Pulmonary immune cells and inflammatory cytokine dysregulation are associated with mortality of IL-1R1 -/-mice infected with influenza virus (H1N1)

STAT1 regulates neutrophil gelatinase B-associated lipocalin induction in influenza-induced myocarditis

Influenza is a significant public health and economic threat around the world. Epidemiological studies have demonstrated a close association between influenza pandemics and cardiovascular mortality. Moreover, it has been shown that there is a decrease in cardiovascular mortality in high-risk patients following vaccination with the influenza vaccine. Here, we have investigated the role of anti-viral STAT1 signaling in influenza-induced myocarditis. Wild-type mice (C57BL/6) were infected with either influenza A/PR/8/34 or control, and cellular response and gene expression analysis from the heart samples were assessed 7 days later. The expression of interferon response genes STAT1, STAT2, Mx1, OASL2, ISG15, chemokines CCL2, CCL3, CXCL9 and CXCL10, and the frequency of neutrophils (CD45+CD11b+Ly6G+) and CD4+ T cells (CD45+CD4+) were all significantly increased in influenza-infected mice when compared to vehicle controls. These data suggest that influenza infection induces interferons, inflammatory chemokines, and cellular recruitment during influenza infection. We further investigated the role of STAT1 in influenza-induced myocarditis. The frequency of neutrophils and the levels of lipocalin 2 were significantly increased in STAT1-/- mice when compared to WT controls. Finally, we investigated the role of Lcn2 in viral-induced myocarditis. We found that in the absence of Lcn2, there was preserved cardiac function in Lcn2-/- mice when compared to WT controls. These data suggest that the absence of Lcn2 is cardioprotective during viral-induced myocarditis.

Sex and molecular differences in cardiovascular parameters at peak influenza disease in mice

There is a growing interest in the detection of subtle changes in cardiovascular physiology in response to viral infection to develop better disease surveillance strategies. This is not only important for earlier diagnosis and better prognosis of symptomatic carriers but also useful to diagnose asymptomatic carriers of the virus. Previous studies provide strong evidence of an association between inflammatory biomarker levels and both blood pressure (BP) and heart rate (HR) during infection. The identification of novel biomarkers during an inflammatory event could significantly improve predictions for cardiovascular events. Thus, we evaluated changes in cardiovascular physiology induced in A/Puerto Rico/8/34 (PR8) influenza infections in female and male C57BL/6J mice and compared them with the traditional method of influenza disease detection using body weight (BW). Using radiotelemetry, changes in BP, HR, and activity were studied. Change in BW of infected females was significantly decreased from 5 to 13 days postinfection (dpi), yet alterations in normal physiology including loss of diurnal rhythm and reduced activity was observed starting at about 3 dpi for HR and 4 dpi for activity and BP; continuing until about 13 dpi. In contrast, males had significantly decreased BW 8 to 12 dpi and demonstrated altered physiological measurements for a shorter period compared with females with a reduction starting at 5 dpi for activity, 6 dpi for BP, and 7 dpi for HR until about 12 dpi, 10 dpi, and 9 dpi, respectively. Finally, females and males exhibited different patterns of inflammatory maker expression in lungs at peak disease by analyzing bulk RNA-sequencing data for lungs and Bio-plex cytokine assay for blood collected from influenza-infected and naïve C57BL/6J female and male mice at 7 dpi. In total, this study provides insight into cardiovascular changes and molecular markers to distinguish sex differences in peak disease caused by influenza virus infection.NEW & NOTEWORTHY This study performed longitudinal cardiovascular measurements of influenza viral infection and identified sex difference in both physiological and molecular markers at peak disease.

A single-shot vaccine approach for the universal influenza A vaccine candidate M2e

Although the need for a universal influenza vaccine has long been recognized, only a handful of candidates have been identified so far, with even fewer advancing in the clinical pipeline. The 24–amino acid ectodomain of M2 protein (M2e) has been developed over the past two decades. However, M2e-based vaccine candidates have shortcomings, including the need for several administrations and the lack of sustained antibody titers over time. We report here a vaccine targeting strategy that has the potential to confer sustained and strong protection upon a single shot of a small amount of M2e antigen. The current COVID-19 pandemic has highlighted the importance of developing versatile, powerful platforms for the rapid deployment of vaccines against any incoming threat.

Influenza, commonly referred to as “flu,” is a major global public health concern and a huge economic burden to societies. Current influenza vaccines need to be updated annually to match circulating strains, resulting in low take-up rates and poor coverage due to inaccurate prediction. Broadly protective universal flu vaccines that do not need to be updated annually have therefore been pursued. The highly conserved 24–amino acid ectodomain of M2 protein (M2e) is a leading candidate, but its poor immunogenicity has been a major roadblock in its clinical development. Here, we report a targeting strategy that shuttles M2e to a specific dendritic cell subset (cDC1) by engineering a recombinant anti-Clec9A monoclonal antibody fused at each of its heavy chains with three copies of M2e. Single administration in mice of 2 µg of the Clec9A–M2e construct triggered an exceptionally sustained anti-M2e antibody response and resulted in a strong anamnestic protective response upon influenza challenge. Furthermore, and importantly, Clec9A–M2e immunization significantly boosted preexisting anti-M2e titers from prior flu exposure. Thus, the Clec9A-targeting strategy allows antigen and dose sparing, addressing the shortcomings of current M2e vaccine candidates. As the cDC1 subset exists in humans, translation to humans is an exciting and realistic avenue.

