Inflammatory Monocytes Drive Influenza A Virus-Mediated Lung Injury in Juvenile Mice

Prevention of severe lung immunopathology associated with influenza infection through adeno-associated virus vector administration

BACKGROUND

Influenza A viruses (IAVs) have long posed a threat to humans, occasionally causing significant morbidity and mortality. The initial immune response is triggered by infected epithelial cells, alveolar macrophages and dendritic cells. However, an exaggerated innate immune response can result in severe lung injury and even host mortality. One notable pathology observed in hosts succumbing to severe influenza is the excessive influx of neutrophils and monocytes into the lung. In this study, we investigated a strategy for controlling lung immunopathology following severe influenza infection.

RESULTS

To evaluate the impact of innate immunity on influenza-associated lung injury, we employed CB17.SCID and NOD.SCID mice. NOD.SCID mice exhibited slower weight loss and longer survival than CB17.SCID mice following influenza infection. Lung inflammation was reduced in NOD.SCID mice compared to CB17.SCID mice. Bulk RNA sequencing analysis of lung tissue showed significant downregulation of 827 genes, and differentially expressed gene analysis indicated that the cytokine-cytokine receptor interaction pathway was predominantly downregulated in NOD.SCID mice. Interestingly, the expression of the Cxcl14 gene was higher in the lungs of influenza-infected NOD.SCID mice than in CB17.SCID mice. Therefore, we induced overexpression of the Cxcl14 gene in the lung using the adeno-associated virus 9 (AAV9)-vector system for target gene delivery. However, when we administered the AAV9 vector carrying the Cxcl14 gene or a control AAV9 vector to BALB/c mice from both groups, the morbidity and mortality rates remained similar. Both groups exhibited lower morbidity and mortality than the naive group that did not receive the AAV9 vector prior to IAV infection, suggesting that the pre-administration of the AAV9 vector conferred protection against lethal influenza infection, irrespective of Cxcl14 overexpression. Furthermore, we found that pre-inoculation of BALB/c mice with AAV9 attenuated the infiltration of trans-macrophages, neutrophils and monocytes in the lungs following IAV infection. Although there was no difference in lung viral titers between the naive group and the AAV9 pre-inoculated group, pre-inoculation with AAV9 conferred lung injury protection against lethal influenza infection in mice.

CONCLUSIONS

Our study demonstrated that pre-inoculation with AAV9 prior to IAV infection protected mouse lungs from immunopathology by reducing the recruitment of inflammatory cells.

Early innate cell interactions with Mycobacterium tuberculosis in protection and pathology of tuberculosis

Tuberculosis (TB) remains a significant global health challenge, claiming the lives of up to 1.5 million individuals annually. TB is caused by the human pathogen Mycobacterium tuberculosis (Mtb), which primarily infects innate immune cells in the lungs. These immune cells play a critical role in the host defense against Mtb infection, influencing the inflammatory environment in the lungs, and facilitating the development of adaptive immunity. However, Mtb exploits and manipulates innate immune cells, using them as favorable niche for replication. Unfortunately, our understanding of the early interactions between Mtb and innate effector cells remains limited. This review underscores the interactions between Mtb and various innate immune cells, such as macrophages, dendritic cells, granulocytes, NK cells, innate lymphocytes-iNKT and ILCs. In addition, the contribution of alveolar epithelial cell and endothelial cells that constitutes the mucosal barrier in TB immunity will be discussed. Gaining insights into the early cellular basis of immune reactions to Mtb infection is crucial for our understanding of Mtb resistance and disease tolerance mechanisms. We argue that a better understanding of the early host-pathogen interactions could inform on future vaccination approaches and devise intervention strategies.

Derivation, Validation, and Clinical Relevance of a Pediatric Sepsis Phenotype With Persistent Hypoxemia, Encephalopathy, and Shock

OBJECTIVES

Untangling the heterogeneity of sepsis in children and identifying clinically relevant phenotypes could lead to the development of targeted therapies. Our aim was to analyze the organ dysfunction trajectories of children with sepsis-associated multiple organ dysfunction syndrome (MODS) to identify reproducible and clinically relevant sepsis phenotypes and determine if they are associated with heterogeneity of treatment effect (HTE) to common therapies.

DESIGN

Multicenter observational cohort study.

SETTING

Thirteen PICUs in the United States.

PATIENTS

Patients admitted with suspected infections to the PICU between 2012 and 2018.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We used subgraph-augmented nonnegative matrix factorization to identify candidate trajectory-based phenotypes based on the type, severity, and progression of organ dysfunction in the first 72 hours. We analyzed the candidate phenotypes to determine reproducibility as well as prognostic, therapeutic, and biological relevance. Overall, 38,732 children had suspected infection, of which 15,246 (39.4%) had sepsis-associated MODS with an in-hospital mortality of 10.1%. We identified an organ dysfunction trajectory-based phenotype (which we termed persistent hypoxemia, encephalopathy, and shock) that was highly reproducible, had features of systemic inflammation and coagulopathy, and was independently associated with higher mortality. In a propensity score-matched analysis, patients with persistent hypoxemia, encephalopathy, and shock phenotype appeared to have HTE and benefit from adjuvant therapy with hydrocortisone and albumin. When compared with other high-risk clinical syndromes, the persistent hypoxemia, encephalopathy, and shock phenotype only overlapped with 50%-60% of patients with septic shock, moderate-to-severe pediatric acute respiratory distress syndrome, or those in the top tier of organ dysfunction burden, suggesting that it represents a nonsynonymous clinical phenotype of sepsis-associated MODS.

CONCLUSIONS

We derived and validated the persistent hypoxemia, encephalopathy, and shock phenotype, which is highly reproducible, clinically relevant, and associated with HTE to common adjuvant therapies in children with sepsis.

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.

Immune response in influenza virus infection and modulation of immune injury by viral neuraminidase

Influenza A viruses cause severe respiratory illnesses in humans and animals. Overreaction of the innate immune response to influenza virus infection results in hypercytokinemia, which is responsible for mortality and morbidity. The influenza A virus surface glycoprotein neuraminidase (NA) plays a vital role in viral attachment, entry, and virion release from infected cells. NA acts as a sialidase, which cleaves sialic acids from cell surface proteins and carbohydrate side chains on nascent virions. Here, we review progress in understanding the role of NA in modulating host immune response to influenza virus infection. We also discuss recent exciting findings targeting NA protein to interrupt influenza-induced immune injury.

Breaking Bad: Inflammasome Activation by Respiratory Viruses

The nucleotide-binding domain leucine-rich repeat-containing receptor (NLR) family is a group of intracellular sensors activated in response to harmful stimuli, such as invading pathogens. Some NLR family members form large multiprotein complexes known as inflammasomes, acting as a platform for activating the caspase-1-induced canonical inflammatory pathway. The canonical inflammasome pathway triggers the secretion of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18 by the rapid rupture of the plasma cell membrane, subsequently causing an inflammatory cell death program known as pyroptosis, thereby halting viral replication and removing infected cells. Recent studies have highlighted the importance of inflammasome activation in the response against respiratory viral infections, such as influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While inflammasome activity can contribute to the resolution of respiratory virus infections, dysregulated inflammasome activity can also exacerbate immunopathology, leading to tissue damage and hyperinflammation. In this review, we summarize how different respiratory viruses trigger inflammasome pathways and what harmful effects the inflammasome exerts along with its antiviral immune response during viral infection in the lungs. By understanding the crosstalk between invading pathogens and inflammasome regulation, new therapeutic strategies can be exploited to improve the outcomes of respiratory viral infections.

Monocyte production of C1q potentiates CD8 + T cell effector function following respiratory viral infection

Respiratory viral infections remain a leading cause of morbidity and mortality. Using a murine model of human metapneumovirus (HMPV), we identified recruitment of a C1q-producing inflammatory monocyte population concomitant with viral clearance by adaptive immune cells. Genetic ablation of C1q led to reduced CD8 + T cell function. Production of C1q by a myeloid lineage was sufficient to enhance CD8 + T cell function. Activated and dividing CD8 + T cells expressed a putative C1q receptor, gC1qR. Perturbation of gC1qR signaling led to altered CD8 + T cell IFN-γ production and metabolic capacity. Autopsy specimens from fatal respiratory viral infections in children demonstrated diffuse production of C1q by an interstitial population. Humans with severe COVID-19 infection also demonstrated upregulation of gC1qR on activated and rapidly dividing CD8 + T cells. Collectively, these studies implicate C1q production from monocytes as a critical regulator of CD8 + T cell function following respiratory viral infection.

