TNF-mediated alveolar macrophage necroptosis drives disease pathogenesis during respiratory syncytial virus infection

Acute lung injury: a view from the perspective of necroptosis

BACKGROUND

ALI/ARDS is a syndrome of acute onset characterized by progressive hypoxemia and noncardiogenic pulmonary edema as the primary clinical manifestations. Necroptosis is a form of programmed cell necrosis that is precisely regulated by molecular signals. This process is characterized by organelle swelling and membrane rupture, is highly immunogenic, involves extensive crosstalk with various cellular stress mechanisms, and is significantly implicated in the onset and progression of ALI/ARDS.

METHODS

The current body of literature on necroptosis and ALI/ARDS was thoroughly reviewed. Initially, an overview of the molecular mechanism of necroptosis was provided, followed by an examination of its interactions with apoptosis, pyroptosis, autophagy, ferroptosis, PANOptosis, and NETosis. Subsequently, the involvement of necroptosis in various stages of ALI/ARDS progression was delineated. Lastly, drugs targeting necroptosis, biomarkers, and current obstacles were presented.

CONCLUSION

Necroptosis plays an important role in the progression of ALI/ARDS. However, since ALI/ARDS is a clinical syndrome caused by a variety of mechanisms, we emphasize that while focusing on necroptosis, it may be more beneficial to treat ALI/ARDS by collaborating with other mechanisms.

Rotavirus non-structural protein 4 usurps host cellular RIPK1-RIPK3 complex to induce MLKL-dependent necroptotic cell death

The dynamic interface between invading viral pathogens and programmed cell death (PCD) of the host is a finely regulated process. Host cellular demise at the end of the viral life cycle ensures the release of progeny virions to initiate new infection cycles. Rotavirus (RV), a diarrheagenic virus with double-stranded RNA genome, has been reported to trigger different types of PCD such as apoptosis and pyroptosis in a highly regulated way to successfully disseminate progeny virions. Recently our lab also showed that induction of MLKL-driven programmed necroptosis by RV. However, the host cellular machinery involved in RV-induced necroptosis and the upstream viral trigger responsible for it remained unaddressed. In the present study, the signalling upstream of MLKL-driven necroptosis has been delineated where the involvement of Receptor interacting serine/threonine kinase 3 (RIPK3) and 1 (RIPK1) from the host side and RV non-structural protein 4 (NSP4) as the viral trigger for necroptosis has been shown. Interestingly, RV-NSP4 was found to be an integral component of the necrosome complex by interacting with RIPK1, thereby bypassing the requirement of RIPK1 kinase activity. Subsequently, NSP4-driven elevated cytosolic Ca2+ concentration and Ca2+-binding to NSP4 lead further to RHIM domain-dependent RIPK1-RIPK3 interaction, RIPK3-dependent MLKL phosphorylation, and eventual necroptosis. Overall, this study presents the interplay between RV-NSP4 and the host cellular necrosome complex to induce necroptotic death of host cells.

Comprehensive expression, prognostic and validation analysis of necroptosis-related lncRNAs in esophageal cancer

BACKGROUND

Previous studies have shown that necroptosis-related long noncoding RNA (lncRNA) risk models can be used to predict prognosis and immune infiltration in patients with esophageal cancer. However, further analysis of the regulatory mechanisms of necroptosis-related lncRNAs used in risk models remains to be conducted. The purpose of the present study was to identify valuable necroptosis-related lncRNAs in esophageal cancer and to verify their molecular and cellular functions.

METHODS

Esophageal cancer data were downloaded from The Cancer Genome Atlas (TCGA). The expression of eight genes (LINC00299, AC090912.2, AC244197.2, AL158166.1, AC079684.1, AP003696.1, AC079684.1 and AP003696.1) in the necroptosis-related lncRNA risk model, their relationships with clinicopathological stage, and their diagnostic receiver operating characteristic (ROC) curves were analyzed. The prognostic value of these lncRNAs for overall survival (OS) and disease specific survival (DSS) was analyzed, and time-dependent ROC curves were generated. The AP003696.1 target gene (lncRNA ENSG00000253385.1) was further investigated through immune infiltration analysis, Gene Ontology/Kyoto Encyclopedia of Genes and Genomes (GO/KEGG) enrichment analyses, and gene coexpression analysis. Finally, in vitro functional assays based on lncRNA ENSG00000253385.1 were conducted to explore its regulatory role in esophageal cancer.

RESULTS

A bioinformatics approach was used to study the eight genes in the necroptosis-related lncRNA risk model. AP003696.1 (lncRNA ENSG00000253385.1) was highly expressed in esophageal cancer tissues, and its high expression was correlated with poor OS and DFdS. Both univariate and multivariate Cox regression analyses revealed that lncRNA ENSG00000253385.1 is an independent prognostic factor. The lncRNA ENSG00000253385.1 gene was demonstrated to play a definite role in the invasion of esophageal cancer immune cells and in signaling pathways in these cells. In vitro cell functional assays revealed that lncRNA ENSG00000253385.1 expression was elevated in the KYSE150 and KYSE410 esophageal cancer cell lines. Small interfering RNA (siRNA)-mediated silencing of lncRNA ENSG00000253385.1 significantly inhibited the proliferation, migration, and invasion of KYSE150 and KYSE410 cells, as well as promoted their apoptosis.

CONCLUSIONS

The ENSG00000253385.1 gene may be a key gene in the occurrence, development, and prognosis of esophageal cancer. These findings provide new ideas and references for the screening of therapeutic targets, as well as the development of targeted drugs, for esophageal cancer treatment.

The role of HPV11 E7 in modulating STING-dependent interferon β response in recurrent respiratory papillomatosis

Recurrent respiratory papillomatosis (RRP) is a rare benign tumor caused mainly by the infection of the respiratory tract epithelial cells by the human papillomavirus (HPV) type 6/11. However, the specific mechanisms underlying the inhibition of the host's innate immune response by HPV remain unclear. For this purpose, we employed single-cell RNA sequencing to analyze the states of various immune cells in RRP samples post-HPV infection and utilized a cellular model of HPV infection to elucidate the mechanisms by which HPV evades the innate immune system in RRP. The results revealed distinct immune cell heterogeneity in RRP and demonstrated that HPV11 E7 can inhibit the phosphorylation of the stimulator of interferon genes protein, thereby circumventing the body's antiviral response. In vitro co-culture experiments demonstrated that stimulation of macrophages to produce interferon-beta induced the death of HPV-infected epithelial cells, also reducing HPV viral levels. In summary, our study preliminarily identifies the potential mechanisms by which HPV evades the host's antiviral immune response, as well as the latent antiviral functions exhibited by activated macrophages. This research serves as an initial exploration of antiviral immune evasion in RRP, laying a solid foundation for investigating immunotherapeutic approaches for the disease.IMPORTANCESurgical tumor reduction is the most common treatment for recurrent respiratory papillomatosis (RRP). One of the characteristics of RRP is its persistent recurrence, and multiple surgeries are usually required to control the symptoms. Recently, some adjuvant therapies have shown effectiveness, but none of them can completely clear human papillomavirus (HPV) infection, and thus, a localized antiviral immune response is significant for disease control; after all, HPV infection is limited to the epithelium. Inhibition of interferon-beta (IFN-β) secretion by HPV11 E7 viral proteins in epithelial cells by affecting stimulator of interferon genes phosphorylation may account for the persistence of low-risk HPV replication in the RRP. Moreover, suppression of the IFN-I pathway in RRP cell types might provide clues regarding the hyporeactive function of local immune cells. However, activation of macrophage groups to produce IFN-β can still destroy HPV-infected cells.

