Excessive neutrophils and neutrophil extracellular traps contribute to acute lung injury of influenza pneumonitis

Maternal probiotic exposure enhances CD8 T cell protective neonatal immunity and modulates offspring metabolome to control influenza virus infection

Maternal gut microbiota composition contributes to the status of the neonatal immune system and could influence the early life higher susceptibility to viral respiratory infections. Using a novel protocol of murine maternal probiotic supplementation, we report that perinatal exposure to Lacticaseibacillus rhamnosus (L.rh) or Bifidobacterium animalis subsp. lactis (B.lac) increases the influenza A/PR8 virus (IAV) clearance in neonates. Following either supplementation, type 1 conventional dendritic cells (cDC1) were amplified in the lymph nodes leading to an enhanced IAV antigen-experienced IFN-γ producing effector CD8 T cells in neonates and IAV-specific resident memory CD8 T cells in adulthood. This was compatible with a higher protection of the offspring upon a secondary infection. Interestingly, only mice born to L.rh supplemented mothers further displayed an increased activation of IFN-γ producing virtual memory CD8 T cells and a production of IL-10 by CD4 and CD8 T cells that could explain a better control of the lung damages upon infection. In the offspring and the mothers, no disturbance of the gut microbiota was observed but, as analyzed through an untargeted metabolomic approach, both exposures modified neonatal plasma metabolites. Among them, we further demonstrated that genistein and 3-(3-hydroxyphenyl)propionic acid recapitulate viral clearance or cDC1 activation in neonates exposed to IAV. We conclude that maternal L.rh or B.lac supplementation confers the neonates specific metabolomic modulations with a better CD8 T cell-mediated immune protection against IAV infection.

Susceptibility from the immunological perspective of COVID-19-associated pulmonary aspergillosis: A literature review

The incidence rate of COVID-19-associated pulmonary aspergillosis (CAPA) is rising. However, the pathogenesis of CAPA remains unclear. Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection disrupts pathways related to type I interferon and Toll-like receptors, key components in innate immunity, thereby elevating the incidence of CAPA. Additionally, SARS-CoV-2 infection results in T and B cell functional deficiencies or exhaustion within adaptive immunity, weakening the defense against invasive Aspergillus. Furthermore, SARS-CoV-2 infection enhances the replication of cytomegalovirus and alters the gut microbiota, factors that may aid in diagnosing CAPA. Immunosuppressive therapy in COVID-19 patients is also believed to heighten the risk of invasive aspergillosis. Therefore, this review, examines the immune response to SARS-CoV-2 infection combined with invasive aspergillosis, and explores the pathogenesis and susceptibility factors of CAPA. We propose that variations in an individual's immune response significantly determine susceptibility to CAPA. The aim of this paper is to deepen clinical understanding of CAPA's pathogenesis, thereby aiding in mitigating susceptibility risk and advancing novel treatment approaches.

Alveolar macrophages critically control infection by seasonal human coronavirus OC43 to avoid severe pneumonia

Seasonal coronaviruses, similar to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), only cause severe respiratory symptoms in a small fraction of infected individuals. However, the host factors that determine the variable responses to coronavirus infection remain unclear. Here, we use seasonal human coronavirus OC43 (HCoV-OC43) infection as an asymptomatic model that triggers both innate and adaptive immune responses in mice. Interestingly, innate sensing pathways as well as adaptive immune cells are not essential in protection against HCoV-OC43. Instead, alveolar macrophage (AMΦ) deficiency in mice results in COVID-19-like severe pneumonia post HCoV-OC43 infection, with abundant neutrophil infiltration, neutrophil extracellular trap (NET) release, and exaggerated pro-inflammatory cytokine production. Mechanistically, AMΦ efficiently phagocytose HCoV-OC43, effectively blocking virus spread, whereas, in their absence, HCoV-OC43 triggers Toll-like receptor (TLR)-dependent chemokine production to cause pneumonia. These findings reveal the central role of AMΦ in defending against seasonal HCoV-OC43 with clinical implications for human immunopathology associated with coronavirus infection.

Innate immunity of the lungs in homeostasis and disease

Humans breathe thousands of litres of non-sterile air each day containing bacteria, viruses, and fungi, as well as pollutants, allergens, and other particles. The continual exposure to foreign particles is juxtaposed with the vast surface area of the blood-air-barrier which becomes extremely thin to allow for efficient gas exchange. To prevent infection and injury, the healthy lung relies on a robust innate immune system to protect itself. Critically, this innate immune system must clear insults while maintaining immune tolerance and minimizing inflammation to avoid disrupting the lung's vital gas exchange function. In this review, we discuss how the innate immune system protects the lung from its environment.

The prion-family protein Doppel exerts a protective role during influenza virus infection

The cellular form of the prion protein (PrPC), known for its involvement as a misfolded isoform in transmissible spongiform encephalopathies, has recently been identified to exert a protective effect against viral infections. In this study, we explored the role of 2 other prion family members, Shadoo and Doppel, in protection against influenza A virus infection in mice. Lung expression levels of these genes revealed marked differences, with high expression of PrPC, low expression of Doppel, while Shadoo remained undetectable. Mice genetically knocked out for the genes encoding PrPC, Prnp-/- or Doppel, Prnd-/-, showed increased susceptibility to the virus, resulting in elevated morbidity compared with wild-type mice and mice knocked out for Shadoo, Sprn-/-. Unlike previous results observed in Prnp-/- mice, the absence of Doppel does not show enhancing effect on virus replication levels. Histological analysis of lung tissue from Prnd-/- mice revealed no difference in lesion size and severity compared with wild-type mice. However, transcriptomic analysis on day 7 postinfection revealed distinct signatures in Prnd-/- mice, highlighting the role of specific genes associated with polymorphonuclear neutrophil cells. Bronchoalveolar lavages confirmed a substantial neutrophil influx and increased inflammatory markers in the lungs of Prnd-/- mice. Neutrophil depletion experiments demonstrated a direct link between excessive neutrophil influx and increased susceptibility, mitigating pathology and partially restoring a wild-type phenotype in Prnd-/- mice. These findings underscore the complex role of Doppel in modulating the host immune response to influenza virus infection, particularly in regulating neutrophil recruitment and its implications on disease outcomes.

The roles of neutrophils in cardiovascular diseases

The immune response plays a vital role in the development of cardiovascular diseases (CVDs). As a crucial component of the innate immune system, neutrophils are involved in the initial inflammatory response following cardiovascular injury, thereby inducing subsequent damage and promoting recovery. Neutrophils exert their functional effects in tissues through various mechanisms, including activation and the formation of neutrophil extracellular traps (NETs). Once activated, neutrophils are recruited to the site of injury, where they release inflammatory mediators and cytokines. This study discusses the main mechanisms associated with neutrophil activity and proposes potential new therapeutic targets. In this review, we systematically summarize the diverse phenotypes of neutrophils in disease regulatory mechanisms, different modes of cell death, and focus on the relevance of neutrophils to various CVDs, including atherosclerosis, acute coronary syndrome, myocardial ischemia/reperfusion injury, hypertension, atrial fibrillation, heart failure, and viral myocarditis. Finally, we also emphasize the preclinical/clinical translational significance of neutrophil-targeted strategies.

Role of platelets and NETs in arterial thrombosis

Arterial thrombosis is one of the main causes of mortality and mortality worldwide. Platelets are effectively targeted by antithrombotic strategies. However, current antiplatelet agents are often associated with a bleeding risk and single antiplatelet agent may not completely prevent thrombosis. Platelets, neutrophils, and neutrophil extracellular traps (NETs) have been found to play crucial synergistic roles in the pathological process of arterial thrombosis in recent years. Platelets play a key regulatory role in the formation of NETs, and NETs can enhance platelet aggregation and activation, further aggravating the process of arterial thrombosis. Targeting the interaction mechanisms of platelets and NETs may provide a promising approach to better prevent arterial thrombosis. This review highlights the current insight in the interaction of platelets and neutrophil-forming NETs and their mechanisms involved in the process of arterial thrombosis. Finally, we discuss the potential of interventions targeting platelets and NETs to treat arterial thrombosis.

The Role of Crosstalk between Nets and Keratinocytes in Skin Immunity

The skin is the principal barrier against pathogens. Skin-resident cells, especially keratinocytes, play essential roles in skin immunity. Damage to the integrity of the skin barrier triggers the localized release of proinflammatory factors from keratinocytes, which attract neutrophils. These infiltrating neutrophils in turn release cytokines to modulate keratinocyte function, thereby amplifying skin inflammation. In addition, neutrophils produce neutrophil extracellular traps in a process called NETosis. Notably, crosstalk between neutrophils and keratinocytes is a prominent feature of skin infection eradication and autoimmune disorder development. In this paper, we review research progress on neutrophil extracellular traps in cutaneous immunity, with a particular emphasis on their modulation of keratinocytes. Moreover, we discuss the implications of neutrophil heterogeneity for immune defense and disease development and treatment.

