-19. The Chicago Experience

Data from Chicago confirm the end of flu season coincides with the beginning of pollen season. More importantly, the end of flu season also coincides with onset of seasonal aerosolization of mold spores. Overall, the data suggest bioaerosols, especially mold spores, compete with viruses for a shared receptor, with the periodicity of influenza-like illnesses, including COVID-19, a consequence of seasonal factors that influence aerosolization of competing species.

A mouse model of human TLR4 D299G/T399I SNPs reveals mechanisms of altered LPS and pathogen responses

Two cosegregating single-nucleotide polymorphisms (SNPs) in human TLR4, an A896G transition at SNP rs4986790 (D299G) and a C1196T transition at SNP rs4986791 (T399I), have been associated with LPS hyporesponsiveness and differential susceptibility to many infectious or inflammatory diseases. However, many studies failed to confirm these associations, and transfection experiments resulted in conflicting conclusions about the impact of these SNPs on TLR4 signaling. Using advanced protein modeling from crystallographic data of human and murine TLR4, we identified homologous substitutions of these SNPs in murine Tlr4, engineered a knock-in strain expressing the D298G and N397I TLR4 SNPs homozygously, and characterized in vivo and in vitro responses to TLR4 ligands and infections in which TLR4 is implicated. Our data provide new insights into cellular and molecular mechanisms by which these SNPs decrease the TLR4 signaling efficiency and offer an experimental approach to confirm or refute human data possibly confounded by variables unrelated to the direct effects of the SNPs on TLR4 functionality.

Potential effects of HMGB1 on viral replication and virus infection-induced inflammatory responses: A promising therapeutic target for virus infection-induced inflammatory diseases

Inflammatory responses, characterized by the overproduction of numerous proinflammatory mediators by immune cells, is essential to protect the host against invading pathogens. Excessive production of proinflammatory cytokines is a key pathogenic factor accounting for severe tissue injury and disease progression during the infection of multiple viruses, which are therefore termed as "cytokine storm". High mobility group box 1 (HMGB1), a ubiquitous DNA-binding protein released either over virus-infected cells or activated immune cells, may act as a proinflammatory cytokine with a robust capacity to potentiate inflammatory response and disease severity. Moreover, HMGB1 is a host factor that potentially participates in the regulation of viral replication cycles with complicated mechanisms. Currently, HMGB1 is regarded as a promising therapeutic target against virus infection. Here, we provide an overview of the updated studies on how HMGB1 is differentially manipulated by distinct viruses to regulate viral diseases.

Targeting TLR4 Signaling to Blunt Viral-Mediated Acute Lung Injury

Respiratory viral infections have been a long-standing global burden ranging from seasonal recurrences to the unexpected pandemics. The yearly hospitalizations from seasonal viruses such as influenza can fluctuate greatly depending on the circulating strain(s) and the congruency with the predicted strains used for the yearly vaccine formulation, which often are not predicted accurately. While antiviral agents are available against influenza, efficacy is limited due to a temporal disconnect between the time of infection and symptom development and viral resistance. Uncontrolled, influenza infections can lead to a severe inflammatory response initiated by pathogen-associated molecular patterns (PAMPs) or host-derived danger-associated molecular patterns (DAMPs) that ultimately signal through pattern recognition receptors (PRRs). Overall, these pathogen-host interactions result in a local cytokine storm leading to acute lung injury (ALI) or the more severe acute respiratory distress syndrome (ARDS) with concomitant systemic involvement and more severe, life threatening consequences. In addition to traditional antiviral treatments, blocking the host's innate immune response may provide a more viable approach to combat these infectious pathogens. The SARS-CoV-2 pandemic illustrates a critical need for novel treatments to counteract the ALI and ARDS that has caused the deaths of millions worldwide. This review will examine how antagonizing TLR4 signaling has been effective experimentally in ameliorating ALI and lethal infection in challenge models triggered not only by influenza, but also by other ALI-inducing viruses.

Immunomodulatory Responses Of Toll Like Receptors Against 2019nCoV

The present review discusses the immune signals via toll like receptors (TLRs) against 2019nCoV. We researched using different database, up to June 18th, 2020. All the included articles were published in English language. The outcome of this review, that some TLRs agonists or antagonists are progressed as drugs to combat and down regulating TLRs immune signals respectively. TLRs 3 and 4 recognized 2019nCoV spike protein through immune and molecular signals that leading to immune stimulation of pro-inflammatory cytokines and even the immune fever. While the TLRs7 and 8 recognized single-stranded ribonucleic acids (ssRNAs) leading to elevation of the tumour necrosis factor α (TNF-α), interleukin (IL)-6 and -12 levels. TLRs agonists or antagonists utilized as immunotherapeutic targets against 2019nCoV via TLRs signals. Chloroquine and hydroxychloroquine; the approval compounds for 2019nCoV therapy can be inhibiting the class II major histocompatibility complex molecules expression and antigen presentation and even immune suppressions of the pro-inflammatory cytokines profile.

