Effect of the novel influenza A (H1N1) virus in the human immune system

Necrotizing Pneumonia in Children: Early Recognition and Management

Necrotizing pneumonia (NP) is an uncommon complicated pneumonia with an increasing incidence. Early recognition and timely management can bring excellent outcomes. The diagnosis of NP depends on chest computed tomography, which has radiation damage and may miss the optimal treatment time. The present review aimed to elaborate on the reported predictors for NP. The possible pathogenesis of Streptococcus pneumoniae, Staphylococcus aureus, Mycoplasma pneumoniae and coinfection, clinical manifestations and management were also discussed. Although there is still a long way for these predictors to be used in clinical, it is necessary to investigate early predictors for NP in children.

Comparison of severe and critical COVID-19 patients imported from Russia with and without influenza A infection in Heilongjiang Province: a retrospective study

Background

The rapid spread of coronavirus disease-19 (COVID-19) poses a global health emergency, and cases entering China from Russia are quite diverse. This study explored and compared the clinical characteristics and outcomes of severe and critically ill COVID-19 patients from Russia with and without influenza A infection, treated in a northern Chinese hospital (Russia imported patients).

Methods

A total of 32 severe and critically ill Russia-imported COVID-19 patients treated in the Heilongjiang Imported Severe and Critical COVID-19 Treatment Center from April 6 to May 11, 2020 were included, including 8 cases (group A) with and 24 cases (group B) without influenza A infection. The clinical characteristics of each group were compared, including prolonged hospital stay, duration of oxygen therapy, time from onset to a negative SARS-CoV-2 qRT-PCR RNA (T_neg) result, and duration of bacterial infection.

Results

The results showed that blood group, PaO₂/FiO₂, prothrombin time (PT), prothrombin activity (PTA), computed tomography (CT) score, hospital stay, duration of oxygenation therapy, T_neg, and duration of bacterial infection were statistically different between the two groups (P<0.05). Multivariant regression analysis showed that the Sequential Organ Failure Assessment (SOFA) score, C-reactive protein (CRP), and influenza A infection were factors influencing hospital stay; SOFA score, CRP, and CT score were factors influencing the duration of oxygenation therapy; PaO₂/FiO₂, platelet count (PLT), and CRP were factors influencing T_neg; and gender, SOFA score, and influenza A infection were factors influencing the duration of bacterial infection.

Conclusions

Influenza A infection is common in Russia-imported COVID-19 patients, which can prolong the hospital stay and duration of bacterial infection. Routinely screening and treating influenza A should be conducted early in such patients.

Virus-Induced Changes of the Respiratory Tract Environment Promote Secondary Infections With Streptococcus pneumoniae

Secondary bacterial infections enhance the disease burden of influenza infections substantially. Streptococcus pneumoniae (the pneumococcus) plays a major role in the synergism between bacterial and viral pathogens, which is based on complex interactions between the pathogen and the host immune response. Here, we discuss mechanisms that drive the pathogenesis of a secondary pneumococcal infection after an influenza infection with a focus on how pneumococci senses and adapts to the influenza-modified environment. We briefly summarize what is known regarding secondary bacterial infection in relation to COVID-19 and highlight the need to improve our current strategies to prevent and treat viral bacterial coinfections.

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 many faces of the anti-COVID immune response

The novel 2019 strain of coronavirus is a source of profound morbidity and mortality worldwide. Compared with recent viral outbreaks, COVID-19 infection has a relatively high mortality rate, the reasons for which are not entirely clear. Furthermore, treatment options for COVID-19 infection are currently limited. In this Perspective, we explore the contributions of the innate and adaptive immune systems to both viral control as well as toxicity during COVID-19 infections and offer suggestions to both understand and therapeutically modulate anti-COVID immunity.

The many faces of the anti-COVID immune response

The novel 2019 strain of coronavirus is a source of profound morbidity and mortality worldwide. Compared with recent viral outbreaks, COVID-19 infection has a relatively high mortality rate, the reasons for which are not entirely clear. Furthermore, treatment options for COVID-19 infection are currently limited. In this Perspective, we explore the contributions of the innate and adaptive immune systems to both viral control as well as toxicity during COVID-19 infections and offer suggestions to both understand and therapeutically modulate anti-COVID immunity.

