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

IL-10 Counteracts IFN-γ to Alleviate Acute Lung Injury in a Viral-Bacterial Superinfection Model

Immune activation is essential for lung control of viral and bacterial infection, but an overwhelming inflammatory response often leads to the onset of acute respiratory distress syndrome. IL-10 plays a crucial role in regulating the balance between antimicrobial immunity and immunopathology. In the present study, we investigated the role of IL-10 in acute lung injury induced by influenza A virus and methicillin-resistant Staphylococcus aureus coinfection. This unique coinfection model resembles patients with acute pneumonia undergoing appropriate antibiotic therapies. Using global IL-10 and IL-10 receptor gene-deficient mice, as well as in vivo neutralizing antibodies, we show that IL-10 deficiency promotes IFN-γ-dominant cytokine responses and triggers acute animal death. Interestingly, this extreme susceptibility is fully preventable by IFN-γ neutralization during coinfection. Further studies using mice with Il10ra deletion in selective myeloid subsets reveal that IL-10 primarily acts on mononuclear phagocytes to prevent IFN-γ/TNF-α hyperproduction and acute mortality. Importantly, this antiinflammatory IL-10 signaling is independent of its inhibitory effect on antiviral and antibacterial defense. Collectively, our results demonstrate a key mechanism of IL-10 in preventing hypercytokinemia and acute respiratory distress syndrome pathogenesis by counteracting the IFN-γ response.

AMG487 alleviates influenza A (H1N1) virus-induced pulmonary inflammation through decreasing IFN-γ-producing lymphocytes and IFN-γ concentrations

BACKGROUND AND PURPOSE

Severe influenza virus-infected patients have high systemic levels of Th1 cytokines (including IFN-γ). Intrapulmonary IFN-γ increases pulmonary IFN-γ-producing T lymphocytes through the CXCR3 pathway. Virus-infected mice lacking IP-10/CXCR3 demonstrate lower pulmonary neutrophilic inflammation. AMG487, an IP-10/CXCR3 antagonist, ameliorates virus-induced lung injury in vivo through decreasing viral loads. This study examined whether AMG487 could treat H1N1 virus-induced mouse illness through reducing viral loads or decreasing the number of lymphocytes or neutrophils.

EXPERIMENTAL APPROACH

Here, we studied the above-mentioned effects and underlying mechanisms in vivo.

KEY RESULTS

H1N1 virus infection caused bad overall condition and pulmonary inflammation characterized by the infiltration of lymphocytes and neutrophils. From Day-5 to Day-10 post-virus infection, bad overall condition, pulmonary lymphocytes, and IFN-γ concentrations increased, while pulmonary H1N1 viral titres and neutrophils decreased. Both anti-IFN-γ and AMG487 alleviated virus infection-induced bad overall condition and pulmonary lymphocytic inflammation. Pulmonary neutrophilic inflammation was mitigated by AMG487 on Day-5 post-infection, but was not mitigated by AMG487 on Day-10 post-infection. H1N1 virus induced increases of IFN-γ, IP-10, and IFN-γ-producing lymphocytes and activation of the Jak2-Stat1 pathways in mouse lungs, which were inhibited by AMG487. Anti-IFN-γ decreased IFN-γ and IFN-γ-producing lymphocytes on Day-5 post-infection. AMG487 but not anti-IFN-γ decreased viral titres in mouse lung homogenates or BALF. Higher virus load did not increase pulmonary inflammation and IFN-γ concentrations when mice were treated with AMG487.

CONCLUSION AND IMPLICATIONS

AMG487 may ameliorate H1N1 virus-induced pulmonary inflammation through decreasing IFN-γ-producing lymphocytes rather than reducing viral loads or neutrophils.

Insights into the mechanism of action of pterostilbene against influenza A virus-induced acute lung injury

BACKGROUND

Severe respiratory system illness caused by influenza A virus infection is associated with excessive inflammation and abnormal apoptosis in alveolar epithelial cells (AEC). However, there are limited therapeutic options for influenza-associated lung inflammation and apoptosis. Pterostilbene (PTE, trans-3,5-dimethoxy-4-hydroxystilbene) is a dimethylated analog of resveratrol that has been reported to limit influenza A virus infection by promoting antiviral innate immunity, but has not been studied for its protective effects on virus-associated inflammation and injury in AEC.

PURPOSE

Our study aimed to investigate the protective effects and underlying mechanisms of PTE in modulating inflammation and apoptosis in AEC, as well as its effects on macrophage polarization during influenza virus infection.

STUDY DESIGN AND METHODS

A murine model of influenza A virus-mediated acute lung injury was established by intranasal inoculation with 5LD50 of mouse-adapted H1N1 viruses. Hematoxylin and eosin staining, immunofluorescence, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, western blotting, Luminex and flow cytometry were performed.