Interleukin-1β exacerbates disease and is a potential therapeutic target to reduce pulmonary inflammation during severe influenza A virus infection

Hyperinflammatory responses including the production of NLRP3-dependent interleukin (IL)-1β is a characteristic feature of severe and fatal influenza A virus (IAV) infections. The NLRP3 inflammasome has been shown to play a temporal role during severe IAV immune responses, with early protective and later detrimental responses. However, the specific contribution of IL-1β in modulating IAV disease in vivo is currently not well defined. Here, we identified that activation of NLRP3-dependent IL-1β responses occurs rapidly following HKx31 H3N2 infection, prior to the onset of severe IAV disease. Mature IL-1β was detectable in vivo in both hemopoietic and nonhemopoietic cells. Significantly, therapeutic inhibition of IL-1β in the airways with intranasal anti-IL-1β antibody treatment from day 3 postinfection, corresponding to the onset of clinical signs of disease, significantly prolonged survival and reduced inflammation in the airways. Importantly, early targeting of IL-1β from day 1 postinfection also improved survival. Together, these studies specifically define a role for IL-1β in contributing to the development of hyperinflammation and disease and indicate that targeting IL-1β is a potential therapeutic strategy for severe IAV infections.

Toll-like receptor 4 mediates blood-brain barrier permeability and disease in C3H mice during Venezuelan equine encephalitis virus infection

Venezuelan equine encephalitis virus (VEEV) is an encephalitic alphavirus that can cause debilitating, acute febrile illness and potentially result in encephalitis. Currently, there are no FDA-licensed vaccines or specific therapeutics for VEEV. Previous studies have demonstrated that VEEV infection results in increased blood-brain barrier (BBB) permeability that is mediated by matrix metalloproteinases (MMPs). Furthermore, after subarachnoid hemorrhage in mice, MMP-9 is upregulated in the brain and mediates BBB permeability in a toll-like receptor 4 (TLR4)-dependent manner. Here, we demonstrate that disease in C3H mice during VEEV TC-83 infection is dependent on TLR4 because intranasal infection of C3H/HeN (TLR4^WT) mice with VEEV TC-83 resulted in mortality as opposed to survival of TLR4-defective C3H/HeJ (TLR4^mut) mice. In addition, BBB permeability was induced to a lesser extent in TLR4^mut mice compared with TLR4^WT mice during VEEV TC-83 infection as determined by sodium fluorescein and fluorescently-conjugated dextran extravasation. Moreover, MMP-9, MMP-2, ICAM-1, CCL2 and IFN-γ were all induced to significantly lower levels in the brains of infected TLR4^mut mice compared with infected TLR4^WT mice despite the absence of significantly different viral titers or immune cell populations in the brains of infected TLR4^WT and TLR4^mut mice. These data demonstrate the critical role of TLR4 in mediating BBB permeability and disease in C3H mice during VEEV TC-83 infection, which suggests that TLR4 is a potential target for the development of therapeutics for VEEV.

In silico Analysis Revealed Potential Anti-SARS-CoV-2 Main Protease Activity by the Zonulin Inhibitor Larazotide Acetate

The most severe outcome of COVID-19 infection is the development of interstitial pneumonia causing acute lung injury (ALI) and/or acute respiratory distress syndrome (ARDS), both responsible for the infected patients' mortality. ALI and ARDS are characterized by a leakage of plasma components into the lungs, compromising their ability to expand and optimally engage in gas exchange with blood, resulting in respiratory failure. We have previously reported that zonulin, a protein dictating epithelial and endothelial permeability in several districts, including the airways, is involved in ALI pathogenesis in mouse models, and that its peptide inhibitor Larazotide acetate (also called AT1001) ameliorated ALI and subsequent mortality by decreasing mucosal permeability to fluid and extravasation of neutrophils into the lungs. With the recent crystallographic resolution of the SARS-CoV-2 main protease (M^pro), an enzyme fundamental in the viral lifecycle, bound to peptidomimetic inhibitors N3 and 13b, we were able to perform molecular modeling investigation showing that AT1001 presents structural motifs similar to co-crystallized ligands. Specifically, molecular docking, MM-GBSA-based predictions and molecular dynamics showed that AT1001 docks extremely well in the M^pro catalytic domain through a global turn conformational arrangement without any unfavorable steric hindrance. Finally, we have observed that AT1001 can be superimposed onto the crystallized structures of N3 and 13b, establishing a higher number of interactions and accordingly a tighter binding. In vitro studies confirmed AT1001 anti-M^pro and preliminary investigation indicted an anti-viral activity. Combined, these studies suggest that AT1001, besides its well-demonstrated effect in ameliorating mucosal permeability in ALI/ARDS, may also exert a direct anti-SARS-CoV-2 effect by blocking the M^pro. AT1001 has been used extensively in a variety of animal models of ALI demonstrating robust safety and efficacy; it is currently in phase 3 trials in celiac subjects showing strong safety and efficacy profiles. We therefore propose its use as a specific anti-SARS-CoV-2 multitargeting treatment for the current pandemic.