CD177, MYBL2, and RRM2 Are Potential Biomarkers for Musculoskeletal Infections

BACKGROUND

Biomarkers of infection are measurable indicators that reflect the presence of an infection in the body. They are particularly valuable for detecting infections and tracking treatment responses. Previous transcriptome analysis of peripheral blood mononuclear cells (PBMCs) collected from patients during the active phase of diabetic foot infection identified the upregulation of several genes, including a neutrophil-specific cell surface glycoprotein, CD177, an Myb-related transcription factor 2 (MYBL2), and ribonucleotide reductase regulatory subunit M2 (RRM2). We aimed to investigate whether these observations in diabetic foot infections could be extrapolated to other musculoskeletal infections.

QUESTIONS/PURPOSES

(1) Are the protein concentrations of CD177, MYBL2, and RRM2 elevated in serum or PBMCs of patients with musculoskeletal infections? (2) Do serum and PBMC concentrations of CD177, MYBL2, and RRM2 decrease in response to antibiotic therapy? (3) Can these biomarkers give diagnostic accuracy and differentiate patients with musculoskeletal infections from controls?

METHODS

From April 2023 to June 2024, we treated 26 patients presenting with clinical symptoms and signs of acute musculoskeletal infections, including elevated inflammatory markers (white blood cell [WBC] and C-reactive protein [CRP]) and local changes such as swelling, erythema, tenderness or pain, warmth, purulent drainage, sinus tract, or wound leading to bone or hardware. Diagnosis included periprosthetic joint infection (PJI), foot and ankle infection (FAI), fracture-related infection (FRI), and septic arthritis of the native joints. Patients with chronic recurrent osteomyelitis, PJI, or FRI were excluded from the study. Among the 26 patients deemed potentially eligible, 19% (5) were excluded for the following reasons: prison inmate (1), unable to provide consent because of severe sepsis (1), mental illness (1), and declined to participate (2). Of the 81% (21) of patients who provided consent, cultures from 9.5% (2) were negative. These two patients were ultimately diagnosed with inflammatory arthritis: gout (1) and rheumatoid arthritis (1); thus, the musculoskeletal infection group for analysis consisted of 73.1% (19 of 26) of patients. A control group of 21 patients undergoing elective foot or ankle deformity correction surgery without infections or systemic inflammation was included. Because foot or ankle deformity is highly unlikely to influence the immunologic profile of the subjects, we believed that these patients would serve as an appropriate control group. Other than the absence of infection and the lower prevalence of diabetes mellitus, the control group was comparable to the study group in terms of demographics and clinical factors, including age and sex distribution. We collected blood samples from both patients and controls and quantified CD177, MYBL2, and RRM2 RNA transcription levels in the PBMC using qRT-PCR. We also assessed protein concentrations in the serum and PBMC using an enzyme-linked immunosorbent assay. A comparative analysis of the three biomarkers was performed on 19 patients with musculoskeletal infections with positive cultures and 21 controls to assess their diagnostic potential using the unpaired nonparametric t-test with the Mann-Whitney test. We obtained 8-week follow-up blood samples from seven patients with musculoskeletal infections who clinically healed. Healing was defined by normalization of inflammatory markers (WBC and CRP) and absence of swelling, erythema, local tenderness or pain, warmth, purulent drainage, sinus tract, or open wound. We performed a comparative analysis of the seven patients during active infection and after treatment to determine a change in the level of CD177, MYBL2, and RRM2 in their serum and PBMCs. These findings were also compared with those of the control group. We evaluated the diagnostic accuracy of CD177, MYBL2, and RRM2 for musculoskeletal infections using receiver operating characteristic (ROC) curve analysis.

RESULTS

The musculoskeletal infections group showed a larger increased serum and PBMC concentrations of CD177, MYBL2, and RRM2 proteins compared with the control group. The mean protein concentrations of CD177, MYBL2, and RRM2 were increased in the serum and PBMC of the musculoskeletal infections group compared with the controls. Serum levels of all biomarkers investigated were higher in musculoskeletal infections group compared with the control group (CD177 227 [155 to 432] versus 54 [10 to 100], difference of medians 173, p < 0.01; MYBL2 255 [231 to 314] versus 180 [148 to 214], difference of medians 75, p < 0.01; RRM2 250 [216 to 305] versus 190 [148 to 255], difference of medians 60, p < 0.01). Similarly, PBMC levels of all biomarkers were higher in the musculoskeletal infections group (CD177 55.3 [39.1 to 80.5] versus 17.5 [10.5 to 27.5], difference of medians 37.8, p < 0.01; MYBL2 144 [114 to 190] versus 91 [70 to 105], difference of medians 53, p < 0.01; RRM2 168 [143 to 202] versus 100 [77.5 to 133], difference of medians 68, p < 0.01). Additionally, serum levels of all biomarkers decreased in seven patients with musculoskeletal infections after infection treatment (CD177 3080 [2690 to 3320] versus 4250 [3100 to 8640], difference of medians 1170, p < 0.01; MYBL2 4340 [4120 to 4750] versus 5010 [4460 to 5880], difference of medians 670, p < 0.01; RRM2 4350 [3980 to 5000] versus 5025 [4430 to 6280], difference of medians 675, p = 0.01). Similarly, PBMC levels of all biomarkers were lower after infection treatment (CD177 805 [680 to 980] versus 1025 [750 to 1610], difference of medians 220, p < 0.01; MYBL2 2300 [2100 to 2550] versus 2680 [2220 to 3400], difference of medians 380, p = 0.02; RRM2 2720 [2500 to 3200] versus 3350 [2825 to 4030], difference of medians 630, p < 0.01). The area under the ROC curve for diagnosing musculoskeletal infections in the serum and PBMC was as follows: CD177 95% confidence interval [CI] > 0.99 and > 0.99, MYBL2 95% CI > 0.99 and > 0.99, and RRM2 95% CI = 0.96 and > 0.99, respectively.

CONCLUSION

We may utilize blood-based tests for CD177, MYBL2, and RRM2 to aid in the diagnosis of musculoskeletal infections, particularly when arthrocentesis or obtaining tissue culture is challenging. They may also assist in monitoring treatment response. As some of these biomarkers may also be elevated in other inflammatory conditions, a large-scale clinical study is needed to confirm their reliability in differentiating musculoskeletal infections from other inflammatory conditions.

CLINICAL RELEVANCE

CD177, MYBL2, and RRM2 proteins in blood samples may serve as novel biomarkers for diagnosing and monitoring treatment response in musculoskeletal infections.

Impact of antiplatelets, anticoagulants and cyclic nucleotide stimulators on neutrophil extracellular traps (NETs) and inflammatory markers during COVID-19

While the association between coronavirus disease-19 (COVID-19) and neutrophils extracellular traps (NETs) is recognized, uncertainties remain regarding its precise onset, timing of resolution and target therapy. To assess changes in inflammatory and NET markers during the first week of COVID-19 hospitalization, and the association with disease severity. "In vitro" experiments investigated the effect of antiplatelets, anticoagulants, and cyclic nucleotide stimulators on NETs release. Prospective cohort study, changes in interleukin (IL)-6, IL-8, IL-17, TNF-α, RANTES, PF4, and citrullinated-H3 (citH3) levels within each outcome group was evaluated using ANOVA. Differences between moderately ill, critically ill, and non-survivors were determined using Kruskal-Wallis and logistic regression. Healthy neutrophils were stimulated with phorbol-12-myristate-13-acetate (PMA) or COVID-19 sera and treated with unfractionated heparin (UFH), low molecular weight heparin (LMWH), aspirin (ASA), ticagrelor, cinaciguat, sildenafil, and milrinone. The proportion of NETosis was assessed using IncuCyte Cell Imager. Of the 125 patients, 40.8% had moderate COVID-19, 40.8% had critical COVID-19 but recovered, and 18.4% died. From admission to hospitalization day 8, IL-6 levels decreased in moderately and critically ill, but not in non-survivors, while citH3 levels increased in critically ill and non-survivors. IL-6, IL-8, and TNF-α levels were associated with critical and fatal COVID-19. The release of NETs by neutrophils stimulated with PMA or COVID-19 sera was decreased in the presence of ASA, UFH, LMWH and cyclic nucleotide stimulators in a dose-dependent manner. In the first week of hospitalization, NET markers rose later than inflammatory markers in severe COVID-19 cases. Cyclic nucleotide stimulators, ASA and heparin may emerge as treatment approaches as they may modulate NETosis.

The Emerging Role of Pleural Macrophages in Influenza Defense

The pleural cavity is gaining recognition as an important player in lung infections. Our recent research revealed that pleural macrophages (PMs) migrate from the pleural cavity into the lung during influenza virus infection, contributing to improved disease outcomes. This summary highlights key findings on the role of PMs in influencing viral lung infection outcomes and explores the potential directions for advancing this emerging field of study.

