Lung epithelial cells: therapeutically inducible effectors of antimicrobial defense

Extracorporeal blood purification treatment options for COVID-19: The role of immunoadsorption

The activation of the innate and adaptive immune systems by SARS-CoV-2 causes the release of several inflammatory cytokines, including IL-6. The inflammatory hypercytokinemia causes immunopathological changes in the lungs including vascular leakage, and alveolar edema. As a result of these changes in the lungs, hypoxia and acute respiratory distress syndrome occur in patients with COVID-19. Even though there are clinical trials on the development of therapeutics and vaccines, there are currently no licensed vaccines or therapeutics for COVID-19. Pharmacological approaches have shown poor results in sepsis-like syndromes caused by the hypercytokinemia. Suppressing the cytokine storm is an important way to prevent the organ damage in patients with COVID-19. Extracorporeal blood purification could be proposed as an adjunctive therapy for sepsis, aiming to control the associated dysregulation of the immune system, which is known to protect organ functions. Several extracorporeal blood purification therapies are now available, and most of them target endotoxins and/or the cytokines and aim improving the immune response. For this purpose, plasmapheresis and immunoadsorption may be an important adjunctive treatment option to manage the complications caused by cytokine storm in critically ill patients with COVID-19.

Microbiota dysbiosis in lung cancer: evidence of association and potential mechanisms

Over the past decade, revolution in microbial research has provided valuable insights into the function of microbes that inhabit human body. This complex community of microbes, collectively named as microbiota, displays tremendous interaction with a host to maintain homeostasis of the local environment. Lungs were even previously regarded as sterile for a long time. With the development of high-throughput next-generation sequencing technology, a low-density, diversified microbial ecosystem is found in bronchoalveolar lavage fluid, sputum, and lung tissues. Current research confirms that, compared with healthy people, patients with lung cancer show changes in the relative abundance of multiple genera. Emerging evidence has suggested that dysbiosis of the lung microbiota may play a critical role in lung carcinogenesis by affecting metabolic, inflammatory pathways and immune response. We briefly summarize the relationship between lung microbiome and lung cancer and discuss the potential mechanisms mediating lung microbiota and lung cancer. Thus, we provide innovative strategies for early prevention and personalized treatment of lung cancer.

A Comprehensive Review of Tocilizumab in COVID-19 Acute Respiratory Distress Syndrome

Currently, the world is facing the pandemic of a novel strain of beta‐coronavirus known as severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2). Acute respiratory distress syndrome (ARDS) is the most devastating complication of SARS‐CoV‐2. It was indicated that cytokine‐release syndrome and dominantly interleukin (IL)‐6 play a central role in the pathophysiology of ARDS related to the novel 2019 coronavirus disease (COVID‐19). Despite the global emergency of the disease, at this time, there are no proven therapies for the management of the disease. Tocilizumab is a potential recombinant monoclonal antibody against IL‐6 and currently is under investigation for the management of ARDS in patients with COVID‐19. Given these points, we reviewed the current evidence regarding the potential therapeutic role of tocilizumab and its important clinical issues in the treatment of ARDS related to COVID‐19.

Dynamic Interleukin-6 Level Changes as a Prognostic Indicator in Patients With COVID-19

Background

Interleukin-6 (IL-6), a proinflammatory cytokine, has been reported to be associated with disease severity and mortality in patients with coronavirus disease 2019 (COVID-19). Yet, dynamic changes in IL-6 levels and their prognostic value as an indicator of lung injury in COVID-19 patients have not been fully elucidated.

Objective

To validate whether IL-6 levels are associated with disease severity and mortality and to investigate whether dynamic changes in IL-6 levels might be a predictive factor for lung injury in COVID-19 patients.

Methods

This retrospective, single-center study included 728 adult COVID-19 patients and used data extracted from electronic medical records for analyses.

Results

The mortality rate was higher in the elevated IL-6 group than in the normal IL-6 group (0.16 vs 5%). Cox proportional hazards and logistic regression analyses for survival (adjusted hazard ratio, 10.39; 95% confidence interval [CI], 1.09–99.23; p = 0.042) and disease severity (adjusted odds ratio, 3.56; 95% CI, 2.06–6.19; p < 0.001) revealed similar trends. Curve-fitting analyses indicated that patient computed tomography (CT) scores peaked on days 22 and 24. An initial decline in IL-6 levels on day 16 was followed by resurgence to a peak, nearly in tandem with the CT scores.

Conclusion

Increased IL-6 level may be an independent risk factor for disease severity and in-hospital mortality and dynamic IL-6 changes may serve as a potential predictor for lung injury in Chinese COVID-19 patients. These findings may guide future treatment of COVID-19 patients.

Combating COVID-19 and Building Immune Resilience: A Potential Role for Magnesium Nutrition?

