Inhibition of the NOD-Like Receptor Protein 3 Inflammasome Is Protective in Juvenile Influenza A Virus Infection

Sangju Cold Granule exerts anti-viral and anti-inflammatory activities against influenza A virus in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Sangju Cold Granule (SJCG) is a classical traditional Chinese medicine (TCM) prescription described in "Item Differentiation of Warm Febrile Diseases". Historically, SJCG was employed to treat respiratory illnesses. Despite its popular usage, the alleviating effect of SJCG on influenza A virus infection and its mechanisms have not been fully elucidated.

AIM OF THE STUDY

Influenza is a severe respiratory disease that threatens human health. This study aims to assess the therapeutic potential of SJCG and the possible molecular mechanism underlying its activity against influenza A virus in vitro and in vivo.

MATERIALS AND METHODS

Ultrahigh-performance liquid chromatography (UPLC)-Q-Exactive was used to identify the components of SJCG. The 50% cytotoxic concentration of SJCG in MDCK and A549 cells were determined using the CCK-8 assay. The activity of SJCG against influenza A virus H1N1 was evaluated in vitro using plaque reduction and progeny virus titer reduction assays. RT-qPCR was performed to obtain the expression levels of inflammatory mediators and the transcriptional regulation of RIG-I and MDA5 in H1N1-infected A549 cells. Then, the mechanism of SJCG effect on viral replication and inflammation was further explored by measuring the expressions of proteins of the RIG-I/NF-kB/IFN(I/III) signaling pathway by Western blot. The impact of SJCG was explored in vivo in an intranasally H1N1-infected BALB/c mouse pneumonia model treated with varying doses of SJCG. The protective role of SJCG in this model was evaluated by survival, body weight monitoring, lung viral titers, lung index, lung histological changes, lung inflammatory mediators, and peripheral blood leukocyte count.

RESULTS

The main SJCG chemical constituents were flavonoids, carbohydrates and glycosides, amino acids, peptides, and derivatives, organic acids and derivatives, alkaloids, fatty acyls, and terpenes. The CC50 of SJCG were 24.43 mg/mL on MDCK cells and 20.54 mg/mL on A549 cells, respectively. In vitro, SJCG significantly inhibited H1N1 replication and reduced the production of TNF-α, IFN-β, IL-6, IL-8, IL-13, IP-10, RANTES, TRAIL, and SOCS1 in infected A549 cells. Intracellularly, SJCG reduced the expression of RIG-I, MDA5, P-NF-κB P65 (P-P65), P-IκBα, P-STAT1, P-STAT2, and IRF9. In vivo, SJCG enhanced the survival rate and decreased body weight loss in H1N1-infected mice. Mice with H1N1-induced pneumonia treated with SJCG showed a lower lung viral load and lung index than untreated mice. SJCG effectively alleviated lung damage and reduced the levels of TNF-α, IFN-β, IL-6, IP-10, RANTES, and SOCS1 in lung tissue. Moreover, SJCG significantly ameliorated H1N1-induced leukocyte changes in peripheral blood.

CONCLUSIONS

SJCG significantly reduced influenza A virus and virus-mediated inflammation through inhibiting the RIG-I/NF-kB/IFN(I/III) signaling pathway. Thus, SJCG could provide an effective TCM for influenza treatment.

NLRP3 Inflammasomes: Dual Function in Infectious Diseases

The Nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome has been the most distinctive polymer protein complex. After recognizing the endogenous and exogenous danger signals, NLRP3 can cause inflammation by pyroptosis and secretion of mature, bioactive forms of IL-1β and IL-18. The NLRP3 inflammasome is essential in the genesis and progression of infectious illnesses. Herein, we provide a comprehensive review of the NLRP3 inflammasome in infectious diseases, focusing on its two-sided effects. As an essential part of host defense with a protective impact, abnormal NLRP3 inflammasome activation, however, result in a systemic high inflammatory response, leading to subsequent damage. In addition, scientific evidence of small molecules, biologics, and phytochemicals acting on the NLRP3 inflammasome has been reviewed. We believe that the NLRP3 inflammasome helps us understand the pathological mechanism of different stages of infectious diseases and that inhibitors targeting the NLRP3 inflammasome will become a new and valuable research direction for the treatment of infectious diseases.

Xiaoer niuhuang qingxin powder alleviates influenza a virus infection by inhibiting the activation of the TLR4/MyD88/NF-κB signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Xiaoer Niuhuang Qingxin Powder (XNQP) is a classic traditional Chinese medicine formula with significant clinical efficacy for treating febrile convulsions and influenza.

AIM OF THE STUDY

This study aims to explore the potential mechanisms of XNQP in combating combating the influenza A virus, providing a theoretical basis for its clinical application.

MATERIALS AND METHODS

The present investigation employed network pharmacology and bioinformatics analysis to determine the TLR4/MyD88/NF-κB signaling pathway as a viable target for XNQP intervention in IAV infection.Subsequently, a mouse model of influenza A virus infection was established, and different doses of XNQP were used for intervention. The protein expression levels of TLR4/MyD88/NF-κB were detected using HE staining, Elisa, immunohistochemistry, immunofluorescence, and western blot.

RESULTS

The results showed that treatment with XNQP after IAV infection reduced the mortality and prolonged the survival time of infected mice. It reduced the release of TNF-α and IFN-γ in the serum and alleviated pathological damage in the lung tissue following infection. Additionally, the levels of TLR4, MyD88, NF-κB, and p-NF-κB P65 proteins were significantly reduced in lung tissue by XNQP. The inhibitory effect of XNQP on the expression of MyD88 and NF-κB was antagonized when TLR4 signaling was overexpressed. Consequently, the expression levels of MyD88, NF-κB, and p-NF-κB P65 were increased in lung tissue. Conversely, the expression levels of the proteins MyD88, NF-κB, and p-NF-κB P65 were downregulated when TLR4 signaling was inhibited.

CONCLUSIONS

XNQP alleviated lung pathological changes, reduced serum levels of inflammatory factors, reduced mortality, and prolonged survival time in mice by inhibiting the overexpression of the TLR4/MyD88/NF-κB signaling pathway in lung tissues after IAV infection.

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.

A pivotal role for the IL-1β and the inflammasome in preterm labor

During labor, monocytes infiltrate massively the myometrium and differentiate into macrophages secreting high levels of reactive oxygen species and of pro-inflammatory cytokines (i.e. IL-1β), leading to myometrial contraction. Although IL-1β is clearly implicated in labor, its function and that of the inflammasome complex that cleaves the cytokine in its active form, has never been studied on steps preceding contraction. In this work, we used our model of lipopolysaccharide-induced preterm labor to highlight their role. We demonstrated that IL-1β was secreted by the human myometrium during labor or in presence of infection and was essential for myometrial efficient contractions as its blockage with an IL-1 receptor antagonist (Anakinra) or a neutralizing antibody completely inhibited the induced contractions. We evaluated the implication of the inflammasome on myometrial contractions and differentiation stages of labor onset. We showed that the effects of macrophage-released IL-1β in myometrial cell transactivation were blocked by inhibition of the inflammasome, suggesting that the inflammasome by producing IL-1β was essential in macrophage/myocyte crosstalk during labor. These findings provide novel innovative approaches in the management of preterm labor, specifically the use of an inflammasome inhibitor to block the precursor stages of labor before the acquisition of the contractile phenotype.