Deficient neutrophil responses early in influenza infection promote viral replication and pulmonary inflammation

Neutrophils play key protective roles in influenza infections, yet excessive neutrophilic inflammation is a hallmark of acute lung injury during severe infections. Phenotypic heterogeneity is increasingly recognized in neutrophil populations; however, how functional variation in neutrophils between individuals determine the diverse outcomes of influenza remains unclear. To examine immunologic responses that may drive varying outcomes in influenza, we infected C57BL/6 (B6) and A/J mice with mouse-adapted influenza A virus A/PR/8/34 H1N1. A self-resolving dose in B6 mice was lethal in A/J mice, which had increased viral load throughout infection accompanied by prominent bronchoalveolar neutrophilia and pulmonary vascular leakage preceding mortality. Notably, the B6 mice heavily recruited neutrophils to lungs early in infection while A/J mice failed to do so. Neutrophils from A/J mice additionally displayed reduced neutrophil extracellular trap (NET) release and reactive oxygen species (ROS) generation compared to B6 mice early in infection, suggesting the failure to control virus in A/J mice was a product of deficient neutrophil response. To determine if variation in neutrophils between strains governed viral control and inflammation, we adoptively transferred bone marrow neutrophils from B6 or A/J donors to A/J recipients early in infection and found that the transfer of B6 neutrophils enhanced viral clearance and abrogated the dissemination of CXCL1 and IL-6. The transfer of A/J neutrophils, however, failed to achieve either. Furthermore, B6 neutrophils were capable of greater levels of viral killing in vitro than their A/J counterparts. These results suggest that a key moderator of inflammation in influenza infection is the control of virus by neutrophils early in infection. Thus, host-specific differences in both the recruitment of these cells as well as interindividual variation in neutrophil ability to support viral clearance may in part dictate differing susceptibility to respiratory viral infections.

Advances in acute COPD exacerbation: clarifying specific immune mechanisms of infectious and noninfectious factors

Acute exacerbation of chronic obstructive pulmonary disease (AECOPD) is the main cause of hospitalization and death of patients with chronic obstructive pulmonary disease. This is largely due to bacterial resistance caused by clinical antibiotic abuse and the limited efficacy of current treatment strategies in managing noninfectious AECOPD, which presents a significant challenge for clinicians. Therefore, it is urgent for clinical treatment and prevention of AECOPD to fully understand the specific mechanism of AECOPD in the immune system and master the key differences between infectious factors and noninfectious factors. This article systematically discusses AECOPD triggered by various factors, including the activation of immune system, the recruitment and activation of inflammatory cells and the role of specific inflammatory responses, and through a comprehensive review of the literature, this article expounds the existing targeted diagnosis and treatment methods and technologies at different stages in order to provide new ideas and strategies for clinical prevention and treatment of AECOPD.

The dual role of toll-like receptors in COVID-19: Balancing protective immunity and immunopathogenesis

Toll-like receptors (TLRs) of human are considered as the most critical immunological mediators of inflammatory pathogenesis of COVID-19. These immunoregulatory glycoproteins are located on the surface and/or intracellular compartment act as innate immune sensors. Upon binding with distinct SARS-CoV-2 ligand(s), TLRs signal activation of different transcription factors that induce expression of the proinflammatory mediators that collectively induce 'cytokine storm'. Similarly, TLR activation is also pivotal in conferring protection to infection and invasion as well as upregulating the tissue repair pathways. This dual role of the human TLRs in deciding the fate of SARS-CoV-2 has made these receptor proteins as the critical mediators of immunoprotective and immunopathogenic consequences associated with COVID-19. Herein, pathbreaking discoveries exploring the immunobiological importance of the TLRs in COVID-19 and developing TLR-directed therapeutic intervention have been reviewed by accessing the up-to-date literatures available in the public domain/databases. In accordance with our knowledge in association with the importance of TLRs' role against viruses and identification of viral particles, they have been recognized as suitable candidates with high potential as vaccine adjuvants. In this regard, the agonists of TLR4 and TLR9 have effective potential in vaccine technology while the others need further investigations. This comprehensive review suggests that basal level expression of TLRs can act as friends to keep our body safe from strangers but act as a foe via overexpression. Therefore, selective inhibition of the overexpressed TLRs appears to be a solution to counteract the cytokine storm while TLR-agonists as vaccine adjuvants could lessen the risk of infection in the naïve population.

TLR7 Promotes Acute Inflammatory-Driven Lung Dysfunction in Influenza-Infected Mice but Prevents Late Airway Hyperresponsiveness

Severe lower respiratory tract disease following influenza A virus (IAV) infection is characterized by excessive inflammation and lung tissue damage, and this can impair lung function. The effect of toll-like receptor 7 (TLR7), which detects viral RNA to initiate antiviral and proinflammatory responses to IAV, on lung function during peak infection and in the resolution phase is not fully understood. Using wild-type (WT) C57BL/6 and TLR7 knockout (TLR7 KO) mice, we found that IAV infection induced airway dysfunction in both genotypes, although in TLR7 KO mice, this dysfunction manifested later, did not affect lung tissue elastance and damping, and was associated with a different immune phenotype. A positive correlation was found between lung dysfunction and the infiltration of neutrophils and Ly6Clo patrolling monocytes at day 7 post-infection. Conversely, in TLR7 KO mice, eosinophil and CD8+ cytotoxic T cells were associated with airway hyperactivity at day 14. IL-5 expression was higher in the airways of IAV-infected TLR7 KO mice, suggesting an enhanced Th2 response due to TLR7 deficiency. This study highlights an underappreciated duality of TLR7 in IAV disease: promoting inflammation-driven lung dysfunction during the acute infection but suppressing eosinophilic and CD8+ T cell-dependent hyperresponsiveness during disease resolution.

Endothelial activation and dysfunction caused by influenza A virus (Alphainfluenzavirus influenzae)

Annual epidemics of influenza result in 3-5 million cases of severe illness and more than 600 000 deaths. Severe forms of influenza are usually characterized by vascular endothelial cells damage. Thus, influenza A viruses, including subtypes A(H1N1)pdm09, A(H3N2), as well as highly pathogenic avian influenza viruses, can infect the vascular endothelium, leading to activation and subsequent dysfunction of these cells. In turn, endothelial dysfunction resulting in systemic morphofunctional changes of endothelial cells, which leads to impaired vascular tone, thrombosis and other complications, and is also a risk factor and profoundly implicated in the pathogenesis of many cardiovascular diseases. Thus, endothelial dysfunction is an important aspect of the pathogenesis of severe influenza, which must be considered in the pathogenetic therapy of this infectious disease. The aim of the review is to analyze the causes and specify mechanisms of development of endothelial activation and dysfunction caused by influenza A virus.

Type I IFN-mediated NET release promotes Mycobacterium tuberculosis replication and is associated with granuloma caseation

Neutrophils are the most abundant cell type in the airways of tuberculosis patients. Mycobacterium tuberculosis (Mtb) infection induces the release of neutrophil extracellular traps (NETs); however, the molecular regulation and impact of NET release on Mtb pathogenesis are unknown. We find that during Mtb infection in neutrophils, PAD4 citrullinates histones to decondense chromatin that gets released as NETs in a manner that can maintain neutrophil viability and promote Mtb replication. Type I interferon promotes the formation of chromatin-containing vesicles that allow NET release without compromising plasma membrane integrity. Analysis of nonhuman primate granulomas supports a model where neutrophils are exposed to type I interferon from macrophages as they migrate into the granuloma, thereby enabling the release of NETs associated with necrosis and caseation. Our data reveal NET release as a promising target to inhibit Mtb pathogenesis.

Entamoeba histolytica-induced NETs are highly cytotoxic on hepatic and colonic cells due to serine proteases and myeloperoxidase activities

During intestinal and liver invasion by the protozoan parasite Entamoeba histolytica, extensive tissue destruction linked to large neutrophil infiltrates is observed. It has been proposed that microbicidal components of neutrophils are responsible for the damage, however, the mechanism by which they are released and act in the extracellular space remains unknown. In previous studies, we have shown that E. histolytica trophozoites induce NET formation, leading to the release of neutrophil granule content into extruded DNA. In this work, we evaluate the possible participation of NETs in the development of amoeba-associated pathology and analyze the contribution of anti-microbial components of the associated granules. E. histolytica-induced NETs were isolated and their effect on the viability and integrity of HCT 116 colonic and Hep G2 liver cultures were evaluated. The results showed that simple incubation of cell monolayers with purified NETs for 24 h resulted in cell detachment and death in a dose-dependent manner. The effect was thermolabile and correlated with the amount of DNA and protein present in NETs. Pretreatment of NETs with specific inhibitors of some microbicidal components suggested that serine proteases, are mostly responsible for the damage caused by NETs on HCT 116 cells, while the MPO activity was the most related to Hep G2 cells damage. Our study also points to a very important role of DNA as a scaffold for the activity of these proteins. We show evidence of the development of NETs in amoebic liver abscesses in hamsters as a preamble to evaluate their participation in tissue damage. In conclusion, these studies demonstrate that amoebic-induced NETs have potent cytotoxic effects on target cells and, therefore, may be responsible for the intense damage associated with tissue invasion by this parasite.