Background: In December 2019, the viral pandemic of respiratory illness caused by COVID-19 began sweeping its way across the globe. Several aspects of this infectious disease mimic metabolic events shown to occur during latent subclinical magnesium deficiency. Hypomagnesemia is a relatively common clinical occurrence that often goes unrecognized since magnesium levels are rarely monitored in the clinical setting. Magnesium is the second most abundant intracellular cation after potassium. It is involved in >600 enzymatic reactions in the body, including those contributing to the exaggerated immune and inflammatory responses exhibited by COVID-19 patients.Methods: A summary of experimental findings and knowledge of the biochemical role magnesium may play in the pathogenesis of COVID-19 is presented in this perspective. The National Academy of Medicine's Standards for Systematic Reviews were independently employed to identify clinical and prospective cohort studies assessing the relationship of magnesium with interleukin-6, a prominent drug target for treating COVID-19.Results: Clinical recommendations are given for prevention and treatment of COVID-19. Constant monitoring of ionized magnesium status with subsequent repletion, when appropriate, may be an effective strategy to influence disease contraction and progression. The peer-reviewed literature supports that several aspects of magnesium nutrition warrant clinical consideration. Mechanisms include its "calcium-channel blocking" effects that lead to downstream suppression of nuclear factor-Kβ, interleukin-6, c-reactive protein, and other related endocrine disrupters; its role in regulating renal potassium loss; and its ability to activate and enhance the functionality of vitamin D, among others.Conclusion: As the world awaits an effective vaccine, nutrition plays an important and safe role in helping mitigate patient morbidity and mortality. Our group is working with the Academy of Nutrition and Dietetics to collect patient-level data from intensive care units across the United States to better understand nutrition care practices that lead to better outcomes.

Immunopathology of SARS-CoV-2 Infection: Immune Cells and Mediators, Prognostic Factors, and Immune-Therapeutic Implications

The present is a comprehensive review of the immunopathology of Covid-19. The immune reaction to SARS-CoV-2 infection is characterized by differentiation and proliferation of a variety of immune cells with immune mediator production and release, and activation of other pathogen resistance mechanisms. We fully address the humoral and cellular immune changes induced by the virus, with particular emphasis on the role of the “cytokine storm” in the evolution of the disease. Moreover, we also propose some immune alterations (i.e., inflammatory parameters, cytokines, leukocytes and lymphocyte subpopulations) as prognostic markers of the disease. Furthermore, we discuss how immune modifying drugs, such as tocilizumab, chloroquine, glucocorticoids and immunoglobulins, and blood purification therapy, can constitute a fundamental moment in the therapy of the infection. Finally, we made a critical analysis of a number of substances, not yet utilized, but potentially useful in SARS-CoV-2 patients, such as IFN lambda, TNF blockers, ulinastatin, siponimod, tacrolimus, mesenchymal stem cells, inhibitors of mononuclear macrophage recruitment, IL-1 family antagonists, JAK-2 or STAT-3 inhibitors.

Characterization and pro-inflammatory potential of indoor mold particles

A number of epidemiological studies find an association between indoor air dampness and respiratory health effects. This is often suggested to be linked to enhanced mold growth. However, the role of mold is obviously difficult to disentangle from other dampness-related exposure including microbes as well as non-biological particles and chemical pollutants. The association may partly be due to visible mycelial growth and a characteristic musty smell of mold. Thus, the potential role of mold exposure should be further explored by evaluating information from experimental studies elucidating possible mechanistic links. Such studies show that exposure to spores and hyphal fragments may act as allergens and pro-inflammatory mediators and that they may damage airways by the production of toxins, enzymes, and volatile organic compounds. In the present review, we hypothesize that continuous exposure to mold particles may result in chronic low-grade pro-inflammatory responses contributing to respiratory diseases. We summarize some of the main methods for detection and characterization of fungal aerosols and highlight in vitro research elucidating how molds may induce toxicity and pro-inflammatory reactions in human cell models relevant for airway exposure. Data suggest that the fraction of fungal hyphal fragments in indoor air is much higher than that of airborne spores, and the hyphal fragments often have a higher pro-inflammatory potential. Thus, hyphal fragments of prevalent mold species with strong pro-inflammatory potential may be particularly relevant candidates for respiratory diseases associated with damp/mold-contaminated indoor air. Future studies linking of indoor air dampness with health effects should assess the toxicity and pro-inflammatory potential of indoor air particulate matter and combined this information with a better characterization of biological components including hyphal fragments from both pathogenic and non-pathogenic mold species. Such studies may increase our understanding of the potential role of mold exposure.

Respiratory microbiome and epithelial interactions shape immunity in the lungs

The airway epithelium represents a physical barrier to the external environment acting as the first line of defence against potentially harmful environmental stimuli including microbes and allergens. However, lung epithelial cells are increasingly recognized as active effectors of microbial defence, contributing to both innate and adaptive immune function in the lower respiratory tract. These cells express an ample repertoire of pattern recognition receptors with specificity for conserved microbial and host motifs. Modern molecular techniques have uncovered the complexity of the lower respiratory tract microbiome. The interaction between the microbiota and the airway epithelium is key to understanding how stable immune homeostasis is maintained. Loss of epithelial integrity following exposure to infection can result in the onset of inflammation in susceptible individuals and may culminate in lung disease. Here we discuss the current knowledge regarding the molecular and cellular mechanisms by which the pulmonary epithelium interacts with the lung microbiome in shaping immunity in the lung. Specifically, we focus on the interactions between the lung microbiome and the cells of the conducting airways in modulating immune cell regulation, and how defects in barrier structure and function may culminate in lung disease. Understanding these interactions is fundamental in the search for more effective therapies for respiratory diseases.