Complex Immune Dysregulation in COVID-19 Patients with Severe Respiratory Failure

Proper management of COVID-19 mandates better understanding of disease pathogenesis. The sudden clinical deterioration 7-8 days after initial symptom onset suggests that severe respiratory failure (SRF) in COVID-19 is driven by a unique pattern of immune dysfunction. We studied immune responses of 54 COVID-19 patients, 28 of whom had SRF. All patients with SRF displayed either macrophage activation syndrome (MAS) or very low human leukocyte antigen D related (HLA-DR) expression accompanied by profound depletion of CD4 lymphocytes, CD19 lymphocytes, and natural killer (NK) cells. Tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) production by circulating monocytes was sustained, a pattern distinct from bacterial sepsis or influenza. SARS-CoV-2 patient plasma inhibited HLA-DR expression, and this was partially restored by the IL-6 blocker Tocilizumab; off-label Tocilizumab treatment of patients was accompanied by increase in circulating lymphocytes. Thus, the unique pattern of immune dysregulation in severe COVID-19 is characterized by IL-6-mediated low HLA-DR expression and lymphopenia, associated with sustained cytokine production and hyper-inflammation.

Association of Arthritis Onset with Influenza: Analysis of the Canadian Early Inflammatory Arthritis Cohort

Objective

To evaluate seasonal patterns of early inflammatory arthritis (IA) onset and potential associations with IA symptom onset.

Methods

The Canadian Early Arthritis Cohort (CATCH) is an inception cohort study of adults with early (12 months or less) IA. We used patient reports of symptom onset as a proxy of IA onset and examined the seasonal distribution of IA onset over 10 years. Influenza time series was based on laboratory‐confirmed influenza A and B from the Canadian FluWatch surveillance from 2010‐2016. Bivariate analysis of influenza and IA was performed using cross‐correlations with different time lags and Poisson regression. IA and influenza were recorded as monthly total frequencies.

Results

Of 2519 IA patients, 88% had confirmed rheumatoid arthritis (RA). Significantly, more IA onsets occurred in winter compared with other seasons (P = 0.03); although IA onset was more frequent in January, the difference between months was not statistically significant. Compared to months with the lowest influenza rates, months with the highest influenza rates had a statistically significant, but trivial, increase of 0.003% in the incidence of IA (incidence rate ratio (95% confidence interval): 1.00003 (1.00005; 1.000053), P = 0.02).

Conclusion

Although IA symptom onset occurs more frequently in winter, we found that flu outbreaks were not associated with a meaningful increase in IA symptom onset in a large, well‐characterized cohort of Canadian adults over 6 years.

Experimental H1N1pdm09 infection in pigs mimics human seasonal influenza infections

Pigs are anatomically, genetically and physiologically comparable to humans and represent a natural host for influenza A virus (IAV) infections. Thus, pigs may represent a relevant biomedical model for human IAV infections. We set out to investigate the systemic as well as the local immune response in pigs upon two subsequent intranasal infections with IAV H1N1pdm09. We detected decreasing numbers of peripheral blood lymphocytes after the first infection. The simultaneous increase in the frequencies of proliferating cells correlated with an increase in infiltrating leukocytes in the lung. Enhanced perforin expression in αβ and γδ T cells in the respiratory tract indicated a cytotoxic T cell response restricted to the route of virus entry such as the nose, the lung and the bronchoalveolar lavage. Simultaneously, increasing frequencies of CD8αα expressing αβ T cells were observed rapidly after the first infection, which may have inhibited uncontrolled inflammation in the respiratory tract. Taking together, the results of this study demonstrate that experimental IAV infection in pigs mimics major characteristics of human seasonal IAV infections.