Immune checkpoints are suppressed during pregnancy following influenza A virus infection

Influenza A virus (IAV) infection is a major health risk during pregnancy. Although vaccination and antiviral agents are widely used and reduce IAV-induced symptoms, they are not sufficient to control IAV infections in pregnancy, especially during pandemics. Respiratory viruses like IAV exploit immune alterations that occur during pregnancy, including the upregulation of immune checkpoint proteins (ICPs) like programmed death ligand-1 (PDL1), programmed cell death receptor 1 (PD1), and cytotoxic T-lymphocyte-associated protein 4 (CTLA4). We hypothesize that blocking expression of PDL1 on innate immune cells will improve maternal immunity following IAV infection. We used murine models of IAV infection during pregnancy with and without treatment with the immune checkpoint inhibitor (ICI), a-PDL1. Pregnant and nonpregnant mice were infected with mouse-adapted IAV (A/PR/8) and assessed at 3 days post infection (3 dpi). Lung cells were analyzed using flow cytometry. Lung mRNA expression of inflammatory and antiviral markers and histology was measured. Protein concentrations of inflammatory and antiviral markers, as well as viral titers were measured from lung bronchiolar lavage fluid (BALF). Lung function was also assessed. Following IAV infection, immune cells from pregnant mice had significant increases in the ICPs, PDL1, PD1, and CTLA4. a-PDL1 treatment effectively suppressed these ICPs and increased the activation marker, CD86. a-PDL1 treatment also reduced lung inflammatory cell infiltration and viral titers, increased antiviral responses, and improved lung function. Overall, IAV infection in pregnancy activates key inhibitory ICPs, leading to worsened disease outcomes. a-PDL1 treatment during IAV infection in pregnancy is an effective method to reduce ICP expression and improve overall immune cell responses.NEW & NOTEWORTHY Influenza infection worsens disease outcomes during pregnancy; however, treatment with anti-PDL1 can restore immune function during pregnancy.

Recent Advances in Immunological Landscape and Immunotherapeutic Agent of Nipah Virus Infection

Over the last two decades, the Nipah virus (NiV) emerged as a highly lethal zoonotic pathogen to humans. Outbreaks occurred occasionally in South and Southeast Asia. Therefore, a safe and effective vaccine against the virus is needed to fight against the deadly virus. Understanding the immunological landscape during this lethal virus infection is necessary in this direction. However, we found scattered information on the immunological landscape of the virus's reservoir, as well as hosts such as humans and livestock. The review provides a recent understanding of the immunological landscape of the virus's reservoir, human hosts, monoclonal antibodies, and vaccines for NiV infection. To describe the immunological landscape, we divided our review article into some points. Firstly, we illustrated bats' immune response as a reservoir during the NiV infection. Secondly, we illustrated an overview of the molecular mechanisms underlying the immune response to the NiV infection, various immune cells, humans' innate immune response, adaptive immunity, and the landscape of cytokines and chemokines. We also discussed INF escape, NET evasion, the T cell landscape, and the B cell landscape during virus infection. Thirdly, we also demonstrated the potential monoclonal antibody therapeutics, and vaccines. Finally, neutralizing antibodies (nAbs) of NiV and potentially other therapeutic strategies were discussed. The review will help researchers for better understanding the immunological landscape, mAbs, and vaccines, enabling them to develop their next-generation versions.

KVX-053, a protein tyrosine phosphatase 4A3 inhibitor, ameliorates SARS-CoV-2 spike protein subunit 1-induced acute lung injury in mice

Acute respiratory distress syndrome (ARDS), often preceded by acute lung injury (ALI), is characterized by the accumulation of inflammatory fluid in the lung alveoli, leaky alveolar epithelium and endothelium, and overexpression of proinflammatory cytokines. This progression from ALI to ARDS is a major contributor to the high mortality observed in patients with COVID-19. The spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) binds to lung angiotensin-converting enzyme 2 (ACE2), and in addition to facilitating viral cell entry, it plays an important role in the development of ALI and ARDS, especially in the later phases of COVID-19 as well as long-COVID. Protein tyrosine phosphatase (PTP) 4A3 is a key mediator of ARDS pathology. This study tested the hypothesis that targeting PTP4A3 would prevent COVID-19-associated ALI. Intratracheal administration of SARS-CoV-2 spike protein subunit 1 to K18-hACE2 transgenic mice expressing human ACE2 elicited pulmonary and systemic inflammation, leaky alveoli, overexpression of cytokines, structural lung injury, and lung dysfunction; all these symptoms were ameliorated by the selective, allosteric inhibitor of PTP4A3, KVX-053. These findings provide the first evidence supporting a role for PTP4A3 in the development of SARS-CoV-2-mediated ALI. SIGNIFICANCE STATEMENT: This study tested the hypothesis that targeting PTP4A3 would prevent COVID-19-associated ALI/ARDS. Intratracheal administration of SARS-CoV-2 spike protein subunit 1 to K18-hACE2 transgenic mice expressing human ACE2 elicited pulmonary and systemic inflammation, leaky alveoli, overexpression of cytokines and chemokines, structural lung injury, and lung dysfunction; all these symptoms were ameliorated by the selective, allosteric inhibitor of PTP4A3, KVX-053. These findings suggest that this novel PTP4A3 inhibitor may be useful against COVID-19 and potentially other viral-induced ARDS.

Neutrophil extracellular traps formation is associated with postoperative complications in congenital cardiac surgery

BACKGROUNDS

Pediatric patients with congenital heart disease (CHD) often require surgical repair using cardiopulmonary bypass. Despite advancements, mortality and complication rates remain significant.

METHODS & RESULTS

We prospectively examined 101 patients undergoing congenital cardiac surgery, identifying a mortality rate of 4.0% and a complication rate of 31.6%. Neonates and infants exhibited multiple complications more frequently. Prolonged bypass time was significantly associated with complications, with each additional 30 min increasing the odds by 1.46 times (95% CI 1.01-2.10, p = 0.042). We further investigated the involvement of damage-associated molecular pattern (DAMP) molecules by proteomics and ELISA. Plasma levels of DAMPs, including histones and high mobility group box 1 (HMGB1), were significantly elevated in the complication group. As these molecules target Toll-like receptor (TLR)2 and TLR4, mRNA expression of TLR2 and TLR4 in neutrophils was upregulated in the complication group. In vitro and in vivo analyses demonstrated that histones and HMGB1 induced the formation of neutrophil extracellular traps (NETs). This finding aligned with greater NETs formation observed at the end of CPB and during the postoperative period in neonates and infants who developed postoperative complications.

CONCLUSION

Targeting NETs and associated DAMPs may provide a novel therapeutic approach to mitigate complications in this patient population.

Treatment with lipoxin A4 improves influenza A infection outcome, induces macrophage reprogramming, anti-inflammatory and pro-resolutive responses

INTRODUCTION

Influenza A is a virus from the Orthomixoviridae family responsible for high lethality rates and morbidity, despite clinically proven vaccination strategies and some anti-viral therapies. The eicosanoid Lipoxin A4 (LXA4) promotes the resolution of inflammation by decreasing cell recruitment and pro-inflammatory cytokines release, but also for inducing activation of apoptosis, efferocytosis, and macrophage reprogramming.

OBJECTIVE

Here, we evaluated whether a synthetic lipoxin mimetic, designated AT-01-KG, would improve the course of influenza A infection in a murine model.

METHOD

Mice were infected with influenza A/H1N1 and treated with AT-01-KG (1.7 μg/kg/day, i.p.) at day 3 post-infection.

RESULTS

AT-01-KG attenuated mortality, reducing leukocyte infiltration and lung damage at day 5 and day 7 post-infection. AT-01-KG is a Formyl Peptide Receptor 2 (designated FPR2/3 in mice) agonist, and the protective responses were not observed in fpr2/3 -/- animals. In mice treated with LXA4 (50 μg/kg/day, i.p., days 3-6 post-infection), at day 7, macrophage reprogramming was observed, as seen by a decrease in classically activated macrophages and an increase in alternatively activated macrophages in the lungs. Furthermore, the number of apoptotic cells and cells undergoing efferocytosis was increased in the lavage of treated mice. Treatment also modulated the adaptive immune response, increasing the number of T helper 2 cells (Th2) and regulatory T (Tregs) cells in the lungs of the treated mice.