Effects of yogurt containing probiotics on respiratory virus infections: Influenza H1N1 and SARS-CoV-2

Respiratory virus infections are an escalating issue and have become common worldwide. Influenza and COVID-19 are typical infectious respiratory diseases, and they sometimes lead to various complications. In a situation in which no established drug or treatment exists, consumption of proper food might be beneficial in maintaining health against external infections. We studied the potential effects of mixtures of probiotic strains on various viral infections. The purpose of this study was to assess the ability of yogurt containing probiotics to reduce the risk of respiratory viruses such as influenza H1N1 and SARS-CoV-2 infection. First, we performed in vitro tests using infected Madin-Darby canine kidney (MDCK) and Vero E6 cells, to evaluate the potential effects of yogurt containing high-dose probiotics against influenza H1N1 and SARS-CoV-2 infection. The yogurt significantly reduced plaque formation in the virus-infected cells. We also performed in vivo tests using influenza H1N1-infected C57BL/6 mice and SARS-CoV-2-infected Syrian golden hamsters, to evaluate the potential effects of yogurt. Yogurt was administered orally once daily during the experimental period. Yogurt was also administered orally as pretreatment once daily for 3 wk before viral infection. Regarding influenza H1N1, it was found that yogurt caused an increase in the survival rate, body weight, and IFN-γ, IgG1, and IL-10 levels against viral infection and a decrease in the inflammatory cytokines TNF-α and IL-6. Although the SARS-CoV-2 copy number was not significantly reduced in the lungs of yogurt-treated SARS-CoV-2-infected hamsters, the body weights and histopathological findings of the lungs were improved in the yogurt-treated group. In conclusion, we suggest that consumption of yogurt containing probiotics can lead to beneficial effects to prevent respiratory viral infections.

A Novel MIP-1-Expressing Macrophage Subtype in BAL Fluid from Healthy Volunteers

Tissue availability remains an important limitation of single-cell genomic technologies for investigating cellular heterogeneity in human health and disease. BAL represents a minimally invasive approach to assessing an individual's lung cellular environment for diagnosis and research. However, the lack of high-quality, healthy lung reference data is a major obstacle to using single-cell approaches to study a plethora of lung diseases. Here, we performed single-cell RNA sequencing on over 40,000 cells isolated from the BAL of four healthy volunteers. Of the six cell types or lineages we identified, macrophages were consistently the most numerous across individuals. Our analysis confirmed the expression of marker genes defining cell types despite background signals because of the ambient RNA found in many single-cell studies. We assessed the variability of gene expression across macrophages and defined a distinct subpopulation of cells expressing a set of genes associated with Macrophage Inflammatory Protein 1 (MIP-1). RNA in situ hybridization and reanalysis of published lung single-cell data validated the presence of this macrophage subpopulation. Thus, our study characterizes lung macrophage heterogeneity in healthy individuals and provides a valuable resource for future studies to understand the lung environment in health and disease.

Major alterations to monocyte and dendritic cell subsets lasting more than 6 months after hospitalization for COVID-19

Introduction

After more than two years the Coronavirus disease-19 (COVID-19) pandemic continues to burden healthcare systems and economies worldwide, and it is evident that the effects on the immune system can persist for months post-infection. The activity of myeloid cells such as monocytes and dendritic cells (DC) is essential for correct mobilization of the innate and adaptive responses to a pathogen. Impaired levels and responses of monocytes and DC to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is likely to be a driving force behind the immune dysregulation that characterizes severe COVID-19.

Methods

Here, we followed a cohort of COVID-19 patients hospitalized during the early waves of the pandemic for 6-7 months. The levels and phenotypes of circulating monocyte and DC subsets were assessed to determine both the early and long-term effects of the SARS-CoV-2 infection.

Results

We found increased monocyte levels that persisted for 6-7 months, mostly attributed to elevated levels of classical monocytes. Myeloid derived suppressor cells were also elevated over this period. While most DC subsets recovered from an initial decrease, we found elevated levels of cDC2/cDC3 at the 6-7 month timepoint. Analysis of functional markers on monocytes and DC revealed sustained reduction in program death ligand 1 (PD-L1) expression but increased CD86 expression across almost all cell types examined. Finally, C-reactive protein (CRP) correlated positively to the levels of intermediate monocytes and negatively to the recovery of DC subsets.

Conclusion

By exploring the myeloid compartments, we show here that alterations in the immune landscape remain more than 6 months after severe COVID-19, which could be indicative of ongoing healing and/or persistence of viral antigens.

The Influenza-Induced Pulmonary Inflammatory Exudate in Susceptible Tpl2-Deficient Mice Is Dictated by Type I IFN Signaling

The most prominent host response to viral infection is the production of type 1 interferons (T1 IFNs). One host regulator of the T1 IFNs is the serine-threonine kinase, tumor progression locus 2 (TPL2). We have previously demonstrated that Tpl2^-/- mice succumb to infection with a low-pathogenicity influenza A strain (x31), in association with with increased pulmonary levels of interferon-β (IFN-β), chemokine CCL2, and excessive monocyte and neutrophil pulmonary infiltration. TPL2-dependent overexpression of IFN-β has been implicated in enhanced susceptibility to Mycobacterium tuberculosis; therefore, we examined the role of T1 IFNs in susceptibility of Tpl2^-/- mice to influenza. CCL2 overexpression and monocyte recruitment were normalized in Ifnar1^-/-Tpl2^-/- mice, confirming that TPL2 constrains inflammatory monocyte recruitment via inhibition of the T1 IFN/CCL2 axis. Unexpectedly, excessive neutrophil recruitment in Ifnar1^-/- strains was further exacerbated by simultaneous TPL2 genetic ablation in Ifnar1^-/-Tpl2^-/- by 7 dpi, accompanied by overexpression of neutrophil-regulating cytokines, CXCL1 and IFN-λ. Collectively, our data suggest that TPL2 and T1 IFNs synergize to inhibit neutrophil recruitment. However, treatment with the neutrophil-depleting anti-Ly6G antibody showed only a modest improvement in disease. Analysis of sorted innate immune populations revealed redundant expression of inflammatory mediators among neutrophils, inflammatory monocytes and alveolar macrophages. These findings suggest that targeting a single cell type or mediator may be inadequate to control severe disease characterized by a mixed inflammatory exudate. Future studies will consider TPL2-regulated pathways as potential predictors of severe influenza progression as well as investigate novel methods to modulate TPL2 function during viral infection.

Predicting Influenza A Virus Infection in the Lung from Hematological Data with Machine Learning

The tracking of pathogen burden and host responses with minimally invasive methods during respiratory infections is central for monitoring disease development and guiding treatment decisions. Utilizing a standardized murine model of respiratory influenza A virus (IAV) infection, we developed and tested different supervised machine learning models to predict viral burden and immune response markers, i.e., cytokines and leukocytes in the lung, from hematological data. We performed independently in vivo infection experiments to acquire extensive data for training and testing of the models. We show here that lung viral load, neutrophil counts, cytokines (such as gamma interferon [IFN-γ] and interleukin 6 [IL-6]), and other lung infection markers can be predicted from hematological data. Furthermore, feature analysis of the models showed that blood granulocytes and platelets play a crucial role in prediction and are highly involved in the immune response against IAV. The proposed in silico tools pave the path toward improved tracking and monitoring of influenza virus infections and possibly other respiratory infections based on minimally invasively obtained hematological parameters. IMPORTANCE During the course of respiratory infections such as influenza, we do have a very limited view of immunological indicators to objectively and quantitatively evaluate the outcome of a host. Methods for monitoring immunological markers in a host's lungs are invasive and expensive, and some of them are not feasible to perform. Using machine learning algorithms, we show for the first time that minimally invasively acquired hematological parameters can be used to infer lung viral burden, leukocytes, and cytokines following influenza virus infection in mice. The potential of the framework proposed here consists of a new qualitative vision of the disease processes in the lung compartment as a noninvasive tool.