COVID-19 and Toll-Like Receptor 4 (TLR4): SARS-CoV-2 May Bind and Activate TLR4 to Increase ACE2 Expression, Facilitating Entry and Causing Hyperinflammation

Causes of mortality from COVID-19 include respiratory failure, heart failure, and sepsis/multiorgan failure. TLR4 is an innate immune receptor on the cell surface that recognizes pathogen-associated molecular patterns (PAMPs) including viral proteins and triggers the production of type I interferons and proinflammatory cytokines to combat infection. It is expressed on both immune cells and tissue-resident cells. ACE2, the reported entry receptor for SARS-CoV-2, is only present on ~1-2% of the cells in the lungs or has a low pulmonary expression, and recently, the spike protein has been proposed to have the strongest protein-protein interaction with TLR4. Here, we review and connect evidence for SARS-CoV-1 and SARS-CoV-2 having direct and indirect binding to TLR4, together with other viral precedents, which when combined shed light on the COVID-19 pathophysiological puzzle. We propose a model in which the SARS-CoV-2 spike glycoprotein binds TLR4 and activates TLR4 signalling to increase cell surface expression of ACE2 facilitating entry. SARS-CoV-2 also destroys the type II alveolar cells that secrete pulmonary surfactants, which normally decrease the air/tissue surface tension and block TLR4 in the lungs thus promoting ARDS and inflammation. Furthermore, SARS-CoV-2-induced myocarditis and multiple-organ injury may be due to TLR4 activation, aberrant TLR4 signalling, and hyperinflammation in COVID-19 patients. Therefore, TLR4 contributes significantly to the pathogenesis of SARS-CoV-2, and its overactivation causes a prolonged or excessive innate immune response. TLR4 appears to be a promising therapeutic target in COVID-19, and since TLR4 antagonists have been previously trialled in sepsis and in other antiviral contexts, we propose the clinical trial testing of TLR4 antagonists in the treatment of severe COVID-19. Also, ongoing clinical trials of pulmonary surfactants in COVID-19 hold promise since they also block TLR4.

Exploring the Pivotal Immunomodulatory and Anti-Inflammatory Potentials of Glycyrrhizic and Glycyrrhetinic Acids

Licorice extract is a Chinese herbal medication most often used as a demulcent or elixir. The extract usually consists of many components but the key ingredients are glycyrrhizic (GL) and glycyrrhetinic acid (GA). GL and GA function as potent antioxidants, anti-inflammatory, antiviral, antitumor agents, and immuneregulators. GL and GA have potent activities against hepatitis A, B, and C viruses, human immunodeficiency virus type 1, vesicular stomatitis virus, herpes simplex virus, influenza A, severe acute respiratory syndrome-related coronavirus, respiratory syncytial virus, vaccinia virus, and arboviruses. Also, GA was observed to be of therapeutic valve in human enterovirus 71, which was recognized as the utmost regular virus responsible for hand, foot, and mouth disease. The anti-inflammatory mechanism of GL and GA is realized via cytokines like interferon-γ, tumor necrotizing factor-α, interleukin- (IL-) 1β, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12, and IL-17. They also modulate anti-inflammatory mechanisms like intercellular cell adhesion molecule 1 and P-selectin, enzymes like inducible nitric oxide synthase (iNOS), and transcription factors such as nuclear factor-kappa B, signal transducer and activator of transcription- (STAT-) 3, and STAT-6. Furthermore, DCs treated with GL were capable of influencing T-cell differentiation toward Th1 subset. Moreover, GA is capable of blocking prostaglandin-E2 synthesis via blockade of cyclooxygenase- (COX-) 2 resulting in concurrent augmentation nitric oxide production through the enhancement of iNOS2 mRNA secretion in Leishmania-infected macrophages. GA is capable of inhibiting toll-like receptors as well as high-mobility group box 1.

Current Insights into the Host Immune Response to Respiratory Viral Infections

Respiratory viral infections often lead to severe illnesses varying from mild or asymptomatic upper respiratory tract infections to severe bronchiolitis and pneumonia or/and chronic obstructive pulmonary disease. Common viral infections, including but not limited to influenza virus, respiratory syncytial virus, rhinovirus and coronavirus, are often the leading cause of morbidity and mortality. Since the lungs are continuously exposed to foreign particles, including respiratory pathogens, it is also well equipped for recognition and antiviral defense utilizing the complex network of innate and adaptive immune cells. Immediately upon infection, a range of proinflammatory cytokines, chemokines and an interferon response is generated, thereby making the immune response a two edged sword, on one hand it is required to eliminate viral pathogens while on other hand it's prolonged response can lead to chronic infection and significant pulmonary damage. Since vaccines to all respiratory viruses are not available, a better understanding of the virus-host interactions, leading to the development of immune response, is critically needed to design effective therapies to limit the severity of inflammatory damage, enhance viral clearance and to compliment the current strategies targeting the virus. In this chapter, we discuss the host responses to common respiratory viral infections, the key players of adaptive and innate immunity and the fine balance that exists between the viral clearance and immune-mediated damage.

Aggravated MRSA pneumonia secondary to influenza A virus infection is derived from decreased expression of IL-1β