The Mobility of Eurasian Avian-like M2 Is Determined by Residue E79 Which Is Essential for Pathogenicity of 2009 Pandemic H1N1 Influenza Virus in Mice

In 2009, a novel H1N1 influenza virus caused the first influenza pandemic of the 21st century. Studies have shown that the influenza M gene played important roles in the pathogenicity and transmissibility of the 2009 H1N1 pandemic ((H1N1)pdm09), whilst the underlying mechanism remains unclear. The influenza M gene encodes two proteins, matrix protein 1 and matrix protein 2, which play important roles in viral replication and assembly. In this study, it is found that the M2 protein of the (H1N1)pdm09 virus showed a lower mobility rate than the North America triple-reassortant influenza M2 protein in Polyacrylamide Gel Electrophoresis (PAGE). The site-directed mutations of the amino acids of (H1N1)pdm09 M2 revealed that E79 is responsible for the mobility rate change. Further animal studies showed that the (H1N1)pdm09 containing a single M2-E79K was significantly attenuated compared with the wild-type virus in mice and induced lower proinflammatory cytokines and IFNs in mouse lungs. Further in vitro studies indicated that this mutation also affected NLRP3 inflammasome activation. To reveal the reason why they have different mobility rates, a circular dichroism spectra assay was employed and showed that the two M2 proteins displayed different secondary structures. Overall, our findings suggest that M2 E79 is important for the virus replication and pathogenicity of (H1N1)pdm09 through NLRP3 inflammasome and proinflammatory response.

Phillyrin ameliorates influenza a virus-induced pulmonary inflammation by antagonizing CXCR2 and inhibiting NLRP3 inflammasome activation

Influenza is an acute viral respiratory illness with high morbidity rates worldwide. Excessive pulmonary inflammation is the main characteristic of lethal influenza A virus (IAV) infections. Therapeutic options for managing influenza are limited to vaccines and some antiviral medications. Phillyrin is one of the major bioactive components of the Chinese herbal medicine Forsythia suspensa, which has the functions of sterilization, heat clearing and detoxification. In this work, the effect and mechanism of phillyrin on H1N1 influenza (PR8)-induced pneumonia were investigated. We reported that phillyrin (15 mg/kg) treatment after viral challenge significantly improved the weight loss, ameliorated pulmonary inflammation and inhibited the accumulation of multiple cytokines and chemokines in bronchoalveolar lavage fluid on 7 days post infection (dpi). In vitro, phillyrin suppressed influenza viral replication (Matrixprotein and nucleoprotein messenger RNA level) and reduced influenza virus-induced cytopathic effect (CPE). Furthermore,chemokine receptor CXCR2 was confirmed to be markedly inhibited by phillyrin. Surface plasmon resonance results reveal that phillyrin exhibits binding affinity to CXCR2, having a binding affinity constant (KD) value of 1.858e-5 M, suggesting that CXCR2 is a potential therapeutic target for phillyrin. Moreover, phillyrin inhibited the mRNA and protein expression levels of Caspase1, ASC and NLRP3 in the lungs of mice with H1N1-induced pneumonia.This study reveals that phillyrin ameliorates IAV-induced pulmonary inflammation by antagonizing CXCR2 and inhibiting NLRP3 inflammasome activation partly.

Interaction among inflammasome, PANoptosise, and innate immune cells in infection of influenza virus: Updated review

BACKGROUND

Influenza virus (IV) is a leading cause of respiratory tract infections, eliciting responses from key innate immune cells such as Macrophages (MQs), Neutrophils, and Dendritic Cells (DCs). These cells employ diverse mechanisms to combat IV, with Inflammasomes playing a pivotal role in viral infection control. Cellular death mechanisms, including Pyroptosis, Apoptosis, and Necroptosis (collectively called PANoptosis), significantly contribute to the innate immune response.

METHODS

In this updated review, we delve into the intricate relationship between PANoptosis and Inflammasomes within innate immune cells (MQs, Neutrophils, and DCs) during IV infections. We explore the strategies employed by IV to evade these immune defenses and the consequences of unchecked PANoptosis and inflammasome activation, including the potential development of severe complications such as cytokine storms and tissue damage.

RESULTS

Our analysis underscores the interplay between PANoptosis and Inflammasomes as a critical aspect of the innate immune response against IV. We provide insights into IV's various mechanisms to subvert these immune pathways and highlight the importance of understanding these interactions to develop effective antiviral medications.

CONCLUSION

A comprehensive understanding of the dynamic interactions between PANoptosis, Inflammasomes, and IV is essential for advancing our knowledge of innate immune responses to viral infections. This knowledge will be invaluable in developing targeted antiviral therapies to combat IV and mitigate potential complications, including cytokine storms and tissue damage.

Bat ASC2 suppresses inflammasomes and ameliorates inflammatory diseases

Bats are special in their ability to live long and host many emerging viruses. Our previous studies showed that bats have altered inflammasomes, which are central players in aging and infection. However, the role of inflammasome signaling in combating inflammatory diseases remains poorly understood. Here, we report bat ASC2 as a potent negative regulator of inflammasomes. Bat ASC2 is highly expressed at both the mRNA and protein levels and is highly potent in inhibiting human and mouse inflammasomes. Transgenic expression of bat ASC2 in mice reduced the severity of peritonitis induced by gout crystals and ASC particles. Bat ASC2 also dampened inflammation induced by multiple viruses and reduced mortality of influenza A virus infection. Importantly, it also suppressed SARS-CoV-2-immune-complex-induced inflammasome activation. Four key residues were identified for the gain of function of bat ASC2. Our results demonstrate that bat ASC2 is an important negative regulator of inflammasomes with therapeutic potential in inflammatory diseases.

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

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

Identification of key proteins of cytopathic biotype bovine viral diarrhoea virus involved in activating NF-κB pathway in BVDV-induced inflammatory response

Bovine viral diarrhoea virus (BVDV) is the etiologic agent of bovine viral diarrhea-mucosal disease, one of the most important viral diseases in cattle, with inflammatory diarrhea, enteritis, and mucosa necrosis as the major clinical manifestations. NF-κB is an important transcription complex that regulates the expression of genes involved in inflammation and immune responses. NLRP3 inflammasome plays a key role in the development of inflammatory diseases. However, whether the activation of NF-κB is crucial for BVDV infection-induced inflammatory responses remains unclear. The results of our present study showed that BVDV infection significantly activated the NF-κB pathway and promoted the expression of NLRP3 inflammasome components (NLRP3, ASC, pro-caspase 1) as well inflammatory cytokine pro-IL-1β in BVDV-infected bovine cells, resulting in the cleavage of pro-caspase 1 and pro-IL-1β into active form caspase 1 and IL-1β. However, the levels of the NLRP3 inflammasome components and inflammatory cytokines were obviously inhibited, as well the cleavage of pro-caspase 1 and pro-IL-1β in the pre-treated bovine cells with NF-κB-specific inhibitors after BVDV infection. Further, cytopathic biotype BVDV (cpBVDV) Erns and NS5A proteins with their key functional domains contributed to BVDV-induced inflammatory responses via activating the NF-κB pathway were confirmed experimentally. Especially, the NS5A can promote cholesterol synthesis and accelerate its augmentation, further activating the NF-κB signalling pathway. Conclusively, our data elucidate that the activation of NF-κB signaling pathway plays a crucial role in cpBVDV infection-induced inflammatory responses.