Boosting the anti MERS-CoV activity and oral bioavailability of resveratrol via PEG-stabilized emulsomal nano-carrier: Factorial design, in-vitro and in-vivo assessments

Resveratrol (RSV) is a phytoceutical polyphenolic compound exhibiting a well evidenced wide range of therapeutic activities. Unfortunately, its diminished aqueous solubility and extensive metabolism in gastro intestinal tract (GIT) and liver prohibit its biological activity and systemic availability. Herein the conducted study PEG stabilized emulsomes (PEMLs) were customized to enclose RSV aiming to boost its biological availability and antiviral activity. PEGylating the vesicles not only grant the promoted steric stability of the system but also being beneficial in exaggerating the intestinal permeability and extending the period of circulation of the drug, hence its targeted clinical use. The Investigation of the influence of predetermined variables on the physical characterization of formulae (entrapment efficiency EE%, particle size PS and zeta potential ZP) was implemented utilizing Design Expert® software. (F4) with desirability value (0.772), picked to be the optimal formula, which is fabricated utilizing 35 mg compritol as the lipidic core and 60 mg 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (DSPE-Mpeg-2000). The dominance of the F4 relative to RSV dispersion was affirmed by the data acquired from ex-vivo and pharmacokinetic studies. In addition, F4 exhibited significant lower EC₅₀ value (0.0127 µg/mL) relative to that of RSV dispersion(0.338 µg/mL) by around 26 times denoting the capability of the formulation to boost the antiviral activity. To a great extent, F4 was able to significantly suppress the inflammatory response and oxidative stress resulted from MERS-CoV infection on comparison with RSV dispersion. Finally, the potentiality of PEMLs as nano-panel with boosted both antiviral and oral bioavailability for RSV could be deduced based on the outcomes mentioned herein.

Heterotypic Influenza Infections Mitigate Susceptibility to Secondary Bacterial Infection

Influenza-associated bacterial superinfections have devastating impacts on the lung and can result in increased risk of mortality. New strains of influenza circulate throughout the population yearly, promoting the establishment of immune memory. Nearly all individuals have some degree of influenza memory before adulthood. Due to this, we sought to understand the role of immune memory during bacterial superinfections. An influenza heterotypic immunity model was established using influenza A/Puerto Rico/8/34 and influenza A/X31. We report in this article that influenza-experienced mice are more resistant to secondary bacterial infection with methicillin-resistant Staphylococcus aureus as determined by wasting, bacterial burden, pulmonary inflammation, and lung leak, despite significant ongoing lung remodeling. Multidimensional flow cytometry and lung transcriptomics revealed significant alterations in the lung environment in influenza-experienced mice compared with naive animals. These include changes in the lung monocyte and T cell compartments, characterized by increased expansion of influenza tetramer-specific CD8+ T cells. The protection that was seen in the memory-experienced mouse model is associated with the reduction in inflammatory mechanisms, making the lung less susceptible to damage and subsequent bacterial colonization. These findings provide insight into how influenza heterotypic immunity reshapes the lung environment and the immune response to a rechallenge event, which is highly relevant to the context of human infection.

Inclusion of a Phytomedicinal Flavonoid in Biocompatible Surface-Modified Chylomicron Mimic Nanovesicles with Improved Oral Bioavailability and Virucidal Activity: Molecular Modeling and Pharmacodynamic Studies

Morin hydrate (MH) is a widely-used Asian phytomedicinal flavonoid with a wide range of reported therapeutic activities. However, MH has limited oral bioavailability due to its low aqueous solubility and intestinal permeability, which in turn hinders its potential antiviral activity. The study reported herein was designed to encapsulate MH in polyethyleneglycolated (PEGylated) chylomicrons (PCMs) and to boost its antiviral activity and biological availability for oral administration using a rat experimental model. The PEGylated edge activator combined with the conventional components of chylomicrons (CMs) amplify the transport of the drug across the intestine and its circulation period, hence its therapeutic impact. The implementation of variables in the in vitro characterization of the vesicles was investigated. Using Design Expert^® software, a 2⁴ factorial design was conducted, and the resulting PCM formulations were fabricated utilizing a thin-film hydration technique. The efficacy of the formulations was assessed according to their zeta potential (ZP), entrapment efficiency percentage (EE%), amount of drug released after 8 h (Q8h), and particle size (PS) data. Formulation F9, which was deemed to be the optimal formula, used compritol as the lipidic core together in defined amounts with phosphatidylcholine (PC) and Brij52. Computer-aided studies revealed that MH alone in a suspension had both diminished intestinal permeability and absorption, but was enhanced when loaded in PCMs. This was affirmed by the superiority of formulation F9 results in ex vivo permeation and pharmacokinetic studies. Furthermore, formulation F9 had a superior safety profile and antiviral activity over a pure MH suspension. Molecular-docking studies revealed the capability of MH to inhibit MERS-CoV 3CL^pro, the enzyme shown to exhibit a crucial role in viral replication. Additionally, F9 suppressed both MERS-CoV-induced histopathological alteration in lung tissue and resulting oxidative and inflammatory biomarkers. Collectively, the results reported herein affirmed the potential of PCMs as nanocarriers for the effective oral administration of MH as an antiviral.

Interferon-γ promotes monocyte-mediated lung injury during influenza infection

Influenza A virus (IAV) infection triggers an exuberant host response that promotes acute lung injury. However, the host response factors that promote the development of a pathologic inflammatory response to IAV remain incompletely understood. In this study, we identify an interferon-γ (IFN-γ)-regulated subset of monocytes, CCR2⁺ monocytes, as a driver of lung damage during IAV infection. IFN-γ regulates the recruitment and inflammatory phenotype of CCR2⁺ monocytes, and mice deficient in CCR2 (CCR2^-/-) or IFN-γ (IFN-γ^-/-) exhibit reduced lung inflammation, pathology, and disease severity. Adoptive transfer of wild-type (WT) (IFN-γR1^+/+) but not IFN-γR1^-/- CCR2⁺ monocytes restore the WT-like pathological phenotype of lung damage in IAV-infected CCR2^-/- mice. CD8⁺ T cells are the main source of IFN-γ in IAV-infected lungs. Collectively, our data highlight the requirement of IFN-γ signaling in the regulation of CCR2⁺ monocyte-mediated lung pathology during IAV infection.

SLAMF7 engagement superactivates macrophages in acute and chronic inflammation

Macrophages regulate protective immune responses to infectious microbes, but aberrant macrophage activation frequently drives pathological inflammation. To identify regulators of vigorous macrophage activation, we analyzed RNA-seq data from synovial macrophages and identified SLAMF7 as a receptor associated with a superactivated macrophage state in rheumatoid arthritis. We implicated IFN-γ as a key regulator of SLAMF7 expression and engaging SLAMF7 drove a strong wave of inflammatory cytokine expression. Induction of TNF-α after SLAMF7 engagement amplified inflammation through an autocrine signaling loop. We observed SLAMF7-induced gene programs not only in macrophages from rheumatoid arthritis patients but also in gut macrophages from patients with active Crohn's disease and in lung macrophages from patients with severe COVID-19. This suggests a central role for SLAMF7 in macrophage superactivation with broad implications in human disease pathology.