Development of innate and adaptive immunity to RSV in young children

Infection of the respiratory tract with respiratory syncytial virus (RSV) is common and occurs repeatedly throughout life with most severe disease occurring at the extremes of age: in young infants and the elderly. Effective anti-viral therapeutics are not available and therefore prevention has been the primary strategy for reducing the disease burden. Our current understanding of respiratory mucosal cell biology and the immune response within the respiratory tract is inadequate to prevent infection caused by a pathogen like RSV that does not disseminate outside of this environment. Gaps in our understanding of the activation of innate and adaptive immunity in response to RSV and the role of age upon infection also limit improvements in the design of therapeutics and vaccines for young infants. However, advancements in structural biology have improved our ability to characterize antibodies against viral proteins and in 2023 the first vaccines for those over 60 years and pregnant women became available, potentially reducing the burden of disease. This review will examine our current understanding of the critical facets of anti-RSV immune responses in infants and young children as well as highlight areas where more research is needed.

Targeting the TRAF3-ULK1-NLRP3 regulatory axis to control alveolar macrophage pyroptosis in acute lung injury

Acute lung injury (ALI) is a serious condition characterized by damage to the lungs. Recent research has revealed that activation of the NLRP3 inflammasome in alveolar macrophages, a type of immune cell in the lungs, plays a key role in the development of ALI. This process, known as pyroptosis, contributes significantly to ALI pathogenesis. Researchers have conducted comprehensive bioinformatics analyses and identified 15 key genes associated with alveolar macrophage pyroptosis in ALI. Among these, NLRP3 has emerged as a crucial regulator. This study further reveal that the ULK1 protein diminishes the expression of NLRP3, thereby reducing the immune response of alveolar macrophages and mitigating ALI. Conversely, TRAF3, another protein, is found to inhibit ULK1 through a process called ubiquitination, leading to increased activation of the NLRP3 inflammasome and exacerbation of ALI. This TRAF3-mediated suppression of ULK1 and subsequent activation of NLRP3 are confirmed through various in vitro and in vivo experiments. The presence of abundant M0 and M1 alveolar macrophages in the ALI tissue samples further support these findings. This research highlights the TRAF3-ULK1-NLRP3 regulatory axis as a pivotal pathway in ALI development and suggests that targeting this axis could be an effective therapeutic strategy for ALI treatment.

Microbiota and Immunity during Respiratory Infections: Lung and Gut Affair

Bacterial and viral respiratory tract infections are the most common infectious diseases, leading to worldwide morbidity and mortality. In the past 10 years, the importance of lung microbiota emerged in the context of pulmonary diseases, although the mechanisms by which it impacts the intestinal environment have not yet been fully identified. On the contrary, gut microbial dysbiosis is associated with disease etiology or/and development in the lung. In this review, we present an overview of the lung microbiome modifications occurring during respiratory infections, namely, reduced community diversity and increased microbial burden, and of the downstream consequences on host-pathogen interaction, inflammatory signals, and cytokines production, in turn affecting the disease progression and outcome. Particularly, we focus on the role of the gut-lung bidirectional communication in shaping inflammation and immunity in this context, resuming both animal and human studies. Moreover, we discuss the challenges and possibilities related to novel microbial-based (probiotics and dietary supplementation) and microbial-targeted therapies (antibacterial monoclonal antibodies and bacteriophages), aimed to remodel the composition of resident microbial communities and restore health. Finally, we propose an outlook of some relevant questions in the field to be answered with future research, which may have translational relevance for the prevention and control of respiratory infections.

Macrophage Tim-3 maintains intestinal homeostasis in DSS-induced colitis by suppressing neutrophil necroptosis

T-cell immunoglobulin domain and mucin domain-3 (Tim-3) is a versatile immunomodulator that protects against intestinal inflammation. Necroptosis is a type of cell death that regulates intestinal homeostasis and inflammation. The mechanism(s) underlying the protective role of macrophage Tim-3 in intestinal inflammation is unclear; thus, we investigated whether specific Tim-3 knockdown in macrophages drives intestinal inflammation via necroptosis. Tim-3 protein and mRNA expression were assessed via double immunofluorescence staining and single-cell RNA sequencing (sc-RNA seq), respectively, in the colonic tissues of patients with inflammatory bowel disease (IBD) and healthy controls. Macrophage-specific Tim3-knockout (Tim-3M-KO) mice were generated to explore the function and mechanism of Tim-3 in dextran sodium sulfate (DSS)-induced colitis. Necroptosis was blocked by pharmacological inhibitors of receptor-interacting protein kinase (RIP)1, RIP3, and reactive oxygen species (ROS). Additionally, in vitro experiments were performed to assess the mechanisms of neutrophil necroptosis induced by Tim-3 knockdown macrophages. Although Tim-3 is relatively inactive in macrophages during colon homeostasis, it is highly active during colitis. Compared to those in controls, Tim-3M-KO mice showed increased susceptibility to colitis, higher colitis scores, and increased pro-inflammatory mediator expression. Following the administration of RIP1/RIP3 or ROS inhibitors, a significant reduction in intestinal inflammation symptoms was observed in DSS-treated Tim-3M-KO mice. Further analysis indicated the TLR4/NF-κB pathway in Tim-3 knockdown macrophages mediates the TNF-α-induced necroptosis pathway in neutrophils. Macrophage Tim-3 regulates neutrophil necroptosis via intracellular ROS signaling. Tim-3 knockdown macrophages can recruit neutrophils and induce neutrophil necroptosis, thereby damaging the intestinal mucosal barrier and triggering a vicious cycle in the development of colitis. Our results demonstrate a protective role of macrophage Tim-3 in maintaining gut homeostasis by inhibiting neutrophil necroptosis and provide novel insights into the pathogenesis of IBD.

