Innate and adaptive immune responses in patients with pandemic influenza A(H1N1)pdm09

Electronic cigarette vapor exposure exaggerates the pro-inflammatory response during influenza A viral infection in human distal airway epithelium

Electronic cigarettes or vaping products have been marketed as a safer alternative to smoking, but very little is known about the health effects in the human lung, particularly in the distal airways, a key site of airway obstruction and destruction in chronic obstructive pulmonary disease that is often exacerbated by viral infections. The aim of this study was to investigate the effects of electronic cigarette vapor (e-vapor) on human distal airway epithelial responses to influenza A virus (IAV) infection. We isolated primary small airway epithelial cells (SAECs) from donor lungs free of lung disease, and cultured them at air-liquid interface (ALI). To measure markers of epithelial injury such as integrity of epithelial barrier structure and function, we selected a regimen of non-toxic, barrier preserving e-vapor exposure of cultured cells to 15 puffs of e-vapor from a commercially available e-cigarette once per day for 3 days, prior to IAV infection. After 72 h of infection, media and cell lysates were collected to measure cytokines involved in inflammatory and antiviral responses. Pre-exposure to e-vapor with IAV infection, compared to IAV infection alone, significantly increased inflammatory and antiviral mediators including IL-8, CXCL10, IFN-beta, and MX1. Our results suggest that e-vapor exposure amplifies human distal airway pro-inflammatory response to IAV infection, independently of the severity of cell injury during viral infection.

Fueling influenza and the immune response: Implications for metabolic reprogramming during influenza infection and immunometabolism

Recent studies support the notion that glycolysis and oxidative phosphorylation are rheostats in immune cells whose bioenergetics have functional outputs in terms of their biology. Specific intrinsic and extrinsic molecular factors function as molecular potentiometers to adjust and control glycolytic to respiratory power output. In many cases, these potentiometers are used by influenza viruses and immune cells to support pathogenesis and the host immune response, respectively. Influenza virus infects the respiratory tract, providing a specific environmental niche, while immune cells encounter variable nutrient concentrations as they migrate in response to infection. Immune cell subsets have distinct metabolic programs that adjust to meet energetic and biosynthetic requirements to support effector functions, differentiation, and longevity in their ever-changing microenvironments. This review details how influenza coopts the host cell for metabolic reprogramming and describes the overlap of these regulatory controls in immune cells whose function and fate are dictated by metabolism. These details are contextualized with emerging evidence of the consequences of influenza-induced changes in metabolic homeostasis on disease progression.

Natural Killer Cell Dysfunction and Its Role in COVID-19

When facing an acute viral infection, our immune systems need to function with finite precision to enable the elimination of the pathogen, whilst protecting our bodies from immune-related damage. In many instances however this "perfect balance" is not achieved, factors such as ageing, cancer, autoimmunity and cardiovascular disease all skew the immune response which is then further distorted by viral infection. In SARS-CoV-2, although the vast majority of COVID-19 cases are mild, as of 24 August 2020, over 800,000 people have died, many from the severe inflammatory cytokine release resulting in extreme clinical manifestations such as acute respiratory distress syndrome (ARDS) and hemophagocytic lymphohistiocytosis (HLH). Severe complications are more common in elderly patients and patients with cardiovascular diseases. Natural killer (NK) cells play a critical role in modulating the immune response and in both of these patient groups, NK cell effector functions are blunted. Preliminary studies in COVID-19 patients with severe disease suggests a reduction in NK cell number and function, resulting in decreased clearance of infected and activated cells, and unchecked elevation of tissue-damaging inflammation markers. SARS-CoV-2 infection skews the immune response towards an overwhelmingly inflammatory phenotype. Restoration of NK cell effector functions has the potential to correct the delicate immune balance required to effectively overcome SARS-CoV-2 infection.

The cellular immunophenotype expression of influenza A virus and influenza B virus infection in children

BACKGROUND

The innate immune response is the primary defense against influenza virus infection.