CONCLUSION

Therefore, treatment with a lipoxin A4 analog was beneficial in a model of influenza A infection in mice. The drug decreased inflammation and promoted resolution and beneficial immune responses, suggesting it may be useful in patients with severe influenza.

The implication of dendritic cells in lung diseases: Immunological role of toll-like receptor 4

The immune responses play a profound role in the progression of lung lesions in both infectious and non-infectious diseases. Dendritic cells, as the "frontline" immune cells responsible for antigen presentation, set up a bridge between innate and adaptive immunity in the course of these diseases. Among the receptors equipped in dendritic cells, Toll-like receptors are a group of specialized receptors as one type of pattern recognition receptors, capable of sensing environmental signals including invading pathogens and self-antigens. Toll-like receptor 4, a pivotal member of the Toll-like receptor family, was formerly recognized as a receptor sensitive to the outer membrane component lipopolysaccharide derived from Gram-negative bacteria, triggering the subsequent response. Moreover, its other essential roles in immune responses have drawn significant attention in the past decade. A better understanding of the implication of Toll-like receptor 4 in dendritic cells could contribute to the management of pulmonary diseases including pneumonia, pulmonary tuberculosis, asthma, acute lung injury, and lung cancer.

Neutrophil extracellular traps and cardiovascular disease: Associations and potential therapeutic approaches

Cardiovascular disease (CVD) is a significant global health concern, ranking among the top five causes of disability-adjusted life-years (DALY) in 190 countries and territories. Neutrophils, key players in the innate immune system, combat infections by releasing neutrophil extracellular traps (NETs) composed of DNA, histones, elastase, myeloperoxidase, and antimicrobial peptides. This paper explores the relationship between NETs and cardiovascular diseases, focusing on conditions such as heart failure, pulmonary hypertension, atrial fibrillation, and ischemia-reperfusion injury. Particularly, it delves into the impact of NETs on atrial fibrillation and pulmonary hypertension, as well as the role of myeloperoxidase (MPO) and neutrophil elastase (NE) in these diseases. Furthermore, the potential of targeting NETs for the treatment of cardiovascular diseases is discussed.

Investigate the potential impact of Hemagglutinin from the H1N1 strain on severe pneumonia

The most prevalent glycoprotein on the influenza virus envelope is called hemagglutinin (HA), yet little is known about its involvement in the pathophysiology and etiology of severe influenza pneumonia. Here, after stimulating human bronchial epithelial cells (16-HBE) and mice with HA of H1N1 for 12 h, we investigated the proliferation, migration, inflammatory cytokines expression, and apoptosis in 16-HBE and the pathological damage in mouse lung tissue. The expression of inflammatory cytokines plasminogen activator inhibitor 1(PAI-1), urokinase-type (uPA) and tissue-type (tPA) plasminogen activators, and apoptosis were all enhanced by HA, which also prevented the proliferation and migration of bronchial epithelial cells. HA enhanced up-regulated PAI-1, uPA, and tPA protein expression within mouse lung tissue and caused lung injury. In conclusion, HA alone, but not the whole H1N1 virus, induces lung tissue injury by inhibiting cell proliferation and migration, while promoting the expression of inflammatory cytokines and apoptosis.

IFN-γ primes bone marrow neutrophils to acquire regulatory functions in severe viral respiratory infections

Neutrophil subsets endowed with regulatory/suppressive properties are widely regarded as deleterious immune cells that can jeopardize antitumoral response and/or antimicrobial resistance. Here, we describe a sizeable fraction of neutrophils characterized by the expression of programmed death-ligand 1 (PD-L1) in biological fluids of humans and mice with severe viral respiratory infections (VRI). Biological and transcriptomic approaches indicated that VRI-driven PD-L1+ neutrophils are endowed with potent regulatory functions and reduced classical antimicrobial properties, as compared to their PD-L1- counterpart. VRI-induced regulatory PD-L1+ neutrophils were generated remotely in the bone marrow in an IFN-γ-dependent manner and were quickly mobilized into the inflamed lungs where they fulfilled their maturation. Neutrophil depletion and PD-L1 blockade during experimental VRI resulted in higher mortality, increased local inflammation, and reduced expression of resolving factors. These findings suggest that PD-L1+ neutrophils are important players in disease tolerance by mitigating local inflammation during severe VRI and that they may constitute relevant targets for future immune interventions.

Risk factor analysis and prediction model construction for severe adenovirus pneumonia in children

BACKGROUND

Severe adenovirus pneumonia in children has a high mortality rate, but research on risk prediction models is lacking. Such models are essential as they allow individualized predictions and assess whether children will likely progress to severe disease.

METHODS

A retrospective analysis was performed on children with adenovirus pneumonia who were hospitalized at the Children's Hospital of Nanjing Medical University from January 2017 to March 2024. The patients were grouped according to clinical factors, and the groups were compared using Ridge regression and multiple logistic regression to identify risk factors associated with severe adenovirus pneumonia. A prediction model was constructed, and its value in clinical application was evaluated.

RESULTS

699 patients were included in the study, with 284 in the severe group and 415 in the general group. Through the screening of 44 variables, the final risk factors for severe adenovirus pneumonia in children as the levels of neutrophils (OR = 1.086, 95% CI: 1.054‒1.119, P < 0.001), D-dimer (OR = 1.005, 95% CI: 1.003‒1.007, P < 0.001), fibrinogen degradation products (OR = 1.341, 95% CI: 1.034‒1.738, P = 0.027), B cells (OR = 1.076, 95%CI: 1.046‒1.107, P < 0.001), and lactate dehydrogenase (OR = 1.008, 95% CI: 1.005‒1.011, P < 0.001). The value of the area under the receiver operating characteristic curve was 0.974, the 95% CI was 0.963-0.985, and the P-value of the Hosmer-Lemeshow test was 0.547 (P > 0.05), indicating that the model had strong predictive power.

CONCLUSION

In this study, the clinical variables of children with adenovirus pneumonia were retrospectively analyzed to identify risk factors for severe disease. A prediction model for severe disease was constructed and evaluated, showing good application value.

The role of cathelicidins in neutrophil biology

Despite their relatively short lifespan, neutrophils are tasked with counteracting pathogens through various functions, including phagocytosis, production of reactive oxygen species, neutrophil extracellular traps (NETs), and host defense peptides. Regarding the latter, small cationic cathelicidins present a conundrum in neutrophil function. Although primarily recognized as microbicides with an ability to provoke pores in microbial cell walls, the ability of cathelicidin to modulate key neutrophil functions is also of great importance, including the release of chemoattractants, cytokines, and reactive oxygen species, plus prolonging neutrophil lifespan. Cumulative evidence indicates a less recognized role of cathelicidin as an "immunomodulator"; however, this term is not always explicit, and its relevance in neutrophil responses during infection and inflammation is seldom discussed. This review compiles and discusses studies of how neutrophils use cathelicidin to respond to infections, while also acknowledging immunomodulatory aspects of cathelicidin through potential crosstalk between sources of the peptide.

Comparative pathogenicity of influenza virus-induced pneumonia mouse model following intranasal and aerosolized intratracheal inoculation

BACKGROUND

Infection of mice with mouse-adapted strains of influenza virus has been widely used to establish mouse pneumonia models. Intranasal inoculation is the traditional route for constructing an influenza virus-induced pneumonia mouse model, while intratracheal inoculation has been gradually applied in recent years. In this article, the pathogenicity of influenza virus-induced pneumonia mouse models following intranasal and aerosolized intratracheal inoculation were compared.

METHODS

By comparing the two ways of influenza inoculation, intranasal and intratracheal, a variety of indices such as survival rate, body weight change, viral titer and load, pathological change, lung wet/dry ratio, and inflammatory factors were investigated. Meanwhile, the transcriptome was applied for the initial exploration of the mechanism underlying the variations in the results between the two inoculation methods.

RESULTS

The findings suggest that aerosolized intratracheal infection leads to more severe lung injury and higher viral loads in the lungs compared to intranasal infection, which may be influenced by the initial site of infection, sialic acid receptor distribution, and host innate immunity.

CONCLUSION

Intratracheal inoculation is a better method for modelling severe pneumonia in mice than intranasal infection.

Taking AIM at Influenza: The Role of the AIM2 Inflammasome

Influenza A viruses (IAV) are dynamic and highly mutable respiratory pathogens that present persistent public health challenges. Inflammasomes, as components of the innate immune system, play a crucial role in the early detection and response to infections. They react to viral pathogens by triggering inflammation to promote immune defences and initiate repair mechanisms. While a strong response is necessary for early viral control, overactivation of inflammasomes can precipitate harmful hyperinflammatory responses, a defining characteristic observed during severe influenza infections. The Absent in Melanoma 2 (AIM2) inflammasome, traditionally recognised for its role as a DNA sensor, has recently been implicated in the response to RNA viruses, like IAV. Paradoxically, AIM2 deficiency has been linked to both enhanced and reduced vulnerability to IAV infection. This review synthesises the current understanding of AIM2 inflammasome activation during IAV and explores its clinical implications. Understanding the nuances of AIM2's involvement could unveil novel therapeutic avenues for mitigating severe influenza outcomes.