Luteolin-7-O-glucoside promotes macrophage release of IFN-β by maintaining mitochondrial function and corrects the disorder of glucose metabolism during RSV infection

Respiratory syncytial virus (RSV) pneumonia is the main cause of acute bronchiolitis in infants. Luteolin-7-O-glucoside (LUT-7G) is a natural flavonoid, which exists in a variety of plants and has the potential to treat viral pneumonia. We established RSV pneumonia mouse models and RSV-infected cell models. Clodronate liposomes were used to deplete macrophages. We used HE staining and immunohistochemistry to determine inflammatory damage and virus replication. We detected the expression levels of inflammatory factors and IFN-β through qPCR and ELISA. JC-1 kit was used for detecting the cell mitochondrial Membrane potential (MMP). ROS, SOD, and MDA kits were used for detecting intracellular oxidative stress damage. Metabolites of TCA in lung tissue and serum of mice were detected by GC-MS. Pharmacodynamic studies have shown that intervention with LUT-7G can alleviate lung tissue damage caused by RSV infection, inhibit RSV replication, and downregulate TNF-α, IL-1β, and IL-6 mRNA expression. LUT-7G upregulated the IFN-β content and the expression of IFN-β, ISG15, and OAS1 mRNA. In vitro, LUT-7G inhibited RSV-induced cell death, reversed the RSV-induced decrease of MMP and decreased intracellular oxidative stress. Target metabonomics showed that RSV infection upregulated the levels of glycolysis and TCA metabolites in lung tissue and serum, while LUT-7G could improve the disorder of glucose metabolism. The results indicate that LUT-7G can promote the release of IFN-β in the lung, alleviate inflammatory damage, and inhibit RSV replication during RSV infection. These effects may be achieved by protecting the mitochondrial function of alveolar macrophages and correcting the disorder of glucose metabolism.

Necroptosis in Pneumonia: Therapeutic Strategies and Future Perspectives

Pneumonia remains a major global health challenge, necessitating the development of effective therapeutic approaches. Recently, necroptosis, a regulated form of cell death, has garnered attention in the fields of pharmacology and immunology for its role in the pathogenesis of pneumonia. Characterized by cell death and inflammatory responses, necroptosis is a key mechanism contributing to tissue damage and immune dysregulation in various diseases, including pneumonia. This review comprehensively analyzes the role of necroptosis in pneumonia and explores potential pharmacological interventions targeting this cell death pathway. Moreover, we highlight the intricate interplay between necroptosis and immune responses in pneumonia, revealing a bidirectional relationship between necrotic cell death and inflammatory signaling. Importantly, we assess current therapeutic strategies modulating necroptosis, encompassing synthetic inhibitors, natural products, and other drugs targeting key components of the programmed necrosis pathway. The article also discusses challenges and future directions in targeting programmed necrosis for pneumonia treatment, proposing novel therapeutic strategies that combine antibiotics with necroptosis inhibitors. This review underscores the importance of understanding necroptosis in pneumonia and highlights the potential of pharmacological interventions to mitigate tissue damage and restore immune homeostasis in this devastating respiratory infection.

Cell type-specific molecular mechanisms and implications of necroptosis in inflammatory respiratory diseases

Necroptosis is generally considered as an inflammatory cell death form. The core regulators of necroptotic signaling are receptor-interacting serine-threonine protein kinases 1 (RIPK1) and RIPK3, and the executioner, mixed lineage kinase domain-like pseudokinase (MLKL). Evidence demonstrates that necroptosis contributes profoundly to inflammatory respiratory diseases that are common public health problem. Necroptosis occurs in nearly all pulmonary cell types in the settings of inflammatory respiratory diseases. The influence of necroptosis on cells varies depending upon the type of cells, tissues, organs, etc., which is an important factor to consider. Thus, in this review, we briefly summarize the current state of knowledge regarding the biology of necroptosis, and focus on the key molecular mechanisms that define the necroptosis status of specific cell types in inflammatory respiratory diseases. We also discuss the clinical potential of small molecular inhibitors of necroptosis in treating inflammatory respiratory diseases, and describe the pathological processes that engage cross talk between necroptosis and other cell death pathways in the context of respiratory inflammation. The rapid advancement of single-cell technologies will help understand the key mechanisms underlying cell type-specific necroptosis that are critical to effectively treat pathogenic lung infections and inflammatory respiratory diseases.

Alveolar macrophages in tissue homeostasis, inflammation, and infection: evolving concepts of therapeutic targeting

Alveolar macrophages (AMs) are the sentinel cells of the alveolar space, maintaining homeostasis, fending off pathogens, and controlling lung inflammation. During acute lung injury, AMs orchestrate the initiation and resolution of inflammation in order to ultimately restore homeostasis. This central role in acute lung inflammation makes AMs attractive targets for therapeutic interventions. Single-cell RNA-Seq and spatial omics approaches, together with methodological advances such as the generation of human macrophages from pluripotent stem cells, have increased understanding of the ontogeny, function, and plasticity of AMs during infectious and sterile lung inflammation, which could move the field closer to clinical application. However, proresolution phenotypes might conflict with proinflammatory and antibacterial responses. Therefore, therapeutic targeting of AMs at vulnerable time points over the course of infectious lung injury might harbor the risk of serious side effects, such as loss of antibacterial host defense capacity. Thus, the identification of key signaling hubs that determine functional fate decisions in AMs is of the utmost importance to harness their therapeutic potential.

Host Responses to Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) infections are a constant public health problem, especially in infants and older adults. Virtually all children will have been infected with RSV by the age of two, and reinfections are common throughout life. Since antigenic variation, which is frequently observed among other respiratory viruses such as SARS-CoV-2 or influenza viruses, can only be observed for RSV to a limited extent, reinfections may result from short-term or incomplete immunity. After decades of research, two RSV vaccines were approved to prevent lower respiratory tract infections in older adults. Recently, the FDA approved a vaccine for active vaccination of pregnant women to prevent severe RSV disease in infants during their first RSV season. This review focuses on the host response to RSV infections mediated by epithelial cells as the first physical barrier, followed by responses of the innate and adaptive immune systems. We address possible RSV-mediated immunomodulatory and pathogenic mechanisms during infections and discuss the current vaccine candidates and alternative treatment options.

THE ALARMIN EFFECT OF HMGB1/RIP3 ON TRANSFUSION-RELATED ACUTE LUNG INJURY VIA TLR4/NF-ΚB OR MAPK PATHWAY

ABSTRACT

Nonantibody-mediated transfusion-related acute lung injury (TRALI) may account for up to 25% of TRALI cases. This indicates the need for further research to understand the pathophysiological mechanisms involved beyond antibody mediation fully. During this research, a TRALI rat model was developed using the trauma-blood loss-massive transfusion method. The severity of pulmonary edema was checked via measurement of lung histopathological changes and the amount of Evans blue dye fluid and bronchoalveolar lavage fluid protein leakage. In addition, potential mechanisms of pathophysiological pathways and inflammation cascades were investigated in TRALI rats in vivo . The findings indicated that TRALI increased inflammatory cytokines and triggered elevated levels of high-mobility group box 1 (HMGB1)/receptor-interacting protein kinase 3 (RIP3), apoptosis protein, and mRNAs in the TM (TRALI model) group as opposed to the normal control. Furthermore, TRALI activated the toll-like receptor 4/nuclear factor kappa B and mitogen-activated protein kinase signaling pathways, which partially regulated the inflammatory response in the TRALI rats. A significant increase was observed in the inflammatory mediators HMGB1 and RIP3 during the early stages of TRALI, suggesting that these mediators could be used as diagnostic markers for TRALI. In addition, HMGB1 and RIP3 promoted the inflammatory response by stimulating the toll-like receptor 44/nuclear factor kappa B and mitogen-activated protein kinase signaling pathways in the lung tissue of rats. Identifying efficient agents from inflammatory mediators such as alarmin can be an innovative scheme for diagnosing and preventing TRALI. These findings give HMGB1 and RIP3 a strong theoretical and experimental foundation for clinical use.