RESULTS

PTE effectively mitigated lung histopathological changes and injury induced by H1N1 viruses in vivo. These beneficial effects of PTE were attributed to the suppression of inflammation and apoptosis in AEC, as well as the modulation of M1 macrophage polarization. Mechanistic investigations revealed that PTE activated the phosphorylated AMP-activated protein kinase alpha (P-AMPKα)/sirtui1 (Sirt1)/PPARγ coactivator 1-alpha (PGC1α) signal axis, leading to the inhibition of nuclear factor kappa-B (NF-κB) and p38 mitogen-activated protein kinase (MAPK) signaling induced by H1N1 viruses, thereby attenuating inflammation and apoptosis in AEC. PTE also forced activation of the P-AMPKα/Sirt1/PGC1α signal axis in RAW264.7 cells, counteracting the activation of phosphorylated signal transducer and activator of transcription 1 (P-STAT1) induced by H1N1 viruses and the augment of P-STAT1 activation in RAW264.7 cells with interferon-gamma (IFN-γ) pretreatment before viral infection, thereby reducing H1N1 virus-mediated M1 macrophage polarization as well as the enhancement of macrophages into M1 phenotypes elicited by IFN-γ pretreatment. Additionally, the promotion of the transition of macrophages towards the M2 phenotype by PTE was also related to activation of the P-AMPKα/Sirt1/PGC1α signal axis. Moreover, co-culturing non-infected AEC with H1N1 virus-infected RAW264.7 cells in the presence of PTE inhibited apoptosis and tight junction disruption, which was attributed to the suppression of pro-inflammatory mediators and pro-apoptotic factors in an AMPKα-dependent manner.

CONCLUSION

In conclusion, our findings suggest that PTE may serve as a promising novel therapeutic option for treating influenza-associated lung injury. Its ability to suppress inflammation and apoptosis in AEC, modulate macrophage polarization, and preserve alveolar epithelial cell integrity highlights its potential as a therapeutic agent in influenza diseases.

Lung influenza virus-specific memory CD4 T cell location and optimal cytokine production are dependent on interactions with lung antigen-presenting cells

Influenza A virus (IAV) infection leads to the formation of mucosal memory CD4 T cells that can protect the host. An in-depth understanding of the signals that shape memory cell development is required for more effective vaccine design. We have examined the formation of memory CD4 T cells in the lung following IAV infection of mice, characterizing changes to the lung landscape and immune cell composition. IAV-specific CD4 T cells were found throughout the lung at both primary and memory time points. These cells were found near lung airways and in close contact with a range of immune cells including macrophages, dendritic cells, and B cells. Interactions between lung IAV-specific CD4 T cells and major histocompatibility complex (MHC)II+ cells during the primary immune response were important in shaping the subsequent memory pool. Treatment with an anti-MHCII blocking antibody increased the proportion of memory CD4 T cells found in lung airways but reduced interferon-γ expression by IAV-specific immunodominant memory CD4 T cells. The immunodominant CD4 T cells expressed higher levels of programmed death ligand 1 (PD1) than other IAV-specific CD4 T cells and PD1+ memory CD4 T cells were located further away from MHCII+ cells than their PD1-low counterparts. This distinction in location was lost in mice treated with anti-MHCII antibodies. These data suggest that sustained antigen presentation in the lung impacts the formation of memory CD4 T cells by regulating their cytokine production and location.

Journey of monocytes and macrophages upon influenza A virus infection

Influenza A virus (IAV) infections pose a global health challenge that necessitates a comprehensive understanding of the host immune response to devise effective therapeutic interventions. As monocytes and macrophages play crucial roles in host defence, inflammation, and repair, this review explores the intricate journey of these cells during and after IAV infection. First, we highlight the dynamics and functions of lung-resident macrophage populations post-IAV. Second, we review the current knowledge of recruited monocytes and monocyte-derived cells, emphasising their roles in viral clearance, inflammation, immunomodulation, and tissue repair. Third, we shed light on the consequences of IAV-induced macrophage alterations on long-term lung immunity. We conclude by underscoring current knowledge gaps and exciting prospects for future research in unravelling the complexities of macrophage responses to respiratory viral infections.

Recombinant mycobacterial DNA-binding protein 1 with post-translational modifications boosts IFN-gamma production from BCG-vaccinated individuals' blood cells in combination with CpG-DNA

Tuberculosis remains a large health threat, despite the availability of the tuberculosis vaccine, BCG. As BCG efficacy gradually decreases from adolescence, BCG-Prime and antigen-booster may be an efficient strategy to confer vaccine efficacy. Mycobacterial DNA-binding protein 1 (MDP1, namely Rv2986c, hupB or HU) is a major Mycobacterium tuberculosis protein that induces vaccine-efficacy by co-administration with CpG DNA. To produce MDP1 for booster-vaccine use, we have created recombinant MDP1 produced in both Escherichia coli (eMDP1) and Mycolicibacterium smegmatis (mMDP1), an avirulent rapid-growing mycobacteria. We tested their immunogenicity by checking interferon (IFN)-gamma production by stimulated peripheral blood cells derived from BCG-vaccinated individuals. Similar to native M. tuberculosis MDP1, we observed that most lysin resides in the C-terminal half of mMDP1 are highly methylated. In contrast, eMDP1 had less post-translational modifications and IFN-gamma stimulation. mMDP1 stimulated the highest amount of IFN-gamma production among the examined native M. tuberculosis proteins including immunodominant MPT32 and Antigen 85 complex. MDP1-mediated IFN-gamma production was more strongly enhanced when combined with a new type of CpG DNA G9.1 than any other tested CpG DNAs. Taken together, these results suggest that the combination of mMDP1 and G9.1 possess high potential use for human booster vaccine against tuberculosis.