Targeting NETosis in Acute Brain Injury: A Systematic Review of Preclinical and Clinical Evidence

Acute brain injury (ABI) remains one of the leading causes of death and disability world-wide. Its treatment is challenging due to the heterogeneity of the mechanisms involved and the variability among individuals. This systematic review aims at evaluating the impact of anti-histone treatments on outcomes in ABI patients and experimental animals and defining the trend of nucleosome levels in biological samples post injury. We performed a search in Pubmed/Medline and Embase databases for randomized controlled trials and cohort studies involving humans or experimental settings with various causes of ABI. We formulated the search using the PICO method, considering ABI patients or animal models as population (P), comparing pharmacological and non-pharmacological therapy targeting the nucleosome as Intervention (I) to standard of care or no treatment as Control (C). The outcome (O) was mortality or functional outcome in experimental animals and patients affected by ABI undergoing anti-NET treatments. We identified 28 studies from 1246 articles, of which 7 were experimental studies and 21 were human clinical studies. Among these studies, only four assessed the effect of anti-NET therapy on circulating markers. Three of them were preclinical and reported better outcome in the interventional arm compared to the control arm. All the studies observed a significant reduction in circulating NET-derived products. NETosis could be a target for new treatments. Monitoring NET markers in blood and cerebrospinal fluid might predict mortality and long-term outcomes. However, longitudinal studies and randomized controlled trials are warranted to fully evaluate their potential, as current evidence is limited.

Nanoparticle targeting of neutrophil glycolysis prevents lung ischemia-reperfusion injury

Neutrophils exacerbate pulmonary ischemia-reperfusion injury (IRI) resulting in poor short and long-term outcomes for lung transplant recipients. Glycolysis powers neutrophil activation, but it remains unclear if neutrophil-specific targeting of this pathway will inhibit IRI. Lipid nanoparticles containing the glycolysis flux inhibitor 2-deoxyglucose (2-DG) were conjugated to neutrophil-specific Ly6G antibodies (NP-Ly6G[2-DG]). Intravenously administered NP-Ly6G(2-DG) to mice exhibited high specificity for circulating neutrophils. NP-Ly6G(2-DG)-treated neutrophils were unable to adapt to hypoglycemic conditions of the lung airspace environment as evident by the loss of demand-induced glycolysis, reductions in glycogen and ATP content, and an increased vulnerability to apoptosis. NP-Ly6G(2-DG) treatment inhibited pulmonary IRI following hilar occlusion and orthotopic lung transplantation. IRI protection was associated with less airspace neutrophil extracellular trap generation, reduced intragraft neutrophilia, and enhanced alveolar macrophage efferocytotic clearance of neutrophils. Collectively, our data show that pharmacologically targeting glycolysis in neutrophils inhibits their activation and survival leading to reduced pulmonary IRI.

The LPS-inactivating enzyme acyloxyacyl hydrolase protects the brain from experimental stroke

Blood-brain-barrier (BBB) disruption is a pathological hallmark of ischemic stroke, and inflammation occurring at the BBB contributes to the pathogenesis of ischemic brain injury. Lipopolysaccharide (LPS), a cell wall component of Gram-negative bacteria, is elevated in patients with acute stroke. The activity of LPS is controlled by acyloxyacyl hydrolase (AOAH), a host enzyme that deacylates LPS to inactivated forms. However, whether AOAH influences the pathogenesis of ischemic stroke remain elusive. We performed in vivo experiments to explore the role and mechanism of AOAH on neutrophil extravasation, BBB disruption, and brain infarction. We found that AOAH was upregulated in neutrophils in peri-infarct areas from mice with transient focal cerebral ischemia. AOAH deficiency increased neutrophil extravasation into the brain parenchyma and proinflammatory cytokine production, broke down the BBB and worsened stroke outcomes in mice. These effects require Toll-like receptor 4 (TLR4) because absence of TLR4 or pharmacologic inhibition of TLR4 signaling prevented the exacerbated inflammation and BBB damage in Aoah-/- mice after ischemic stroke. Importantly, neutrophil depletion or inhibition of neutrophil trafficking by blocking LFA-1 integrin dramatically reduced stroke-induced BBB breakdown in Aoah-/- mice. Furthermore, virus-mediated overexpression of AOAH induced a substantial decrease in neutrophil recruitment that was accompanied by reducing BBB damage and stroke volumes. Our findings show the importance of AOAH in regulating neutrophil-dependent BBB breakdown and cerebral infarction. Consequently, strategies that modulate AOAH may be a new therapeutic approach for treatment of ischemic stroke.

Ventilator-associated pneumonia: pathobiological heterogeneity and diagnostic challenges

Ventilator-associated pneumonia (VAP) affects up to 20% of critically ill patients and induces significant antibiotic prescription pressure, accounting for half of all antibiotic use in the ICU. VAP significantly increases hospital length of stay and healthcare costs yet is also associated with long-term morbidity and mortality. The diagnosis of VAP continues to present challenges and pitfalls for the currently available clinical, radiological and microbiological diagnostic armamentarium. Biomarkers and artificial intelligence offer an innovative potential direction for ongoing future research. In this Review, we summarise the pathobiological heterogeneity and diagnostic challenges associated with VAP.

Adenosine Triphosphate Release From Influenza-Infected Lungs Enhances Neutrophil Activation and Promotes Disease Progression

BACKGROUND

Adenosine triphosphate (ATP) enhances neutrophil responses, but little is known about the role of ATP in influenza infections.

METHODS

We used a mouse influenza model to study if ATP release is associated with neutrophil activation and disease progression.

RESULTS

Influenza infection increased pulmonary ATP levels 5-fold and plasma ATP levels 3-fold vs healthy mice. Adding ATP at those concentrations to blood from healthy mice primed neutrophils and enhanced CD11b and CD63 expression, CD62L shedding, and reactive oxygen species production in response to formyl peptide receptor stimulation. Influenza infection also primed neutrophils in vivo, resulting in formyl peptide receptor-induced CD11b expression and CD62L shedding up to 3 times higher than that of uninfected mice. In infected mice, large numbers of neutrophils entered the lungs. These cells were significantly more activated than the peripheral neutrophils of infected mice and pulmonary neutrophils of healthy mice. Plasma ATP levels of infected mice and influenza disease progression corresponded with the numbers and activation level of their pulmonary neutrophils.

CONCLUSIONS

Findings suggest that ATP release from the lungs of infected mice promotes influenza disease progression by priming peripheral neutrophils, which become strongly activated and cause pulmonary tissue damage after their recruitment to the lungs.

Building a human lung from pluripotent stem cells to model respiratory viral infections

To protect against the constant threat of inhaled pathogens, the lung is equipped with cellular defenders. In coordination with resident and recruited immune cells, this defence is initiated by the airway and alveolar epithelium following their infection with respiratory viruses. Further support for viral clearance and infection resolution is provided by adjacent endothelial and stromal cells. However, even with these defence mechanisms, respiratory viral infections are a significant global health concern, causing substantial morbidity, socioeconomic losses, and mortality, underlining the need to develop effective vaccines and antiviral medications. In turn, the identification of new treatment options for respiratory infections is critically dependent on the availability of tractable in vitro experimental models that faithfully recapitulate key aspects of lung physiology. For such models to be informative, it is important these models incorporate human-derived, physiologically relevant versions of all cell types that normally form part of the lungs anti-viral response. This review proposes a guideline using human induced pluripotent stem cells (iPSCs) to create all the disease-relevant cell types. iPSCs can be differentiated into lung epithelium, innate immune cells, endothelial cells, and fibroblasts at a large scale, recapitulating in vivo functions and providing genetic tractability. We advocate for building comprehensive iPSC-derived in vitro models of both proximal and distal lung regions to better understand and model respiratory infections, including interactions with chronic lung diseases.

Rebalancing Viral and Immune Damage versus Tissue Repair Prevents Death from Lethal Influenza Infection

Maintaining tissue function while eliminating infected cells is fundamental to host defense. Innate inflammatory damage contributes to lethal influenza and COVID-19, yet other than steroids, immunomodulatory drugs have modest effects. Among more than 50 immunomodulatory regimes tested in mouse lethal influenza infection, only the previously reported early depletion of neutrophils showed efficacy, suggesting that the infected host passes an early tipping point in which limiting innate immune damage alone cannot rescue physiological function. To re-balance the system late in infection, we investigated whether partial limitation of viral spread using oseltamivir (Tamiflu) together with enhancement of epithelial repair by blockade of interferon signaling or the limitation of further epithelial cell loss mediated by cytotoxic CD8 + T cells would prevent death. These treatments salvaged a large fraction of infected animals, providing new insight into the importance of repair processes and the timing of adaptive immune responses in survival of pulmonary infections.