Influenza a virus triggers acute exacerbation of chronic obstructive pulmonary disease by increasing proinflammatory cytokines secretion via NLRP3 inflammasome activation

Background

Influenza A virus (IAV) triggers acute exacerbation of chronic obstructive pulmonary disease (AECOPD), but the molecular mechanisms remain unclear. In this study, we investigated the role of IAV induced NLRP3 inflammasome activation to increase airway inflammation response in the progression of AECOPD.

Methods

Human bronchial epithelial cells were isolated and cultured from normal and COPD bronchial tissues and co-cultured with IAV. The NLRP3 inflammasome associated genes were identified using RNA sequencing, and the expressions of NLRP3 inflammasome components were measured using qRT-PCR and western blot after cells were transfected with siRNA and treated with MCC950. Moreover, IAV-induced COPD rat models were established to confirm the results; 37 AECOPD patients were included to measure the serum and bronchoalveolar lavage fluid (BALF) of interleukin (IL)-18 and IL-1β.

Results

Increased levels of NLRP3 inflammasome components were not seen until 6 h post-inoculation in normal cells. However, both cell groups reached peak NLRP3 level at 12 h post-inoculation and maintained it for up to 24 h. ASC, Caspase-1, IL-1β and IL-18 were also elevated in a similar time-dependent pattern in both cell groups. The mRNA and protein expression of the NLRP3 inflammasome components were decreased when COPD cells treated with siRNA and MCC950. In COPD rats, the NLRP3 inflammasome components were elevated by IAV. MCC950 alleviated lung damage, improved survival time, and reduced NLRP3 inflammasome components expression in COPD rats. Additionally, the serum and BALF levels of IL-1β and IL-18 were increased in AECOPD patients.

Conclusions

NLRP3 inflammasome is activated in COPD patients as a pre-existing condition that is further exacerbated by IAV infection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12950-022-00305-y.

The multifaceted roles of NLRP3-modulating proteins in virus infection

The innate immune response to viruses is critical for the correct establishment of protective adaptive immunity. Amongst the many pathways involved, the NLRP3 [nucleotide-binding oligomerisation domain (NOD)-like receptor protein 3 (NLRP3)] inflammasome has received considerable attention, particularly in the context of immunity and pathogenesis during infection with influenza A (IAV) and SARS-CoV-2, the causative agent of COVID-19. Activation of the NLRP3 inflammasome results in the secretion of the proinflammatory cytokines IL-1β and IL-18, commonly coupled with pyroptotic cell death. While this mechanism is protective and key to host defense, aberrant NLRP3 inflammasome activation causes a hyperinflammatory response and excessive release of cytokines, both locally and systemically. Here, we discuss key molecules in the NLRP3 pathway that have also been shown to have significant roles in innate and adaptive immunity to viruses, including DEAD box helicase X-linked (DDX3X), vimentin and macrophage migration inhibitory factor (MIF). We also discuss the clinical opportunities to suppress NLRP3-mediated inflammation and reduce disease severity.

The cytokine storms of COVID-19, H1N1 influenza, CRS and MAS compared. Can one sized treatment fit all?

An analysis of published data appertaining to the cytokine storms of COVID-19, H1N1 influenza, cytokine release syndrome (CRS), and macrophage activation syndrome (MAS) reveals many common immunological and biochemical abnormalities. These include evidence of a hyperactive coagulation system with elevated D-dimer and ferritin levels, disseminated intravascular coagulopathy (DIC) and microthrombi coupled with an activated and highly permeable vascular endothelium. Common immune abnormalities include progressive hypercytokinemia with elevated levels of TNF-α, interleukin (IL)-6, and IL-1β, proinflammatory chemokines, activated macrophages and increased levels of nuclear factor kappa beta (NFκB). Inflammasome activation and release of damage associated molecular patterns (DAMPs) is common to COVID-19, H1N1, and MAS but does not appear to be a feature of CRS. Elevated levels of IL-18 are detected in patients with COVID-19 and MAS but have not been reported in patients with H1N1 influenza and CRS. Elevated interferon-γ is common to H1N1, MAS, and CRS but levels of this molecule appear to be depressed in patients with COVID-19. CD4+ T, CD8+ and NK lymphocytes are involved in the pathophysiology of CRS, MAS, and possibly H1N1 but are reduced in number and dysfunctional in COVID-19. Additional elements underpinning the pathophysiology of cytokine storms include Inflammasome activity and DAMPs. Treatment with anakinra may theoretically offer an avenue to positively manipulate the range of biochemical and immune abnormalities reported in COVID-19 and thought to underpin the pathophysiology of cytokine storms beyond those manipulated via the use of, canakinumab, Jak inhibitors or tocilizumab. Thus, despite the relative success of tocilizumab in reducing mortality in COVID-19 patients already on dexamethasone and promising results with Baricitinib, the combination of anakinra in combination with dexamethasone offers the theoretical prospect of further improvements in patient survival. However, there is currently an absence of trial of evidence in favour or contravening this proposition. Accordingly, a large well powered blinded prospective randomised controlled trial (RCT) to test this hypothesis is recommended.

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.

Nrf2 activation putatively mediates clinical benefits of low-dose radiotherapy in COVID-19 pneumonia and acute respiratory distress syndrome (ARDS): Novel mechanistic considerations

Novel mechanistic insights are discussed herein that link a single, nontoxic, low-dose radiotherapy (LDRT) treatment (0.5-1.0 Gy) to (1) beneficial subcellular effects mediated by the activation of nuclear factor erythroid 2-related transcription factor (Nrf2) and to (2) favorable clinical outcomes for COVID-19 pneumonia patients displaying symptoms of acute respiratory distress syndrome (ARDS). We posit that the favorable clinical outcomes following LDRT result from potent Nrf2-mediated antioxidant responses that rebalance the oxidatively skewed redox states of immunological cells, driving them toward anti-inflammatory phenotypes. Activation of Nrf2 by ionizing radiation is highly dose dependent and conforms to the features of a biphasic (hormetic) dose-response. At the cellular and subcellular levels, hormetic doses of <1.0 Gy induce polarization shifts in the predominant population of lung macrophages, from an M1 pro-inflammatory to an M2 anti-inflammatory phenotype. Together, the Nrf2-mediated antioxidant responses and the subsequent shifts to anti-inflammatory phenotypes have the capacity to suppress cytokine storms, resolve inflammation, promote tissue repair, and prevent COVID-19-related mortality. Given these mechanistic considerations-and the historical clinical success of LDRT early in the 20th century-we opine that LDRT should be regarded as safe and effective for use at almost any stage of COVID-19 infection. In theory, however, optimal life-saving potential is thought to occur when LDRT is applied prior to the cytokine storms and before the patients are placed on mechanical oxygen ventilators. The administration of LDRT either as an intervention of last resort or too early in the disease progression may be far less effective in saving the lives of ARDS patients.