Spatiotemporal orchestration of macrophage activation trajectories by Vγ4 T cells during skin wound healing

Dysregulated macrophage polarization from pro-inflammatory M1 to anti-inflammatory M2 phenotypes underlies impaired cutaneous wound healing. This study reveals Vγ4+ γδ T cells spatiotemporally calibrate macrophage trajectories during skin repair via sophisticated interferon-γ (IFN-γ) conditioning across multiple interconnected tissues. Locally within wound beds, infiltrating Vγ4+ γδ T cells directly potentiate M1 activation and suppress M2 polarization thereby prolonging local inflammation. In draining lymph nodes, infiltrated Vγ4+ γδ T cells expand populations of IFN-γ-competent lymphocytes which disseminate systemically and infiltrate into wound tissues, further enforcing M1 macrophages programming. Moreover, Vγ4+γδ T cells flushed into bone marrow stimulate increased IFN-γ production, which elevates the output of pro-inflammatory Ly6C+monocytes. Mobilization of these monocytes continually replenishes the M1 macrophage pool in wounds, preventing phenotypic conversion to M2 activation. Thus, multi-axis coordination of macrophage activation trajectories by trafficking Vγ4+ γδ T cells provides a sophisticated immunological mechanism regulating inflammation timing and resolution during skin repair.

Ex Pluribus Unum: The CD4 T Cell Response against Influenza A Virus

Current Influenza A virus (IAV) vaccines, which primarily aim to generate neutralizing antibodies against the major surface proteins of specific IAV strains predicted to circulate during the annual 'flu' season, are suboptimal and are characterized by relatively low annual vaccine efficacy. One approach to improve protection is for vaccines to also target the priming of virus-specific T cells that can protect against IAV even in the absence of preexisting neutralizing antibodies. CD4 T cells represent a particularly attractive target as they help to promote responses by other innate and adaptive lymphocyte populations and can also directly mediate potent effector functions. Studies in murine models of IAV infection have been instrumental in moving this goal forward. Here, we will review these findings, focusing on distinct subsets of CD4 T cell effectors that have been shown to impact outcomes. This body of work suggests that a major challenge for next-generation vaccines will be to prime a CD4 T cell population with the same spectrum of functional diversity generated by IAV infection. This goal is encapsulated well by the motto 'ex pluribus unum': that an optimal CD4 T cell response comprises many individual specialized subsets responding together.

Mammalian Target of Rapamycin Complex 1 Activation in Macrophages Contributes to Persistent Lung Inflammation following Respiratory Tract Viral Infection

Respiratory tract virus infections cause millions of hospitalizations worldwide each year. Severe infections lead to lung damage that coincides with persistent inflammation and a lengthy repair period. Vaccination and antiviral therapy help to mitigate severe infections before or during the acute stage of disease, but there are currently limited specific treatment options available to individuals experiencing the long-term sequelae of respiratory viral infection. Herein, C57BL/6 mice were infected with influenza A/PR/8/34 as a model for severe viral lung infection and allowed to recover for 21 days. Mice were treated with rapamycin, a well-characterized mammalian target of rapamycin complex 1 (mTORC1) inhibitor, on days 12 to 20 after infection, a time period after viral clearance. Persistent inflammation following severe influenza infection in mice was primarily driven by macrophages and T cells. Uniform manifold approximation and projection analysis of flow cytometry data revealed that lung macrophages had high activation of mTORC1, an energy-sensing kinase involved in inflammatory immune cell effector functions. Rapamycin treatment reduced lung inflammation and the frequency of exudate macrophages, T cells, and B cells in the lung, while not impacting epithelial progenitor cells or adaptive immune memory. These data highlight mTORC1's role in sustaining persistent inflammation following clearance of a viral respiratory pathogen and suggest a possible intervention for post-viral chronic lung inflammation.

Long-Term Autoimmune Inflammatory Rheumatic Outcomes of COVID-19 : A Binational Cohort Study

BACKGROUND

Some data suggest a higher incidence of diagnosis of autoimmune inflammatory rheumatic diseases (AIRDs) among patients with a history of COVID-19 compared with uninfected patients. However, these studies had methodological shortcomings.

OBJECTIVE

To investigate the effect of COVID-19 on long-term risk for incident AIRD over various follow-up periods.

DESIGN

Binational, longitudinal, propensity-matched cohort study.

SETTING

Nationwide claims-based databases in South Korea (K-COV-N cohort) and Japan (JMDC cohort).

PARTICIPANTS

10 027 506 Korean and 12 218 680 Japanese patients aged 20 years or older, including those with COVID-19 between 1 January 2020 and 31 December 2021, matched to patients with influenza infection and to uninfected control patients.

MEASUREMENTS

The primary outcome was onset of AIRD (per appropriate codes from the International Classification of Diseases, 10th Revision) 1, 6, and 12 months after COVID-19 or influenza infection or the respective matched index date of uninfected control patients.

RESULTS

Between 2020 and 2021, among the 10 027 506 Korean participants (mean age, 48.4 years [SD, 13.4]; 50.1% men), 394 274 (3.9%) and 98 596 (0.98%) had a history of COVID-19 or influenza, respectively. After propensity score matching, beyond the first 30 days after infection, patients with COVID-19 were at increased risk for incident AIRD compared with uninfected patients (adjusted hazard ratio, 1.25 [95% CI, 1.18 to 1.31]) and influenza-infected control patients (adjusted hazard ratio, 1.30 [CI, 1.02 to 1.59]). The risk for incident AIRD was higher with more severe acute COVID-19. Similar patterns were observed in the Japanese cohort.