Dysregulated proteasome activity and steroid hormone biosynthesis are associated with mortality among patients with acute COVID-19

The persistence of coronavirus disease 2019 (COVID-19)-related hospitalization severely threatens medical systems worldwide and has increased the need for reliable detection of acute status and prediction of mortality. We applied a systems biology approach to discover acute-stage biomarkers that could predict mortality. A total 247 plasma samples were collected from 103 COVID-19 (52 surviving COVID-19 patients and 51 COVID-19 patients with mortality), 51 patients with other infectious diseases (IDCs) and 41 healthy controls (HCs). Paired plasma samples were obtained from survival COVID-19 patients within 1 day after hospital admission and 1-3 days before discharge. There were clear differences between COVID-19 patients and controls, as well as substantial differences between the acute and recovery phases of COVID-19. Samples from patients in the acute phase showed suppressed immunity and decreased steroid hormone biosynthesis, as well as elevated inflammation and proteasome activation. These findings were validated by enzyme-linked immunosorbent assays and metabolomic analyses in a larger cohort. Moreover, excessive proteasome activity was a prominent signature in the acute phase among patients with mortality, indicating that it may be a key cause of poor prognosis. Based on these features, we constructed a machine learning panel, including four proteins [C-reactive protein (CRP), proteasome subunit alpha type (PSMA)1, PSMA7, and proteasome subunit beta type (PSMB)1)] and one metabolite (urocortisone), to predict mortality among COVID-19 patients (area under the receiver operating characteristic curve: 0.976) on the first day of hospitalization. Our systematic analysis provides a novel method for the early prediction of mortality in hospitalized COVID-19 patients.

Extracellular traps in skin lesions infected with lymphocystis disease virus in black rockfish (Sebastes schlegelii)

The lymphocystis disease (LCD), caused by Lymphocystis disease virus (LCDV), is a benign and self-limiting disease described in a many freshwater and marine fish species. Hypertrophic fibroblasts and extensive aggregation of inflammatory cells are characteristics of LCD. In the present study, small animal imaging and ultrastructural investigations were carried out on the lymphocystis nodules of black rockfish (Sebastes schlegelii) naturally infected with lymphocystis iridovirus, to assess pathology, and the exudate with particular attention to the formation of extracellular traps (ETs) in vivo. Ex vivo were examined by nodules sections and primary cells stimulation. By histopathological analysis, the nodules contained infiltrated inflammatory cells and extensive basophilic fibrillar filaments at the periphery of the hypertrophied fibroblasts. ETs were assessed in nodules samples using indirect immunofluorescence to detect DNA and myeloperoxidase. Moreover, LCDV was able to infect peritoneal cells of black rockfish in vitro and induce the formation of ETs within 4 h. In summary, this study proved that ETs are involved in the response to LCDV infection and may be involved in formation of lymphoid nodules. Taken together, the findings provide a new perspective to determine the impact factors on the growth of nodules.

ARAP3 protects from excessive formylated peptide-induced microvascular leakage by acting on endothelial cells and neutrophils

Vascular permeability is temporarily heightened during inflammation, but excessive inflammation-associated microvascular leakage can be detrimental, as evidenced in the inflamed lung. Formylated peptides regulate vascular leakage indirectly via formylated peptide receptor-1 (FPR1)-mediated recruitment and activation of neutrophils. Here we identify how the GTPase-activating protein ARAP3 protects against formylated peptide-induced microvascular permeability via endothelial cells and neutrophils. In vitro, Arap3-/- endothelial monolayers were characterised by enhanced formylated peptide-induced permeability due to upregulated endothelial FPR1 and enhanced vascular endothelial cadherin internalisation. In vivo, enhanced inflammation-associated microvascular leakage was observed in Arap3-/- mice. Leakage of plasma protein into the lungs of Arap3-/- mice increased within hours of formylated peptide administration. Adoptive transfer experiments indicated this was dependent upon ARAP3 deficiency in both immune and non-immune cells. Bronchoalveolar lavages of formylated peptide-challenged Arap3-/- mice contained neutrophil extracellular traps (NETs). Pharmacological inhibition of NET formation abrogated excessive microvascular leakage, indicating a critical function of NETs in this context. The observation that Arap3-/- mice developed more severe influenza suggests these findings are pertinent to pathological situations characterised by abundant formylated peptides. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

A Cyclic Peptide Based on Pheasant Cathelicidin Inhibits Influenza A H1N1 Virus Infection

Influenza viruses are the leading cause of upper respiratory tract infections, leading to several global pandemics and threats to public health. Due to the continuous mutation of influenza A viruses, there is a constant need for the development of novel antiviral therapeutics. Recently, natural antimicrobial peptides have provided an opportunity for the discovery of anti-influenza molecules. Here, we designed several peptides based on pheasant cathelicidin and tested their antiviral activities and mechanisms against the H1N1 virus. Of note, the designed peptides Pc-4 and Pc-5 were found to inhibit replication of the H1N1 virus with an IC50 = 8.14 ± 3.94 µM and 2.47 ± 1.95 µM, respectively. In addition, the cyclic peptide Pc-5 was found to induce type I interferons and the expression of interferon-induced genes. An animal study showed that the cyclic peptide Pc-5 effectively inhibited H1N1 virus infection in a mouse model. Taken together, our work reveals a strategy for designing cyclic peptides and provides novel molecules with therapeutic potential against influenza A virus infection.

Macrophage biomimetic nanoparticle-targeted functional extracellular vesicle micro-RNAs revealed via multiomics analysis alleviate sepsis-induced acute lung injury

Patients who suffer from sepsis typically experience acute lung injury (ALI). Extracellular vesicles (EVs) contain miRNAs, which are potentially involved in ALI. However, strategies to screen more effective EV-miRNAs as therapeutic targets are yet to be elucidated. In this study, functional EV-miRNAs were identified based on multiomics analysis of single-cell RNA sequencing of targeted organs and serum EV (sEV) miRNA profiles in patients with sepsis. The proportions of neutrophils and macrophages were increased significantly in the lungs of mice receiving sEVs from patients with sepsis compared with healthy controls. Macrophages released more EVs than neutrophils. MiR-125a-5p delivery by sEVs to lung macrophages inhibited Tnfaip3, while miR-221-3p delivery to lung neutrophils inhibited Fos. Macrophage membrane nanoparticles (MM NPs) loaded with an miR-125a-5p inhibitor or miR-221-3p mimic attenuated the response to lipopolysaccharide (LPS)-induced ALI. Transcriptome profiling revealed that EVs derived from LPS-stimulated bone marrow-derived macrophages (BMDMs) induced oxidative stress in neutrophils. Blocking toll-like receptor, CXCR2, or TNFα signaling in neutrophils attenuated the oxidative stress induced by LPS-stimulated BMDM-EVs. This study presents a novel method to screen functional EV-miRNAs and highlights the pivotal role of macrophage-derived EVs in ALI. MM NPs, as delivery systems of key sEV-miRNA mimics or inhibitors, alleviated cellular responses observed in sepsis-induced ALI. This strategy can be used to reduce septic organ damage, particularly lung damage, by targeting EVs.

Treatment with lipoxin A 4 improves influenza A infection outcome through macrophage reprogramming, anti-inflammatory and pro-resolutive responses

Objective and design

Here, we evaluated whether a synthetic lipoxin mimetic, designated AT-01-KG, would improve the course of influenza A infection in a murine model.

Treatment

Mice were infected with influenza A/H1N1 and treated with AT-01-KG (1.7 mg/kg/day, i.p.) at day 3 post-infection.

Methods

Mortality rate was assessed up to day 21 and inflammatory parameters were assessed at days 5 and 7.

Results

AT-01-KG attenuated mortality, reducing leukocyte infiltration and lung damage at day 5 and day 7 post-infection. AT-01-KG is a Formyl Peptide Receptor 2 (designated FPR2/3 in mice) agonist, and the protective responses were not observed in FPR2/3 -/- animals. In mice treated with LXA4 (50mg/kg/day, i.p., days 3-6 post-infection), at day 7, macrophage reprogramming was observed, as seen by a decrease in classically activated macrophages and an increase in alternatively activated macrophages in the lungs. Furthermore, the number of apoptotic cells and cells undergoing efferocytosis was increased in the lavage of treated mice. Treatment also modulated the adaptive immune response, increasing the number of anti-inflammatory T cells (Th2) and regulatory T (Tregs) cells in the lungs of the treated mice.

Conclusions

Therefore, treatment with a lipoxin A4 analog was beneficial in a model of influenza A infection in mice. The drug decreased inflammation and promoted resolution and beneficial immune responses, suggesting it may be useful in patients with severe influenza.