Pharmacological Inhibition of the Nod-Like Receptor Family Pyrin Domain Containing 3 Inflammasome with MCC950

Activation of the Nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome drives release of the proinflammatory cytokines interleukin (IL)-1β and IL-18 and induces pyroptosis (lytic cell death). These events drive chronic inflammation, and as such, NLRP3 has been implicated in a large number of human diseases. These range from autoimmune conditions, the simplest of which is NLRP3 gain-of-function mutations leading to an orphan disease, cryopyrin-associated period syndrome, to large disease burden indications, such as atherosclerosis, heart failure, stroke, neurodegeneration, asthma, ulcerative colitis, and arthritis. The potential clinical utility of NLRP3 inhibitors is substantiated by an expanding list of indications in which NLRP3 activation has been shown to play a detrimental role. Studies of pharmacological inhibition of NLRP3 in nonclinical models of disease using MCC950 in combination with human genetics, epigenetics, and analyses of the efficacy of biologic inhibitors of IL-1β, such as anakinra and canakinumab, can help to prioritize clinical trials of NLRP3-directed therapeutics. Although MCC950 shows excellent (nanomolar) potency and high target selectivity, its pharmacokinetic and toxicokinetic properties limited its therapeutic development in the clinic. Several improved, next-generation inhibitors are now in clinical trials. Hence the body of research in a plethora of conditions reviewed herein may inform analysis of the potential translational value of NLRP3 inhibition in diseases with significant unmet medical need. SIGNIFICANCE STATEMENT: The nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome is one of the most widely studied and best validated biological targets in innate immunity. Activation of NLRP3 can be inhibited with MCC950, resulting in efficacy in more than 100 nonclinical models of inflammatory diseases. As several next-generation NLRP3 inhibitors are entering proof-of-concept clinical trials in 2020, a review of the pharmacology of MCC950 is timely and significant.

The Role of Innate Immunity in Pulmonary Infections

Innate immunity forms a protective line of defense in the early stages of pulmonary infection. The primary cellular players of the innate immunity against respiratory infections are alveolar macrophages (AMs), dendritic cells (DCs), neutrophils, natural killer (NK) cells, and innate lymphoid cells (ILCs). They recognize conserved structures of microorganisms through membrane-bound and intracellular receptors to initiate appropriate responses. In this review, we focus on the prominent roles of innate immune cells and summarize transmembrane and cytosolic pattern recognition receptor (PRR) signaling recognition mechanisms during pulmonary microbial infections. Understanding the mechanisms of PRR signal recognition during pulmonary pathogen infections will help us to understand pulmonary immunopathology and lay a foundation for the development of effective therapies to treat and/or prevent pulmonary infections.

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.

Inhibition of the NLRP3 inflammasome can prevent sterile intra-amniotic inflammation, preterm labor/birth, and adverse neonatal outcomes†

Sterile intra-amniotic inflammation is commonly observed in patients with spontaneous preterm labor, a syndrome that commonly precedes preterm birth, the leading cause of perinatal morbidity and mortality worldwide. However, the mechanisms leading to sterile intra-amniotic inflammation are poorly understood and no treatment exists for this clinical condition. Herein, we investigated whether the alarmin S100B could induce sterile intra-amniotic inflammation by activating the NLRP3 inflammasome, and whether the inhibition of this pathway could prevent preterm labor/birth and adverse neonatal outcomes. We found that the ultrasound-guided intra-amniotic administration of S100B induced a 50% rate of preterm labor/birth and a high rate of neonatal mortality (59.7%) without altering the fetal and placental weights. Using a multiplex cytokine array and immunoblotting, we reported that S100B caused a proinflammatory response in the amniotic cavity and induced the activation of the NLRP3 inflammasome in the fetal membranes, indicated by the upregulation of the NLRP3 protein and increased release of active caspase-1 and mature IL-1β. Inhibition of the NLRP3 inflammasome via the specific inhibitor MCC950 prevented preterm labor/birth by 35.7% and reduced neonatal mortality by 26.7%. Yet, inhibition of the NLRP3 inflammasome at term did not drastically obstruct the physiological process of parturition. In conclusion, the data presented herein indicate that the alarmin S100B can induce sterile intra-amniotic inflammation, preterm labor/birth, and adverse neonatal outcomes by activating the NLRP3 inflammasome, which can be prevented by inhibiting such a pathway. These findings provide evidence that sterile intra-amniotic inflammation could be treated by targeting the NLRP3 inflammasome.

Intra-amniotic inflammation induces preterm birth by activating the NLRP3 inflammasome†

Intra-amniotic inflammation is strongly associated with spontaneous preterm labor and birth, the leading cause of perinatal mortality and morbidity worldwide. Previous studies have suggested a role for the NLRP3 (NLR family pyrin domain-containing protein 3) inflammasome in the mechanisms that lead to preterm labor and birth. However, a causal link between the NLRP3 inflammasome and preterm labor/birth induced by intra-amniotic inflammation has not been established. Herein, using an animal model of lipopolysaccharide-induced intra-amniotic inflammation (IAI), we demonstrated that there was priming of the NLRP3 inflammasome (1) at the transcriptional level, indicated by enhanced mRNA expression of inflammasome-related genes (Nlrp3, Casp1, Il1b); and (2) at the protein level, indicated by greater protein concentrations of NLRP3, in both the fetal membranes and decidua basalis prior to preterm birth. Additionally, we showed that there was canonical activation of the NLRP3 inflammasome in the fetal membranes, but not in the decidua basalis, prior to IAI-induced preterm birth as evidenced by increased protein levels of active caspase-1. Protein concentrations of released IL1β were also increased in both the fetal membranes and decidua basalis, as well as in the amniotic fluid, prior to IAI-induced preterm birth. Finally, using the specific NLRP3 inhibitor, MCC950, we showed that in vivo inhibition of the NLRP3 inflammasome reduced IAI-induced preterm birth and neonatal mortality. Collectively, these results provide a causal link between NLRP3 inflammasome activation and spontaneous preterm labor and birth in the context of intra-amniotic inflammation. We also showed that, by targeting the NLRP3 inflammasome, adverse pregnancy and neonatal outcomes can be significantly reduced.

Recent Insight into SARS-CoV2 Immunopathology and Rationale for Potential Treatment and Preventive Strategies in COVID-19

As the outbreak of the new coronavirus (SARS-CoV-2) infection is spreading globally, great effort is being made to understand the disease pathogenesis and host factors that predispose to disease progression in an attempt to find a window of opportunity for intervention. In addition to the direct cytopathic effect of the virus, the host hyper-inflammatory response has emerged as a key factor in determining disease severity and mortality. Accumulating clinical observations raised hypotheses to explain why some patients develop more severe disease while others only manifest mild or no symptoms. So far, Covid-19 management remains mainly supportive. However, many researches are underway to clarify the role of antiviral and immunomodulating drugs in changing morbidity and mortality in patients who become severely ill. This review summarizes the current state of knowledge on the interaction between SARS-CoV-2 and the host immune system and discusses recent findings on proposed pharmacologic treatments.

Pharmacological inhibition of the NLRP3 inflammasome reduces blood pressure, renal damage, and dysfunction in salt-sensitive hypertension

Aims

Renal inflammation, leading to fibrosis and impaired function is a major contributor to the development of hypertension. The NLRP3 inflammasome mediates inflammation in several chronic diseases by processing the cytokines pro-interleukin (IL)-1β and pro-IL-18. In this study, we investigated whether MCC950, a recently-identified inhibitor of NLRP3 activity, reduces blood pressure (BP), renal inflammation, fibrosis and dysfunction in mice with established hypertension.