Recombinant Human Elafin Ameliorates Chronic Hyperoxia-Induced Lung Injury by Inhibiting Nuclear Factor-Kappa B Signaling in Neonatal Mice

The study aimed to investigate whether recombinant human elafin can prevent hyperoxia-induced pulmonary inflammation in newborn mice, and to explore the mechanism underlying the inhibitory effects of elafin on nuclear factor-kappa B (NF-κB) signaling pathway. Neonatal C57BL/6J mice were exposed to 85% O₂ for 1, 3, 7, 14, or 21 days. Then, elafin was administered daily for 20 days through intraperitoneal injection. After treatment, morphometric analysis, quantitative real-time polymerase chain reaction, terminal deoxynucleotidyl transferase dUTP nick end labeling staining, and Western blotting were carried out to determine the key markers involved in inflammatory process and the potential signaling pathways in hyperoxia-exposed newborn mice treated with elafin. In neonatal bronchopulmonary dysplasia (BPD) mice, hyperoxia induced apoptosis by increasing Bcl-2-associated X protein expression, and triggered inflammation by upregulating the expression levels of interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor-α. Moreover, hyperoxia activated NF-κB signaling pathway by promoting the nuclear translocation of p65 in lung tissue. However, all these changes could be inhibited or reversed by elafin at least partially. Elafin reduced apoptosis, suppressed inflammation cytokines, and improved NF-κB p65 nuclear accumulation in hyperoxia-exposed neonatal mice, indicating that this recombinant protein can serve as a novel target for the treatment of BPD.

Competitive Cell Death Interactions in Pulmonary Infection: Host Modulation Versus Pathogen Manipulation

In the context of pulmonary infection, both hosts and pathogens have evolved a multitude of mechanisms to regulate the process of host cell death. The host aims to rapidly induce an inflammatory response at the site of infection, promote pathogen clearance, quickly resolve inflammation, and return to tissue homeostasis. The appropriate modulation of cell death in respiratory epithelial cells and pulmonary immune cells is central in the execution of all these processes. Cell death can be either inflammatory or anti-inflammatory depending on regulated cell death (RCD) modality triggered and the infection context. In addition, diverse bacterial pathogens have evolved many means to manipulate host cell death to increase bacterial survival and spread. The multitude of ways that hosts and bacteria engage in a molecular tug of war to modulate cell death dynamics during infection emphasizes its relevance in host responses and pathogen virulence at the host pathogen interface. This narrative review outlines several current lines of research characterizing bacterial pathogen manipulation of host cell death pathways in the lung. We postulate that understanding these interactions and the dynamics of intracellular and extracellular bacteria RCD manipulation, may lead to novel therapeutic approaches for the treatment of intractable respiratory infections.

Cytokine release syndrome in severe COVID-19: interleukin-6 receptor antagonist tocilizumab may be the key to reduce mortality

Since December 2019, a viral pneumonia, named coronavirus disease 2019 (COVID-19), from Wuhan, China, has swept the world. Although the case fatality rate is not high, the number of people infected is large and there is still a large number of patients dying. With the collation and publication of more and more clinical data, a large number of data suggest that there are mild or severe cytokine storms in severe patients, which is an important cause of death. Therefore, treatment of the cytokine storm has become an important part of rescuing severe COVID-19 patients. Interleukin-6 (IL-6) plays an important role in cytokine release syndrome. If it is possible to block the signal transduction pathway of IL-6, it is expected to become a new method for the treatment of severe COVID-19 patients. Tocilizumab is an IL-6 receptor (IL-6R) blocker that can effectively block the IL-6 signal transduction pathway and thus is likely to become an effective drug for patients with severe COVID-19.

RSV Reprograms the CDK9•BRD4 Chromatin Remodeling Complex to Couple Innate Inflammation to Airway Remodeling

Respiratory syncytial virus infection is responsible for seasonal upper and lower respiratory tract infections worldwide, causing substantial morbidity. Self-inoculation of the virus into the nasopharynx results in epithelial replication and distal spread into the lower respiratory tract. Here, respiratory syncytial virus (RSV) activates sentinel cells important in the host inflammatory response, resulting in epithelial-derived cytokine and interferon (IFN) expression resulting in neutrophilia, whose intensity is associated with disease severity. I will synthesize key findings describing how RSV replication activates intracellular NFκB and IRF signaling cascades controlling the innate immune response (IIR). Recent studies have implicated a central role for Scg1a1⁺ expressing progenitor cells in IIR, a cell type uniquely primed to induce neutrophilic-, T helper 2 (Th2)-polarizing-, and fibrogenic cytokines that play distinct roles in disease pathogenesis. Molecular studies have linked the positive transcriptional elongation factor-b (P-TEFb), a pleiotrophic chromatin remodeling complex in immediate-early IIR gene expression. Through intrinsic kinase activity of cyclin dependent kinase (CDK) 9 and atypical histone acetyl transferase activity of bromodomain containing protein 4 (BRD4), P-TEFb mediates transcriptional elongation of IIR genes. Unbiased proteomic studies show that the CDK9•BRD4 complex is dynamically reconfigured by the innate response and targets TGFβ-dependent fibrogenic gene networks. Chronic activation of CDK9•BRD4 mediates chromatin remodeling fibrogenic gene networks that cause epithelial mesenchymal transition (EMT). Mesenchymal transitioned epithelial cells elaborate TGFβ and IL6 that function in a paracrine manner to expand the population of subepithelial myofibroblasts. These findings may account for the long-term reduction in pulmonary function in children with severe lower respiratory tract infection (LRTI). Modifying chromatin remodeling properties of the CDK9•BRD4 coactivators may provide a mechanism for reducing post-infectious airway remodeling that are a consequence of severe RSV LRTIs.