Rocking Pneumonia and the Boogie Woogie Flu

The relation between pneumonia and influenza is regularly addressed in modern music. Epidemiological data obtained during influenza pandemics, as well as during seasonal influenza, illustrate and underscore this association. Even though the number of pneumonia cases are generally under-reported and blood tests show a lack of sensitivity, a clear link between influenza and pneumonia can still be observed. In fact, the majority of mortality during influenza pandemics is due to pneumonia caused by a bacterial superinfection, in most cases Streptococcus pneumoniae. Vaccination is a powerful tool to prevent the development of both influenza and pneumonia in children, as well as in the elderly. Cellular and molecular data show that influenza can lead to changes in the integrity of lung epithelial cells, including desialysation of carbohydrate moieties, which favour attachment and invasion of S. pneumoniae. Further elucidation of these mechanisms could lead to targeted intervention strategies, in which universal influenza vaccines could play a role.

The role of respiratory epithelium in host defence against influenza virus infection

The respiratory epithelium is the major interface between the environment and the host. Sophisticated barrier, sensing, anti-microbial and immune regulatory mechanisms have evolved to help maintain homeostasis and to defend the lung against foreign substances and pathogens. During influenza virus infection, these specialised structural cells and populations of resident immune cells come together to mount the first response to the virus, one which would play a significant role in the immediate and long term outcome of the infection. In this review, we focus on the immune defence machinery of the respiratory epithelium and briefly explore how it repairs and regenerates after infection.

Contributions of Influenza Virus Hemagglutinin and Host Immune Responses Toward the Severity of Influenza Virus: Streptococcus pyogenes Superinfections

Influenza virus infections can be complicated by bacterial superinfections, which are medically relevant because of a complex interaction between the host, the virus, and the bacteria. Studies to date have implicated several influenza virus genes, varied host immune responses, and bacterial virulence factors, however, the host-pathogen interactions that predict survival versus lethal outcomes remain undefined. Previous work by our group showed that certain influenza viruses could yield a survival phenotype (A/swine/Texas/4199-2/98-H3N2, TX98), whereas others were associated with a lethal phenotype (A/Puerto Rico/8/34-H1N1, PR8). Based on this observation, we developed the hypothesis that individual influenza virus genes could contribute to a superinfection, and that the host response after influenza virus infection could influence superinfection severity. The present study analyzes individual influenza virus gene contributions to superinfection severity using reassortant viruses created using TX98 and PR8 viral genes. Host and pathogen interactions, relevant to survival and lethal phenotypes, were studied with a focus on pathogen clearance, host cellular infiltrates, and cytokine levels after infection. Specifically, we found that the hemagglutinin gene expressed by an influenza virus can contribute to the severity of a secondary bacterial infection, likely through modulation of host proinflammatory responses. Altogether, these results advance our understanding of molecular mechanisms underlying influenza virus-bacteria superinfections and identify viral and corresponding host factors that may contribute to morbidity and mortality.

Contribution of innate immune cells to pathogenesis of severe influenza virus infection

Influenza A viruses (IAVs) cause respiratory illness of varying severity based on the virus strains, host predisposition and pre-existing immunity. Ultimately, outcome and recovery from infection rely on an effective immune response comprising both innate and adaptive components. The innate immune response provides the first line of defence and is crucial to the outcome of infection. Airway epithelial cells are the first cell type to encounter the virus in the lungs, providing antiviral and chemotactic molecules that shape the ensuing immune response by rapidly recruiting innate effector cells such as NK cells, monocytes and neutrophils. Each cell type has unique mechanisms to combat virus-infected cells and limit viral replication, however their actions may also lead to pathology. This review focuses how innate cells contribute to protection and pathology, and provides evidence for their involvement in immune pathology in IAV infections.

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.

Dynamic variations of the peripheral blood immune cell subpopulation in patients with critical H7N9 swine-origin influenza A virus infection: A retrospective small-scale study