LIMITATIONS

Referral bias due to the pandemic; residual confounding.

CONCLUSION

SARS-CoV-2 infection was associated with increased risk for incident AIRD compared with matched patients without SARS-CoV-2 infection or with influenza infection. The risk for incident AIRD was higher with greater severity of acute COVID-19.

PRIMARY FUNDING SOURCE

National Research Foundation of Korea.

Efficacy and safety of Lianhua Qingwen as an adjuvant treatment for influenza in Chinese patients: A meta-analysis

BACKGROUND

Lianhua Qingwen (LHQW) is a proprietary traditional Chinese medicine for the treatment of influenza (FLu). It is composed of 2 prescriptions, Maxing Shigan and Yinqiao, which has antiviral, antibacterial, and immunomodulatory effects. However its clinical suitability has not yet been investigated.

OBJECTIVE

This study aimed to evaluate the efficacy and safety of LHQW in the treatment of FLu.

METHODS

We searched several databases, including PubMed and China Biomedical Database for literature research, from inception to July 1, 2023. This meta-analysis included RCTs that compared the safety and efficacy of the combination of LHQW and conventional drugs (CD) with CD alone for IFU. The extracted data were analyzed using Revman5.4 software with risk ratio (RR), 95% confidence intervals (CI), and standardized mean difference.

RESULTS

Our meta-analysis included 32 articles with 3592 patients. The results showed that the effects of LHQW adjuvant therapy were superior to those of CD (clinical effective rate: RR = 1.22, 95% CI: 1.18-1.26, P < .00001; cure rate: RR = 1.54, 95% CI: 1.35-1.75, P < .00001), and adverse reactions after treatment were significantly lower than those before treatment (RR = 0.70, 95% CI: 0.50-0.98, P = .04).

CONCLUSION

This meta-analysis indicates that LHQW combined with CD may be more effective than CD alone for the treatment of FLu.

The chemokine receptor CXCR3 promotes CD8+ T cell-dependent lung pathology during influenza pathogenesis

The dual role of CD8+ T cells in influenza control and lung pathology is increasingly appreciated. To explore whether protective and pathological functions can be linked to specific subsets, we dissected CD8+ T responses in influenza-infected murine lungs. Our single-cell RNA-sequencing (scRNA-seq) analysis revealed notable diversity in CD8+ T subpopulations during peak viral load and infection-resolved state. While enrichment of a Cxcr3hi CD8+ T effector subset was associated with a more robust cytotoxic response, both CD8+ T effector and central memory exhibited equally potent effector potential. The scRNA-seq analysis identified unique regulons regulating the cytotoxic response in CD8+ T cells. The late-stage CD8+ T blockade in influenza-cleared lungs or continuous CXCR3 blockade mitigated lung injury without affecting viral clearance. Furthermore, adoptive transfer of wild-type CD8+ T cells exacerbated influenza lung pathology in Cxcr3-/- mice. Collectively, our data imply that CXCR3 interception could have a therapeutic effect in preventing influenza-linked lung injury.

Mathematical Modeling of the Lethal Synergism of Coinfecting Pathogens in Respiratory Viral Infections: A Review

Influenza A virus (IAV) infections represent a substantial global health challenge and are often accompanied by coinfections involving secondary viruses or bacteria, resulting in increased morbidity and mortality. The clinical impact of coinfections remains poorly understood, with conflicting findings regarding fatality. Isolating the impact of each pathogen and mechanisms of pathogen synergy during coinfections is challenging and further complicated by host and pathogen variability and experimental conditions. Factors such as cytokine dysregulation, immune cell function alterations, mucociliary dysfunction, and changes to the respiratory tract epithelium have been identified as contributors to increased lethality. The relative significance of these factors depends on variables such as pathogen types, infection timing, sequence, and inoculum size. Mathematical biological modeling can play a pivotal role in shedding light on the mechanisms of coinfections. Mathematical modeling enables the quantification of aspects of the intra-host immune response that are difficult to assess experimentally. In this narrative review, we highlight important mechanisms of IAV coinfection with bacterial and viral pathogens and survey mathematical models of coinfection and the insights gained from them. We discuss current challenges and limitations facing coinfection modeling, as well as current trends and future directions toward a complete understanding of coinfection using mathematical modeling and computer simulation.

IL-17RA promotes pathologic epithelial inflammation in a mouse model of upper respiratory influenza infection

The upper respiratory tract (nasopharynx or NP) is the first site of influenza replication, allowing the virus to disseminate to the lower respiratory tract or promoting community transmission. The host response in the NP regulates an intricate balance between viral control and tissue pathology. The hyper-inflammatory responses promote epithelial injury, allowing for increased viral dissemination and susceptibility to secondary bacterial infections. However, the pathologic contributors to influenza upper respiratory tissue pathology are incompletely understood. In this study, we investigated the role of interleukin IL-17 recetor A (IL-17RA) as a modulator of influenza host response and inflammation in the upper respiratory tract. We used a combined experimental approach involving IL-17RA-/- mice and an air-liquid interface (ALI) epithelial culture model to investigate the role of IL-17 response in epithelial inflammation, barrier function, and tissue pathology. Our data show that IL-17RA-/- mice exhibited significantly reduced neutrophilia, epithelial injury, and viral load. The reduced NP inflammation and epithelial injury in IL-17RA-/- mice correlated with increased resistance against co-infection by Streptococcus pneumoniae (Spn). IL-17A treatment, while potentiating the apoptosis of IAV-infected epithelial cells, caused bystander cell death and disrupted the barrier function in ALI epithelial model, supporting the in vivo findings.