Controlling viral inflammatory lesions by rebalancing immune response patterns

In this review, we discuss a variety of immune modulating approaches that could be used to counteract tissue-damaging viral immunoinflammatory lesions which typify many chronic viral infections. We make the point that in several viral infections the lesions can be largely the result of one or more aspects of the host response mediating the cell and tissue damage rather than the virus itself being directly responsible. However, within the reactive inflammatory lesions along with the pro-inflammatory participants there are also other aspects of the host response that may be acting to constrain the activity of the damaging components and are contributing to resolution. This scenario should provide the prospect of rebalancing the contributions of different host responses and hence diminish or even fully control the virus-induced lesions. We identify several aspects of the host reactions that influence the pattern of immune responsiveness and describe approaches that have been used successfully, mainly in model systems, to modulate the activity of damaging participants and which has led to lesion control. We emphasize examples where such therapies are, or could be, translated for practical use in the clinic to control inflammatory lesions caused by viral infections.

Oxidative Stress Initiates Receptor-Interacting Protein Kinase-3/Mixed Lineage Kinase Domain-Like-Mediated Corneal Epithelial Necroptosis and Nucleotide-Binding Oligomerization Domain-Like Receptor Protein 3 Inflammasome Signaling during Fungal Keratitis

Fungal keratitis remains a major cause of severe visual loss in developing countries because of limited choices of therapy. The progression of fungal keratitis is a race between the innate immune system and the outgrowth of fungal conidia. Programmed necrosis (necroptosis), a type of proinflammatory cell death, has been recognized as a critical pathologic change in several diseases. However, the role and potential regulatory mechanisms of necroptosis have not been investigated in corneal diseases. The current study showed, for the first time, that fungal infection triggered significant corneal epithelial necroptosis in human/mouse/in vitro models. Moreover, a reduction in excessive reactive oxygen species release effectively prevented necroptosis. NLRP3 knockout did not affect necroptosis in vivo. In contrast, ablation of necroptosis via RIPK3 knockout significantly delayed migration and inhibited the nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome in macrophages, which enhanced the progression of fungal keratitis. Taking these findings together, the study indicated that overproduction of reactive oxygen species in fungal keratitis leads to significant necroptosis in the corneal epithelium. Furthermore, the necroptotic stimuli-mediated NLRP3 inflammasome serves as a driving force in host defense against fungal infection.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

TREM-1 triggers necroptosis of macrophages through mTOR-dependent mitochondrial fission during acute lung injury

BACKGROUND

Necroptosis of macrophages is a necessary element in reinforcing intrapulmonary inflammation during acute lung injury (ALI). However, the molecular mechanism that sparks macrophage necroptosis is still unclear. Triggering receptor expressed on myeloid cells-1 (TREM-1) is a pattern recognition receptor expressed broadly on monocytes/macrophages. The influence of TREM-1 on the destiny of macrophages in ALI requires further investigation.

METHODS

TREM-1 decoy receptor LR12 was used to evaluate whether the TREM-1 activation induced necroptosis of macrophages in lipopolysaccharide (LPS)-induced ALI in mice. Then we used an agonist anti-TREM-1 Ab (Mab1187) to activate TREM-1 in vitro. Macrophages were treated with GSK872 (a RIPK3 inhibitor), Mdivi-1 (a DRP1 inhibitor), or Rapamycin (an mTOR inhibitor) to investigate whether TREM-1 could induce necroptosis in macrophages, and the mechanism of this process.

RESULTS

We first observed that the blockade of TREM-1 attenuated alveolar macrophage (AlvMs) necroptosis in mice with LPS-induced ALI. In vitro, TREM-1 activation induced necroptosis of macrophages. mTOR has been previously linked to macrophage polarization and migration. We discovered that mTOR had a previously unrecognized function in modulating TREM-1-mediated mitochondrial fission, mitophagy, and necroptosis. Moreover, TREM-1 activation promoted DRP1^Ser616 phosphorylation through mTOR signaling, which in turn caused surplus mitochondrial fission-mediated necroptosis of macrophages, consequently exacerbating ALI.

CONCLUSION

In this study, we reported that TREM-1 acted as a necroptotic stimulus of AlvMs, fueling inflammation and aggravating ALI. We also provided compelling evidence suggesting that mTOR-dependent mitochondrial fission is the underpinning of TREM-1-triggered necroptosis and inflammation. Therefore, regulation of necroptosis by targeting TREM-1 may provide a new therapeutic target for ALI in the future.

Expression Profiles of Hepatic Immune Response Genes in HEV Infection

Hepatitis E is a liver inflammation caused by infection with the hepatitis E virus (HEV). Every year, there are an estimated 20 million HEV infections worldwide, leading to an estimated 3.3 million symptomatic cases of hepatitis E. HEV viral load has been studied about the disease progression; however, hepatic the host gene expression against HEV infection remains unknown. Methods: We identified the expression profiles of hepatic immune response genes in HEV infections. Fresh blood samples were collected from all the study subjects (130 patients and 124 controls) in 3ml EDTA vacutainers. HEV viral load was determined by a real-time PCR. The total RNA was isolated from the blood using the TRIZOL method. The expression of theCCL2, CCL5, CXCL10, CXCL16, TNF, IFNGR1, and SAMSN1 genes was studied in the blood of 130 HEV patients and 124 controls using a real-time PCR. Results: Gene expression profiles indicate high levels of CCL2, CCL5, CXCL10, CXCL16, TNF, IFNGR1, and SAMSN1 genes that might lead to the recruitment of leukocytes and infected cell apoptosis. Conclusion: Our study demonstrated distinct differences in the expression profiles of host immune response-related genes of HEV infections and provided valuable insight into the potential impact of these genes on disease progression.