Recruitment and training of alveolar macrophages after pneumococcal pneumonia

Recovery from pneumococcal pneumonia remodels the pool of alveolar macrophages so that they exhibit new surface marker profiles, transcriptomes, metabolomes, and responses to infection. Mechanisms mediating alveolar macrophage phenotypes after pneumococcal pneumonia have not been delineated. IFN-γ and its receptor on alveolar macrophages were essential for certain, but not all, aspects of the remodeled alveolar macrophage phenotype. IFN-γ was produced by CD4⁺ T cells plus other cells, and CD4⁺ cell depletion did not prevent alveolar macrophage remodeling. In mice infected or recovering from pneumococcus, monocytes were recruited to the lungs, and the monocyte-derived macrophages developed characteristics of alveolar macrophages. CCR2 mediated the early monocyte recruitment but was not essential to the development of the remodeled alveolar macrophage phenotype. Lineage tracing demonstrated that recovery from pneumococcal pneumonias converted the pool of alveolar macrophages from being primarily of embryonic origin to being primarily of adult hematopoietic stem cell origin. Alveolar macrophages of either origin demonstrated similar remodeled phenotypes, suggesting that ontogeny did not dictate phenotype. Our data reveal that the remodeled alveolar macrophage phenotype in lungs recovered from pneumococcal pneumonia results from a combination of new recruitment plus training of both the original cells and the new recruits.

NLRP3 inflammasome activation in COVID-19: an interlink between risk factors and disease severity

NLRP3 inflammasome is a critical immune component that plays a crucial role in mounting innate immune responses. The deleterious effects of inflammasome activation have been correlated with the COVID-19 disease severity. In the presence of several underlying disorders, the immune components of our bodies are dysregulated, creating conditions that could adversely affect us other than providing a required level of protection. In this review, we focused on the occurrence of NLRP3 inflammasome activation in response to SARS-COV-2 infection, dysregulation of NLRP3 activation events in the presence of several comorbidities, the contribution of activated NLRP3 inflammasome to the severity of COVID-19, and available therapeutics for the treatment of such NLRP3 inflammasome related diseases based on current knowledge. The primed state of immunity in individuals with comorbidities (risk factors) could accelerate many deaths and severe COVID-19 cases via activation of NLRP3 inflammasome and the release of downstream inflammatory molecules. Therefore, a detailed understanding of the host-pathogen interaction is needed to clarify the pathophysiology and select a potential therapeutic approach.

Macrophages play a role in inflammatory transformation of colorectal cancer

Colorectal cancer (CRC) is one of the most common and fatal cancers worldwide, and it is also a typical inflammatory cancer. The function of macrophages is very important in the tissue immune microenvironment during inflammatory and carcinogenic transformation. Here, we evaluated the function and mechanism of macrophages in intestinal physiology and in different pathological stages. Furthermore, the role of macrophages in the immune microenvironment of CRC and the influence of the intestinal population and hypoxic environment on macrophage function are summarized. In addition, in the era of tumor immunotherapy, CRC currently has a limited response rate to immune checkpoint inhibitors, and we summarize potential therapeutic strategies for targeting tumor-associated macrophages.

ADAM10 partially protects mice against influenza pneumonia by suppressing specific myeloid cell population

The influenza virus infection poses a serious health threat worldwide. Myeloid cells play pivotal roles in regulating innate and adaptive immune defense. A disintegrin and metalloproteinase (ADAM) family of proteins contributes to various immune responses; however, the role of a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) in influenza virus infection remains largely unknown. Herein, we investigated its role, focusing on myeloid cells, during influenza virus infection in mice. ADAM10 gene (Adam10)^flox/flox/Lyz2-Cre (Adam10^ΔLyz2) and control Adam10^flox/flox mice were intranasally infected with 200 plaque-forming units of influenza virus A/H1N1/PR8/34. Adam10^ΔLyz2 mice exhibited a significantly higher mortality rate, stronger lung inflammation, and a higher virus titer in the lungs than control mice. Macrophages and inflammatory cytokines, such as TNF-α, IL-1β, and CCL2, were increased in bronchoalveolar lavage fluid from Adam10^ΔLyz2 mice following infection. CD11b⁺Ly6G^-F4/80⁺ myeloid cells, which had an inflammatory monocyte/macrophage-like phenotype, were significantly increased in the lungs of Adam10^ΔLyz2 mice. Adoptive transfer experiments suggested that these cells likely contributed to the poorer prognosis in Adam10^ΔLyz2 mice. Seven days after infection, CD11b⁺Ly6G^-F4/80⁺ lung cells exhibited significantly higher arginase-1 expression levels in Adam10^ΔLyz2 mice than in control mice, whereas an arginase-1 inhibitor improved the prognosis of Adam10^ΔLyz2 mice. Enhanced granulocyte-macrophage colony-stimulating factor (GM-CSF)/GM-CSF receptor signaling likely contributed to this process. Collectively, these results indicate that myeloid ADAM10 protects against influenza virus pneumonia and may be a promising therapeutic target.

Innate immune responses at the asymptomatic stage of influenza A viral infections of Streptococcus pneumoniae colonized and non-colonized mice

Seasonal Influenza A virus (IAV) infections can promote dissemination of upper respiratory tract commensals such as Streptococcus pneumoniae to the lower respiratory tract resulting in severe life-threatening pneumonia. Here, we aimed to compare innate immune responses in the lungs of healthy colonized and non-colonized mice after IAV challenge at the initial asymptomatic stage of infection. Responses during a severe bacterial pneumonia were profiled for comparison. Cytokine and innate immune cell imprints of the lungs were analyzed. Irrespective of the colonization status, mild H1N1 IAV infection was characterized by a bi-phasic disease progression resulting in full recovery of the animals. Already at the asymptomatic stage of viral infection, the pro-inflammatory cytokine response was as high as in pneumococcal pneumonia. Flow cytometry analyses revealed an early influx of inflammatory monocytes into the lungs. Neutrophil influx was mostly limited to bacterial infections. The majority of cells, except monocytes, displayed an activated phenotype characterized by elevated CCR2 and MHCII expression. In conclusion, we show that IAV challenge of colonized healthy mice does not automatically result in severe co-infection. However, a general local inflammatory response was noted at the asymptomatic stage of infection irrespective of the infection type.

Tpl2 Ablation Leads to Hypercytokinemia and Excessive Cellular Infiltration to the Lungs During Late Stages of Influenza Infection

Tumor progression locus 2 (Tpl2) is a serine-threonine kinase known to promote inflammation in response to various pathogen-associated molecular patterns (PAMPs), inflammatory cytokines and G-protein-coupled receptors and consequently aids in host resistance to pathogens. We have recently shown that Tpl2-/- mice succumb to infection with a low-pathogenicity strain of influenza (x31, H3N2) by an unknown mechanism. In this study, we sought to characterize the cytokine and immune cell profile of influenza-infected Tpl2-/- mice to gain insight into its host protective effects. Although Tpl2-/- mice display modestly impaired viral control, no virus was observed in the lungs of Tpl2-/- mice on the day of peak morbidity and mortality suggesting that morbidity is not due to virus cytopathic effects but rather to an overactive antiviral immune response. Indeed, increased levels of interferon-β (IFN-β), the IFN-inducible monocyte chemoattractant protein-1 (MCP-1, CCL2), Macrophage inflammatory protein 1 alpha (MIP-1α; CCL3), MIP-1β (CCL4), RANTES (CCL5), IP-10 (CXCL10) and Interferon-γ (IFN-γ) was observed in the lungs of influenza-infected Tpl2-/- mice at 7 days post infection (dpi). Elevated cytokine and chemokines were accompanied by increased infiltration of the lungs with inflammatory monocytes and neutrophils. Additionally, we noted that increased IFN-β correlated with increased CCL2, CXCL1 and nitric oxide synthase (NOS2) expression in the lungs, which has been associated with severe influenza infections. Bone marrow chimeras with Tpl2 ablation localized to radioresistant cells confirmed that Tpl2 functions, at least in part, within radioresistant cells to limit pro-inflammatory response to viral infection. Collectively, this study suggests that Tpl2 tempers inflammation during influenza infection by constraining the production of interferons and chemokines which are known to promote the recruitment of detrimental inflammatory monocytes and neutrophils.