METHODS

This is a prospective study carried out in children <18 years of age who were diagnosed with influenza A or influenza B infection. Demographic and clinical data, laboratory findings and cell immunophenotypes on first presentation were compared.

RESULTS

With respect to immunophenotype, influenza A infection resulted in a higher fraction of CD14⁺ and CD4⁺IL-17A⁺cells compared to children infected with influenza B. By contrast, influenza B infection resulted in a comparatively higher percentage of double-negative CD4^-CD8^- lymphocyte subsets. Influenza A infection was associated with comparatively higher percentages of CD4⁺CD25^highFoxp3⁺ and CD4⁺CD25^lowFoxp3⁺ cells. By contrast, the percentage of CD8⁺CD25^high and CD8⁺CD25^low cells was similar among patients with influenza A infection and influenza B infection.

CONCLUSIONS

An improved understanding of the fraction of regulatory T cells with influenza virus infections may provide further understandings on immune responses.

Differential Viral-Host Immune Interactions Associated with Oseltamivir-Resistant H275Y and Wild-Type H1N1 A(pdm09) Influenza Virus Pathogenicity

Oseltamivir is a common therapy against influenza A virus (IAV) infections. The acquisition of oseltamivir resistance (OR) mutations, such as H275Y, hampers viral fitness. However, OR H1N1 viruses have demonstrated the ability to spread throughout different populations. The objective of this work was to compare the fitness of two strains of OR (R6 and R7) containing the H275Y mutation, and a wild-type (F) pandemic influenza A (H1N1) 2009 (pdm09) virus both in vitro and in vivo in mice and to select one OR strain for a comparison with F in ferrets. R6 showed faster replication and pathogenicity than R7 in vitro and in mice. Subsequently, R6 was selected for the fitness comparison with the F strain in ferrets. Ferrets infected with the F virus showed more severe clinical signs, histopathological lung lesions, and viral quantification when compared to OR R6-infected animals. More importantly, differential viral kinetics correlated with differential pro-inflammatory host immune responses in the lungs of infected ferrets, where OR-infected animals developed a protective higher expression of type I IFN and Retinoid acid Inducible Gene I (RIG-I) genes early after infection, resulting in the development of milder disease. These results suggest the presence of early specific viral-host immune interactions relevant in the development of influenza-associated lung pathology.

Risk Factors for Influenza Virus Related Severe Lower Respiratory Tract Infection in Children

BACKGROUND

Influenza virus is one of the most common respiratory pathogens for all age groups and may cause seasonal outbreaks. Our aim was to identify risk groups and factors associated with severe clinical course including mortality in children with influenza-related lower respiratory tract infection (LRTI).

METHODS

We conducted a retrospective study in children hospitalized with influenza virus LRTI from 2008 to 2018. Data on demographic features, influenza type, viral coinfection, primary and secondary bacterial infections (SBIs), time of onset of antiviral treatment, comorbidities, hospitalization length, pediatric intensive care unit admission/invasive mechanical ventilation (IMV) need and mortality were collected from medical records.

RESULTS

There were 280 patients hospitalized with LRTI and median hospitalization length was 9 days. Congenital heart disease, neuromuscular disease, SBIs and late-onset antiviral treatment were independent risk factors for prolonged hospital stay (P < 0.05). Pediatric intensive care unit admission was present in 20.4% (57) of the patients and 17.1% (48) of all patients required IMV. SBIs, lymphopenia, neutrophilia, immunosuppression and human bocavirus coinfection were independent risk factors for IMV support (P < 0.05). Eighteen patients died and immunosuppression, lymphopenia and SBIs were independent risk factors for mortality (P < 0.05).

CONCLUSIONS

Presence of comorbidity, SBIs, neutrophilia and lymphopenia at admission identified as risk factors for severe influenza infections including need for IMV and death. Although several studies showed that antiviral treatment reduce hospitalization, complications and mortality, there is a lack of prospective trials and patients for antiviral therapy should be carefully chosen by the clinician.