Methods and results

C57BL6/J mice were made hypertensive by uninephrectomy and treatment with deoxycorticosterone acetate (2.4 mg/day, s.c.) and 0.9% NaCl in the drinking water (1K/DOCA/salt). Normotensive controls were uninephrectomized and received normal drinking water. Ten days later, mice were treated with MCC950 (10 mg/kg/day, s.c.) or vehicle (saline, s.c.) for up to 25 days. BP was monitored by tail-cuff or radiotelemetry; renal function by biochemical analysis of 24-h urine collections; and kidney inflammation/pathology was assessed by real-time PCR for inflammatory gene expression, flow cytometry for leucocyte influx, and Picrosirius red histology for collagen. Over the 10 days post-surgery, 1K/DOCA/salt-treated mice became hypertensive, developed impaired renal function, and displayed elevated renal levels of inflammatory markers, collagen and immune cells. MCC950 treatment from day 10 attenuated 1K/DOCA/salt-induced increases in renal expression of inflammasome subunits (NLRP3, ASC, pro-caspase-1) and inflammatory/injury markers (pro-IL-18, pro-IL-1β, IL-17A, TNF-α, osteopontin, ICAM-1, VCAM-1, CCL2, vimentin), each by 25–40%. MCC950 reduced interstitial collagen and accumulation of certain leucocyte subsets in kidneys of 1K/DOCA/salt-treated mice, including CD206⁺ (M2-like) macrophages and interferon-gamma-producing T cells. Finally, MCC950 partially reversed 1K/DOCA/salt-induced elevations in BP, urine output, osmolality, [Na⁺], and albuminuria (each by 20–25%). None of the above parameters were altered by MCC950 in normotensive mice.

Conclusion

MCC950 was effective at reducing BP and limiting renal inflammation, fibrosis and dysfunction in mice with established hypertension. This study provides proof-of-concept that pharmacological inhibition of the NLRP3 inflammasome is a viable anti-hypertensive strategy.

Newcastle disease virus RNA-induced IL-1β expression via the NLRP3/caspase-1 inflammasome

Newcastle disease virus (NDV) infection causes severe inflammation and is a highly contagious disease in poultry. Virulent NDV strains (GM) induce large quantities of interleukin-1β (IL-1β), which is the central mediator of the inflammatory reaction. Excessive expression of IL-1β exacerbates inflammatory damage. Therefore, exploring the mechanisms underlying NDV-induced IL-1β expression can aid in further understanding the pathogenesis of Newcastle disease. Here, we showed that anti-IL-1β neutralizing antibody treatment decreased body temperature and mortality following infection with virulent NDV. We further explored the primary molecules involved in NDV-induced IL-1β expression from the perspective of both the host and virus. This study showed that overexpression of NLRP3 resulted in increased IL-1β expression, whereas inhibition of NLRP3 or caspase-1 caused a significant reduction in IL-1β expression, indicating that the NLRP3/caspase-1 axis is involved in NDV-induced IL-1β expression. Moreover, ultraviolet-inactivated GM (chicken/Guangdong/GM/2014) NDV failed to induce the expression of IL-1β. We then collected virus from GM-infected cell culture supernatant using ultracentrifugation, extracted the viral RNA, and stimulated the cells further with GM RNA. The results revealed that RNA alone was capable of inducing IL-1β expression. Moreover, NLRP3/caspase-1 was involved in GM RNA-induced IL-1β expression. Thus, our study elucidated the critical role of IL-1β in the pathogenesis of Newcastle disease while also demonstrating that inhibition of IL-1β via anti-IL-1β neutralizing antibodies decreased the damage associated with NDV infection; furthermore, GM RNA induced IL-1β expression via NLRP3/caspase-1.

Genetic and pharmacological inhibition of inflammasomes reduces the survival of Mycobacterium tuberculosis strains in macrophages

Mycobacterium tuberculosis infection causes high rates of morbidity and mortality. Host-directed therapy may enhance the immune response, reduce tissue damage and shorten treatment duration. The inflammasome is integral to innate immune responses but over-activation has been described in tuberculosis (TB) pathology and TB-immune reconstitution syndrome. Here we explore how clinical isolates differentially activate the inflammasome and how inflammasome inhibition can lead to enhanced bacterial clearance. Wild-type, Nlrp3^−/−/Aim2^−/−, Casp1/11^−/− and Asc^−/− murine bone-marrow derived macrophages (BMDMs) were infected with laboratory strain M. tuberculosis H37Rv or clinical isolates from various lineages. Inflammasome activation and bacterial numbers were measured, and pharmacological inhibition of NLRP3 was achieved using MCC950. Clinical isolates of M. tuberculosis differed in their ability to activate inflammasomes. Beijing isolates had contrasting effects on IL-1β and caspase-1 activation, but all clinical isolates induced lower IL-1β release than H37Rv. Our studies suggest the involvement of NLRP3, AIM2 and an additional unknown sensor in IL-1β maturation. Pharmacological blockade of NLRP3 with MCC950 reduced bacterial survival, and combined treatment with the antimycobacterial drug rifampicin enhanced the effect. Modulating the inflammasome is an attractive adjunct to current anti-mycobacterial therapy that warrants further investigation.

NLRP3 Inflammasome-A Key Player in Antiviral Responses

The NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome is an oligomeric complex comprised of the NOD-like receptor NLRP3, the adaptor ASC, and caspase-1. This complex is crucial to the host's defense against microbes as it promotes IL-1β and IL-18 secretion and induces pyroptosis. NLRP3 recognizes variety of pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) generated during viral replication that triggers the NLRP3 inflammasome-dependent antiviral immune responses and facilitates viral eradication. Meanwhile, several viruses have evolved elaborate strategies to evade the immune system by targeting the NLRP3 inflammasome. In this review, we will focus on the crosstalk between the NLRP3 inflammasome and viruses, provide an overview of viral infection-induced NLRP3 inflammasome activation, and the immune escape strategies of viruses through their modulation of the NLRP3 inflammasome activity.

Rhein Suppresses Lung Inflammatory Injury Induced by Human Respiratory Syncytial Virus Through Inhibiting NLRP3 Inflammasome Activation via NF-κB Pathway in Mice

Rhein is one of active anthraquinone components in traditional Chinese herbal medicine Rheum palmatum L., possessing anti-inflammatory, antioxidant, antitumor, antiviral, and hepatoprotective activities. Human respiratory syncytial virus (RSV), a common virus, is able to result in pneumonia and bronchitis, which usually can be seen in infants. However, so far the effects of Rhein on RSV-induced pneumonia are still unknown. As the NLRP3 inflammasome is activated excessively, it is able to lead to inflammatory response and tissue injury in most viral infection process (including RSV infection) of respiratory tract. Therefore, we designed experiments to reveal whether Rhein can treat RSV-induced pneumonia by inhibiting NLRP3 inflammasome activation. In present research, we established the pneumonia model of BALB/C mice caused by RSV. First of all, the pathology of lung tissue and the weight of mice were evaluated, and the corresponding lung index was calculated. Additionally, the expression of pro-inflammatory mediators in serum and lung tissues, and related proteins (NLRP3, ASC and Caspase-1) of NLRP3 inflammasome and NF-κB pathway were detected by Enzyme-linked immunosorbent assay (ELISA), Real-time PCR (RT-PCR), Immunohistochemistry (IHC), and Western blot (WB), respectively. The determination of lung index and lung tissue pathological evaluation revealed that Rhein was able to alleviate lung infection and injury caused by RSV. The results of ELISA showed that Rhein was able to reduce the release of pro-inflammatory cytokines in the serum and lung tissues of RSV-induced BALB/c mice, including IL-1β, IL-6, TNF-α, IL-18, and IL-33. Additionally, it was revealed that Rhein inhibited the immune inflammatory response of RSV-infected mice, which was likely to be associated with the inhibition the NLRP3 inflammasome activation via NF-κB pathway. To sum up, our results indicated that Rhein may inhibit RSV-induced pulmonary inflammatory response effectively; meanwhile, it is emphasized that Rhein therapy is likely to be a promising treatment on the RSV-infected lung inflammation and avoidance of lung tissue damage.