Lung CD4+ resident memory T cells remodel epithelial responses to accelerate neutrophil recruitment during pneumonia

Previous pneumococcal experience establishes lung-resident IL-17A-producing CD4⁺ memory T_RM cells that accelerate neutrophil recruitment against heterotypic pneumococci. Herein, we unravel a novel crosstalk between CD4⁺ T_RM cells and lung epithelial cells underlying this protective immunity. Depletion of CD4⁺ cells in pneumococcus-experienced mice diminished CXCL5 (but not CXCL1 or CXCL2) and downstream neutrophil accumulation in the lungs. Epithelial cells from experienced lungs exhibited elevated mRNA for CXCL5 but not other epithelial products such as GM-CSF or CCL20, suggesting a skewing by CD4⁺ T_RM cells. Genome-wide expression analyses revealed a significant remodeling of the epithelial transcriptome of infected lungs due to infection history, ~80% of which was CD4⁺ cell-dependent. The CD4⁺ T_RM cell product IL-17A stabilized CXCL5 but not GM-CSF or CCL20 mRNA in cultured lung epithelial cells, implicating posttranscriptional regulation as a mechanism for altered epithelial responses. These results suggest that epithelial cells in experienced lungs are effectively different, owing to their communication with T_RM cells. Our study highlights the role of tissue-resident adaptive immune cells in fine-tuning epithelial functions to hasten innate immune responses and optimize defense in experienced lungs, a concept that may apply broadly to mucosal immunology.

Microenvironmental Alterations in Carbon Nanotube-Induced Lung Inflammation and Fibrosis

Carbon nanotube (CNT)-induced pulmonary inflammation and fibrosis have been intensively observed and characterized in numerous animal studies in the past decade. Remarkably, CNT-induced fibrotic lesions highly resemble some human fibrotic lung diseases, such as IPF and pneumoconiosis, regarding disease development and pathological features. This notion leads to a serious concern over the health impact of CNTs in exposed human populations, considering the rapidly expanding production of CNT materials for diverse industrial and commercial applications, and meanwhile provides the rationale for exploring CNT-induced pathologic effects in the lung. Accumulating mechanistic understanding of CNT lung pathology at the systemic, cellular, and molecular levels has demonstrated the potential of using CNT-exposed animals as a new disease model for the studies on inflammation, fibrosis, and the interactions between these two disease states. Tissue microenvironment plays critical roles in maintaining homeostasis and physiological functions of organ systems. When aberrant microenvironment forms under intrinsic or extrinsic stimulation, tissue abnormality, organ dysfunction, and pathological outcomes are induced, resulting in disease development. In this article, the cellular and molecular alterations that are induced in tissue microenvironment and implicated in the initiation and progression of inflammation and fibrosis in CNT-exposed lungs, including effector cells, soluble mediators, and functional events exemplified by cell differentiation and extracellular matrix (ECM) modification, are summarized and discussed. This analysis would provide new insights into the mechanistic understanding of lung inflammation and fibrosis induced by CNTs, as well as the development of CNT-exposed animals as a new model for human lung diseases.

Influenza A Virus Pre-Infection Exacerbates Pseudomonas aeruginosa-Mediated Lung Damage Through Increased MMP-9 Expression, Decreased Elafin Production and Tissue Resilience

Individuals with impaired immune responses, such as ventilated and cystic fibrosis patients are often infected with Pseudomonas aeruginosa (P.a) bacteria, and a co-infection with the Influenza virus (IAV) is often present. It has been known for many years that infection with IAV predisposes the host to secondary bacterial infections (such as Streptococcus pneumoniae or Staphylococcus aureus), and there is an abundance of mechanistic studies, including those studying the role of desensitization of TLR signaling, type I IFN- mediated impairment of neutrophil chemokines and antimicrobial production, attenuation of IL1β production etc., showing this. However, little is known about the mechanistic events underlying the potential deleterious synergy between Influenza and P.a co-infections. We demonstrate here in vitro in epithelial cells and in vivo in three independent models (two involving mice given IAV +/– P.a, and one involving mice given IAV +/– IL-1β) that IAV promotes secondary P.a-mediated lung disease or augmented IL-1β-mediated inflammation. We show that IAV-P.a-mediated deleterious responses includes increased matrix metalloprotease (MMP) activity, and MMP-9 in particular, and that the use of the MMP inhibitor improves lung resilience. Furthermore, we show that IAV post-transcriptionally inhibits the antimicrobial/anti-protease molecule elafin/trappin-2, which we have shown previously to be anti-inflammatory and to protect the host against maladaptive neutrophilic inflammation in P.a infections. Our work highlights the capacity of IAV to promote further P.a-mediated lung damage, not necessarily through its interference with host resistance to the bacterium, but by down-regulating tissue resilience to lung inflammation instead. Our study therefore suggests that restoring tissue resilience in clinical settings where IAV/P.a co-exists could prove a fruitful strategy.

Mechanisms of Epithelial Immunity Evasion by Respiratory Bacterial Pathogens

Bacterial lung infections are major healthcare challenges killing millions of people worldwide and resulting in a huge economic burden. Both basic and clinical research have elucidated host mechanisms that contribute to the bacterial clearance where an indispensable role of immune cells has been established. However, the role of respiratory epithelial cells in bacterial clearance has garnered limited attention due to their weak inflammatory or phagocytic ability compared to immune cells such as macrophages and neutrophils. These studies often underappreciate the fact that epithelial cells are the most abundant cells in the lung, not only serving as building blocks but also providing immune protection throughout the lung. Epithelial cells function either independently to eradicate the pathogen or communicate with immune cells to orchestrate pathogen clearance. The epithelial cells have multiple mechanisms that include mucus production, antimicrobial peptide production, muco-ciliary clearance, and phagocytosis, all of which contribute to their direct antibacterial function. Secretion of cytokines to recruit immune cells and potentiate their antimicrobial activities is a pathway by which the epithelium contributes to bacterial clearance. Successful pathogens outsmart epithelial resistance and find a way to replicate in sufficient numbers to establish infections in the airway or lung epithelial surfaces. In this mini-review, we discuss evidences that establish important roles for epithelial host defense against invading respiratory bacterial pathogens and demonstrate how pathogens outsmart these epithelial immune mechanisms to successfully establish infection. Finally, we discuss briefly how to boost epithelial immunity to improve outcomes in bacterial lung infections.