CCR2 mediates increased susceptibility to post-H1N1 bacterial pneumonia by limiting dendritic cell induction of IL-17

Post influenza bacterial pneumonia is associated with significant mortality and morbidity. Dendritic cells (DCs) play a crucial role in host defense against bacterial pneumonia, but their contribution to post influenza-susceptibility to secondary bacterial pneumonia is incompletely understood. WT and CCR2^-/- mice were infected with 100 plaque forming units (pfu) H1N1 intranasally alone or were challenged on day 5 with 7 × 10⁷ colony forming units (cfu) methicillin-resistant Staphylococcus aureus intratracheally. WT mice express abundant CCL2 mRNA and protein post-H1N1 alone or dual infection. CCR2^-/- mice had significantly higher survival as compared to WT mice, associated with significantly improved bacterial clearance at 24 and 48 h (10-fold and 14-fold, respectively) post bacterial challenge. There was robust upregulation of IL-23 and IL-17 as well as downregulation of IL-27 expression in CCR2^-/- mice following sequential infection as compared to WT mice, which was also associated with significantly greater accumulation of CD103⁺ DC. Finally, WT mice treated with a CCR2 inhibitor showed improved bacterial clearance in association with similar cytokine profiles as CCR2^-/- mice. Thus, CCR2 significantly contributes to increased susceptibility to bacterial infection after influenza pneumonia likely via altered dendritic cell responses and thus, CCR2 antagonism represents a potential therapeutic strategy.

Quis Custodiet Ipsos Custodes? Regulation of Cell-Mediated Immune Responses Following Viral Lung Infections

Viral lung infections are leading causes of morbidity and mortality. Effective immune responses to these infections require precise immune regulation to preserve lung function after viral clearance. One component of airway pathophysiology and lung injury associated with acute respiratory virus infection is effector T cells, yet these are the primary cells required for viral clearance. Accordingly, multiple immune mechanisms exist to regulate effector T cells, limiting immunopathology while permitting clearance of infection. Much has been learned in recent years about regulation of T cell function during chronic infection and cancer, and it is now clear that many of these mechanisms also control inflammation in acute lung infection. In this review, we focus on regulatory T cells, inhibitory receptors, and other cells and molecules that regulate cell-mediated immunity in the context of acute respiratory virus infection.

Regulatory T cell frequencies and phenotypes following anti-viral vaccination

Regulatory T cells (Treg) function in the prevention of excessive inflammation and maintenance of immunological homeostasis. However, these cells may also interfere with resolution of infections or with immune reactions following vaccination. Effects of Treg on vaccine responses are nowadays investigated, but the impact of vaccination on Treg homeostasis is still largely unknown. This may be a relevant safety aspect, since loss of tolerance through reduced Treg may trigger autoimmunity. In exploratory clinical trials, healthy adults were vaccinated with an influenza subunit vaccine plus or minus the adjuvant MF59®, an adjuvanted hepatitis B subunit vaccine or a live attenuated yellow fever vaccine. Frequencies and phenotypes of resting (rTreg) and activated (aTreg) subpopulations of circulating CD4+ Treg were determined and compared to placebo immunization. Vaccination with influenza vaccines did not result in significant changes in Treg frequencies and phenotypes. Vaccination with the hepatitis B vaccine led to slightly increased frequencies of both rTreg and aTreg subpopulations and a decrease in expression of functionality marker CD39 on aTreg. The live attenuated vaccine resulted in a decrease in rTreg frequency, and an increase in expression of activation marker CD25 on both subpopulations, possibly indicating a conversion from resting to migratory aTreg due to vaccine virus replication. To study the more local effects of vaccination on Treg in lymphoid organs, we immunized mice and analyzed the CD4+ Treg frequency and phenotype in draining lymph nodes and spleen. Vaccination resulted in a transient local decrease in Treg frequency in lymph nodes, followed by a systemic Treg increase in the spleen. Taken together, we showed that vaccination with vaccines with an already established safe profile have only minimal impact on frequencies and characteristics of Treg over time. These findings may serve as a bench-mark of inter-individual variation of Treg frequencies and phenotypes following vaccination.