Defining the Innate Immune Responses for SARS-CoV-2-Human Macrophage Interactions

Host innate immune response follows severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, and it is the driver of the acute respiratory distress syndrome (ARDS) amongst other inflammatory end-organ morbidities. Such life-threatening coronavirus disease 2019 (COVID-19) is heralded by virus-induced activation of mononuclear phagocytes (MPs; monocytes, macrophages, and dendritic cells). MPs play substantial roles in aberrant immune secretory activities affecting profound systemic inflammation and end-organ malfunctions. All follow the presence of persistent viral components and virions without evidence of viral replication. To elucidate SARS-CoV-2-MP interactions we investigated transcriptomic and proteomic profiles of human monocyte-derived macrophages. While expression of the SARS-CoV-2 receptor, the angiotensin-converting enzyme 2, paralleled monocyte-macrophage differentiation, it failed to affect productive viral infection. In contrast, simple macrophage viral exposure led to robust pro-inflammatory cytokine and chemokine expression but attenuated type I interferon (IFN) activity. Both paralleled dysregulation of innate immune signaling pathways, specifically those linked to IFN. We conclude that the SARS-CoV-2-infected host mounts a robust innate immune response characterized by a pro-inflammatory storm heralding end-organ tissue damage.

Implications of Innate Immunity in Post-Acute Sequelae of Non-Persistent Viral Infections

Non-persistent viruses classically cause transient, acute infections triggering immune responses aimed at the elimination of the pathogen. Successful viruses evolved strategies to manipulate and evade these anti-viral defenses. Symptoms during the acute phase are often linked to dysregulated immune responses that disappear once the patient recovers. In some patients, however, symptoms persist or new symptoms emerge beyond the acute phase. Conditions resulting from previous transient infection are termed post-acute sequelae (PAS) and were reported for a wide range of non-persistent viruses such as rota-, influenza- or polioviruses. Here we provide an overview of non-persistent viral pathogens reported to be associated with diverse PAS, among them chronic fatigue, auto-immune disorders, or neurological complications and highlight known mechanistic details. Recently, the emergence of post-acute sequelae of COVID-19 (PASC) or long COVID highlighted the impact of PAS. Notably, PAS of non-persistent infections often resemble symptoms of persistent viral infections, defined by chronic inflammation. Inflammation maintained after the acute phase may be a key driver of PAS of non-persistent viruses. Therefore, we explore current insights into aberrant activation of innate immune signaling pathways in the post-acute phase of non-persistent viruses. Finally, conclusions are drawn and future perspectives for treatment and prevention of PAS are discussed.

Offspring born to influenza A virus infected pregnant mice have increased susceptibility to viral and bacterial infections in early life

Influenza during pregnancy can affect the health of offspring in later life, among which neurocognitive disorders are among the best described. Here, we investigate whether maternal influenza infection has adverse effects on immune responses in offspring. We establish a two-hit mouse model to study the effect of maternal influenza A virus infection (first hit) on vulnerability of offspring to heterologous infections (second hit) in later life. Offspring born to influenza A virus infected mothers are stunted in growth and more vulnerable to heterologous infections (influenza B virus and MRSA) than those born to PBS- or poly(I:C)-treated mothers. Enhanced vulnerability to infection in neonates is associated with reduced haematopoetic development and immune responses. In particular, alveolar macrophages of offspring exposed to maternal influenza have reduced capacity to clear second hit pathogens. This impaired pathogen clearance is partially reversed by adoptive transfer of alveolar macrophages from healthy offspring born to uninfected dams. These findings suggest that maternal influenza infection may impair immune ontogeny and increase susceptibility to early life infections of offspring.

Influenza infection during pregnancy can affect health of offspring but it is not clear how this affects immune responses. Here the authors use a mouse model to show that influenza infection during pregnancy can increase susceptibility to secondary infection and alter immune cell function in offspring.

Influenza colloidal gold method and blood routine tests combination for rapid diagnosis of influenza: a decision tree-based analysis

Rapid influenza diagnosis can facilitate targeted treatment and reduce antibiotic misuse. However, diagnosis efficacy remains unclear. This study examined the efficacy of a colloidal gold rapid test for rapid influenza diagnosis. Clinical characteristics of 520 patients with influenza-like illness presenting at a fever outpatient clinic during two influenza seasons (2017–2018; 2018–2019) were evaluated. The clinical manifestations and results of routine blood, colloidal gold, and nucleic acid tests were used to construct a decision tree with three layers, nine nodes, and five terminal nodes. The combined positive predictive value of a positive colloidal gold test result and monocyte level within 10.95–12.55% was 88.2%. The combined negative predictive value of a negative colloidal gold test result and white blood cell count > 9.075 × 10⁹/L was 84.9%. The decision-tree model showed the satisfactory accuracy of an early influenza diagnosis based on colloidal gold and routine blood test results.

Defining the Immune Responses for SARS-CoV-2-Human Macrophage Interactions

Host innate immune response follows severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, and it is the driver of the acute respiratory distress syndrome (ARDS) amongst other inflammatory end-organ morbidities. Such life-threatening coronavirus disease 2019 (COVID-19) is heralded by virus-induced activation of mononuclear phagocytes (MPs; monocytes, macrophages, and dendritic cells). MPs play substantial roles in aberrant immune secretory activities affecting profound systemic inflammation and end organ malfunctions. All follow an abortive viral infection. To elucidate SARS-CoV-2-MP interactions we investigated transcriptomic and proteomic profiles of human monocyte-derived macrophages. While expression of the SARS-CoV-2 receptor, the angiotensin-converting enzyme 2, paralleled monocyte-macrophage differentiation it failed to affect productive viral infection. In contrast, simple macrophage viral exposure led to robust pro-inflammatory cytokine and chemokine expression but attenuated type I interferon (IFN) activity. Both paralleled dysregulation of innate immune signaling pathways specifically those linked to IFN. We conclude that the SARS-CoV-2-infected host mounts a robust innate immune response characterized by a pro-inflammatory storm heralding consequent end-organ tissue damage.

The Mechanism behind Influenza Virus Cytokine Storm

Influenza viruses are still a serious threat to human health. Cytokines are essential for cell-to-cell communication and viral clearance in the immune system, but excessive cytokines can cause serious immune pathology. Deaths caused by severe influenza are usually related to cytokine storms. The recent literature has described the mechanism behind the cytokine–storm network and how it can exacerbate host pathological damage. Biological factors such as sex, age, and obesity may cause biological differences between different individuals, which affects cytokine storms induced by the influenza virus. In this review, we summarize the mechanism behind influenza virus cytokine storms and the differences in cytokine storms of different ages and sexes, and in obesity.

Statistical optimization of bile salt deployed nanovesicles as a potential platform for oral delivery of piperine: accentuated antiviral and anti-inflammatory activity in MERS-CoV challenged mice

The objective of this paper is to confine piperine, a poor oral bioavailable herbal drug into bile salt based nano vesicles for improving its aqueous solubility, hence, its therapeutic activity. Piperine-loaded bilosomes were fabricated adopting thin film hydration technique according to 3².2¹ full factorial design to investigate the impact of different formulation variables on the characters of bilosomes: entrapment efficiency (EE%), particle size, and % of drug released post 8 h (Q8hr). The selected optimum formula was F2 (enclosing 1% bile salt, brij72 as a surfactant, and ratio of surfactant:cholesterol was 9:1) with desirability value 0.801, exhibiting high EE% (97.2 ± 0.8%) nanosized spherical vesicles (220.2 ± 20.5 nm) and Q8hr (88.2%±5.6). The superiority of the optimized formula (F2) over the drug suspension was revealed via ex vivo permeation study, also pharmacokinetic study denoted to the boosted oral bioavailability of piperine-loaded bilosome compared to piperine suspension. Moreover, antiviral activity and safety margin of F2 was significantly higher than that of the drug suspension. The ability of piperine to interact with the key amino acids in the receptor binding domain 4L3N as indicated by its docking configuration, rationalized its observed activity. Furthermore, F2 significantly reduce oxidant markers, inflammatory cytokines in MERS-CoV-infected mice. Hence, bilosomes can be considered as a carrier of choice for piperine with potential antiviral and anti-inflammatory activities.