Generation of "OP7 chimera" defective interfering influenza A particle preparations free of infectious virus that show antiviral efficacy in mice

Influenza A virus (IAV) defective interfering particles (DIPs) are considered as new promising antiviral agents. Conventional DIPs (cDIPs) contain a deletion in the genome and can only replicate upon co-infection with infectious standard virus (STV), during which they suppress STV replication. We previously discovered a new type of IAV DIP "OP7" that entails genomic point mutations and displays higher antiviral efficacy than cDIPs. To avoid safety concerns for the medical use of OP7 preparations, we developed a production system that does not depend on infectious IAV. We reconstituted a mixture of DIPs consisting of cDIPs and OP7 chimera DIPs, in which both harbor a deletion in their genome. To complement the defect, the deleted viral protein is expressed by the suspension cell line used for production in shake flasks. Here, DIP preparations harvested are not contaminated with infectious virions, and the fraction of OP7 chimera DIPs depended on the multiplicity of infection. Intranasal administration of OP7 chimera DIP material was well tolerated in mice. A rescue from an otherwise lethal IAV infection and no signs of disease upon OP7 chimera DIP co-infection demonstrated the remarkable antiviral efficacy. The clinical development of this new class of broad-spectrum antiviral may contribute to pandemic preparedness.

Allergen exposure functionally alters influenza-specific CD4+ Th1 memory cells in the lung

CD4+ lung-resident memory T cells (TRM) generated in response to influenza infection confer effective protection against subsequent viral exposures. Whether these cells can be altered by environmental antigens and cytokines released during heterologous, antigen-independent immune responses is currently unclear. We therefore investigated how influenza-specific CD4+ Th1 TRM in the lung are impacted by a subsequent Th2-inducing respiratory house dust mite (HDM) exposure. Although naïve influenza-specific CD4+ T cells in the lymph nodes do not respond to HDM, influenza-specific CD4+ TRM in the lungs do respond to a subsequent allergen exposure by decreasing expression of the transcription factor T-bet. This functional alteration is associated with decreased IFN-γ production upon restimulation and improved disease outcomes following heterosubtypic influenza challenge. Further investigation revealed that ST2 signaling in CD4+ T cells during allergic challenge is necessary to induce these changes in lung-resident influenza-specific CD4+ TRM. Thus, heterologous antigen exposure or ST2-signaling can drive persistent changes in CD4+ Th1 TRM populations and impact protection upon reinfection.

Single-cell analysis reveals the immune heterogeneity and interactions in lungs undergoing hepatic ischemia-reperfusion

Hepatic ischemia-reperfusion IR (HIR) is an unavoidable pathophysiological process during liver transplantation, resulting in systematic sterile inflammation and remote organ injury. Acute lung injury (ALI) is a serious complication after liver transplantation with high postoperative morbidity and mortality. However, the underlying mechanism is still unclear. To assess the phenotype and plasticity of various cell types in the lung tissue microenvironment after HIR at the single-cell level, single-cell RNA sequencing (scRNA-seq) was performed using the lungs from HIR-induced mice. In our results, we identified 23 cell types in the lungs after HIR and found that this highly complex ecosystem was formed by subpopulations of bone marrow-derived cells that signaled each other and mediated inflammatory responses in different states and different intervals. We described the unique transcriptional profiles of lung cell clusters and discovered two novel cell subtypes (Tspo+Endothelial cells and Vcan+ monocytes), as well as the endothelial cell-immune cell and immune cell-T cell clusters interactome. In addition, we found that S100 calcium binding protein (S100a8/a9), specifically and highly expressed in immune cell clusters of lung tissues and exhibited detrimental effects. Finally, the cellular landscape of the lung tissues after HIR was established, highlighting the heterogeneity and cellular interactions between major immune cells in HIR-induced lungs. Our findings provided new insights into the mechanisms of HIR-induced ALI and offered potential therapeutic target to prevent ALI after liver transplantation.

A mammalian lung's immune system minimizes tissue damage by initiating five major sequential phases of defense

The mammalian lungs encounter several pathogens, but have a sophisticated multi-phase immune defense. Furthermore, several immune responses to suppress pulmonary pathogens can damage the airway epithelial cells, particularly the vital alveolar epithelial cells (pneumocytes). The lungs have a sequentially activated, but overlapping, five phase immune response to suppress most pathogens, while causing minimal damage to the airway epithelial cells. Each phase of the immune response may suppress the pathogens, but if the previous phase proves inadequate, a stronger phase of immune response is activated, but with an increased risk of airway epithelial cell damage. The first phase immune response involves the pulmonary surfactants, which have proteins and phospholipids with potentially sufficient antibacterial, antifungal and antiviral properties to suppress many pathogens. The second phase immune response involves the type III interferons, having pathogen responses with comparatively minimal risk of damage to airway epithelial cells. The third phase immune response involves type I interferons, which implement stronger immune responses against pathogens with an increased risk of damage to airway epithelial cells. The fourth phase immune response involves the type II interferon, interferon-γ, which activates stronger immune responses, but with considerable risk of airway epithelial cell damage. The fifth phase immune response involves antibodies, potentially activating the complement system. In summary, five major phases of immune responses for the lungs are sequentially initiated to create an overlapping immune response which can suppress most pathogens, while usually causing minimal damage to the airway epithelial cells, including the pneumocytes.