Necroptosis of macrophage is a key pathological feature in biliary atresia via GDCA/S1PR2/ZBP1/p-MLKL axis

Biliary atresia (BA) is a severe inflammatory and fibrosing neonatal cholangiopathy disease characterized by progressive obstruction of extrahepatic bile ducts, resulting in cholestasis and progressive hepatic failure. Cholestasis may play an important role in the inflammatory and fibrotic pathological processes, but its specific mechanism is still unclear. Necroptosis mediated by Z-DNA-binding protein 1 (ZBP1)/phosphorylated-mixed lineage kinase domain-like pseudokinase (p-MLKL) is a prominent pathogenic factor in inflammatory and fibrotic diseases, but its function in BA remains unclear. Here, we aim to determine the effect of macrophage necroptosis in the BA pathology, and to explore the specific molecular mechanism. We found that necroptosis existed in BA livers, which was occurred in liver macrophages. Furthermore, this process was mediated by ZBP1/p-MLKL, and the upregulated expression of ZBP1 in BA livers was correlated with liver fibrosis and prognosis. Similarly, in the bile duct ligation (BDL) induced mouse cholestatic liver injury model, macrophage necroptosis mediated by ZBP1/p-MLKL was also observed. In vitro, conjugated bile acid-glycodeoxycholate (GDCA) upregulated ZBP1 expression in mouse bone marrow-derived monocyte/macrophages (BMDMs) through sphingosine 1-phosphate receptor 2 (S1PR2), and the induction of ZBP1 was a prerequisite for the enhanced necroptosis. Finally, after selectively knocking down of macrophage S1pr2 in vivo, ZBP1/p-MLKL-mediated necroptosis was decreased, and further collagen deposition was markedly attenuated in BDL mice. Furthermore, macrophage Zbp1 or Mlkl specific knockdown also alleviated BDL-induced liver injury/fibrosis. In conclusion, GDCA/S1PR2/ZBP1/p-MLKL mediated macrophage necroptosis plays vital role in the pathogenesis of BA liver fibrosis, and targeting this process may represent a potential therapeutic strategy for BA.

Apigenin suppresses mycoplasma-induced alveolar macrophages necroptosis via enhancing the methylation of TNF-α promoter by PPARγ-Uhrf1 axis

BACKGROUND

Mycoplasma-associated pneumonia is characterized by severe lung inflammation and immunological dysfunction. However, current anti-mycoplasma agents used in clinical practice do not prevent dysfunction of alveolar macrophages caused by the high level of the cytokine tumor necrosis factor-α (TNF-α) after mycoplasma infection. Apigenin inhibits the production of TNF-α in variet inflammation associated disease.

PURPOSE

This study aimed to investigate apigenin's effect on mycoplasma-induced alveolar immune cell injury and the mechanism by which it inhibits TNF-α transcription.

METHODS

In this study, we performed a mouse model of Mycoplasma hyopneumoniae infection to evaluate the effect of apigenin on reducing mycoplasma-induced alveolar immune cell injury. Furthermore, we carried out transcriptome analysis, RNA interference assay, methylated DNA bisulfite sequencing assay, and chromatin immunoprecipitation assay to explore the mechanism of action for apigenin in reducing TNF-α.

RESULTS

We discovered that M. hyopneumoniae infection-induced necroptosis in alveolar macrophages MH-S cells and primary mouse alveolar macrophages, which was activated by TNF-α autocrine. Apigenin inhibited M. hyopneumoniae-induced elevation of TNF-α and necroptosis in alveolar macrophages. Apigenin inhibited TNF-a mRNA production via increasing ubiquitin-like with PHD and RING finger domains 1 (Uhrf1)-dependent DNA methylation of the TNF-a promotor. Finally, we demonstrated that apigenin regulated Uhrf1 transcription via peroxisome proliferator activated receptor gamma (PPARγ) activation, which acts as a transcription factor binding to the Uhrf1 promoter and protected infected mice's lungs, and promoted alveolar macrophage survival.

CONCLUTSION

This study identified a novel mechanism of action for apigenin in reducing alveolar macrophage necroptosis via the PPARγ/ Uhrf1/TNF-α pathway, which may have implications for the treatment of Mycoplasma pneumonia.

Approaches to Evaluating Necroptosis in Virus-Infected Cells

The immune system functions to protect the host from pathogens. To counter host defense mechanisms, pathogens have developed unique strategies to evade detection or restrict host immune responses. Programmed cell death is a major contributor to the multiple host responses that help to eliminate infected cells for obligate intracellular pathogens like viruses. Initiation of programmed cell death pathways during the early stages of viral infections is critical for organismal survival as it restricts the virus from replicating and serves to drive antiviral inflammation immune recruitment through the release of damage-associated molecular patterns (DAMPs) from the dying cell. Necroptosis has been implicated as a critical programmed cell death pathway in a diverse set of diseases and pathological conditions including acute viral infections. This cell death pathway occurs when certain host sensors are triggered leading to the downstream induction of mixed-lineage kinase domain-like protein (MLKL). MLKL induction leads to cytoplasmic membrane disruption and subsequent cellular destruction with the release of DAMPs. As the role of this cell death pathway in human disease becomes apparent, methods identifying necroptosis patterns and outcomes will need to be further developed. Here, we discuss advances in our understanding of how viruses counteract necroptosis, methods to quantify the pathway, its effects on viral pathogenesis, and its impact on cellular signaling.

The impact of infection with COVID-19 on the respiratory microbiome: A narrative review

Coronavirus disease 2019 (COVID-19), caused by SARS-CoV-2, has affected millions of individuals with various implications. Consistent with the crucial role of the microbiome in determining health and disease in humans, various studies have investigated the gut and respiratory microbiome effect on the COVID-19. Microbiota dysbiosis might support the entry, replication, and establishment of SARS-CoV-2 infection by modulating various mechanisms. One of the main mechanisms that the modulation of respiratory microbiota composition during the COVID-19 infection affects the magnitude of the disease is changes in innate and acquired immune responses, including inflammatory markers and cytokines and B- and T-cells. The diversity of respiratory microbiota in COVID-19 patients is controversial; some studies reported low microbial diversity, while others found high diversity, suggesting the role of respiratory microbiota in this disease. Modulating microbiota diversity and profile by supplementations and nutrients can be applied prophylactic and therapeutic in combating COVID-19. Here, we discussed the lung microbiome dysbiosis during various lung diseases and its interaction with immune cells, focusing on COVID-19.

Alveolar macrophages and airway hyperresponsiveness associated with respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is a ubiquitous pathogen of viral bronchiolitis and pneumonia in children younger than 2 years of age, which is closely associated with recurrent wheezing and airway hyperresponsiveness (AHR). Alveolar macrophages (AMs) located on the surface of the alveoli cavity are the important innate immune barrier in the respiratory tract. AMs are recognized as recruited airspace macrophages (RecAMs) and resident airspace macrophages (RAMs) based on their origins and roaming traits. AMs are polarized in the case of RSV infection, forming two macrophage phenotypes termed as M1-like and M2-like macrophages. Both M1 macrophages and M2 macrophages are involved in the modulation of inflammatory responses, among which M1 macrophages are capable of pro-inflammatory responses and M2 macrophages are capable of anti-proinflammatory responses and repair damaged tissues in the acute and convalescent phases of RSV infection. Polarized AMs affect disease progression through the alteration of immune cell surface phenotypes as well as participate in the regulation of T lymphocyte differentiation and the type of inflammatory response, which are closely associated with long-term AHR. In recent years, some progress have been made in the regulatory mechanism of AM polarization caused by RSV infection, which participates in acute respiratory inflammatory response and mediating AHR in infants. Here we summarized the role of RSV-infection-mediated AM polarization associated with AHR in infants.