Secondary methicillin-resistant Staphylococcus aureus (MRSA) infection is a cause of severe pneumonia with high mortality during influenza A virus (IAV) pandemics. Alveolar macrophages (AMs) mount cellular defenses against IAV and MRSA infection, which occurs via the nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome. However, the activity and function of the NLRP3 inflammasome in MRSA pneumonia secondary to IAV infection remain unclear. To clarify this, we studied MRSA infection secondary to IAV both in vitro and in mouse model. The expression of the NLRP3 inflammasome was evaluated by quantitative reverse transcription polymerase chain reaction, immunofluorescence, Western blot, and enzyme-linked immunosorbent assay. The lung pathology and the rate of weight change were observed. We found that IAV infection for 1 week activated NLRP3 inflammasome. The enhanced expression of NLRP3, caspase-1, and cleaved caspase-1 was associated with MRSA infection secondary to IAV, but the expression of interleukin (IL)-1β decreased in superinfection with MRSA both in vitro and in vivo. The aggravated inflammatory pathology in MRSA pneumonia secondary to IAV infection was associated with decreased expression of IL-1β. And increased weight loss in MRSA pneumonia secondary to IAV infection was related to decreased concentration of IL-1β in serum. It infers that superinfection with MRSA reduces expression of IL-1β someway, and decreased expression of IL-1β impairs the host immunity and leads to aggravated pneumonia. These results contributed to our understanding of the detailed activity of the NLRP3 inflammasome, IL-1β, and their relationship with aggravation of MRSA pneumonia secondary to IAV infection. Immunotherapy targeting the IL-1β signaling pathway could be possible therapeutic strategy for secondary MRSA pneumonia.

Evaluation of mechanisms of action of re-purposed drugs for treatment of COVID-19

Coronavirus disease 2019 (COVID-19) is a global health emergency caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). The rapid worldwide spread of SARS-CoV-2 infection has necessitated a global effort to identify effective therapeutic strategies in the absence of vaccine. Among the re-purposed drugs being tested currently, hydroxychloroquine (HCQ), without or with zinc ion (Zn++) and the antibiotic azithromycin (AZM), has been administered to prevent or treat patients with COVID-19. The outcome of multiple clinical studies on HCQ has been mixed. Zn++ interferes with viral replication by inhibiting replicative enzymes and its entry into cells may be facilitated by HCQ. Another immunomodulatory drug, methotrexate (MTX), is well known for its ability to mitigate overactive immune system by upregulating the anti-inflammatory protein, A20. However, its beneficial effect in treating COVID-19 has not drawn much attention. This review provides an overview of the virology of SARS-CoV-2 and an analysis of the mechanisms by which these anti-inflammatory agents may act in the treatment of COVID-19 patients. We propose a rationale for the combinatorial use of these re-purposed drugs that may help to combat this ongoing pandemic health emergency.

Antiviral and Immunomodulatory Effects of Phytochemicals from Honey against COVID-19: Potential Mechanisms of Action and Future Directions

The new coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), has recently put the world under stress, resulting in a global pandemic. Currently, there are no approved treatments or vaccines, and this severe respiratory illness has cost many lives. Despite the established antimicrobial and immune-boosting potency described for honey, to date there is still a lack of evidence about its potential role amid COVID-19 outbreak. Based on the previously explored antiviral effects and phytochemical components of honey, we review here evidence for its role as a potentially effective natural product against COVID-19. Although some bioactive compounds in honey have shown potential antiviral effects (i.e., methylglyoxal, chrysin, caffeic acid, galangin and hesperidinin) or enhancing antiviral immune responses (i.e., levan and ascorbic acid), the mechanisms of action for these compounds are still ambiguous. To the best of our knowledge, this is the first work exclusively summarizing all these bioactive compounds with their probable mechanisms of action as antiviral agents, specifically against SARS-CoV-2.

Blocking IL-1 to prevent respiratory failure in COVID-19

COVID-19 is an emerging disease that can manifest itself as asymptomatic or mild respiratory tract infection in the majority of individuals, but in some, it can progress into severe pneumonia and acute respiratory distress syndrome (ARDS). Inflammation is known to play a crucial role in the pathogenesis of severe infections and ARDS and evidence is emerging that the IL-1/IL-6 pathway is highly upregulated in patients with severe disease. These findings open new avenues for host-directed therapies in patients with symptomatic SARS-CoV-2 infection and might in addition to antiviral treatment be enough to curb the currently unacceptably high morbidity and mortality associated with COVID-19.

Innate Immune Sensing of Influenza A Virus

Influenza virus infection triggers host innate immune response by stimulating various pattern recognition receptors (PRRs). Activation of these PRRs leads to the activation of a plethora of signaling pathways, resulting in the production of interferon (IFN) and proinflammatory cytokines, followed by the expression of interferon-stimulated genes (ISGs), the recruitment of innate immune cells, or the activation of programmed cell death. All these antiviral approaches collectively restrict viral replication inside the host. However, influenza virus also engages in multiple mechanisms to subvert the innate immune responses. In this review, we discuss the role of PRRs such as Toll-like receptors (TLRs), Retinoic acid-inducible gene I (RIG-I), NOD-, LRR-, pyrin domain-containing protein 3 (NLRP3), and Z-DNA binding protein 1 (ZBP1) in sensing and restricting influenza viral infection. Further, we also discuss the mechanisms influenza virus utilizes, especially the role of viral non-structure proteins NS1, PB1-F2, and PA-X, to evade the host innate immune responses.

Glycyrrhetinic acid alleviates hepatic inflammation injury in viral hepatitis disease via a HMGB1-TLR4 signaling pathway

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Licorice defect in TCM recipes leads to the hepatotoxicity in administrated mice.

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GA inhibits viral hepatitis by suppressing HMGB1 release and cytokine activity.

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GA treatment effect on infected mice is similar with HMGB1 neutralizing antibody.

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HMGB1-TLR4 axis is involved in murine hepatic injury during MHV infection.