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.

Acute Amelioration of Inflammatory Activity Caused by Endothelin-2 Deficiency during Acute Lung Injury

In acute lung injury (ALI), a severe insult induces a hyperinflammatory state in the lungs. The mortality rate of severe ALI remains high, and novel mechanistic insights are required to improve therapeutic strategies. Endothelin-2 (Edn2), the least studied isoform of endothelin, is involved in lung physiology and development and can be affected by various factors. One of them is inflammation, and another isoform of endothelin, endothelin-1 (Edn1), affects lung inflammatory responses. Considering the importance of Edn2 in the lungs and how Edn2 works through the same receptors as Edn1, we postulated that Edn2 may affect inflammatory responses that are central to ALI pathophysiology. In this study, we performed 24 hours intratracheal lipopolysaccharide (LPS) instillation or PBS control as an in vivo ALI model in eight-week-old conditional Edn2 knockout mice (Edn2-iKO), with Edn2-floxed mice as controls. Bronchoalveolar lavage (BAL) fluid and tissue were collected after exsanguination and analyzed for its cellular, molecular, functional, and histological inflammatory phenotypes. We found that Edn2-iKO mice displayed a reduced pro-neutrophilic inflammatory phenotype even after acute LPS treatment, shown by the reduction in the overall protein concentration and neutrophil count in bronchoalveolar lavage fluids. Further investigation revealed a reduction in mRNA interferon gamma (IFNγ) level of Edn2-iKO lungs and suppression of its downstream signaling, including phosphorylated level of STAT1 and IL-1β secretion, leading to reduced NFĸB activation. To conclude, Edn2 deletion suppressed acute lung inflammation by reducing neutrophil-mediated IFNγ/STAT1/IL-1β/NFĸB signaling cascade. Targeting Edn2 signaling may be beneficial for the development of novel treatment options for ALI.

Tissue-resident memory T cells and lung immunopathology

Rapid reaction to microbes invading mucosal tissues is key to protect the host against disease. Respiratory tissue-resident memory T (TRM ) cells provide superior immunity against pathogen infection and/or re-infection, due to their presence at the site of pathogen entry. However, there has been emerging evidence that exuberant TRM -cell responses contribute to the development of various chronic respiratory conditions including pulmonary sequelae post-acute viral infections. In this review, we have described the characteristics of respiratory TRM cells and processes underlying their development and maintenance. We have reviewed TRM -cell protective functions against various respiratory pathogens as well as their pathological activities in chronic lung conditions including post-viral pulmonary sequelae. Furthermore, we have discussed potential mechanisms regulating the pathological activity of TRM cells and proposed therapeutic strategies to alleviate TRM -cell-mediated lung immunopathology. We hope that this review provides insights toward the development of future vaccines or interventions that can harness the superior protective abilities of TRM cells, while minimizing the potential for immunopathology, a particularly important topic in the era of coronavirus disease 2019 (COVID-19) pandemic.

Recent progress and prospects for anti-cytokine therapy in preclinical and clinical acute lung injury

Acute respiratory distress syndrome (ARDS) is a heterogeneous cause of respiratory failure that has a rapid onset, a high mortality rate, and for which there is no effective pharmacological treatment. Current evidence supports a critical role of excessive inflammation in ARDS, resulting in several cytokines, cytokine receptors, and proteins within their downstream signalling pathways being putative therapeutic targets. However, unsuccessful trials of anti-inflammatory drugs have thus far hindered progress in the field. In recent years, the prospects of precision medicine and therapeutic targeting of cytokines coevolving into effective treatments have gained notoriety. There is an optimistic and growing understanding of ARDS subphenotypes as well as advances in treatment strategies and clinical trial design. Furthermore, large trials of anti-cytokine drugs in patients with COVID-19 have provided an unprecedented amount of information that could pave the way for therapeutic breakthroughs. While current clinical and nonclinical ARDS research suggest relatively limited potential in monotherapy with anti-cytokine drugs, combination therapy has emerged as an appealing strategy and may provide new perspectives on finding safe and effective treatments. Accurate evaluation of these drugs, however, also relies on well-founded experimental research and the implementation of biomarker-guided stratification in future trials. In this review, we provide an overview of anti-cytokine therapy for acute lung injury and ARDS, highlighting the current preclinical and clinical evidence for targeting the main cytokines individually and the therapeutic prospects for combination therapy.