Acetate Downregulates the Activation of NLRP3 Inflammasomes and Attenuates Lung Injury in Neonatal Mice With Bronchopulmonary Dysplasia

Background: Bronchopulmonary dysplasia (BPD) is a common pulmonary complication in preterm infants. Acetate is a metabolite produced by the gut microbiota, and its anti-inflammatory function is well known. The role of acetate in BPD has not been studied. Here, we investigate the effects of acetate on lung inflammation and damage in mice model of BPD. Objective: To investigate the role of acetate in the development of BPD. Methods: C57BL/6 mice were randomly divided into three groups on the 3rd day after birth: room air group, hyperoxia group, and hyperoxia + acetate (250 mM, 0.02 ml/g) group. The expression of inflammatory factors was determined by ELISA and RT-PCR, and NLRP3 and caspase-1 were detected by Western blot. High-throughput sequencing was used to detect bacterial communities in the mice intestines. Results: After acetate treatment, the expression levels of TNF-α, IL-1β, IL-18, NLRP3, and caspase-1 were significantly reduced, while the expression of GPR43 was increased. In the BPD mice treated with acetate, the proportion of Escherichia-Shigella was lower than in placebo-treated BPD mice, while the abundance of Ruminococcus was increased. Conclusions: These results indicate that acetate may regulate intestinal flora and reduce inflammatory reactions and lung injury in BPD. Therefore, acetate may be an effective drug to protect against neonatal BPD.

AT-533, a Hsp90 inhibitor, attenuates HSV-1-induced inflammation

Inflammatory events are tightly associated with the death caused by Herpes simplex virus 1 (HSV-1) infection of the brain. Heat shock protein 90 (Hsp90) is a molecular chaperone that is stimulated in response to many stressful conditions (e.g., inflammation and hypoxia) and Hsp90 inhibitors are suggested to be potent inhibitors of the inflammatory response. The aim of this study was to investigate the effect of Hsp90 inhibitor AT-533 on HSV-1-induced inflammation. AT-533 at a non-antiviral concentration was found to show a prominent inhibitory effect on the production of cytokines induced by HSV-1 infection, such as tumor necrosis factor α (TNF-α), interleukin 6 (IL-6) and interleukin 1β (IL-1β). Mechanically, HSV-1 early infection induced inflammation through NF-κB signaling and NLRP3 inflammasome activation, as illustrated by the nuclear translocation of NF-κB and the enhanced cleavage of caspase-1. Besides, HSV-1 enhanced the interaction between NLRP3 and Hsp90. Moreover, AT-533 reduced the nuclear translocation of NF-κB and inflammasome activation via inhibiting the chaperone function of Hsp90. Furthermore, AT-533 inhibited the cleavage of pro-IL-1β to mature IL-1β in a NLRP3-independent manner. In summary, AT-533 may be a promising therapeutic strategy in HSV-1-infected inflammation management.

Ventilator-induced lung injury is alleviated by inhibiting NLRP3 inflammasome activation

BACKGROUND

Mechanical ventilation (MV) is frequently used but can aggravate or cause lung injury, known as ventilator-induced lung injury (VILI). However, the mechanisms are unclear. The NLR family pyrin domain containing 3 (NLRP3) inflammasome is a vital component of innate immunity and is closely related to VILI.

METHODS

Mouse lung epithelial (MLE-12) cells were transfected with NLRP3 small interfering RNA (siRNA) or scramble siRNA (sc siRNA) and subjected to 20% cyclic stretch (CS). Wild-type C57BL/6 mice were injected with a liquid complex of NLRP3 siRNA/sc siRNA-Lipofectamine 2000 through the fundus venous plexus before mechanical ventilation. Western blots, immunoprecipitation, ELISAs, flow cytometry, immunofluorescence, and hematoxylin-eosin staining were used to assess the effects of the NLRP3 inflammasome on VILI and the mechanisms of those effects.

RESULTS

CS activated the NLRP3 inflammasome by activating NIMA-related kinase 7 (NEK7). NLRP3 depletion inhibited NLRP3 inflammasome activation; alleviated the degradation of cell junction proteins, including p120-catenin (p120) and occludin; ameliorated the colocalization of p120 and E-cadherin; and mitigated the decrease in mitochondrial membrane potential caused by mechanical stretch. Furthermore, after NLRP3 depletion, VILI was attenuated by decreasing IL-1β secretion and pulmonary edema.

CONCLUSIONS

Inhibiting NLRP3 inflammasome activation ameliorated VILI, suggesting a potential therapeutic target for the clinical treatment of VILI.

Cardiac glycosides decrease influenza virus replication by inhibiting cell protein translational machinery

Cardiac glycosides (CGs) are used primarily for cardiac failure and have been reported to have other effects, including inhibition of viral replication. Here we set out to study mechanisms by which CGs as inhibitors of the Na-K-ATPase decrease influenza A virus (IAV) replication in the lungs. We found that CGs inhibit influenza virus replication in alveolar epithelial cells by decreasing intracellular potassium, which in turn inhibits protein translation, independently of viral entry, mRNA transcription, and protein degradation. These effects were independent of the Src signaling pathway and intracellular calcium concentration changes. We found that short-term treatment with ouabain prevented IAV replication without cytotoxicity. Rodents express a Na-K-ATPase-α1 resistant to CGs. Thus we utilized Na-K-ATPase-α₁-sensitive mice, infected them with high doses of influenza virus, and observed a modest survival benefit when treated with ouabain. In summary, we provide evidence that the inhibition of the Na-K-ATPase by CGs decreases influenza A viral replication by modulating the cell protein translational machinery and results in a modest survival benefit in mice.

Intranasal Application of Budesonide Attenuates Lipopolysaccharide-Induced Acute Lung Injury by Suppressing Nucleotide-Binding Oligomerization Domain-Like Receptor Family, Pyrin Domain-Containing 3 Inflammasome Activation in Mice

Aim

To investigate the protective effects of budesonide against lipopolysaccharide- (LPS-) induced acute lung injury (ALI) in a murine model and its underlying mechanism.