Various human disorders are cured by the use of licorice, a key ingredient of herbal remedies. Glycyrrhizic acid (GL), a triterpenoid glycoside, is the aqueous extract from licorice root. Glycyrrhetinic acid (GA) has been reported to be a major bioactive hydrolysis product of GL and has been regarded as an anti-inflammatory agent for the treatment of a variety of inflammatory diseases, including hepatitis. However, the mechanism by which GA inhibits viral hepatic inflammatory injury is not completely understood. In this study, we found that, by consecutively treating mice with a traditional herbal recipe, licorice plays an important role in the detoxification of mice. We also employed a murine hepatitis virus (MHV) infection model to illustrate that GA treatment inhibited activation of hepatic inflammatory responses by blocking high-mobility group box 1 (HMGB1) cytokine activity. Furthermore, decreased HMGB1 levels and downstream signaling triggered by injection of a neutralizing HMGB1 antibody or TLR4 gene deficiency, also significantly protected against MHV-induced severe hepatic injury. Thus, our findings characterize GA as a hepatoprotective therapy agent in hepatic infectious disease not only by suppressing HMGB1 release and blocking HMGB1 cytokine activity, but also via an underlying viral-induced HMGB1-TLR4 immunological regulation axis that occurs during the cytokine storm. The present study provides a new therapy strategy for the treatment of acute viral hepatitis in the clinical setting.

Extracellular HMGB1: a therapeutic target in severe pulmonary inflammation including COVID-19?

BACKGROUND

The 2019 novel coronavirus disease (COVID-19) causes for unresolved reasons acute respiratory distress syndrome in vulnerable individuals. There is a need to identify key pathogenic molecules in COVID-19-associated inflammation attainable to target with existing therapeutic compounds. The endogenous damage-associated molecular pattern (DAMP) molecule HMGB1 initiates inflammation via two separate pathways. Disulfide-HMGB1 triggers TLR4 receptors generating pro-inflammatory cytokine release. Extracellular HMGB1, released from dying cells or secreted by activated innate immunity cells, forms complexes with extracellular DNA, RNA and other DAMP or pathogen-associated molecular (DAMP) molecules released after lytic cell death. These complexes are endocytosed via RAGE, constitutively expressed at high levels in the lungs only, and transported to the endolysosomal system, which is disrupted by HMGB1 at high concentrations. Danger molecules thus get access to cytosolic proinflammatory receptors instigating inflammasome activation. It is conceivable that extracellular SARS-CoV-2 RNA may reach the cellular cytosol via HMGB1-assisted transfer combined with lysosome leakage. Extracellular HMGB1 generally exists in vivo bound to other molecules, including PAMPs and DAMPs. It is plausible that these complexes are specifically removed in the lungs revealed by a 40% reduction of HMGB1 plasma levels in arterial versus venous blood. Abundant pulmonary RAGE expression enables endocytosis of danger molecules to be destroyed in the lysosomes at physiological HMGB1 levels, but causing detrimental inflammasome activation at high levels. Stress induces apoptosis in pulmonary endothelial cells from females but necrosis in cells from males.

CONCLUSION

Based on these observations we propose extracellular HMGB1 to be considered as a therapeutic target for COVID-19.

Die Another Way: Interplay between Influenza A Virus, Inflammation and Cell Death

Influenza A virus (IAV) is a major concern to human health due to the ongoing global threat of a pandemic. Inflammatory and cell death signalling pathways play important roles in host defence against IAV infection. However, severe IAV infections in humans are characterised by excessive inflammation and tissue damage, often leading to fatal disease. While the molecular mechanisms involved in the induction of inflammation during IAV infection have been well studied, the pathways involved in IAV-induced cell death and their impact on immunopathology have not been fully elucidated. There is increasing evidence of significant crosstalk between cell death and inflammatory pathways and a greater understanding of their role in host defence and disease may facilitate the design of new treatments for IAV infection.

Targeting Inflammation Driven by HMGB1

High mobility group box 1 (HMGB1) is a highly conserved, nuclear protein present in all cell types. It is a multi-facet protein exerting functions both inside and outside of cells. Extracellular HMGB1 has been extensively studied for its prototypical alarmin functions activating innate immunity, after being actively released from cells or passively released upon cell death. TLR4 and RAGE operate as the main HMGB1 receptors. Disulfide HMGB1 activates the TLR4 complex by binding to MD-2. The binding site is separate from that of LPS and it is now feasible to specifically interrupt HMGB1/TLR4 activation without compromising protective LPS/TLR4-dependent functions. Another important therapeutic strategy is established on the administration of HMGB1 antagonists precluding RAGE-mediated endocytosis of HMGB1 and HMGB1-bound molecules capable of activating intracellular cognate receptors. Here we summarize the role of HMGB1 in inflammation, with a focus on recent findings on its mission as a damage-associated molecular pattern molecule and as a therapeutic target in inflammatory diseases. Recently generated HMGB1-specific inhibitors for treatment of inflammatory conditions are discussed.