H7N9 influenza is a recently emerging infection with a high mortality rate. The aim of the present study was to investigate dynamic fluctuations of peripheral blood immune cell subgroups in patients with critical H7N9 infection. Flow cytometry was used to assess the cells in whole blood samples from 9 cases. With regard to the innate immune system, in the majority of patients, the natural killer (NK) cell counts were similar to those of monocytes, which demonstrated a gradual increase in the progression period and an early increase followed by a reduction during recovery. B cells exhibited a reduction during progression and were further decreased during recovery. The CD4⁺T cells of all patients decreased during progression, and further decreased during recovery. By contrast, CD8⁺T cells increased in the majority of patients in the progression stage, and underwent an initial reduction followed by a gradual increase during recovery. However, CD8⁺ programmed death (PD)-1⁺T cell and T helper (Th) 1 cell frequencies demonstrated a moderate increase in all patients during the progression stage, and regulatory T cell (Treg) frequencies tended to be reduced during progression and increased during recovery. Notably, this preliminary data also showed that the frequencies of B cells, Th2 cells and Th17 cells in the progression period were higher than those in the recovery period. The frequencies of monocytes, CD4⁺T cell, CD8⁺T cell, CD4⁺PD-1⁺T cells and CD8⁺PD-1⁺T cells in the progression period were lower than those during recovery. In conclusion, different levels of peripheral blood immune cell subgroups during the pathogenesis of H7N9 infection may be associated with elimination of the virus and immune damage.

Infection with a Mouse-Adapted Strain of the 2009 Pandemic Virus Causes a Highly Severe Disease Associated with an Impaired T Cell Response

Despite a relatively low fatality rate, the 2009 H1N1 pandemic virus differed from other seasonal viruses in that it caused mortality and severe pneumonia in the young and middle-aged population (18–59 years old). The mechanisms underlying this increased disease severity are still poorly understood. In this study, a human isolate of the 2009 H1N1 pandemic virus was adapted to the mouse (MAp2009). The pathogenicity of the MAp2009 virus and the host immune responses were evaluated in the mouse model and compared to the laboratory H1N1 strain A/Puerto Rico/8/1934 (PR8). The MAp2009 virus reached consistently higher titers in the lungs over 14 days compared to the PR8 virus, and caused severe disease associated with high morbidity and 85% mortality rate, contrasting with the 0% death rate in the PR8 group. During the early phase of infection, both viruses induced similar pathology in the lungs. However, MAp2009-induced lung inflammation was sustained until the end of the study (day 14), while there was no sign of inflammation in the PR8-infected group by day 10. Furthermore, at day 3 post-infection, MAp2009 induced up to 10- to 40-fold more cytokine and chemokine gene expression, respectively. More importantly, the numbers of CD4⁺ T cells and virus-specific CD8⁺ T cells were significantly lower in the lungs of MAp2009-infected mice compared to PR8-infected mice. Interestingly, there was no difference in the number of dendritic cells in the lung and in the draining lymph node. Moreover, mice infected with PR8 or MAp2009 had similar numbers of CCR5 and CXCR3-expressing T cells, suggesting that the impaired T cell response was not due to a lack of chemokine responsiveness or priming of T cells. This study demonstrates that a mouse-adapted virus from an isolate of the 2009 pandemic virus interferes with the adaptive immune response leading to a more severe disease.

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.

Pulmonary immune responses to 2009 pandemic influenza A (H1N1) virus in mice

BACKGROUND

Well-characterized mice models will afford a cheaper, easy-handling opportunity for a more comprehensive understanding of 2009 influenza A (H1N1) virus's pathogenesis potential. We aimed to provide a robust description of pulmonary immune responses in the mice infected by the virus.

METHODS

BALB/c mice were inoculated intranasally with A/Beijing/501/2009(H1N1) (BJ501) and A/PR/8/34(H1N1) (PR8) viruses and compared for survival rate, viral replication, and kinetics of pulmonary immune responses.

RESULTS

BJ501 virus replicated less efficiently in the lungs than PR8, and both caused lethal illness in the mice. The transient increases of pulmonary TNF-α 2 days post infection for BJ501 and of INF-γ and IL-10 at 6 days post infection for PR8 were observed. IL-2+ and IL-4+ secreting cells showed significant increase 12 days post infection, while IFN-γ+, IgG+ and IgA+ secreting cells increased 6 days post infection. The different patterns of pulmonary immunological parameters between two viruses were at most seen in IL-6, IL-17 secretion and IgG1/IgG2a ratio.

CONCLUSIONS

The BALB/c mouse is evaluated as a good pathogenic model for studying BJ501 2009 H1N1 virus. The work provided some basic and detailed data, which might be referred when further evaluating innate and adapted pulmonary immune responses and local viral load in mice.