Spontaneous Lethal Outbreak of Influenza A Virus Infection in Vaccinated Sows on Two Farms Suggesting the Occurrence of Vaccine-Associated Enhanced Respiratory Disease with Eosinophilic Lung Pathology

Influenza A virus (IAV) infections in swine are usually subclinical, but they can reach high morbidity rates. The mortality rate is normally low. In this study, six vaccinated, spontaneously deceased sows revealed IAV infection and enhanced neutrophilic bronchopneumonia with unexpectedly large numbers of infiltrating eosinophils. The purpose of this study was to characterize these lung lesions with special emphasis on the phenotypes of inflammatory cells, the presence of eosinophilic peroxidase (EPO), and neutrophil extracellular traps (NETs). The number of Sirius red-stained eosinophils was significantly higher in the lungs of IAV-infected sows compared to healthy pigs, indicating a migration of eosinophils from blood vessels into the lung tissue stimulated by IAV infection. The detection of intra- and extracellular EPO in the lungs suggests its contribution to pulmonary damage. The presence of CD3+ T lymphocytes, CD20+ B lymphocytes, and Iba-1+ macrophages indicates the involvement of cell-mediated immune responses in disease progression. Furthermore, high numbers of myeloperoxidase-positive cells were detected. However, DNA-histone-1 complexes were reduced in IAV-infected sows, leading to the hypothesis that NETs are not formed in the IAV-infected sows. In conclusion, our findings in the lungs of IAV-infected vaccinated sows suggest the presence of so far unreported field cases of vaccine-associated enhanced respiratory disease.

The Synthetic Surfactant CHF5633 Restores Lung Function and Lung Architecture in Severe Acute Respiratory Distress Syndrome in Adult Rabbits

PURPOSE

Acute respiratory distress syndrome (ARDS) is a major cause of hypoxemic respiratory failure in adults. In ARDS extensive inflammation and leakage of fluid into the alveoli lead to dysregulation of pulmonary surfactant metabolism and function. Altered surfactant synthesis, secretion, and breakdown contribute to the clinical features of decreased lung compliance and alveolar collapse. Lung function in ARDS could potentially be restored with surfactant replacement therapy, and synthetic surfactants with modified peptide analogues may better withstand inactivation in ARDS alveoli than natural surfactants.

METHODS

This study aimed to investigate the activity in vitro and the bolus effect (200 mg phospholipids/kg) of synthetic surfactant CHF5633 with analogues of SP-B and SP-C, or natural surfactant Poractant alfa (Curosurf®, both preparations Chiesi Farmaceutici S.p.A.) in a severe ARDS model (the ratio of partial pressure arterial oxygen and fraction of inspired oxygen, P/F ratio ≤ 13.3 kPa) induced by hydrochloric acid instillation followed by injurious ventilation in adult New Zealand rabbits. The animals were ventilated for 4 h after surfactant treatment and the respiratory parameters, histological appearance of lung parenchyma and levels of inflammation, oxidative stress, surfactant dysfunction, and endothelial damage were evaluated.

RESULTS

Both surfactant preparations yielded comparable improvements in lung function parameters, reductions in lung injury score, pro-inflammatory cytokines levels, and lung edema formation compared to untreated controls.

CONCLUSIONS

This study indicates that surfactant replacement therapy with CHF5633 improves lung function and lung architecture, and attenuates inflammation in severe ARDS in adult rabbits similarly to Poractant alfa. Clinical trials have so far not yielded conclusive results, but exogenous surfactant may be a valid supportive treatment for patients with ARDS given its anti-inflammatory and lung-protective effects.

Medical ozone alleviates acute lung injury by enhancing phagocytosis targeting NETs via AMPK/SR-A1 axis

Acute lung injury (ALI) linked to sepsis has a high mortality rate, with limited treatment options available. In recent studies, medical ozone has shown promising results in alleviating inflammation and infection. Here, we aimed to evaluate the therapeutic potential of medical ozone in sepsis-induced ALI using a mouse model, measuring behavioral assessments, lung function, and blood flow. Western blot was used to quantify the levels of protein. In vitro, experiments on BMDM cells examine the impact of AMPK inhibitors and agonists on phagocytic activity. Results indicate that medical ozone can enhance the survival rate, ameliorate lung injury, and improve lung function and limb microcirculation in mice with ALI. Notably, it inhibits NETs formation, a crucial player in ALI development. Medical ozone also counteracts elevated TF, MMP-9, and IL-1β levels. In ALI mice, the effects of ozone are nullified and BMDMs exhibit impaired engulfment of NETs following Sr-a1 knockout. Under normal physiological conditions, the use of an AMPK antagonist produces similar effects to Sr-a1 knockout, significantly inhibiting the phagocytosis of NETs by BMDMs. On the contrary, AMPK agonists enhance this phagocytic process. In conclusion, medical ozone can alleviate sepsis-induced lung injury via the AMPK/SR-A1 pathway, thereby enhancing phagocytosis of NETs by macrophages.

SARS-CoV-2 and Influenza Co-Infection: Fair Competition or Sinister Combination?

The COVID-19 pandemic remains a serious public health problem globally. During winter influenza seasons, more aggressive SARS-CoV-2 infections and fatalities have been documented, indicating that influenza co-infections may significantly impact the disease outcome of COVID-19. Both influenza and SARS-CoV-2 viruses share many similarities in their transmission and their cellular tropism for replication in the human respiratory tract. However, the complex intricacies and multi-faceted dynamics of how the two pathogens interact to ensure their survival in the same lung microenvironment are still unclear. In addition, clinical studies on influenza co-infections in COVID-19 patients do not provide conclusive evidence of how influenza co-infection mechanistically modifies disease outcomes of COVID-19. This review discusses various viral as well as host factors that potentially influence the survival or synergism of these two respiratory pathogens in the infected lung microenvironment.

In Vivo Immune-Modulatory Activity of Lefamulin in an Influenza Virus A (H1N1) Infection Model in Mice

Lefamulin is a first-in-class systemic pleuromutilin antimicrobial and potent inhibitor of bacterial translation, and the most recent novel antimicrobial approved for the treatment of community-acquired pneumonia (CAP). It exhibits potent antibacterial activity against the most prevalent bacterial pathogens that cause typical and atypical pneumonia and other infectious diseases. Early studies indicate additional anti-inflammatory activity. In this study, we further investigated the immune-modulatory activity of lefamulin in the influenza A/H1N1 acute respiratory distress syndrome (ARDS) model in BALB/c mice. Comparators included azithromycin, an anti-inflammatory antimicrobial, and the antiviral oseltamivir. Lefamulin significantly decreased the total immune cell infiltration, specifically the neutrophils, inflammatory monocytes, CD4+ and CD8+ T-cells, NK cells, and B-cells into the lung by Day 6 at both doses tested compared to the untreated vehicle control group (placebo), whereas azithromycin and oseltamivir did not significantly affect the total immune cell counts at the tested dosing regimens. Bronchioalveolar lavage fluid concentrations of pro-inflammatory cytokines and chemokines including TNF-α, IL-6, IL-12p70, IL-17A, IFN-γ, and GM-CSF were significantly reduced, and MCP-1 concentrations were lowered (not significantly) by lefamulin at the clinically relevant 'low' dose on Day 3 when the viral load peaked. Similar effects were also observed for oseltamivir and azithromycin. Lefamulin also decreased the viral load (TCID50) by half a log10 by Day 6 and showed positive effects on the gross lung pathology and survival. Oseltamivir and lefamulin were efficacious in the suppression of the development of influenza-induced bronchi-interstitial pneumonia, whereas azithromycin did not show reduced pathology at the tested treatment regimen. The observed anti-inflammatory and immune-modulatory activity of lefamulin at the tested treatment regimens highlights a promising secondary pharmacological property of lefamulin. While these results require confirmation in a clinical trial, they indicate that lefamulin may provide an immune-modulatory activity beyond its proven potent antibacterial activity. This additional activity may benefit CAP patients and potentially prevent acute lung injury (ALI) and ARDS.

Platelets: Orchestrators of immunity in host defense and beyond

Platelets prevent blood loss during vascular injury and contribute to thrombus formation in cardiovascular disease. Beyond these classical roles, platelets are critical for the host immune response. They guard the vasculature against pathogens via specialized receptors, intracellular signaling cascades, and effector functions. Platelets also skew inflammatory responses by instructing innate immune cells, support adaptive immunosurveillance, and influence antibody production and T cell polarization. Concomitantly, platelets contribute to tissue reconstitution and maintain vascular function after inflammatory challenges. However, dysregulated activation of these multitalented cells exacerbates immunopathology with ensuing microvascular clotting, excessive inflammation, and elevated risk of macrovascular thrombosis. This dichotomy underscores the critical importance of precisely defining and potentially modulating platelet function in immunity.