Human hantavirus infection elicits pronounced redistribution of mononuclear phagocytes in peripheral blood and airways

Hantaviruses infect humans via inhalation of virus-contaminated rodent excreta. Infection can cause severe disease with up to 40% mortality depending on the viral strain. The virus primarily targets the vascular endothelium without direct cytopathic effects. Instead, exaggerated immune responses may inadvertently contribute to disease development. Mononuclear phagocytes (MNPs), including monocytes and dendritic cells (DCs), orchestrate the adaptive immune responses. Since hantaviruses are transmitted via inhalation, studying immunological events in the airways is of importance to understand the processes leading to immunopathogenesis. Here, we studied 17 patients infected with Puumala virus that causes a mild form of hemorrhagic fever with renal syndrome (HFRS). Bronchial biopsies as well as longitudinal blood draws were obtained from the patients. During the acute stage of disease, a significant influx of MNPs expressing HLA-DR, CD11c or CD123 was detected in the patients’ bronchial tissue. In parallel, absolute numbers of MNPs were dramatically reduced in peripheral blood, coinciding with viremia. Expression of CCR7 on the remaining MNPs in blood suggested migration to peripheral and/or lymphoid tissues. Numbers of MNPs in blood subsequently normalized during the convalescent phase of the disease when viral RNA was no longer detectable in plasma. Finally, we exposed blood MNPs in vitro to Puumala virus, and demonstrated an induction of CCR7 expression on MNPs. In conclusion, the present study shows a marked redistribution of blood MNPs to the airways during acute hantavirus disease, a process that may underlie the local immune activation and contribute to immunopathogenesis in hantavirus-infected patients.

Inhalation of hantavirus-infected rodent droppings can cause a wide range of disease ranging from mild symptoms to deaths in humans. Central to hantavirus disease is vascular leakage that can manifest in different organs, including the lungs. Although the virus can infect endothelial cells lining the blood vessels, it does not cause cell death. Instead, activation of the immune system in response to viral infection has been implicated in causing vascular leakage. In this study, we investigated how monocytes and dendritic cells (DCs) are involved in hantavirus disease, given their capacity to activate other immune cells. We obtained unique clinical material from 17 Puumala virus-infected patients including mucosal biopsies from the airways as well as multiple blood draws over the course of disease. In the airways of these patients, we observed an infiltration of monocytes and DCs. In parallel, there was a dramatic depletion in peripheral blood—more than ten-fold—of monocytes and DCs that was sustained throughout the first two weeks of disease. Taken together, this study provides novel insights into immune mediated processes underlying human hantavirus pathogenesis.

Human Lung Mononuclear Phagocytes in Health and Disease

The lungs are vulnerable to attack by respiratory insults such as toxins, allergens, and pathogens, given their continuous exposure to the air we breathe. Our immune system has evolved to provide protection against an array of potential threats without causing collateral damage to the lung tissue. In order to swiftly detect invading pathogens, monocytes, macrophages, and dendritic cells (DCs)-together termed mononuclear phagocytes (MNPs)-line the respiratory tract with the key task of surveying the lung microenvironment in order to discriminate between harmless and harmful antigens and initiate immune responses when necessary. Each cell type excels at specific tasks: monocytes produce large amounts of cytokines, macrophages are highly phagocytic, whereas DCs excel at activating naïve T cells. Extensive studies in murine models have established a division of labor between the different populations of MNPs at steady state and during infection or inflammation. However, a translation of important findings in mice is only beginning to be explored in humans, given the challenge of working with rare cells in inaccessible human tissues. Important progress has been made in recent years on the phenotype and function of human lung MNPs. In addition to a substantial population of alveolar macrophages, three subsets of DCs have been identified in the human airways at steady state. More recently, monocyte-derived cells have also been described in healthy human lungs. Depending on the source of samples, such as lung tissue resections or bronchoalveolar lavage, the specific subsets of MNPs recovered may differ. This review provides an update on existing studies investigating human respiratory MNP populations during health and disease. Often, inflammatory MNPs are found to accumulate in the lungs of patients with pulmonary conditions. In respiratory infections or inflammatory diseases, this may contribute to disease severity, but in cancer patients this may improve clinical outcomes. By expanding on this knowledge, specific lung MNPs may be targeted or modulated in order to attain favorable responses that can improve preventive or treatment strategies against respiratory infections, lung cancer, or lung inflammatory diseases.