Immunophenotype expressions and cytokine profiles of influenza A H1N1 virus infection in pediatric patients in 2009

Background. A novel swine-origin influenza A H1N1 virus (S-OIV) caused human infection and acute respiratory illness in 2009, resulting in an influenza pandemic. Objectives. This study characterized the immune responses of S-OIV infection in pediatric patients at risk of pulmonary complications. Methods. All enrolled pediatric patients were confirmed virologically for S-OIV infection in 2009-2010, prospectively. Changes in cellular immunophenotypes were analyzed using flow cytometry. Plasma cytokine levels associated with S-OIV infection by pulmonary and without pulmonary complications were measured using cytokine cytometric bead assay kits. Results. A total of 85 patients with a mean age of 10.3 years were recruited. The level of C-reactive protein (CRP) was high in patients exhibiting pulmonary complications. The percentage of cellular immunophenotypes did not change between patients with and without pulmonary complications. The absolute numbers of peripheral blood mononuclear cells (PBMC), CD3, CD8, and CD16CD56 decreased with acute S-OIV pulmonary complications. Acute influenza infection with pulmonary complications was associated with high plasma concentrations of IL-1β, IL-6, IL-12, and IFN-γ. Conclusion. Immunophenotype studies have reported variability in immune response to the severity of S-OIV infections. Acute phase cytokine profiles of the 2009 S-OIV infection might have contributed to the pathogenesis of the pulmonary complications.

Immunopathogenesis of 2009 pandemic influenza

Three years after the pandemic, major advances have been made in our understanding of the innate and adaptive immune responses to the influenza A(H1N1)pdm09 virus and those responses' contribution to the immunopathology associated with this infection. Severe disease is characterized by early secretion of proinflammatory and immunomodulatory cytokines. This cytokine secretion persisted in patients with severe viral pneumonia and was directly associated with the degree of viral replication in the respiratory tract. Cytokines play important roles in the antiviral defense, but persistent hypercytokinemia may cause inflammatory tissue damage and participate in the genesis of the respiratory failure observed in these patients. An absence of pre-existing protective antibodies was the rule for both mild and severe cases. A role for pathogenic immunocomplexes has been proposed for this disease. Defective T cell responses characterize severe cases of infection caused by the influenza A(H1N1)pdm09 virus. Immune alterations associated with accompanying conditions such as obesity, pregnancy or chronic obstructive pulmonary disease may interfere with the normal development of the specific response to the virus. The role of host immunogenetic factors associated with disease severity is also discussed in this review. In conclusion, currently available information suggests a complex immunological dysfunction/alteration that characterizes the severe cases of 2009 pandemic influenza. The potential benefits of prophylactic/therapeutic interventions aimed at preventing/correcting such dysfunction warrant investigation.

Influenza A induced cellular signal transduction pathways

Influenza A is a negative sense single stranded RNA virus that belongs to the Orthomyxoviridae Family. This enveloped virus contains 8 segments of viral RNA which encodes 11 viral proteins. Influenza A infects humans and is the causative agent of the flu. Annually it infects approximately 5% to 15% of the population world wide and results in an estimated 250,000 to 500,000 deaths a year. The nature of influenza A replication results in a high mutation rate which results in the need for seasonal vaccinations. In addition the zoonotic nature of the influenza virus allows for recombination of viral segments from different strains creating new variants that have not been encountered before. This type of mutation is the method by which pandemic strains of the flu arises. Infection with influenza results in a respiratory illness that for most individuals is self limiting. However in susceptible populations which include individuals with pre-existing pulmonary or cardiac conditions, the very young and the elderly fatal complications may arise. The most serious of these is the development of viral pneumonia which may be accompanied by secondary bacterial infections. Progression of pneumonia leads to the development of acute respiratory distress syndrome (ARDS), acute lung injury (ALI) and potentially respiratory failure. This progression is a combined effect of the host immune system response to influenza infection and the viral infection itself. This review will focus on molecular aspects of viral replication in alveolar cells and their response to infection. The response of select innate immune cells and their contribution to viral clearance and lung epithelial damage will also be discussed. Molecular aspects of antiviral response in the cells in particular the protein kinase RNA dependent response, and the oligoadenylate synthetase RNAse L system in relation to influenza infection.