Methods

Adult male C57BL/6 mice were divided into three groups: control, ALI, and ALI + budesonide groups. LPS (5 mg/kg) was intratracheally injected to induce ALI in mice. Budesonide (0.5 mg/kg) was intranasally given 1 h before LPS administration in the ALI + budesonide group. Twelve hours after LPS administration, all mice were sacrificed. Hematoxylin-eosin staining and pathological scores were used to evaluate pathological injury. Bronchoalveolar lavage was performed. The numbers of total cells, neutrophils, and macrophages in the bronchoalveolar lavage fluid (BALF) were counted. Enzyme-linked immunosorbent assay was employed to detect the proinflammatory cytokines in BALF and serum, including tumor necrosis factor- (TNF-) α, monocyte chemoattractant protein- (MCP-) 1, and interleukin- (IL-) 1β. The expression of the nucleotide-binding oligomerization domain-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome was detected by western blotting. A lethal dose of LPS (40 mg/kg, intraperitoneally) was injected to evaluate the effects of budesonide on survival rates.

Results

Budesonide pretreatment dramatically attenuated pathological injury and reduced pathological scores in mice with ALI. Budesonide pretreatment obviously reduced the numbers of total cells, neutrophils, and macrophages in the BALF of mice with ALI. Additionally, budesonide dramatically reduced TNF-α and MCP-1 expression in the BALF and serum of mice with ALI. Budesonide significantly suppressed NLRP3 and pro-caspase-1 expression in the lung and reduced IL-1β content in the BALF, indicating that budesonide inhibited the activation of the NLRP3 inflammasome. Furthermore, we found that budesonide improved the survival rates of mice with ALI receiving a lethal dose of LPS.

Conclusion

Suppression of NLRP3 inflammasome activation in mice via budesonide attenuated lung injury induced by LPS in mice with ALI.

Dampened NLRP3-mediated inflammation in bats and implications for a special viral reservoir host

Bats are special in their ability to host emerging viruses. As the only flying mammal, bats endure high metabolic rates yet exhibit elongated lifespans. It is currently unclear whether these unique features are interlinked. The important inflammasome sensor, NLR family pyrin domain containing 3 (NLRP3), has been linked to both viral-induced and age-related inflammation. Here, we report significantly dampened activation of the NLRP3 inflammasome in bat primary immune cells compared to human or mouse counterparts. Lower induction of apoptosis-associated speck-like protein containing a CARD (ASC) speck formation and secretion of interleukin-1β in response to both 'sterile' stimuli and infection with multiple zoonotic viruses including influenza A virus (-single-stranded (ss) RNA), Melaka virus (PRV3M, double-stranded RNA) and Middle East respiratory syndrome coronavirus (+ssRNA) was observed. Importantly, this reduction of inflammation had no impact on the overall viral loads. We identified dampened transcriptional priming, a novel splice variant and an altered leucine-rich repeat domain of bat NLRP3 as the cause. Our results elucidate an important mechanism through which bats dampen inflammation with implications for longevity and unique viral reservoir status.

Rapamycin ameliorates lipopolysaccharide-induced acute lung injury by inhibiting IL-1β and IL-18 production

Interleukin (IL)-1β and IL-18 play central and detrimental roles in the development of acute lung injury (ALI), and mammalian target of rapamycin (mTOR) is involved in regulating IL-1β and IL-18 production. However, it is not clear whether the mTOR specific inhibitor rapamycin can attenuate lipopolysaccharide (LPS)-induced ALI by modulating IL-1β and IL-18 production. In this study, we found that rapamycin ameliorated LPS-induced ALI by inhibiting NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome-mediated IL-1β and IL-18 secretion. Mechanistically, elevated autophagy and decreased nuclear factor (NF)-κB activation were associated with downregulated IL-1β and IL-18. Moreover, rapamycin reduced leukocyte infiltration in the lung tissue and bronchoalveolar lavage fluid (BALF), and contributed to the alleviation of LPS-induced ALI. Consistently, rapamycin also significantly inhibited IL-1β and IL-18 production by RAW264.7 cells via increased autophagy and decreased NF-κB signaling in vitro. Our results demonstrated that rapamycin protects mice against LPS-induced ALI partly by inhibiting the production and secretion of IL-1β and IL-18. mTOR and rapamycin might represent an appropriate therapeutic target and strategy for preventing ALI induced by LPS.

Delayed oseltamivir plus sirolimus treatment attenuates H1N1 virus-induced severe lung injury correlated with repressed NLRP3 inflammasome activation and inflammatory cell infiltration

Severe influenza A virus infection causes high mortality and morbidity worldwide due to delayed antiviral treatment and inducing overwhelming immune responses, which contribute to immunopathological lung injury. Sirolimus, an inhibitor of mammalian target of rapamycin (mTOR), was effective in improving clinical outcomes in patients with severe H1N1 infection; however, the mechanisms by which it attenuates acute lung injury have not been elucidated. Here, delayed oseltamivir treatment was used to mimic clinical settings on lethal influenza A (H1N1) pdm09 virus (pH1N1) infection mice model. We revealed that delayed oseltamivir plus sirolimus treatment protects mice against lethal pH1N1 infection by attenuating severe lung damage. Mechanistically, the combined treatment reduced viral titer and pH1N1-induced mTOR activation. Subsequently, it suppressed the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome-mediated secretion of interleukin (IL)-1β and IL-18. It was noted that decreased NLRP3 inflammasome activation was associated with inhibited nuclear factor (NF)-κB activation, reduced reactive oxygen species production and increased autophagy. Additionally, the combined treatment reduced the expression of other proinflammatory cytokines and chemokines, and decreased inflammatory cell infiltration in lung tissue and bronchioalveolar lavage fluid. Consistently, it inhibited the mTOR-NF-κB-NLRP3 inflammasome-IL-1β axis in a lung epithelial cell line. These results demonstrated that combined treatment with sirolimus and oseltamivir attenuates pH1N1-induced severe lung injury, which is correlated with suppressed mTOR-NLRP3-IL-1β axis and reduced viral titer. Therefore, treatment with sirolimus as an adjuvant along with oseltamivir may be a promising immunomodulatory strategy for managing severe influenza.

The severity and lethality of influenza A virus infection are frequently aggravated by virus-induced tissue destruction and overwhelming immune responses. Combined therapy with antiviral medications and immunomodulators, which not only inhibit viral replication, but also reduce the damaging consequences of host immune responses, will be beneficial in the treatment of severe influenza. In the present study, we revealed that pH1N1-induced activation of mTOR promotes lung immunopathological injury, which is correlated with upregulated NF-κB activity and increased reactive oxygen species production. Subsequently, it induces NLRP3 inflammasome activation and the secretion of IL-1β and IL-18. Combined treatment with oseltamivir and the mTOR inhibitor sirolimus (as an adjuvant) not only blocks viral replication, but also suppresses mTOR-NLRP3-IL-1β axis-mediated immune damage, thus protecting mice against lethal pH1N1 infection. Our findings provide the theoretical and experimental basis for the clinical investigation of sirolimus as an adjunct treatment for severe influenza.

Cytosolic Recognition of Microbes and Pathogens: Inflammasomes in Action

Infection is a dynamic biological process underpinned by a complex interplay between the pathogen and the host. Microbes from all domains of life, including bacteria, viruses, fungi, and protozoan parasites, have the capacity to cause infection. Infection is sensed by the host, which often leads to activation of the inflammasome, a cytosolic macromolecular signaling platform that mediates the release of the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18 and cleavage of the pore-forming protein gasdermin D, leading to pyroptosis. Host-mediated sensing of the infection occurs when pathogens inject or carry pathogen-associated molecular patterns (PAMPs) into the cytoplasm or induce damage that causes cytosolic liberation of danger-associated molecular patterns (DAMPs) in the host cell. Recognition of PAMPs and DAMPs by inflammasome sensors, including NLRP1, NLRP3, NLRC4, NAIP, AIM2, and Pyrin, initiates a cascade of events that culminate in inflammation and cell death. However, pathogens can deploy virulence factors capable of minimizing or evading host detection. This review presents a comprehensive overview of the mechanisms of microbe-induced activation of the inflammasome and the functional consequences of inflammasome activation in infectious diseases. We also explore the microbial strategies used in the evasion of inflammasome sensing at the host-microbe interaction interface.