Monocyte dysregulation: consequences for hepatic infections

Liver disorders due to infections are a substantial health concern in underdeveloped and industrialized countries. This includes not only hepatotropic viruses (e.g., hepatitis B, hepatitis C) but also bacterial and parasitic infections such as amebiasis, leishmaniasis, schistosomiasis, or echinococcosis. Recent studies of the immune mechanisms underlying liver disease show that monocytes play an essential role in determining patient outcomes. Monocytes are derived from the mononuclear phagocyte lineage in the bone marrow and are present in nearly all tissues of the body; these cells function as part of the early innate immune response that reacts to challenge by external pathogens. Due to their special ability to develop into tissue macrophages and dendritic cells and to change from an inflammatory to an anti-inflammatory phenotype, monocytes play a pivotal role in infectious and non-infectious liver diseases: they can maintain inflammation and support resolution of inflammation. Therefore, tight regulation of monocyte recruitment and termination of monocyte-driven immune responses in the liver is prerequisite to appropriate healing of organ damage. In this review, we discuss monocyte-dependent immune mechanisms underlying hepatic infectious disorders. Better understanding of these immune mechanisms may lead to development of new interventions to treat acute liver disease and prevent progression to organ failure.

Pericyte-like cells undergo transcriptional reprogramming and distinct functional adaptations in acute lung injury

We previously reported on the role of pericyte-like cells as functional sentinel immune cells in lung injury. However, much about the biological role of pericytes in lung injury remains unknown. Lung pericyte-like cells are well-positioned to sense disruption to the epithelial barrier and coordinate local inflammatory responses due to their anatomic niche within the alveoli. In this report, we characterized transcriptional responses and functional changes in pericyte-like cells following activation by alveolar components from injured and uninjured lungs in a mouse model of acute lung injury (ALI). Purified pericyte-like cells from lung digests using PDGFRβ as a selection marker were expanded in culture as previously described (1). We induced sterile acute lung injury in mice with recombinant human Fas ligand (rhFasL) instillation followed by mechanical ventilation (1). We then collected bronchoalveolar lavage fluid (BALF) from injured and uninjured mice. Purified pericyte-like cells in culture were exposed to growth media only (control), BALF from uninjured mice, and BALF from injured mice for 6 and 24 hours. RNA collected from these treatment conditions were processed for RNAseq. Targets of interest identified by pathway analysis were validated using in vitro and in vivo assays. We observed robust global transcriptional changes in pericyte-like cells following treatment with uninjured and injured BALF at 6 hours, but this response persisted for 24 hours only after exposure to injured BALF. Functional enrichment analysis of pericytes treated with injured BALF revealed the activation of pro-inflammatory, cell migration, and angiogenesis-related pathways, whereas processes associated with tissue development and cell differentiation were down-regulated. We validated select upregulated targets in the inflammatory, angiogenic, and cell migratory pathways using functional biological assays in vitro and in vivo. We conclude that lung pericyte-like cells are highly responsive to alveolar compartment content from both uninjured and injured lungs, but injured BALF elicits a more sustained response. The inflammatory, angiogenic, and migratory changes exhibited by activated pericyte-like cells underscore the phenotypic plasticity of these specialized stromal cells in the setting of acute lung injury.

Neuroimmune interactions and osteoarthritis pain: focus on macrophages

Bidirectional interactions between the immune system and the nervous system are increasingly appreciated as playing a pathogenic role in chronic pain. Unraveling the mechanisms by which inflammatory pain is mediated through communication between nerves and immune cells may lead to exciting new strategies for therapeutic intervention. In this narrative review, we focus on the role of macrophages in the pathogenesis of osteoarthritis (OA) pain. From regulating homeostasis to conducting phagocytosis, and from inducing inflammation to resolving it, macrophages are plastic cells that are highly adaptable to their environment. They rely on communicating with the environment through cytokines, growth factors, neuropeptides, and other signals to respond to inflammation or injury. The contribution of macrophages to OA joint damage has garnered much attention in recent years. Here, we discuss how macrophages may participate in the initiation and maintenance of pain in OA. We aim to summarize what is currently known about macrophages in OA pain and identify important gaps in the field to fuel future investigations.

Impaired Cellular Immune Responses During the First Week of Severe Acute Influenza Infection

BACKGROUND

Cellular immune responses are not well characterized during the initial days of acute symptomatic influenza infection.

METHODS

We developed a prospective cohort of human subjects with confirmed influenza illness of varying severity who presented within a week after symptom onset. We characterized lymphocyte and monocyte populations as well as antigen-specific CD8+ T-cell and B-cell responses from peripheral blood mononuclear cells using flow cytometry and enzyme-linked immunospot assays.

RESULTS

We recruited 68 influenza-infected individuals on average 3.5 days after the onset of symptoms. Three patients required mechanical ventilation. Influenza-specific CD8+ T-cell responses expanded before the appearance of plasmablast B cells. However, the influenza-specific CD8+ T-cell response was lower in infected subjects than responses seen in uninfected control subjects. Circulating populations of inflammatory monocytes were increased in most subjects compared with healthy controls. Inflammatory monocytes were significantly reduced in the 3 subjects requiring mechanical ventilation. Inflammatory monocytes were also reduced in a separate validation cohort of mechanically ventilated patients.

CONCLUSIONS

Antigen-specific CD8+ T cells respond early during acute influenza infection at magnitudes that are lower than responses seen in uninfected individuals. Circulating inflammatory monocytes increase during acute illness and low absolute numbers are associated with very severe disease.

CXCL17 Is a Specific Diagnostic Biomarker for Severe Pandemic Influenza A(H1N1) That Predicts Poor Clinical Outcome

The C-X-C motif chemokine ligand 17 (CXCL17) is chemotactic for myeloid cells, exhibits bactericidal activity, and exerts anti-viral functions. This chemokine is constitutively expressed in the respiratory tract, suggesting a role in lung defenses. However, little is known about the participation of CXCL17 against relevant respiratory pathogens in humans. Here, we evaluated the serum levels and lung tissue expression pattern of CXCL17 in a cohort of patients with severe pandemic influenza A(H1N1) from Mexico City. Peripheral blood samples obtained on admission and seven days after hospitalization were processed for determinations of serum CXCL17 levels by enzyme-linked immunosorbent assay (ELISA). The expression of CXCL17 was assessed by immunohistochemistry (IHQ) in lung autopsy specimens from patients that succumbed to the disease. Serum CXCL17 levels were also analyzed in two additional comparative cohorts of coronavirus disease 2019 (COVID-19) and pulmonary tuberculosis (TB) patients. Additionally, the expression of CXCL17 was tested in lung autopsy specimens from COVID-19 patients. A total of 122 patients were enrolled in the study, from which 68 had pandemic influenza A(H1N1), 24 had COVID-19, and 30 with PTB. CXCL17 was detected in post-mortem lung specimens from patients that died of pandemic influenza A(H1N1) and COVID-19. Interestingly, serum levels of CXCL17 were increased only in patients with pandemic influenza A(H1N1), but not COVID-19 and PTB. CXCL17 not only differentiated pandemic influenza A(H1N1) from other respiratory infections but showed prognostic value for influenza-associated mortality and renal failure in machine-learning algorithms and regression analyses. Using cell culture assays, we also identified that human alveolar A549 cells and peripheral blood monocyte-derived macrophages increase their CXCL17 production capacity after influenza A(H1N1) pdm09 virus infection. Our results for the first time demonstrate an induction of CXCL17 specifically during pandemic influenza A(H1N1), but not COVID-19 and PTB in humans. These findings could be of great utility to differentiate influenza and COVID-19 and to predict poor prognosis specially at settings of high incidence of pandemic A(H1N1). Future studies on the role of CXCL17 not only in severe pandemic influenza, but also in seasonal influenza, COVID-19, and PTB are required to validate our results.