Select targeting of intracellular Toll-interleukin-1 receptor resistance domains for protection against influenza-induced disease

TLRs are a family of PRRs that respond to PAMPs or host-derived Danger-Associated Molecular Patterns (DAMPs) to initiate host inflammation and immune responses. TLR dimerization and recruitment of adapter molecules is critical for intracellular signaling and is mediated through intracellular Toll-Interleukin 1 Receptor Resistance (TIR) domain interactions. Human TIR domains, including reported structures of TIR1, TIR2, TIR6, TIR10, TIRAP, and MyD88, contain Cysteine (Cys) interactions or modifications that are disproportionally at, or near, reported biological TIR interfaces, or in close proximity to functionally important regions. Therefore, we hypothesized that intracellular TIR Cys regulation may have greater functional importance than previously appreciated. Expression of mutant TLR4-C747S or treatment of TLR4 reporter cells with a small molecule, Cys-binding inhibitor of TLR4, TAK-242, abrogated LPS signaling in vitro . Using TAK-242, mice were protected from lethal influenza challenge as previously reported for extracellular TLR4 antagonists. Molecular modeling and sequence analysis of the region surrounding TLR4-Cys747 indicate conservation of a WxxxE motif identified among bacterial and NAD+-consuming TIRs, as well as within the TIRs domains of surface TLRs 1, 2, 4, 6, and 10. Together, these data support the hypothesis that critical Cys within the TIR domain are essential for TLR4 functionality.

Breaking Down Barriers: How Understanding Celiac Disease Pathogenesis Informed the Development of Novel Treatments

For decades, the pathogenesis of a variety of human diseases has been attributed to increased intestinal paracellular permeability even though scientific evidence supporting this hypothesis has been tenuous. Nevertheless, during the past decade, there have been a growing number of publications focused on human genetics, the gut microbiome, and proteomics, suggesting that loss of mucosal barrier function, particularly in the gastrointestinal tract, may substantially affect antigen trafficking, ultimately causing chronic inflammation, including autoimmunity, in genetically predisposed individuals. The gut mucosa works as a semipermeable barrier in that it permits nutrient absorption and also regulates immune surveillance while retaining potentially harmful microbes and environmental antigens within the intestinal lumen. Celiac disease (CD), a systemic, immune-mediated disorder triggered by gluten in genetically susceptible individuals, is associated with altered gut permeability. Pre-clinical and clinical studies have shown that gliadin, a prolamine component of gluten that is implicated in CD pathogenesis, is capable to disassembling intercellular junctional proteins by upregulating the zonulin pathway, which can be inhibited by the zonulin antagonist larazotide acetate. In this review, we will focus on CD as a paradigm of chronic inflammatory diseases in order to outline the contribution of gut paracellular permeability toward disease pathogenesis; moreover, we will summarize current evidence derived from available clinical trials of larazotide acetate in CD.

The Effect of a Lipopolysaccharide from Rhodobacter capsulatus PG on Inflammation Caused by Various Influenza Strains

The development of a specific inflammation in mice that had been infected by two influenza virus strains, A/chicken/Kurgan/5/2005 (H5N1) and A/Hamburg/2009 MA (H1N1), was studied. We investigated the effect of a non-toxic lipopolysaccharide from Rhodobacter capsulatus PG on the survival and body weight of the mice, production of IgG antibodies, and the induction of pro- and anti-inflammatory cytokines in blood serum. The administration of the R. capsulatus PG lipopolysaccharide was shown to induce interferon-β synthesis, both in healthy and influenza A virus-infected mice, and to promote production of antiviral antibodies in the blood of the influenza-infected animals.

Ponatinib Protects Mice From Lethal Influenza Infection by Suppressing Cytokine Storm

Excessive inflammation associated with the uncontrolled release of pro-inflammatory cytokines is the main cause of death from influenza virus infection. Previous studies have indicated that inhibition of interferon gamma-induced protein 10 (IP-10), interleukin-8 (IL-8), monocyte chemoattractant protein 1 (MCP-1), or their cognate receptors has beneficial effects. Here, by using monocytic U937 cells that capable of secreting the three important cytokines during influenza A virus infection, we measured the inhibitory activities on the production of three cytokines of six anti-inflammatory compounds reported in other models of inflammation. We found that ponatinib had a highly inhibitory effect on the production of all three cytokines. We tested ponatinib in a mouse influenza model to assess its therapeutic effects with different doses and administration times and found that the delayed administration of ponatinib was protective against lethal influenza A virus infection without reducing virus titers. Therefore, we suggest that ponatinib may serve as a new immunomodulator in the treatment of influenza.

Influenza "Trains" the Host for Enhanced Susceptibility to Secondary Bacterial Infection

Enhanced susceptibility to 2° bacterial infections following infection with influenza virus is a global health concern that accounts for many hospitalizations and deaths, particularly during pandemics. The complexity of the impaired host immune response during 2° bacterial infection has been widely studied. Both type I IFN and neutrophil dysfunction through decreased chemokine production have been implicated as mechanisms underlying enhanced susceptibility to 2° bacterial infections. Our findings support the conclusion that selective suppression of CXCL1/CXCL2 represents an IFN-β-mediated “training” of the macrophage transcriptional response to TLR2 agonists and that blocking of TLR4 therapeutically with Eritoran after influenza virus infection reverses this suppression by blunting influenza-induced IFN-β.