M1-like, but not M0- or M2-like, macrophages, reduce RSV infection of primary bronchial epithelial cells in a media-dependent fashion

Respiratory syncytial virus (RSV) is a common childhood infection that in young infants can progress into severe bronchiolitis and pneumonia. Disease pathogenesis results from both viral mediated and host immune processes of which alveolar macrophages play an important part. Here, we investigated the role of different types of alveolar macrophages on RSV infection using an in vitro co-culture model involving primary tissue-derived human bronchial epithelial cells (HBECs) and human blood monocyte-derived M0-like, M1-like, or M2-like macrophages. It was hypothesized that the in vitro model would recapitulate previous in vivo findings of a protective effect of macrophages against RSV infection. It was found that macrophages maintained their phenotype for the 72-hour co-culture time period and the bronchial epithelial cells were unaffected by the macrophage media. HBEC infection with RSV was decreased by M1-like macrophages but enhanced by M0- or M2-like macrophages. The medium used during the co-culture also impacted the outcome of the infection. This work demonstrates that alveolar macrophage phenotypes may have differential roles during epithelial RSV infection, and demonstrates that an in vitro co-culture model could be used to further investigate the roles of macrophages during bronchial viral infection.

Necroptosis in inflammatory bowel disease: A potential effective target

The morbidity of inflammatory bowel diseases (IBD) is rising rapidly but no curative therapies to prevent its recurrence. Cell death is crucial to maintaining homeostasis. Necroptosis is a newly identified programmed cell death and its roles played in IBD need to be explored. Necroptosis is mediated by receptor interacting protein kinase 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like protein (MLKL), which resulted in cell swelling, plasma membrane rupture, intracellular content leaking, and eventually cell death as well as the promotion of inflammation. Studies have found that inhibiting necroptosis alleviated IBD in animal models and IBD patients with an increased level of necroptosis in inflammatory tissues, indicating that necroptosis is related to the pathogenesis of IBD. However, due to the complexity in regulation of necroptosis and the involvement of multiple functions of relevant signaling molecules, the specific mechanism remains elusive. Necroptosis may play a vital regulatory role in the pathogenesis of IBD, which provides a new idea and method for further exploring the therapeutic target of IBD.

Acteoside attenuates RSV-induced lung injury by suppressing necroptosis and regulating metabolism

Background: Necroptosis and inflammation are closely related to the pathogenesis of respiratory syncytial virus (RSV). Acteoside (AC), a natural phenylpropanoid glycoside from Kuding Tea, has significant anti-RSV effect. However, the roles of AC on RSV-induced lung necroptosis and inflammation are yet to be elucidated.

Methods: The effects of AC were investigated in BALB/c mice and A549 cells. Lung histopathology was observed through H&E staining. The viral titer was assessed via plaque assay. The RSV-F expression was determined by RT-qPCR and immunohistochemistry assay. The levels of cytokines were detected by ELISA and RT-qPCR. The necroptosis rate and mitochondrial membrane potential were evaluated via flow cytometry. The expressions of HMGB1/NF-κB and RIP1/RIP3/MLKL/PGAM5/DRP1 were detected by western blot. Additionally, untargeted metabolomics was conducted to investigate the metabolic profiles and related metabolic pathways via Gas Chromatography-Mass Spectrometry.

Results: The results showed that compared with the RSV-infected group, AC treatment significantly attenuated lung pathological damage, virus replication, and cytokines levels. AC also alleviated RSV-induced necroptosis and mitochondrial dysfunction in vitro and in vivo. Moreover, AC treatment down-regulated the expression of HMGB1, p-Iκbα/Iκbα, p-p65/p65, RIP1, RIP3, MLKL, PGAM5, and DRP1. Furthermore, metabolomic analyses suggested that the perturbations in major metabolites of AC therapy were related to variations in amino acid and energy metabolism.

Conclusion: Our findings validated the beneficial effects of AC in suppressing necroptosis and regulating metabolism, suggesting AC may be a new drug candidate for RSV infection.

Increased Heme Oxygenase 1 Expression upon a Primary Exposure to the Respiratory Syncytial Virus and a Secondary Mycobacterium bovis Infection

The human respiratory syncytial virus (hRSV) is the leading cause of severe lower respiratory tract infections in infants. Because recurrent epidemics based on reinfection occur in children and adults, hRSV has gained interest as a potential primary pathogen favoring secondary opportunistic infections. Several infection models have shown different mechanisms by which hRSV promotes immunopathology to prevent the development of adaptive protective immunity. However, little is known about the long-lasting effects of viral infection on pulmonary immune surveillance mechanisms. As a first approach, here we evaluated whether a primary infection by hRSV, once resolved, dampens the host immune response to a secondary infection with an attenuated strain of Mycobacterium bovis (M. Bovis) strain referred as to Bacillus Calmette-Guerin (BCG). We analyzed leukocyte dynamics and immunomodulatory molecules in the lungs after eleven- and twenty-one-days post-infection with Mycobacterium, using previous hRSV infected mice, by flow cytometry and the expression of critical genes involved in the immune response by real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR). Among the latter, we analyzed the expression of Heme Oxygenase (HO)-1 in an immunization scheme in mice. Our data suggest that a pre-infection with hRSV has a conditioning effect promoting lung pathology during a subsequent mycobacterial challenge, characterized by increased infiltration of innate immune cells, including interstitial and alveolar macrophages. Our data also suggest that hRSV impairs pulmonary immune responses, promoting secondary mycobacterial colonization and lung survival, which could be associated with an increase in the expression of HO-1. Additionally, BCG is a commonly used vaccine that can be used as a platform for the generation of new recombinant vaccines, such as a recombinant BCG strain expressing the nucleoprotein of hRSV (rBCG-N-hRSV). Therefore, we evaluated if the immunization with rBCG-N-hRSV could modulate the expression of HO-1. We found a differential expression pattern for HO-1, where a higher induction of HO-1 was detected on epithelial cells compared to dendritic cells during late infection times. This is the first study to demonstrate that infection with hRSV produces damage in the lung epithelium, promoting subsequent mycobacterial colonization, characterized by an increase in the neutrophils and alveolar macrophages recruitment. Moreover, we determined that immunization with rBCG-N-hRSV modulates differentially the expression of HO-1 on immune and epithelial cells, which could be involved in the repair of pulmonary tissue.