Green synthesis of gold nanoparticles modulates lipopolysaccharide-induced lung inflammation in Wistar rats

This study aimed to investigate the effect of intranasal treatment of gold nanoparticles (GNPs) and Curcumin (Cur) on the lipopolysaccharide (LPS)-induced acute pulmonary inflammatory response. A single intraperitoneal injection of LPS (0.5 mg/Kg) was performed, and the animals in the Sham group were injected with 0.9% saline. Treatment was daily intranasally with GNPs (2.5 mg/L), Cur (10 mg/kg) and GNP-Cur started 12 h after LPS administration and ended on the seventh day. The results show that the treatment performed with GNP-Cur was the most effective to attenuate the action of pro-inflammatory cytokines, and a lower leukocyte count in the bronchoalveolar lavage, in addition to positively regulating anti-inflammatory cytokines in relation to other groups. As a result, it promoted an oxirreductive balanced environment in the lung tissue, providing a histological outcome with a reduction in inflammatory cells and greater alveolar area. The group treated with GNPs-Cur was superior to the other groups, with better anti-inflammatory activity and reduced oxidative stress, resulting in less morphological damage to lung tissue. In conclusion, the use of reduced GNPs with curcumin demonstrates promising effects in the control of the acute inflammatory response, helping to protect the lung tissue at the biochemical and morphological levels.

Epitope Mapping of an Anti-Mouse CCR2 Monoclonal Antibody (C2Mab-6) Using Enzyme-Linked Immunosorbent Assay

CC chemokine receptor type-2 (CCR2) is a member of the G protein-coupled receptors, and is mainly expressed on cell surface of immune cells. CCR2 binds to its ligand, C-C motif chemokine 2 (also named as monocyte chemoattractant protein-1), which involves in the tumor progression by modulating the tumor microenvironment. Therefore, the monoclonal antibody (mAb) targeting CCR2 could be one of the strategies for cancer treatment. In this study, we investigated the critical epitope of C₂Mab-6, an anti-mouse CCR2 (mCCR2) mAb developed by N-terminal peptides immunization. We first performed enzyme-linked immunosorbent assay (ELISA) using N-terminal peptides of mCCR2 and demonstrated that C₂Mab-6 recognizes 1-19 amino acids of mCCR2. We further performed ELISA using 20 alanine-substituted peptides of mCCR2. C₂Mab-6 lost the reaction to the alanine-substituted peptides of D3A, N4A, M6A, P8A, Q9A, and F10A. These results indicate that the binding epitope of C₂Mab-6 includes Asp3, Asn4, Met6, Pro8, Gln9, and Phe10 of mCCR2.

5-Methoxyflavone alleviates LPS-mediated lung injury by promoting Nrf2-mediated the suppression of NOX4/TLR4 axis in bronchial epithelial cells and M1 polarization in macrophages

BACKGROUND

Acute lung injury (ALI) arises from sepsis or bacterial infection, which are life-threatening respiratory disorders that cause the leading cause of death worldwide. 5-Methoxyflavone, a methylated flavonoid, is gaining increased attention for its various health benefits. In the current study, we investigated the potential effects of 5-methoxyflavone against LPS-mediated ALI and elucidated the corresponding possible mechanism.

METHODS

A mouse model with ALI was established by intratracheal instillation of LPS, and lung pathological changes, signaling pathway related proteins and apoptosis in lung tissues were estimated by H&E staining, immunofluorescence and TUNEL assay, respectively. Cell viability was evaluated by MTT assay; protein levels of pro-inflammatory mediators were measured by ELISA assay; levels of ROS and M1 macrophage polarization were assayed by flow cytometry; the expression of Nrf2 signaling, NOX4/TLR4 axis and P-STAT1 were detected by western blotting.

RESULTS

Our results showed that 5-methoxyflavone treatment inhibited LPS-induced expression of NOX4 and TLR4 as well as the activation of downstream signaling (NF-κB and P38 MAPK), which was accompanied by markedly decreased ROS levels and pro-inflammatory cytokines (IL-6, TNF-α, MCP-1, and IL-8) in BEAS-2B cells. Moreover, we revealed that these effects of 5-methoxyflavone were related to its Nrf2 activating property, and blockade of Nrf2 prevented its inhibitory effects on NOX4/TLR4/NF-κB/P38 MAPK signaling, thus abrogating the anti-inflammatory effects of 5-methoxyflavone. Besides, the Nrf2 activating property of 5-methoxyflavone in RAW264.7 cells led to inhibition of LPS/IFN-γ-mediated STAT1 signaling, resulting in suppression of LPS/IFN-γ-induced M1 macrophage polarization and the repolarization of M2 macrophages to M1. In a mouse model of LPS-induced ALI, 5-methoxyflavone administration ameliorated LPS-mediated lung pathological changes, the increased lung index (lung/body weight ratio), and epithelial cell apoptosis. Meanwhile, we found 5-methoxyflavone effectively suppressed the hyperactive signaling pathways and the production of excessive pro-inflammatory mediators. Moreover, 5-methoxyflavone reduced LPS-mediated M1 macrophage polarization associated with elevated P-STAT1 activation in the lung tissues. In addition, 5-methoxyflavone improved the survival of LPS-challenged mice.

CONCLUSION

These results indicated that 5-methoxyflavone might be suitable for the development of a novel drug for ALI therapeutic.