We previously reported that the Toll-like receptor 4 (TLR4) antagonist Eritoran blocks acute lung injury (ALI) therapeutically in mouse and cotton rat models of influenza. However, secondary (2°) bacterial infection following influenza virus infection is associated with excess morbidity and mortality. Wild-type (WT) mice infected with mouse-adapted influenza A/Puerto Rico/8/34 virus (PR8) and, 7 days later, with Streptococcus pneumoniae serotype 3 (Sp3) exhibited significantly enhanced lung pathology and lethality that was reversed by Eritoran therapy after PR8 infection but before Sp3 infection. Cotton rats infected with nonadapted pH1N1 influenza virus and then superinfected with methicillin-resistant Staphylococcus aureus also exhibited increased lung pathology and serum high-mobility-group box 1 (HMGB1) levels, both of which were blunted by Eritoran therapy. In mice, PR8 infection suppressed Sp3-induced CXCL1 and CXCL2 mRNA, reducing neutrophil infiltration and increasing the bacterial burden, all of which were reversed by Eritoran treatment. While beta interferon (IFN-β)-deficient (IFN-β^−/−) mice are highly susceptible to PR8, they exhibited delayed death upon Sp3 superinfection, indicating that while IFN-β was protective against influenza, it negatively impacted the host response to Sp3. IFN-β-treated WT macrophages selectively suppressed Sp3-induced CXCL1/CXCL2 transcriptionally, as evidenced by reduced recruitment of RNA polymerase II to the CXCL1 promoter. Thus, influenza establishes a “trained” state of immunosuppression toward 2° bacterial infection, in part through the potent induction of IFN-β and its downstream transcriptional regulation of chemokines, an effect reversed by Eritoran.

The Single Nucleotide Polymorphism Mal-D96N Mice Provide New Insights into Functionality of Mal in TLR Immune Responses

MyD88 adaptor-like (Mal) protein is the most polymorphic of the four key adaptor proteins involved in TLR signaling. TLRs play a critical role in the recognition and immune response to pathogens through activation of the prototypic inflammatory transcription factor NF-κB. The study of single nucleotide polymorphisms in TLRs, adaptors, and signaling mediators has provided key insights into the function of the corresponding genes but also into the susceptibility to infectious diseases in humans. In this study, we have analyzed the immune response of mice carrying the human Mal-D96N genetic variation that has previously been proposed to confer protection against septic shock. We have found that Mal-D96N macrophages display reduced cytokine expression in response to TLR4 and TLR2 ligand challenge. Mal-D96N macrophages also display reduced MAPK activation, NF-κB transactivation, and delayed NF-κB nuclear translocation, presumably via delayed kinetics of Mal interaction with MyD88 following LPS stimulation. Importantly, Mal-D96N genetic variation confers a physiological protective phenotype to in vivo models of LPS-, Escherichia coli-, and influenza A virus-induced hyperinflammatory disease in a gene dosage-dependent manner. Together, these results highlight the critical role Mal plays in regulating optimal TLR-induced inflammatory signaling pathways and suggest the potential therapeutic advantages of targeting the Mal D96 signaling nexus.

Novel carboxylate-based glycolipids: TLR4 antagonism, MD-2 binding and self-assembly properties

New monosaccharide-based lipid A analogues were rationally designed through MD-2 docking studies. A panel of compounds with two carboxylate groups as phosphates bioisosteres, was synthesized with the same glucosamine-bis-succinyl core linked to different unsaturated and saturated fatty acid chains. The binding of the synthetic compounds to purified, functional recombinant human MD-2 was studied by four independent methods. All compounds bound to MD-2 with similar affinities and inhibited in a concentration-dependent manner the LPS-stimulated TLR4 signaling in human and murine cells, while being inactive as TLR4 agonists when provided alone. A compound of the panel was tested in vivo and was not able to inhibit the production of proinflammatory cytokines in animals. This lack of activity is probably due to strong binding to serum albumin, as suggested by cell experiments in the presence of the serum. The interesting self-assembly property in solution of this type of compounds was investigated by computational methods and microscopy, and formation of large vesicles was observed by cryo-TEM microscopy.

Novel role of gastrin releasing peptide-mediated signaling in the host response to influenza infection

Gastrin-releasing peptide (GRP) is an evolutionarily well-conserved neuropeptide that was originally recognized for its ability to mediate gastric acid secretion in the gut. More recently, however, GRP has been implicated in pulmonary lung inflammatory diseases including bronchopulmonary dysplasia, chronic obstructive pulmonary disease, emphysema, and others. Antagonizing GRP or its receptor mitigated lethality associated with the onset of viral pneumonia in a well-characterized mouse model of influenza. In mice treated therapeutically with the small-molecule GRP inhibitor, NSC77427, increased survival was accompanied by decreased numbers of GRP-producing pulmonary neuroendocrine cells, improved lung histopathology, and suppressed cytokine gene expression. In addition, in vitro studies in macrophages indicate that GRP synergizes with the prototype TLR4 agonist, lipopolysaccharide, to induce cytokine gene expression. Thus, these findings reveal that GRP is a previously unidentified mediator of influenza-induced inflammatory disease that is a potentially novel target for therapeutic intervention.