High-throughput analysis of lung immune cells in a combined murine model of agriculture dust-triggered airway inflammation with rheumatoid arthritis

Rheumatoid arthritis (RA)-associated lung disease is a leading cause of mortality in RA, yet the mechanisms linking lung disease and RA remain unknown. Using an established murine model of RA-associated lung disease combining collagen-induced arthritis (CIA) with organic dust extract (ODE)-induced airway inflammation, differences among lung immune cell populations were analyzed by single cell RNA-sequencing. Additionally, four lung myeloid-derived immune cell populations including macrophages, monocytes/macrophages, monocytes, and neutrophils were isolated by fluorescence cell sorting and gene expression was determined by NanoString analysis. Unsupervised clustering revealed 14 discrete clusters among Sham, CIA, ODE, and CIA+ODE treatment groups: 3 neutrophils (inflammatory, resident/transitional, autoreactive/suppressor), 5 macrophages (airspace, differentiating/recruited, recruited, resident/interstitial, and proliferative airspace), 2 T-cells (differentiating and effector), and a single cluster each of inflammatory monocytes, dendritic cells, B-cells and natural killer cells. Inflammatory monocytes, autoreactive/suppressor neutrophils, and recruited/differentiating macrophages were predominant with arthritis induction (CIA and CIA+ODE). By specific lung cell isolation, several interferon-related and autoimmune genes were disproportionately expressed among CIA and CIA+ODE (e.g. Oasl1, Oas2, Ifit3, Gbp2, Ifi44, and Zbp1), corresponding to RA and RA-associated lung disease. Monocytic myeloid-derived suppressor cells were reduced, while complement genes (e.g. C1s1 and Cfb) were uniquely increased in CIA+ODE mice across cell populations. Recruited and inflammatory macrophages/monocytes and neutrophils expressing interferon-, autoimmune-, and complement-related genes might contribute towards pro-fibrotic inflammatory lung responses following airborne biohazard exposures in setting of autoimmune arthritis and could be predictive and/or targeted to reduce disease burden.

The Gut-Lung Axis in Systemic Inflammation. Role of Mesenteric Lymph as a Conduit

Emerging evidence shows that after injury or infection, the mesenteric lymph acts as a conduit for gut-derived toxic factors to enter the blood circulation, causing systemic inflammation and acute lung injury. Neither the cellular and molecular identity of lymph factors nor their mechanisms of action have been well understood and thus have become a timely topic of investigation. This review will first provide a summary of background knowledge on gut barrier and mesenteric lymphatics, followed by a discussion focusing on the current understanding of potential injurious factors in the lymph and their mechanistic contributions to lung injury. We also examine lymph factors with antiinflammatory properties as well as the bidirectional nature of the gut-lung axis in inflammation.

Effects of IFN-γ on immune cell kinetics during the resolution of acute lung injury

The immunologic responses that occur early in the acute respiratory distress syndrome (ARDS) elicit immune‐mediated damage. The mechanisms underlying the resolution of ARDS, particularly the role of signaling molecules in regulating immune cell kinetics, remain important questions. Th1‐mediated responses can contribute to the pathogenesis of acute lung injury (ALI). Interferon‐gamma (IFN‐γ) orchestrates early inflammatory events, enhancing immune‐mediated damage. The current study investigated IFN‐γ during resolution in several experimental models of ALI. The absence of IFN‐γ resulted in altered kinetics of lymphocyte and macrophage responses, suggesting that IFN‐γ present in this microenvironment is influential in ALI resolution. Genetic deficiency of IFN‐γ or administering neutralizing IFN‐γ antibodies accelerated the pace of resolution. Neutralizing IFN‐γ decreased the numbers of interstitial and inflammatory macrophages and increased alveolar macrophage numbers during resolution. Our results underline the complexity of lung injury resolution and provide insight into the effects through which altered IFN‐γ concentrations affect immune cell kinetics and the rate of resolution. These findings suggest that therapies that spatially or temporally control IFN‐γ signaling may promote ALI resolution. Identifying and elucidating the mechanisms critical to ALI resolution will allow the development of therapeutic approaches to minimize collateral tissue damage without adversely altering the response to injury.

SARS-CoV-2 (COVID-19): Beginning to Understand a New Virus

Within the last two decades, several members of the Coronaviridae family demonstrated epidemic potential. In late 2019, an unnamed genetic relative, later named SARS-CoV-2 (COVID-19), erupted in the highly populous neighborhoods of Wuhan, China. Unchecked, COVID-19 spread rapidly among interconnected communities and related households before containment measures could be enacted. At present, the mortality rate of COVID-19 infection worldwide is 6.6%. In order to mitigate the number of infections, restrictions or recommendations on the number of people that can gather in a given area have been employed by governments worldwide. For governments to confidently lift these restrictions as well as counter a potential secondary wave of infections, alternative medications and diagnostic strategies against COVID-19 are urgently required. This review has focused on these issues.

Age-Dependent Differences in T-Cell Responses to Influenza A Virus

Respiratory infections from influenza A virus (IAV) cause substantial morbidity and mortality in children relative to adults. T cells play a critical role in the host response to IAV by supporting the innate and humoral responses, mediating cytotoxic activity, and promoting recovery. There are age-dependent differences in the number, subsets, and localization of T cells, which impact the host response to pathogens. In this article, we first review how T cells recognize IAV and examine differences in the resting T-cell populations between juveniles and adults. Next, we describe how the juvenile CD4⁺, CD8⁺, and regulatory T-cell responses compare with those in adults and discuss the potential physiologic and clinical consequences of the differences. Finally, we explore the roles of two unconventional T-cell types in the juvenile response to influenza, natural-killer T cells and γδ T cells. A clear understanding of age-dependent differences in the T-cell response is essential to developing therapies to prevent or reverse the deleterious effects of IAV in children.

PM2.5 in poultry houses synergizes with Pseudomonas aeruginosa to aggravate lung inflammation in mice through the NF-κB pathway

Background

High concentrations of particulate matter less than 2.5 µm in diameter (PM2.5) in poultry houses is an important cause of respiratory disease in animals and humans. Pseudomonas aeruginosa is an opportunistic pathogen that can induce severe respiratory disease in animals under stress or with abnormal immune functions. When excessively high concentrations of PM2.5 in poultry houses damage the respiratory system and impair host immunity, secondary infections with P. aeruginosa can occur and produce a more intense inflammatory response, resulting in more severe lung injury.

Objectives

In this study, we focused on the synergistic induction of inflammatory injury in the respiratory system and the related molecular mechanisms induced by PM2.5 and P. aeruginosa in poultry houses.

Methods

High-throughput 16S rDNA sequence analysis was used for characterizing the bacterial diversity and relative abundance of the PM2.5 samples, and the effects of PM2.5 and P. aeruginosa stimulation on inflammation were detected by in vitro and in vivo.

Results

Sequencing results indicated that the PM2.5 in poultry houses contained a high abundance of potentially pathogenic genera, such as Pseudomonas (2.94%). The lung tissues of mice had more significant pathological damage when co-stimulated by PM2.5 and P. aeruginosa, and it can increase the expression levels of interleukin (IL)-6, IL-8, and tumor necrosis factor-α through nuclear factor (NF)-κB pathway in vivo and in vitro.

Conclusions

The results confirmed that poultry house PM2.5 in combination with P. aeruginosa could aggravate the inflammatory response and cause more severe respiratory system injuries through a process closely related to the activation of the NF-κB pathway.

Monocytopenia, monocyte morphological anomalies and hyperinflammation characterise severe COVID-19 in type 2 diabetes

Early in the COVID-19 pandemic, type 2 diabetes (T2D) was marked as a risk factor for severe disease and mortality. Inflammation is central to the aetiology of both conditions where variations in immune responses can mitigate or aggravate disease course. Identifying at-risk groups based on immunoinflammatory signatures is valuable in directing personalised care and developing potential targets for precision therapy. This observational study characterised immunophenotypic variation associated with COVID-19 severity in T2D. Broad-spectrum immunophenotyping quantified 15 leucocyte populations in peripheral circulation from a cohort of 45 hospitalised COVID-19 patients with and without T2D. Lymphocytopenia and specific loss of cytotoxic CD8+ lymphocytes were associated with severe COVID-19 and requirement for intensive care in both non-diabetic and T2D patients. A morphological anomaly of increased monocyte size and monocytopenia restricted to classical CD14Hi CD16- monocytes was specifically associated with severe COVID-19 in patients with T2D requiring intensive care. Increased expression of inflammatory markers reminiscent of the type 1 interferon pathway (IL6, IL8, CCL2, INFB1) underlaid the immunophenotype associated with T2D. These immunophenotypic and hyperinflammatory changes may contribute to increased voracity of COVID-19 in T2D. These findings allow precise identification of T2D patients with severe COVID-19 as well as provide evidence that the type 1 interferon pathway may be an actionable therapeutic target for future studies.