Airway Administration of Bacterial Lysate OM-85 Protects Mice Against Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is a seasonal pathogen responsible for the highest percentage of viral bronchiolitis in pediatric patients. There are currently no vaccine available and therapeutic methods to mitigate the severity of RSV bronchiolitis are limited. OM-85, an oral standardized bacterial lysate isolated from human respiratory strains and widely used to prevent recurrent infections and/or exacerbations in populations at risk, has been shown to be effective and safe in children and adults. Here, we demonstrate that airway administration of OM-85 in Balb/c mice prior to infection prevents RSV-induced disease, resulting in inhibition of viral replication associated with less perivascular and peribronchial inflammation in the lungs. These protective effects are dose and time-dependent with complete protection using 1mg dose of OM-85 only four times intranasally. Mechanistic insights using this topical route in the airways revealed increased alveolar macrophages, a selective set of tolerogenic DCs, Treg and Th1 expansion in the lung, even in the absence of infection, contributing to a better Th1/Th2 balance and preventing ILC2 recruitment in the airways and associated inflammatory sequelae. OM-85 preventive treatment also improved antiviral response by increasing IFNβ and its responsive genes in the lung. In vitro, OM-85 protects against RSV infection in a type I interferon pathway. Our animal model data suggest that intranasal use of OM-85 should be considered as a potential prophylactic product to prevent RSV bronchiolitis once human studies confirm these findings.

Osteopontin aggravates acute lung injury in influenza virus infection by promoting macrophages necroptosis

Infection with influenza A virus (IAV) can trigger pulmonary inflammation and lung damage. Osteopontin (OPN) is an essential regulator of cell death and immunity. However, the role and underlying mechanism of OPN in cell death in IAV-induced pulmonary injury remain poorly understood. Here, we demonstrated that OPN-deficient (OPN^-/-) mice were insensitive to IAV, exhibiting decreased viral loads and attenuated lung injury after IAV infection compared to those in wild-type (WT) mice. Moreover, macrophage necroptosis was significantly reduced in OPN^-/- mice infected with IAV compared to that in infected WT mice. OPN increased the expression of necroptosis-related genes and exacerbated macrophage necroptosis in IAV-infected THP1 cells. Notably, adoptive transfer of WT bone marrow-derived macrophages (BMDMs) or OPN^-/- BMDMs into mice restored resistance to influenza infection, and the rescue effect of OPN^-/- BMDMs was better than that of WT BMDMs. Collectively, these results suggest that OPN deficiency in macrophages reduces necroptosis, which leads to a decrease in viral titers and protects against IAV infection. Therefore, OPN is a potential target for the treatment of IAV infection.

Interferon-γ Preferentially Promotes Necroptosis of Lung Epithelial Cells by Upregulating MLKL

Necroptosis, a form of programmed lytic cell death, has emerged as a driving factor in the pathogenesis of acute lung injury (ALI). As ALI is often associated with a cytokine storm, we determined whether pro-inflammatory cytokines modulate the susceptibility of lung cells to necroptosis and which mediators dominate to control necroptosis. In this study, we pretreated/primed mouse primary lung epithelial and endothelial cells with various inflammatory mediators and assessed cell type-dependent responses to different necroptosis inducers and their underlying mechanisms. We found that interferon-γ (IFNγ) as low as 1 ng/mL preferentially promoted necroptosis and accelerated the release of damage-associated molecular patterns from primary alveolar and airway epithelial cells but not lung microvascular endothelial cells. Type-I IFNα was about fifty-fold less effective than IFNγ. Conversely, TNFα or agonists of Toll-like receptor-3 (TLR3), TLR4, TLR7 and TLR9 had a minor effect. The enhanced necroptosis in IFNγ-activated lung epithelial cells was dependent on IFNγ signaling and receptor-interacting protein kinase-3. We further showed that necroptosis effector mixed lineage kinase domain-like protein (MLKL) was predominantly induced by IFNγ, contributing to the enhanced necroptosis in lung epithelial cells. Collectively, our findings indicate that IFNγ is a potent enhancer of lung epithelial cell susceptibility to necroptosis.

The role of necroptosis in common respiratory diseases in children

Studies have shown that necroptosis (NEC) relies on a unique gene-regulated molecular pathway to cause cell death. With the development of knockout mouse models and specific molecular inhibitors of necrotic proteins, this cell death pathway has been considered one of the important causes of the pathogenesis of human diseases. In this review, we explored the possible roles and mechanisms of NEC in common respiratory diseases in children, such as acute lung injury, acute respiratory distress syndrome, pulmonary infection, childhood asthma, pulmonary hypertension, etc., in order to provide new ideas for the prevention and treatment of such diseases.

Autocrine, Paracrine, and Endocrine Signals That Can Alter Alveolar Macrophages Function

Alveolar macrophages (AMs) are extremely versatile cells with complex functions involved in health or diseases such as pneumonia, asthma, and pulmonary alveolar proteinosis. In recent years, it has been widely identified that the different functions and states of macrophages are the results from the complex interplay between microenvironmental signals and macrophage lineage. Diverse and complicated signals to which AMs respond are mentioned when they are described individually or in a particular state of AMs. In this review, the microenvironmental signals are divided into autocrine, paracrine, and endocrine signals based on their secreting characteristics. This new perspective on classification provides a more comprehensive and systematic introduction to the complex signals around AMs and is helpful for understanding the roles of AMs affected by physiological environment. The existing possible treatments of AMs are also mentioned in it. The thorough understanding of AMs signals modulation may be contributed to the development of more effective therapies for AMs-related lung diseases.

Rotavirus activates MLKL-mediated host cellular necroptosis concomitantly with apoptosis to facilitate dissemination of viral progeny

Reprogramming the host cellular environment is an obligatory facet of viral pathogens to foster their replication and perpetuation. One of such reprogramming events is the dynamic cross-talk between viruses and host cellular death signaling pathways. Rotaviruses (RVs) have been reported to develop multiple mechanisms to induce apoptotic programmed cell death for maximizing viral spread and pathogenicity. However, the importance of non-apoptotic programmed death events has remained elusive in context of RV infection. Here, we report that RV-induced apoptosis accompanies another non-apoptotic mode of programmed cell death pathway called necroptosis to promote host cellular demise at late phase of infection. Phosphorylation of mixed lineage kinase-domain like (MLKL) protein indicative of necroptosis was observed to concur with caspase-cleavage (apoptotic marker) beyond 6 hours of RV infection. Subsequent studies demonstrated phosphorylated-MLKL to oligomerize and to translocate to plasma membrane in RV infected cells, resulting in loss of plasma membrane integrity and release of alarmin molecules e.g., high mobility group box protein 1 (HMGB1) in the extracellular media. Moreover, inhibiting caspase-cleavage and apoptosis could not fully rescue virus-induced cell death but rather potentiated the necroptotic trigger. Interestingly, preventing both apoptosis and necroptosis by small molecules significantly rescued virus-induced host cytopathy by inhibiting viral dissemination.