Mechanisms of Epithelial Immunity Evasion by Respiratory Bacterial Pathogens

Bacterial lung infections are major healthcare challenges killing millions of people worldwide and resulting in a huge economic burden. Both basic and clinical research have elucidated host mechanisms that contribute to the bacterial clearance where an indispensable role of immune cells has been established. However, the role of respiratory epithelial cells in bacterial clearance has garnered limited attention due to their weak inflammatory or phagocytic ability compared to immune cells such as macrophages and neutrophils. These studies often underappreciate the fact that epithelial cells are the most abundant cells in the lung, not only serving as building blocks but also providing immune protection throughout the lung. Epithelial cells function either independently to eradicate the pathogen or communicate with immune cells to orchestrate pathogen clearance. The epithelial cells have multiple mechanisms that include mucus production, antimicrobial peptide production, muco-ciliary clearance, and phagocytosis, all of which contribute to their direct antibacterial function. Secretion of cytokines to recruit immune cells and potentiate their antimicrobial activities is a pathway by which the epithelium contributes to bacterial clearance. Successful pathogens outsmart epithelial resistance and find a way to replicate in sufficient numbers to establish infections in the airway or lung epithelial surfaces. In this mini-review, we discuss evidences that establish important roles for epithelial host defense against invading respiratory bacterial pathogens and demonstrate how pathogens outsmart these epithelial immune mechanisms to successfully establish infection. Finally, we discuss briefly how to boost epithelial immunity to improve outcomes in bacterial lung infections.

Respiratory Barrier as a Safeguard and Regulator of Defense Against Influenza A Virus and Streptococcus pneumoniae

The primary function of the respiratory system of gas exchange renders it vulnerable to environmental pathogens that circulate in the air. Physical and cellular barriers of the respiratory tract mucosal surface utilize a variety of strategies to obstruct microbe entry. Physical barrier defenses including the surface fluid replete with antimicrobials, neutralizing immunoglobulins, mucus, and the epithelial cell layer with rapidly beating cilia form a near impenetrable wall that separates the external environment from the internal soft tissue of the host. Resident leukocytes, primarily of the innate immune branch, also maintain airway integrity by constant surveillance and the maintenance of homeostasis through the release of cytokines and growth factors. Unfortunately, pathogens such as influenza virus and Streptococcus pneumoniae require hosts for their replication and dissemination, and prey on the respiratory tract as an ideal environment causing severe damage to the host during their invasion. In this review, we outline the host-pathogen interactions during influenza and post-influenza bacterial pneumonia with a focus on inter- and intra-cellular crosstalk important in pulmonary immune responses.

Role of extracellular vesicles in cell-cell communication and inflammation following exposure to pulmonary toxicants

Extracellular vesicles (EVs) have emerged as key regulators of cell-cell communication during inflammatory responses to lung injury induced by diverse pulmonary toxicants including cigarette smoke, air pollutants, hyperoxia, acids, and endotoxin. Many lung cell types, including epithelial cells and endothelial cells, as well as infiltrating macrophages generate EVs. EVs appear to function by transporting cargo to recipient cells that, in most instances, promote their inflammatory activity. Biologically active cargo transported by EVs include miRNAs, cytokines/chemokines, damage-associated molecular patterns (DAMPs), tissue factor (TF)s, and caspases. Findings that EVs are taken up by target cells such as macrophages, and that this leads to increased proinflammatory functioning provide support for their role in the development of pathologies associated with toxicant exposure. Understanding the nature of EVs responding to toxic exposures and their cargo may lead to the development of novel therapeutic approaches to mitigating lung injury.

Potential role of medicinal plants and their constituents in the mitigation of SARS-CoV-2: identifying related therapeutic targets using network pharmacology and molecular docking analyses

Since the outbreak of Coronavirus disease (COVID-19) caused by SARS-CoV-2 in December 2019, there has been no vaccine or specific antiviral medication for treatment of the infection where supportive care and prevention of complications is the current management strategy. In this work, the potential use of medicinal plants and more than 16 500 of their constituents was investigated within two suggested therapeutic strategies in the fight against SARS-CoV-2 including prevention of SARS-CoV-2 RNA synthesis and replication, through targeting vital proteins and enzymes as well as modulation of the host's immunity through production of virulence factors. Molecular docking studies on the viral enzymes 3Clpro, PLpro and RdRp suggested rocymosin B, verbascoside, rutin, caftaric acid, luteolin 7-rutinoside, fenugreekine and cyanidin 3-(6′′-malonylglucoside) as promising molecules for further drug development. Meanwhile, the medicinal plants Glycyrrhiza glabra, Hibiscus sabdariffa, Cichorium intybus, Chrysanthemum coronarium, Nigella sativa, Anastatica hierochuntica, Euphorbia species, Psidium guajava and Epilobium hirsutum were enriched in compounds with the multi-targets PTGS2, IL2, IL1b, VCAM1 and TNF such as quercetin, ursolic acid, kaempferol, isorhamnetin, luteolin, glycerrhizin and apigenin. Enriched pathways of the molecular targets included cytokine–cytokine receptor interaction, TNF signaling pathway, NOD-like receptor signaling pathway, Toll-like receptor signaling pathway, NF-kappa B signaling pathway and JAK-STAT3 signaling pathway which are all closely related to inflammatory, innate and adaptive immune responses. The present study identified natural compounds targeting SARS-CoV-2 for further in vitro and in vivo studies and emphasizes the potential role of medicinal plants in the mitigation of SARS-CoV-2.