Intermittent fasting, a possible priming tool for host defense against SARS-CoV-2 infection: Crosstalk among calorie restriction, autophagy and immune response

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the causative pathogen of deadly Coronavirus disease-19 (COVID-19) pandemic, which emerged as a major threat to public health across the world. Although there is no clear gender or socioeconomic discrimination in the incidence of COVID-19, individuals who are older adults and/or with comorbidities and compromised immunity have a relatively higher risk of contracting this disease. Since no specific drug has yet been discovered, strengthening immunity along with maintaining a healthy living is the best way to survive this disease. As a healthy practice, calorie restriction in the form of intermittent fasting (IF) in several clinical settings has been reported to promote several health benefits, including priming of the immune response. This dietary restriction also activates autophagy, a cell surveillance system that boosts up immunity. With these prevailing significance in priming host defense, IF could be a potential strategy amid this outbreak to fighting off SARS-CoV-2 infection. Currently, no review so far available proposing IF as an encouraging strategy in the prevention of COVID-19. A comprehensive review has therefore been planned to highlight the beneficial role of fasting in immunity and autophagy, that underlie the possible defense against SARS-CoV-2 infection. The COVID-19 pathogenesis and its impact on host immune response have also been briefly outlined. This review aimed at revisiting the immunomodulatory potential of IF that may constitute a promising preventive approach against COVID-19.

Intranasal Bifidobacterium longum protects against viral-induced lung inflammation and injury in a murine model of lethal influenza infection

Background

Prophylactic strategies are urgently needed for prevention of severe inflammatory responses to respiratory viral infections. Bacterial-host interactions may modify the immune response to viral infections.

Methods

We examined the contribution of Intranasal administration of two different Bifidobacterium longum strains or its isolated cell wall in controlling viral induced inflammation using a murine model of influenza infection. We monitored mortality and morbidity over a 10-day period and viral load, differential broncho alveolar lavage (BAL) fluid inflammatory cell counts, Lung tissue histology, BAL and serum cytokines, markers of vascular damage and cell death were quantified.

Findings

Intranasal administration of Bifidobacterium longum35624® or its isolated cell wall prior to virus inoculation significantly reduced viral load within the lungs and significantly improved survival. Reduced viral load was associated with reduced lung injury as suggested by cell death and vascular leakage markers, a shift from neutrophil to macrophage recruitment, reduced inflammatory cytokine levels (including IL-6), reduced type 1 and 2 interferon levels, but increased levels of interferon-λ and surfactant protein D. These protective effects were maintained when the bifidobacterial cell wall preparation was administered 24 h after viral inoculation. The protective effects were also observed for the Bifidobacterium longumPB-VIR™ strain.

Interpretation

Exposure to these bifidobacterial strains protect against the inflammatory sequelae and damage associated with uncontrolled viral replication within the lung.

Funding

This work has been funded, in part, by a research grant from GlaxoSmithKline, PrecisionBiotics Group Ltd., Swiss National Science Foundation grants (project numbers CRSII3_154488, 310030_144219, 310030_127356 and 310030_144219) and Christine Kühne – Center for Allergy Research and Education (CK-CARE).

Inflammasome Fuels Dengue Severity

Dengue is an acute febrile disease triggered by dengue virus. Dengue is the widespread and rapidly transmitted mosquito-borne viral disease of humans. Diverse symptoms and diseases due to Dengue virus (DENV) infection ranges from dengue fever, dengue hemorrhagic fever (life-threatening) and dengue shock syndrome characterized by shock, endothelial dysfunction and vascular leakage. Several studies have linked the severity of dengue with the induction of inflammasome. DENV activates the NLRP3-specific inflammasome in DENV infected human patients, mice; specifically, mouse bone marrow derived macrophages (BMDMs), dendritic cells, endothelial cells, human peripheral blood mononuclear cells (PBMCs), keratinocytes, monocyte-differentiated macrophages (THP-1), and platelets. Dengue virus mediated inflammasome initiates the maturation of IL-1β and IL-18, which are critical for dengue pathology and inflammatory response. Several studies have reported the molecular mechanism through which (host and viral factors) dengue induces inflammasome, unravels the possible mechanisms of DENV pathogenesis and sets up the stage for the advancement of DENV therapeutics. In this perspective article, we discuss the potential implications and our understanding of inflammasome mechanisms of dengue virus and highlight research areas that have potential to inhibit the pathogenesis of viral diseases, specifically for dengue.

Androgen receptor signaling in the lungs mitigates inflammation and improves the outcome of influenza in mice

Circulating androgens can modulate immune cell activity, but the impact of androgens on viral pathogenesis remains unclear. Previous data demonstrate that testosterone reduces the severity of influenza A virus (IAV) infection in male mice by mitigating pulmonary inflammation rather than by affecting viral replication. To examine the immune responses mediated by testosterone to mitigate IAV-induced inflammation, adult male mice remained gonadally intact or were gonadectomized and treated with either placebo or androgen-filled (i.e., testosterone or dihydrotestosterone) capsules prior to sublethal IAV infection. Like intact males, treatment of gonadectomized males with androgens improved the outcome of IAV infection, which was not mediated by changes in the control of virus replication or pulmonary cytokine activity. Instead, androgens accelerated pulmonary leukocyte contraction to limit inflammation. To identify which immune cells were contracting in response to androgens, the composition of pulmonary cellular infiltrates was analyzed and revealed that androgens specifically accelerated the contraction of total pulmonary inflammatory monocytes during peak disease, as well as CD8+ T cells, IAV-specific CD8+ T numbers, cytokine production and degranulation by IAV-specific CD8+ T cells, and the influx of eosinophils into the lungs following clearance of IAV. Neither depletion of eosinophils nor adoptive transfer of CD8+ T cells could reverse the ability of testosterone to protect males against IAV suggesting these were secondary immunologic effects. The effects of testosterone on the contraction of immune cell numbers and activity were blocked by co-administration of the androgen receptor antagonist flutamide and mimicked by treatment with dihydrotestosterone, which was also able to reduce the severity of IAV in female mice. These data suggest that androgen receptor signaling creates a local pulmonary environment that promotes downregulation of detrimental inflammatory immune responses to protect against prolonged influenza disease.

One hundred years of (influenza) immunopathology

It has been over 100 years since the 1918 influenza pandemic, one of the most infamous examples of viral immunopathology. Since that time, there has been an inevitable repetition of influenza pandemics every few decades and yearly influenza seasons, which have a significant impact on human health. Recently, noteworthy progress has been made in defining the cellular and molecular mechanisms underlying pathology induced by an exuberant host response to influenza virus infection. Infection with influenza viruses is associated with a wide spectrum of disease, from mild symptoms to severe complications including respiratory failure, and the severity of influenza disease is driven by a complex interplay of viral and host factors. This chapter will discuss mechanisms of infection severity using concepts of disease resistance and tolerance as a framework for understanding the balance between viral clearance and immunopathology. We review mechanistic studies in animal models of infection and correlational studies in humans that have begun to define these factors and discuss promising host therapeutic targets to improve outcomes from severe influenza disease.

The Role of Type I IFNs in Influenza: Antiviral Superheroes or Immunopathogenic Villains?

The important role of interferons (IFNs) in antiviral innate immune defense is well established. Although recombinant IFN-α was approved for cancer and chronic viral infection treatment by regulatory agencies in many countries starting in 1986, no IFNs are approved for treatment of influenza A virus (IAV) infection. This is partially due to the complex effects of IFNs in acute influenza infection. IAV attacks the human respiratory system and causes significant morbidity and mortality globally. During influenza infection, depending on the strain of IAV and the individual host, type I IFNs can have protective antiviral effects or can contribute to immunopathology. In the context of virus infection, the immune system has complicated mechanisms regulating the expression and effects of type I IFN to maximize the antiviral response by both activating and enhancing beneficial innate cell function, while limiting immunopathological responses that lead to exaggerated tissue damage. In this review, we summarize the complicated, but important, role of type I IFNs in influenza infections. This includes both protective and harmful effects of these important cytokines during infection.