Interferon mediated prophylactic protection against respiratory viruses conferred by a prototype live attenuated influenza virus vaccine lacking non-structural protein 1

The influenza A non-structural protein 1 (NS1) is known for its ability to hinder the synthesis of type I interferon (IFN) during viral infection. Influenza viruses lacking NS1 (ΔNS1) are under clinical development as live attenuated human influenza virus vaccines and induce potent influenza virus-specific humoral and cellular adaptive immune responses. Attenuation of ΔNS1 influenza viruses is due to their high IFN inducing properties, that limit their replication in vivo. This study demonstrates that pre-treatment with a ΔNS1 virus results in an antiviral state which prevents subsequent replication of homologous and heterologous viruses, preventing disease from virus respiratory pathogens, including SARS-CoV-2. Our studies suggest that ΔNS1 influenza viruses could be used for the prophylaxis of influenza, SARS-CoV-2 and other human respiratory viral infections, and that an influenza virus vaccine based on ΔNS1 live attenuated viruses would confer broad protection against influenza virus infection from the moment of administration, first by non-specific innate immune induction, followed by specific adaptive immunity.

Evaluation of Nutritional Gel Supplementation in C57BL/6J Mice Infected with Mouse-Adapted Influenza A/PR/8/34 Virus

Mice are a common animal model for the study of influenza virus A (IAV). IAV infection causes weight loss due to anorexia and dehydration, which can result in early removal of mice from a study when they reach a humane endpoint. To reduce the number of mice prematurely removed from an experiment, we assessed nutritional gel (NG) supplementation as a support strategy for mice infected with mouse-adapted Influenza A/Puerto Rico/8/34 (A/PR/8/34; H1N1) virus. We hypothesized that, compared with the standard of care (SOC), supplementation with NG would reduce weight loss and increase survival in mice infected with IAV without impacting the initial immune response to infection. To assess the effects of NG, male and female C57BL/6J mice were infected with IAV at low, intermediate, or high doses. When compared with SOC, mice given NG showed a significant decrease in the maximal percent weight loss at all viral doses in males and at the intermediate dose for females. Mice supplemented with NG had no deaths for either sex at the intermediate dose and a significant increase in survival in males at the high viral dose. Supplementation with NG did not alter the viral titer or the pulmonary recruitment of immune cells as measured by cell counts and flow cytometry of cells recovered in bronchoalveolar lavage (BAL) fluid in either sex. However, mice given NG had a significant reduction in IL6 and TNFα in BAL fluid and no significant differences in CCL2, IL4, IL10, CXCL1, CXCL2, and VEGF. The results of this study show that as compared with infected SOC mice, infected mice supplemented with NG have reduced weight loss and increased survival, with males showing a greater benefit. These results suggest that NG should be considered as a support strategy and indicate that sex is an important biologic variable in mice infected with IAV.

Toonaciliatin K attenuates the lung injury induced by lung infection of H1N1 influenza virus by regulating the NF-κB/MyD88/TLR-7 pathway in mice

INTRODUCTION

H1N1 infection has a high mortality rate due to lung injury and respiratory distress. The present study determines the protective effect of toonaciliatin K against the lung injury induced by the lung infection of H1N1 influenza mice and also postulates the molecular mechanism.

MATERIAL AND METHODS

Infection was induced by exposing the anesthetized mice to H1N1 virus (10 LD50 in a volume of 30 ml) intranasally at day zero and mice were treated with toonaciliatin K 16.5 and 33 mg/kg intragastrically for 2 weeks. The effect of toonaciliatin K was assessed by estimating survival rate and lung edema by the lung index. Histopathological changes were determined by H + E staining and western blot and an RT-PCR study was also performed on the lung tissue homogenate.

RESULTS

Data of the study suggest that toonaciliatin K treatment enhances the survival rate and reduces the lung index compared to infected mice. There was a decrease in the level of chemokines and cytokines in the lung tissue of the toonaciliatin K treated group compared to infected mice. Moreover, expression of TLR-7, NF-κB p65 and MyD88 protein was found to be reduced in the lung tissue of the toonaciliatin K treated group compared to infected mice.

CONCLUSIONS

Data of the study suggested that toonaciliatin K protects against lung injury in lung H1N1 lung infection by regulating the TLR-7/Myd88/NF-κB p65 pathway.

Proinflammatory Effects of Respiratory Syncytial Virus-Induced Epithelial HMGB1 on Human Innate Immune Cell Activation

High mobility group box 1 (HMGB1) is a multifunctional nuclear protein that translocates to the cytoplasm and is subsequently released to the extracellular space during infection and injury. Once released, it acts as a damage-associated molecular pattern and regulates immune and inflammatory responses. Respiratory syncytial virus (RSV) is a major cause of acute lower respiratory tract infections in infants and elderly, for which no effective treatment or vaccine is currently available. This study investigated the effects of HMGB1 on cytokine secretion, as well as the involvement of NF-κB and TLR4 pathways in RSV-induced HMGB1 release in human airway epithelial cells (AECs) and its proinflammatory effects on several human primary immune cells. Purified HMGB1 was incubated with AECs (A549 and small alveolar epithelial cells) and various immune cells and measured the release of proinflammatory mediators and the activation of NF-κB and P38 MAPK. HMGB1 treatment significantly increased the phosphorylation of NF-κB and P38 MAPK but did not induce the release of cytokines/chemokines from AECs. However, addition of HMGB1 to immune cells did significantly induce the release of cytokines/chemokines and activated the NF-κB and P38 MAPK pathways. We found that activation of NF-κB accounted for RSV-induced HMGB1 secretion in AECs in a TLR4-dependent manner. These results indicated that HMGB1 secreted from AECs can facilitate the secretion of proinflammatory mediators from immune cells in a paracrine mechanism, thus promoting the inflammatory response that contributes to RSV pathogenesis. Therefore, blocking the proinflammatory function of HMGB1 may be an effective approach for developing novel therapeutics.

The inflammasome potentiates influenza/Staphylococcus aureus superinfection in mice

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