Since the outbreak of Coronavirus disease (COVID-19) caused by SARS-CoV-2 in December 2019, there has been no vaccine or specific antiviral medication for treatment of the infection where supportive care and prevention of complications is the current management strategy.

Early Events in Coccidioidomycosis

Since its description nearly 130 years ago, hundreds of studies have deepened our understanding of coccidioidomycosis, also known as valley fever (VF), and provided useful diagnostic tests and treatments for the disease caused by the dimorphic fungi Coccidioides spp. In general, most of the literature has addressed well-established infections and has described patients who have experienced major complications. In contrast, little attention has been given to the earliest consequences of the pathogen-host interaction and its implications for disease manifestation, progression, and resolution. The purpose of this review is to highlight published studies on early coccidioidomycosis, identify gaps in our knowledge, and suggest new or former research areas that might be or remain fertile ground for insight into the early stages of this invasive fungal disease.

Infection resisters: targets of new research for uncovering natural protective immunity against Mycobacterium tuberculosis

“Infection resisters” are broadly defined as individuals who despite significant exposure to Mycobacterium tuberculosis remain persistently unreactive to conventional detection assays, suggesting that they remain uninfected or rapidly clear their infection early on following exposure. In this review, we highlight recent studies that point to underlying host immune mechanisms that could mediate this natural resistance. We also illustrate some additional avenues that are likely to be differently modulated in resisters and possess the potential to be targeted, ranging from early mycobacterial sensing leading up to subsequent killing. Emerging research in this area can be harnessed to provide valuable insights into the development of novel therapeutic and vaccine strategies against M. tuberculosis.

Lipopolysaccharide enhances DNA-induced IFN-β expression and autophagy by upregulating cGAS expression in A549 cells

Cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) is a newly identified cytosolic DNA sensor, but its function in lung epithelial cells is relatively unknown. In the present study, the effects of lipopolysaccharide (LPS) on the expression and function of cGAS in the A549 lung epithelial cell line was investigated. The cells were treated with LPS at different concentrations (e.g., 100, 200, 400 and 800 ng/ml), and the cGAS expression levels were examined via western blot analysis and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The cells were pretreated with LPS, followed by E. coli DNA transfection using Lipofectamine^® 3000. After 24 h, interferon (IFN)-β production was measured using ELISA and the expression of the autophagic markers, microtubule-associated proteins 1A/1B light chain 3 and sequestosome-1, were determined using western blot analysis. The cells were also pretreated with either a toll-like receptor (TLR) 4 inhibitor, a serine/threonine-protein kinase TBK1 (TBK1) inhibitor or an nuclear factor (NF)-κB inhibitor, followed by LPS treatment, and the cGAS expression levels were examined via western blot analysis and RT-qPCR. The result showed that LPS treatment upregulated cGAS expression in a dose-dependent manner. E. coli DNA treatment could induce IFN-β production and autophagy via cGAS, which was enhanced by LPS pretreatment. The effect of LPS on cGAS expression was suppressed by treatment with a TLR4 inhibitor, a TBK1 inhibitor and an NF-κB inhibitor. In conclusion, LPS enhances DNA-induced IFN-β production and autophagy by upregulating cGAS expression through the myeloid differentiation primary response protein MyD88-independent TLR4 signaling pathway in A549 cells.

Pseudomonas aeruginosa Induced Host Epithelial Cell Mitochondrial Dysfunction

The pathogenicity of P. aeruginosa is dependent on quorum sensing (QS), an inter-bacterial communication system that can also modulate host biology. The innate immune function of the lung mucosal barrier is dependent on proper mitochondrial function. The purpose of this study was to define the mechanism by which bacterial factors modulate host lung epithelial cell mitochondrial function and to investigate novel therapies that ameliorate this effect. 3-oxo-C12-HSL disrupts mitochondrial morphology, attenuates mitochondrial bioenergetics, and induces mitochondrial DNA oxidative injury. Mechanistically, we show that 3-oxo-C12-HSL attenuates expression of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a master regulator of mitochondrial biogenesis, antioxidant defense, and cellular respiration, and its downstream effectors in both BEAS-2B and primary lung epithelial cells. Overexpression of PGC-1α attenuates the inhibition in cellular respiration caused by 3-oxo-C12-HSL. Pharmacologic activation of PGC-1α restores barrier integrity in cells treated with 3-oxo-C12-HSL. These data demonstrate that the P. aeruginosa QS molecule, 3-oxo-C12-HSL, alters mitochondrial pathways critical for lung mucosal immunity. Genetic and pharmacologic strategies that activate the PGC-1α pathway enhance host epithelial cell mitochondrial function and improve the epithelial innate response to P. aeruginosa. Therapies that rescue PGC-1α function may provide a complementary approach in the treatment of P. aeruginosa infection.

Personalizing the Management of Pneumonia

Pneumonia is a highly prevalent disease with considerable morbidity and mortality. However, diagnosis and therapy still rely on antiquated methods, leading to the vast overuse of antimicrobials, which carries risks for both society and the individual. Furthermore, outcomes in severe pneumonia remain poor. Genomic techniques have the potential to transform the management of pneumonia through deep characterization of pathogens as well as the host response to infection. This characterization will enable the delivery of selective antimicrobials and immunomodulatory therapy that will help to offset the disorder associated with overexuberant immune responses.