Regulatory T cells and IL10 suppress pulmonary host defense during early-life exposure to radical containing combustion derived ultrafine particulate matter

Background

Exposure to elevated levels of particulate matter (PM) is associated with increased risk of morbidity and mortality due to respiratory tract viral infections in infants. Recent identification of environmentally persistent free radicals (EPFRs) in the PM from a variety of combustion sources suggests its role in the enhancement of disease severity of lower respiratory tract infections (LRTI). Our previous studies demonstrated that acute exposure to EPFRs induces pulmonary immunosuppression allowing for enhanced influenza disease severity. Here, we determine the mechanism of EPFR-induced immunosuppression and its impact on the immune response towards influenza infection.

Methods

Neonatal mice (3 days old) were acutely exposed to DCB (combustion derived PM with chemisorbed EPFR) for seven consecutive days. Four days post-exposure (dpe), mice were infected with influenza virus. Pulmonary T cell phenotypes including regulatory T cells (Tregs) were analyzed by flow cytometry. The role of IL10 in EPFR-induced exacerbation of influenza disease severity was determined by administering recombinant IL10 (rIL10) to wild type mice or by using IL10 deficient (IL10^−/−) neonatal mice. Mice were assessed for morbidity by measuring percent weight change and pulmonary viral load.

Results

Neonatal mice exposed to EPFRs had a significant increase in pulmonary Tregs and the immunosuppressive cytokine IL10 following influenza infection, which coincided with decreased protective T cell responses to influenza infection at 6 dpi. Depletion of Tregs in EPFR-exposed neonatal mice resulted in increased protective, adaptive T cell responses, whereas adoptive transfer of Tregs from EPFR-exposed neonates to air-exposed neonatal mice suppressed adaptive T cell responses towards influenza infection. Further, treatment with rIL10 could recapitulate EPFR-induced exacerbation of morbidity and pulmonary viral load compared to air exposed and influenza infected mice, whereas, EPFR-exposed IL10^−/− neonates exhibited significant reductions in morbidity, pulmonary viral load and adaptive T cell responses following influenza infection.

Conclusions

Neonatal exposure to EPFRs induced Tregs and IL10 resulting in suppressed adaptive T cell responses and enhanced influenza disease severity in neonatal mice. Depletion of Tregs increased adaptive T cell responses and deficiency of IL10 reduced morbidity and conferred enhanced protection against influenza virus.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-016-0487-4) contains supplementary material, which is available to authorized users.

Innate immune sensing and response to influenza

Influenza viruses pose a substantial threat to human and animal health worldwide. Recent studies in mouse models have revealed an indispensable role for the innate immune system in defense against influenza virus. Recognition of the virus by innate immune receptors in a multitude of cell types activates intricate signaling networks, functioning to restrict viral replication. Downstream effector mechanisms include activation of innate immune cells and, induction and regulation of adaptive immunity. However, uncontrolled innate responses are associated with exaggerated disease, especially in pandemic influenza virus infection. Despite advances in the understanding of innate response to influenza in the mouse model, there is a large knowledge gap in humans, particularly in immunocompromised groups such as infants and the elderly. We propose here, the need for further studies in humans to decipher the role of innate immunity to influenza virus, particularly at the site of infection. These studies will complement the existing work in mice and facilitate the quest to design improved vaccines and therapeutic strategies against influenza.