Immunopathology of RSV: An Updated Review

RSV is a leading cause of respiratory tract disease in infants and the elderly. RSV has limited therapeutic interventions and no FDA-approved vaccine. Gaps in our understanding of virus-host interactions and immunity contribute to the lack of biological countermeasures. This review updates the current understanding of RSV immunity and immunopathology with a focus on interferon responses, animal modeling, and correlates of protection.

Alveolar macrophages: novel therapeutic targets for respiratory diseases

Alveolar macrophages (AMs) are lung-resident myeloid cells that sit at the interface of the airway and lung tissue. Under homeostatic conditions, their primary function is to clear debris, dead cells and excess surfactant from the airways. They also serve as innate pulmonary sentinels for respiratory pathogens and environmental airborne particles and as regulators of pulmonary inflammation. However, they have not typically been viewed as primary therapeutic targets for respiratory diseases. Here, we discuss the role of AMs in various lung diseases, explore the potential therapeutic strategies to target these innate cells and weigh the potential risks and challenges of such therapies. Additionally, in the context of the COVID-19 pandemic, we examine the role AMs play in severe disease and the therapeutic strategies that have been harnessed to modulate their function and protect against severe lung damage. There are many novel approaches in development to target AMs, such as inhaled antibiotics, liposomal and microparticle delivery systems, and host-directed therapies, which have the potential to provide critical treatment to patients suffering from severe respiratory diseases, yet there is still much work to be done to fully understand the possible benefits and risks of such approaches.

Diversity of Macrophages in Lung Homeostasis and Diseases

Lung macrophages play important roles in the maintenance of homeostasis, pathogen clearance and immune regulation. The different types of pulmonary macrophages and their roles in lung diseases have attracted attention in recent years. Alveolar macrophages (AMs), including tissue-resident alveolar macrophages (TR-AMs) and monocyte-derived alveolar macrophages (Mo-AMs), as well as interstitial macrophages (IMs) are the major macrophage populations in the lung and have unique characteristics in both steady-state conditions and disease states. The different characteristics of these three types of macrophages determine the different roles they play in the development of disease. Therefore, it is important to fully understand the similarities and differences among these three types of macrophages for the study of lung diseases. In this review, we will discuss the physiological characteristics and unique functions of these three types of macrophages in acute and chronic lung diseases. We will also discuss possible methods to target macrophages in lung diseases.

Alveolar-like Macrophages Attenuate Respiratory Syncytial Virus Infection

Respiratory Syncytial Virus (RSV) is the leading cause of acute lower respiratory infections in young children and infection has been linked to the development of persistent lung disease in the form of wheezing and asthma. Despite substantial research efforts, there are no RSV vaccines currently available and an effective monoclonal antibody targeting the RSV fusion protein (palivizumab) is of limited general use given the associated expense. Therefore, the development of novel approaches to prevent RSV infection is highly desirable to improve pediatric health globally. We have developed a method to generate alveolar-like macrophages (ALMs) from pluripotent stem cells. These ALMs have shown potential to promote airway innate immunity and tissue repair and so we hypothesized that ALMs could be used as a strategy to prevent RSV infection. Here, we demonstrate that ALMs are not productively infected by RSV and prevent the infection of epithelial cells. Prevention of epithelial infection was mediated by two different mechanisms: phagocytosis of RSV particles and release of an antiviral soluble factor different from type I interferon. Furthermore, intratracheal administration of ALMs protected mice from subsequent virus-induced weight loss and decreased lung viral titres and inflammation, indicating that ALMs can impair the pathogenesis of RSV infection. Our results support a prophylactic role for ALMs in the setting of RSV infection and warrant further studies on stem cell-derived ALMs as a novel cell-based therapy for pulmonary viral infections.

Molecular Mechanism of Jinchan Oral Liquid in the Treatment of Children with Respiratory Syncytial Virus Pneumonia Based on Network Pharmacology and Molecular Docking Technology

Objective

Exploration of the underlying molecular mechanism of Jinchan Oral Liquid (JOL) in treating children with the respiratory syncytial virus (RSV) pneumonia to provide new evidence for the clinical application.

Methods

The active components and target genes of JOL were screened by the TCMSP database. The targets of RSV pneumonia were obtained from the GeneCards, OMIM, DrugBank, and PharmGKB database. Then, we constructed the active component-target network and screened the core genes. The overlaps were screened for PPI network analysis, GO analysis, and KEGG analysis. Finally, result validation was performed by molecular docking.

Results

According to the screening criteria of the ADME, 74 active compounds of JOL were obtained; after removing redundant targets, we selected 180 potential targets. By screening the online database, 893 RSV pneumonia-related targets were obtained. A total of 82 overlapping genes were chosen by looking for the intersection. The STRING online database was used to acquire PPI relationships, and 16 core genes were obtained. GO and KEGG analyses showed that the main pathways of JOL in treating RSV pneumonia include TNF signaling pathway and IL17 signaling pathway. The molecular docking results showed that the active compounds of JOL had a good affinity with the core genes.

Conclusion

In this study, we preliminarily discussed the main active ingredients, related targets, and pathways of JOL and predicted the pharmacodynamic basis and the potential therapeutic mechanisms of RSV pneumonia. In summary, the network pharmacology strategy may be helpful for the discovery of multitarget drugs against complex diseases.

Role of G2-S16 Polyanionic Carbosilane Dendrimer in the Prevention of Respiratory Syncytial Virus Infection In Vitro and In Vivo in Mice

The respiratory syncytial virus (RSV) causes respiratory infection and bronchiolitis, requiring hospitalization mainly in infants. The interaction between RSV, envelope glycoproteins G and F, and cell surface heparan sulfate proteoglycans (HSPG) is required for binding and entry into the host cells. A G2-S16 polyanionic carbosilane dendrimer was identified as a possible RSV inhibitor. We speculated that the G2-S16 dendrimer adheres to the host cell-surface HSPG, acts through binding to HS receptors, and prevents further RSV infection. The G2-S16 dendrimer was non-toxic when applied intranasally to Balb/c mice, and interestingly enough, this G2-S16 dendrimer inhibits 85% RSV. Therefore, our G2-S16 dendrimer could be a candidate for developing a new possible therapy against RSV infection.

M1 Macrophages Are More Susceptible to Necroptosis

Macrophages play a crucial role in host innate immune defense against infection and tissue injury. Although macrophage activation and polarization has been well studied, we know less regarding the role of macrophage activation/polarization in inflammation-associated necrotic cell death. By using bone marrow-derived macrophages, we have recently demonstrated that M1 macrophages are much more susceptible than M0 and M2 subtypes of macrophages to necrotic cell death. Moreover, we showed that the enhanced necroptosis in M1 macrophages is dependent on the kinase activity of receptor-interacting protein kinase-3 (RIPK3) and may involve the upregulation of key necroptosis signaling molecules including RIPK3, mixed lineage kinase domain-like protein, and Z-DNA/ RNA binding protein 1. Our findings provide novel insights into the mechanisms of M1 macrophage engagement in inflammation and tissue injury.