Novel aroylated phenylenediamine compounds enhance antimicrobial defense and maintain airway epithelial barrier integrity

Aroylated phenylenediamines (APDs) are novel inducers of innate immunity enhancing cathelicidin gene expression in human bronchial epithelial cell lines. Here we present two newly developed APDs and aimed at defining the response and signaling pathways for these compounds with reference to innate immunity and antimicrobial peptide (AMP) expression. Induction was initially defined with respect to dose and time and compared with the APD Entinostat (MS-275). The induction applies to several innate immunity effectors, indicating that APDs trigger a broad spectrum of antimicrobial responses. The bactericidal effect was shown in an infection model against Pseudomonas aeruginosa by estimating bacteria entering cells. Treatment with a selected APD counteracted Pseudomonas mediated disruption of epithelial integrity. This double action by inducing AMPs and enhancing epithelial integrity for one APD compound is unique and taken as a positive indication for host directed therapy (HDT). The APD effects are mediated through Signal transducer and activator of transcription 3 (STAT3) activation. Utilization of induced innate immunity to fight infections can reduce antibiotic usage, might be effective against multidrug resistant bacteria and is in line with improved stewardship in healthcare.

Therapeutic Synergy Between Antibiotics and Pulmonary Toll-Like Receptor 5 Stimulation in Antibiotic-Sensitive or -Resistant Pneumonia

Bacterial infections of the respiratory tract constitute a major cause of death worldwide. Given the constant rise in bacterial resistance to antibiotics, treatment failure is increasingly frequent. In this context, innovative therapeutic strategies are urgently needed. Stimulation of innate immune cells in the respiratory tract [via activation of Toll-like receptors (TLRs)] is an attractive approach for rapidly activating the body's immune defenses against a broad spectrum of microorganisms. Previous studies of the TLR5 agonist flagellin in animal models showed that standalone TLR stimulation does not result in the effective treatment of pneumococcal respiratory infection but does significantly improve the therapeutic outcome of concomitant antibiotic treatment. Here, we investigated the antibacterial interaction between antibiotic and intranasal flagellin in a mouse model of pneumococcal respiratory infection. Using various doses of orally administered amoxicillin or systemically administered cotrimoxazole, we found that the intranasal instillation of flagellin (a dose that promotes maximal lung pro-inflammatory responses) induces synergistic rather than additive antibacterial effects against antibiotic–susceptible pneumococcus. We next set up a model of infection with pneumococcus that is resistant to multiple antibiotics in the context of influenza superinfection. Remarkably, the combination of amoxicillin and flagellin effectively treated superinfection with the amoxicillin-resistant pneumococcus since the bacterial clearance was increased by more than 100-fold compared to standalone treatments. Our results also showed that, in response to flagellin, the lung tissue generated an innate immune response even though it had been damaged by the influenza virus and pneumococcal infections. In conclusion, we demonstrated that the selective boosting of lung innate immunity is a conceptually advantageous approach for improving the effectiveness of antibiotic treatment and fighting antibiotic-resistant bacteria.

Inducible lung epithelial resistance requires multisource reactive oxygen species generation to protect against bacterial infections

Pneumonia remains a global health threat, in part due to expanding categories of susceptible individuals and increasing prevalence of antibiotic resistant pathogens. However, therapeutic stimulation of the lungs’ mucosal defenses by inhaled exposure to a synergistic combination of Toll-like receptor (TLR) agonists known as Pam2-ODN promotes mouse survival of pneumonia caused by a wide array of pathogens. This inducible resistance to pneumonia relies on intact lung epithelial TLR signaling, and inducible protection against viral pathogens has recently been shown to require increased production of epithelial reactive oxygen species (ROS) from multiple epithelial ROS generators. To determine whether similar mechanisms contribute to inducible antibacterial responses, the current work investigates the role of ROS in therapeutically-stimulated protection against Pseudomonas aerugnosa challenges. Inhaled Pam2-ODN treatment one day before infection prevented hemorrhagic lung cytotoxicity and mouse death in a manner that correlated with reduction in bacterial burden. The bacterial killing effect of Pam2-ODN was recapitulated in isolated mouse and human lung epithelial cells, and the protection correlated with inducible epithelial generation of ROS. Scavenging or targeted blockade of ROS production from either dual oxidase or mitochondrial sources resulted in near complete loss of Pam2-ODN-induced bacterial killing, whereas deficiency of induced antimicrobial peptides had little effect. These findings support a central role for multisource epithelial ROS in inducible resistance against a bacterial pathogen and provide mechanistic insights into means to protect vulnerable patients against lethal infections.

Nucleic Acid Sensing in Allergic Disorders

Recent advances indicate that there is crosstalk between allergic disorders and nucleic acid sensing. Triggers that activate inflammatory mechanisms via nucleic acid sensors affect both allergic phenotypes and anti-viral responses, depending on the timing and the order of exposure. Viral respiratory infections, such as those caused by the rhinovirus, influenza, and respiratory syncytial virus, are the most frequent cause of significant asthma exacerbations through effects mediated predominantly by TLR3. However, agonists of other nucleic acid sensors, such as TLR7/8 and TLR9 agonists, may inhibit allergic inflammation and reduce clinical manifestations of disease. The allergic state can predispose the immune system to both exaggerated responses to viral infections or protection from anti-viral inflammatory responses. T_H2 cytokines appear to alter the epithelium, leading to defective viral clearance or exaggerated responses to viral infections. However, a T_H2 skewed allergic response may be protective against a T_H1-dependent inflammatory anti-viral response. This review briefly introduces the receptors involved in nucleic acid sensing, addresses mechanisms by which nucleic acid sensing and allergic responses can counteract one another, and discusses the strategies in experimental settings, both in animal and human studies, to harness the nucleic acid sensing machinery for the intervention of allergic disorders.