Combined effect of anti-high-mobility group box-1 monoclonal antibody and peramivir against influenza A virus-induced pneumonia in mice

Human pandemic H1N1 2009 influenza virus causes significant morbidity and mortality with severe acute lung injury due to the excessive inflammatory reaction, even with neuraminidase inhibitor use. The anti-inflammatory effect of anti-high-mobility group box-1 (HMGB1) monoclonal antibody (mAb) against influenza pneumonia has been reported. In this study, we evaluated the combined effect of anti-HMGB1 mAb and peramivir against pneumonia induced by influenza A (H1N1) virus in mice. Nine-week-old male C57BL/6 mice were inoculated with H1N1 and treated with intramuscularly administered peramivir at 2 and 3 days post-infection (dpi). The anti-HMGB1 mAb or a control mAb was administered at 2, 3, and 4 dpi. Survival rates were assessed, and lung lavage and pathological analyses were conducted at 5 and 7 dpi. The combination of peramivir with the anti-HMGB1 mAb significantly improved survival rate whereas the anti-HMGB1 mAb alone did not affect virus proliferation in the lungs. This combination therapy also significantly ameliorated histopathological changes, neutrophil infiltration, and macrophage aggregation by inhibiting HMGB1, inflammatory cytokines, and oxidative stress. Fluorescence immunostaining showed that the anti-HMGB1 mAb inhibited HMGB1 translocation from type I alveolar epithelial cells. In summary, combining anti-HMGB1 with conventional anti-influenza therapy might be useful against severe influenza virus infection.

Advancements in Host-Based Interventions for Influenza Treatment

Influenza is a major acute respiratory infection that causes mortality and morbidity worldwide. Two classes of conventional antivirals, M2 ion channel blockers and neuraminidase inhibitors, are mainstays in managing influenza disease to lessen symptoms while minimizing hospitalization and death in patients with severe influenza. However, the development of viral resistance to both drug classes has become a major public health concern. Vaccines are prophylaxis mainstays but are limited in efficacy due to the difficulty in matching predicted dominant viral strains to circulating strains. As such, other potential interventions are being explored. Since viruses rely on host cellular functions to replicate, recent therapeutic developments focus on targeting host factors involved in virus replication. Besides controlling virus replication, potential targets for drug development include controlling virus-induced host immune responses such as the recently suggested involvement of innate lymphoid cells and NADPH oxidases in influenza virus pathogenesis and immune cell metabolism. In this review, we will discuss the advancements in novel host-based interventions for treating influenza disease.

Serum High-Mobility-Group Box 1 as a Biomarker and a Therapeutic Target during Respiratory Virus Infections

Host-derived “danger-associated molecular patterns” (DAMPs) contribute to innate immune responses and serve as markers of disease progression and severity for inflammatory and infectious diseases. There is accumulating evidence that generation of DAMPs such as oxidized phospholipids and high-mobility-group box 1 (HMGB1) during influenza virus infection leads to acute lung injury (ALI). Treatment of influenza virus-infected mice and cotton rats with the Toll-like receptor 4 (TLR4) antagonist Eritoran blocked DAMP accumulation and ameliorated influenza virus-induced ALI. However, changes in systemic HMGB1 kinetics during the course of influenza virus infection in animal models and humans have yet to establish an association of HMGB1 release with influenza virus infection. To this end, we used the cotton rat model that is permissive to nonadapted strains of influenza A and B viruses, respiratory syncytial virus (RSV), and human rhinoviruses (HRVs). Serum HMGB1 levels were measured by an enzyme-linked immunosorbent assay (ELISA) prior to infection until day 14 or 18 post-infection. Infection with either influenza A or B virus resulted in a robust increase in serum HMGB1 levels that decreased by days 14 to 18. Inoculation with the live attenuated vaccine FluMist resulted in HMGB1 levels that were significantly lower than those with infection with live influenza viruses. RSV and HRVs showed profiles of serum HMGB1 induction that were consistent with their replication and degree of lung pathology in cotton rats. We further showed that therapeutic treatment with Eritoran of cotton rats infected with influenza B virus significantly blunted serum HMGB1 levels and improved lung pathology, without inhibiting virus replication. These findings support the use of drugs that block HMGB1 to combat influenza virus-induced ALI.

Influenza virus is a common infectious agent causing serious seasonal epidemics, and there is urgent need to develop an alternative treatment modality for influenza virus infection. Recently, host-derived DAMPs, such as oxidized phospholipids and HMGB1, were shown to be generated during influenza virus infection and cause ALI. To establish a clear link between influenza virus infection and HMGB1 as a biomarker, we have systematically analyzed temporal patterns of serum HMGB1 release in cotton rats infected with nonadapted strains of influenza A and B viruses and compared these patterns with a live attenuated influenza vaccine and infection by other respiratory viruses. Towards development of a new therapeutic modality, we show herein that blocking serum HMGB1 levels by Eritoran improves lung pathology in influenza B virus-infected cotton rats. Our study is the first report of systemic HMGB1 as a potential biomarker of severity in respiratory virus infections and confirms that drugs that block virus-induced HMGB1 ameliorate ALI.

Immune responses in influenza A virus and human coronavirus infections: an ongoing battle between the virus and host

Respiratory viruses, especially influenza A viruses and coronaviruses such as MERS-CoV, represent continuing global threats to human health. Despite significant advances, much needs to be learned. Recent studies in virology and immunology have improved our understanding of the role of the immune system in protection and in the pathogenesis of these infections and of co-evolution of viruses and their hosts. These findings, together with sophisticated molecular structure analyses, omics tools and computer-based models, have helped delineate the interaction between respiratory viruses and the host immune system, which will facilitate the development of novel treatment strategies and vaccines with enhanced efficacy.