MicroR-9-5p suppresses EV71 replication through targeting NFκB of the RIG-I-mediated innate immune response

Accumulating evidence demonstrates that there is a causative link between hsa-microRNA-9-5p (miR-9) and pathophysiological processes. Enterovirus 71 (EV71) has been found to contribute to numerous severe clinical symptoms which result in death. The exact mechanism by which EV71 influences miR-9 expression is unknown, and the relationship between miR-9 and EV71 is still unclear. Here, miR-9 expression was found to be impaired upon EV71 infection in several cell lines and in an EV71 infection mouse model. Additionally, we confirmed that EV71 infection induces robust expression of pro-inflammatory cytokines (TNF-α, IL-6, and IL-1) and interferons (IFN-α and IFN-β). Overexpression of miR-9 attenuated EV71 proliferation and reduced protein and gene expressions of virion protein 1 (VP1) of EV71. Furthermore, we observed that the inflammation caused by EV71 infection was restored to a moderate level via miR-9 overexpression. Nuclear factor kappa B (NFκB) in the retinoic acid-induced gene 1 (RIG-I) signaling pathway, but not interferon regulating factor 3 (IRF3), was significantly decreased and inactivated by ectopic miR-9 expression. Moreover, in mouse infection experiments, administration of miR-9 agomirs caused a significant decrease in VP1 levels and pro-inflammatory cytokine production after viral inoculation. Taken together, the present data demonstrate that miR-9 exerts an anti-EV71 effect in cells and a mouse model via mediating NFκB activity of the RIG-I signal pathway, thereby suggesting a new candidate for antiviral drug development.

Targeting the NLRP3 inflammasome in inflammatory diseases

Danger signals are a hallmark of many common inflammatory diseases, and these stimuli can function to activate the cytosolic innate immune signalling receptor NLRP3 (NOD-, LRR- and pyrin domain-containing 3). Once activated, NLRP3 nucleates the assembly of an inflammasome, leading to caspase 1-mediated proteolytic activation of the interleukin-1β (IL-1β) family of cytokines, and induces an inflammatory, pyroptotic cell death. Pharmacological inhibition of NLRP3 activation results in potent therapeutic effects in a wide variety of rodent models of inflammatory diseases, effects that are mirrored by genetic ablation of NLRP3. Although these findings highlight the potential of NLRP3 as a drug target, an understanding of NLRP3 structure and activation mechanisms is incomplete, which has hampered the discovery and development of novel therapeutics against this target. Here, we review recent advances in our understanding of NLRP3 activation and regulation, highlight the evolving landscape of NLRP3 modulators and discuss opportunities for pharmacologically targeting NLRP3 with novel small molecules.

The inflammasome potentiates influenza/Staphylococcus aureus superinfection in mice

Secondary bacterial respiratory infections are commonly associated with both acute and chronic lung injury. Influenza complicated by bacterial pneumonia is an effective model to study host defense during pulmonary superinfection due to its clinical relevance. Multiprotein inflammasomes are responsible for IL-1β production in response to infection and drive tissue inflammation. In this study, we examined the role of the inflammasome during viral/bacterial superinfection. We demonstrate that ASC-/- mice are protected from bacterial superinfection and produce sufficient quantities of IL-1β through an apoptosis-associated speck-like protein containing CARD (ASC) inflammasome-independent mechanism. Despite the production of IL-1β by ASC-/- mice in response to bacterial superinfection, these mice display decreased lung inflammation. A neutrophil elastase inhibitor blocked ASC inflammasome-independent production of IL-1β and the IL-1 receptor antagonist, anakinra, confirmed that IL-1 remains crucial to the clearance of bacteria during superinfection. Delayed inhibition of NLRP3 during influenza infection by MCC950 decreases bacterial burden during superinfection and leads to decreased inflammatory cytokine production. Collectively, our results demonstrate that ASC augments the clearance of bacteria, but can also contribute to inflammation and mortality. ASC should be considered as a therapeutic target to decrease morbidity and mortality during bacterial superinfection.

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

Healthy children are more likely to die of influenza A virus (IAV) infection than healthy adults. However, little is known about the mechanisms underlying the impact of young age on the development of life-threatening IAV infection. We report increased mortality in juvenile mice compared with adult mice at each infectious dose of IAV. Juvenile mice had sustained elevation of type I IFNs and persistent NLRP3 inflammasome activation in the lungs, both of which were independent of viral titer. Juvenile mice, but not adult mice, had increased MCP-1 levels that remained high even after viral clearance. Importantly, continued production of MCP-1 was associated with persistent recruitment of monocytes to the lungs and prolonged elevation of inflammatory cytokines. Transcriptional signatures of recruited monocytes to the juvenile and adult IAV-infected lungs were assessed by RNA-seq. Genes associated with a proinflammatory signature were upregulated in the juvenile monocytes compared with adult monocytes. Depletion of monocytes with anti-CCR2 Ab decreased type I IFN secretion, NLRP3 inflammasome activation, and lung injury in juvenile mice. This suggests an exaggerated inflammatory response mediated by increased recruitment of monocytes to the lung, and not an inability to control viral replication, is responsible for severe IAV infection in juvenile mice. This study provides insight into severe IAV infection in juveniles and identifies key inflammatory monocytes that may be central to pediatric acute lung injury secondary to IAV.

The role of the NLRP3 inflammasome in regulation of antiviral responses to influenza A virus infection

The innate immune system provides the host with both a dynamic barrier to prevent infection and a means to which rapid anti-microbial responses can be mounted. The inflammasome pathway is a critical host early response mechanism that enables detection of pathogens and initiates production of inflammatory cytokines, inducing recruitment of effector cells to the site of infection. The complete mechanism of inflammasome activation requires two signals: an initial priming step upon detection of pathogen, followed by activation of intracellular pattern recognition receptors critical to the formation of the inflammasome complex. The inflammasome complex is made of intracellular multiprotein oligomers which includes a sensor protein such as the nucleotide-binding oligomerization domain (NOD) like receptor proteins (NLRP), and an adapter protein, ASC, which critically activates pro-caspase-1. The mature caspase-1 then proteolytically cleaves cytosolic pro-IL-1β and pro-IL-18, which are then secreted as inflammatory cytokines that activate the inflammatory arm of the immune response to infection. Active caspase-1 also results in pyroptosis, which is a form of cell death triggered by inflammation. The induction and activation of IL-1β and IL-18 are considered critical signatures for inflammasome activation. With focus upon influenza A virus infection, this review will address present knowledge on the mechanisms of inflammasome complex activation, particularly how the viral components modulate activation of the cytosolic NOD-like receptor protein-3 (NLRP3)-dependent inflammasome complex. We also discuss potential therapeutic strategies that target the inflammasome to ameliorate illness, as well as novel methods of vaccination that target inflammasome stimulation with the aim to increase efficacy.