The Risk G Allele of the Single-Nucleotide Polymorphism rs928413 Creates a CREB1-Binding Site That Activates IL33 Promoter in Lung Epithelial Cells

Cytokine interleukin 33 (IL-33) is constitutively expressed by epithelial barrier cells, and promotes the development of humoral immune responses. Along with other proinflammatory mediators released by the epithelium of airways and lungs, it plays an important role in a number of respiratory pathologies. In particular, IL-33 significantly contributes to pathogenesis of allergy and asthma; genetic variations in the IL33 locus are associated with increased susceptibility to asthma. Large-scale genome-wide association studies have identified minor “G” allele of the single-nucleotide polymorphism rs928413, located in the IL33 promoter area, as a susceptible variant for early childhood and atopic asthma development. Here, we demonstrate that the rs928413(G) allele creates a binding site for the cAMP response element-binding protein 1 (CREB1) transcription factor. In a pulmonary epithelial cell line, activation of CREB1, presumably via the p38 mitogen-activated protein kinases (MAPK) cascade, activates the IL33 promoter containing the rs928413(G) allele specifically and in a CREB1-dependent manner. This mechanism may explain the negative effect of the rs928413 minor “G” allele on asthma development.

Epithelial MHC Class II Expression and Its Role in Antigen Presentation in the Gastrointestinal and Respiratory Tracts

As the primary barrier between an organism and its environment, epithelial cells are well-positioned to regulate tolerance while preserving immunity against pathogens. Class II major histocompatibility complex molecules (MHC class II) are highly expressed on the surface of epithelial cells (ECs) in both the lung and intestine, although the functional consequences of this expression are not fully understood. Here, we summarize current information regarding the interactions that regulate the expression of EC MHC class II in health and disease. We then evaluate the potential role of EC as non-professional antigen presenting cells. Finally, we explore future areas of study and the potential contribution of epithelial surfaces to gut-lung crosstalk.

Fatty Acid Metabolism is Associated With Disease Severity After H7N9 Infection

BACKGROUND

Human infections with the H7N9 virus could lead to lung damage and even multiple organ failure, which is closely associated with a high mortality rate. However, the metabolic basis of such systemic alterations remains unknown.

METHODS

This study included hospitalized patients (n = 4) with laboratory-confirmed H7N9 infection, healthy controls (n = 9), and two disease control groups comprising patients with pneumonia (n = 9) and patients with pneumonia who received steroid treatment (n = 10). One H7N9-infected patient underwent lung biopsy for histopathological analysis and expression analysis of genes associated with lung homeostasis. H7N9-induced systemic alterations were investigated using metabolomic analysis of sera collected from the four patients by using ultra-performance liquid chromatography-mass spectrometry. Chest digital radiography and laboratory tests were also conducted.

FINDINGS

Two of the four patients did not survive the clinical treatments with antiviral medication, steroids, and oxygen therapy. Biopsy revealed disrupted expression of genes associated with lung epithelial integrity. Histopathological analysis demonstrated severe lung inflammation after H7N9 infection. Metabolomic analysis indicated that fatty acid metabolism may be inhibited during H7N9 infection. Serum levels of palmitic acid, erucic acid, and phytal may negatively correlate with the extent of lung inflammation after H7N9 infection. The changes in fatty acid levels may not be due to steroid treatment or pneumonia.

INTERPRETATION

Altered structural and secretory properties of the lung epithelium may be associated with the severity of H7N9-infection-induced lung disease. Moreover, fatty acid metabolism level may predict a fatal outcome after H7N9 virus infection.

Surviving Deadly Lung Infections: Innate Host Tolerance Mechanisms in the Pulmonary System

Much research on infectious diseases focuses on clearing the pathogen through the use of antimicrobial drugs, the immune response, or a combination of both. Rapid clearance of pathogens allows for a quick return to a healthy state and increased survival. Pathogen-targeted approaches to combating infection have inherent limitations, including their pathogen-specific nature, the potential for antimicrobial resistance, and poor vaccine efficacy, among others. Another way to survive an infection is to tolerate the alterations to homeostasis that occur during a disease state through a process called host tolerance or resilience, which is independent from pathogen burden. Alterations in homeostasis during infection are numerous and include tissue damage, increased inflammation, metabolic changes, temperature changes, and changes in respiration. Given its importance and sensitivity, the lung is a good system for understanding host tolerance to infectious disease. Pneumonia is the leading cause of death for children under five worldwide. One reason for this is because when the pulmonary system is altered dramatically it greatly impacts the overall health and survival of a patient. Targeting host pathways involved in maintenance of pulmonary host tolerance during infection could provide an alternative therapeutic avenue that may be broadly applicable across a variety of pathologies. In this review, we will summarize recent findings on tolerance to host lung infection. We will focus on the involvement of innate immune responses in tolerance and how an initial viral lung infection may alter tolerance mechanisms in leukocytic, epithelial, and endothelial compartments to a subsequent bacterial infection. By understanding tolerance mechanisms in the lung we can better address treatment options for deadly pulmonary infections.