Cellular Heterogeneity and Molecular Reprogramming of the Host Response during Influenza Acute Lung Injury

An exuberant host response contributes to influenza A virus (IAV) (or influenza)-mediated lung injury. However, despite significant information on the host response to IAV, the cellular framework and molecular interactions that dictate the development of acute injury in IAV-infected lungs remain incompletely understood. We performed an unbiased single-cell RNA sequencing (scRNAseq) analysis to examine the cellular heterogeneity and regulation of host responses in the IAV model of acute lung injury. At the cellular level, IAV infection promoted the overwhelming recruitment of monocytes that exhibited the cell differentiation trajectory to monocyte-derived macrophages. Together, monocytes and monocyte-derived myeloid cells constituted over 50% of the total immune cells in IAV-infected lungs. In contrast, IAV infection resulted in a significant loss of nonhematopoietic cells. Molecularly, our data show the multidimensional cell-cell communication dynamics of interferon and chemokine signaling between immune and nonimmune cells and the cell-specific molecular pathways regulating the host responses during IAV-induced lung injury. Our data provide a foundation for further exploring the mechanistic association of the IAV host response with acute lung injury. IMPORTANCE A dysregulated host response develops acute lung injury during IAV infection. However, the pathological immune mechanism(s) associated with acute lung injury during IAV infection is yet to be elucidated. In this study, we performed scRNAseq to examine the dynamics of host responses during the peak of IAV-mediated lung injury. At the cellular level, our data reveal significant myelopoiesis predominated by monocytes and macrophages and the simultaneous disruption of the nonhematopoietic cell framework, crucial for regulating inflammation and barrier integrity in IAV-infected lungs. Molecularly, we observed a complex cellular network involving cell-cell communications and a number of unique regulons dictating the outcome of interferon and chemokine responses during peak lung injury. Our data present a unique atlas of cellular changes and the regulation of global and cell-specific host responses during IAV infection. We expect that this information will open new avenues to identify targets for therapeutic intervention against IAV lung injury.

Human placental hematopoietic stem cell-derived natural killer cells (CYNK) recognize and eliminate influenza A virus-infected cells

Influenza A virus (IAV) infections are a significant recurrent threat to public health and a significant burden on global economy, highlighting the need for developing more effective therapies. Natural killer (NK) cells play a pivotal role in the control of pulmonary IAV infection, however, little is known about the therapeutic potential of adoptively transferred NK cells for viral infections. Here, we investigated the antiviral activity of CYNK, human placental hematopoietic stem cell-derived NK cells, against IAV infection in vitro. Virus infection induced the expression of NK cell activating ligands on respiratory epithelial cells, resulting in enhanced recognition by CYNK cells. Upon co-culture with IAV-infected epithelial cells, CYNK exhibited elevated degranulation and increased production of IFN-γ, TNF-α and GM-CSF in a virus dose-dependent manner. Furthermore, CYNK showed virus dose-dependent cytotoxicity against IAV-infected cells. The antiviral activity of CYNK was mediated by NKp46 and NKG2D. Together, these data demonstrate that CYNK possesses potent antiviral function against IAV and warrant clinical investigations for adoptive NK cell therapies against viral infections.

IFN-γ transforms the transcriptomic landscape and triggers myeloid cell hyperresponsiveness to cause lethal lung injury

Acute Respiratory Distress Syndrome (ARDS) is an inflammatory disease that is associated with high mortality but no specific treatment. Our understanding of initial events that trigger ARDS pathogenesis is limited. We have developed a mouse model of inflammatory lung injury by influenza and methicillin-resistant Staphylococcus aureus (MRSA) coinfection plus daily antibiotic therapy. Using this pneumonic ARDS model, here we show that IFN-γ receptor signaling drives inflammatory cytokine storm and lung tissue damage. By single-cell RNA sequencing (scRNA-seq) analysis, we demonstrate that IFN-γ signaling induces a transcriptional shift in airway immune cells, particularly by upregulating macrophage and monocyte expression of genes associated with inflammatory diseases. Further evidence from conditional knockout mouse models reveals that IFN-γ receptor signaling in myeloid cells, particularly CD11c+ mononuclear phagocytes, directly promotes TNF-α hyperproduction and inflammatory lung damage. Collectively, the findings from this study, ranging from cell-intrinsic gene expression to overall disease outcome, demonstrate that influenza-induced IFN-γ triggers myeloid cell hyperresponsiveness to MRSA, thereby leading to excessive inflammatory response and lethal lung damage during coinfection.

Considerations of CD8+ T Cells for Optimized Vaccine Strategies Against Respiratory Viruses

The primary goal of vaccines that protect against respiratory viruses appears to be the induction of neutralizing antibodies for a long period. Although this goal need not be changed, recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants have drawn strong attention to another arm of acquired immunity, CD8⁺ T cells, which are also called killer T cells. Recent evidence accumulated during the coronavirus disease 2019 (COVID-19) pandemic has revealed that even variants of SARS-CoV-2 that escaped from neutralizing-antibodies that were induced by either infection or vaccination could not escape from CD8⁺ T cell-mediated immunity. In addition, although traditional vaccine platforms, such as inactivated virus and subunit vaccines, are less efficient in inducing CD8⁺ T cells, newly introduced platforms for SARS-CoV-2, namely, mRNA and adenoviral vector vaccines, can induce strong CD8⁺ T cell-mediated immunity in addition to inducing neutralizing antibodies. However, CD8⁺ T cells function locally and need to be at the site of infection to control it. To fully utilize the protective performance of CD8⁺ T cells, it would be insufficient to induce only memory cells circulating in blood, using injectable vaccines; mucosal immunization could be required to set up CD8⁺ T cells for the optimal protection. CD8⁺ T cells might also contribute to the pathology of the infection, change their function with age and respond differently to booster vaccines in comparison with antibodies. Herein, we overview cutting-edge ideas on CD8⁺ T cell-mediated immunity that can enable the rational design of vaccines for respiratory viruses.