Bacterial superinfection following lung inflammatory disorders

The lung environment is designed to prevent innate responses to harmless commensal microorganisms and environmental antigens. Features of an intact respiratory epithelium are critical to this process. A damaged or altered lung epithelial surface will therefore remove or alter the suppressive signals delivered to local innate immune cells, and inflammation ensues. Timely resolution of inflammation is important to prevent bystander tissue damage. However, if resolving pathways themselves are prolonged or repeated, they too can cause undesirable consequences, including bacterial superinfections, which we discuss here.

Plasma cytokine levels and cytokine gene polymorphisms in Mexican patients during the influenza pandemic A(H1N1)pdm09

BACKGROUND

In Mexico, the initial severe cases of the 2009 influenza pandemic virus A (H1N1) [A(H1N1)pdm09] were detected in early March. The immune mechanisms associated with the severe pneumonia caused by infection with this new virus have not been completely elucidated. Polymorphisms in interleukin genes have previously been associated with susceptibility to infectious diseases due to their influence on cytokine production.

OBJECTIVES

The present case-control study was performed to compare several immunologic and genetic parameters of patients and controls during the initial phase of the pandemic.

STUDY DESIGN

Sixty-five patients who were hospitalized due to infection with the influenza A(H1N1)pdm09 virus and 46 healthy controls were studied. A hemagglutination inhibition assay (HIA) was performed to measure anti-influenza antibody titers in these subjects. Protein levels of the cytokines interleukin (IL)-4, IL-6, IL-8, IL-10, tumor necrosis factor-α (TNFα), interferon gamma (IFNγ), transforming growth factor beta (TGFβ)1 and TGFβ2 were quantified in plasma. Single nucleotide polymorphisms in IL6, IL10 and TNFα were also assessed.

RESULTS

Influenza patients had lower antibody titers and produced significantly higher levels of IL-6, IL-10 and TNFα than healthy controls. The frequencies of the TNFα -308G, IL-10 -592C and IL-10 -1082A alleles and the IL10 -1082(A/A) genotype were associated with susceptibility to severe disease, while the haplotypes TNFα AG and IL-10 GTA and GCA were associated with protection from severe disease [P=0.016, OR (CI)=0.11 (0.01-0.96); P=0.0187, OR (CI)=0.34 (0.13-0.85); P=0.013, OR (CI)=0.39 (0.18-0.83)].

CONCLUSIONS

This study demonstrates that the influenza A(H1N1)pdm09 patients and healthy controls have different profiles of immune parameters and that there is an association between IL-10 and TNFα polymorphisms and the outcome of this disease.

Microarray analysis of microRNA expression in peripheral blood mononuclear cells of critically ill patients with influenza A (H1N1)

BACKGROUND

With concerns about the disastrous health and economic consequences caused by the influenza pandemic, comprehensively understanding the global host response to influenza virus infection is urgent. The role of microRNA (miRNA) has recently been highlighted in pathogen-host interactions. However, the precise role of miRNAs in the pathogenesis of influenza virus infection in humans, especially in critically ill patients is still unclear.

METHODS

We identified cellular miRNAs involved in the host response to influenza virus infection by performing comprehensive miRNA profiling in peripheral blood mononuclear cells (PBMCs) from critically ill patients with swine-origin influenza pandemic H1N1 (2009) virus infection via miRNA microarray and quantitative reverse-transcription polymerase chain reaction (qRT-PCR) assays. Receiver operator characteristic (ROC) curve analysis was conducted and area under the ROC curve (AUC) was calculated to evaluate the diagnostic accuracy of severe H1N1 influenza virus infection. Furthermore, an integrative network of miRNA-mediated host-influenza virus protein interactions was constructed by integrating the predicted and validated miRNA-gene interaction data with influenza virus and host-protein-protein interaction information using Cytoscape software. Moreover, several hub genes in the network were selected and validated by qRT-PCR.

RESULTS

Forty-one significantly differentially expressed miRNAs were found by miRNA microarray; nine were selected and validated by qRT-PCR. QRT-PCR assay and ROC curve analyses revealed that miR-31, miR-29a and miR-148a all had significant potential diagnostic value for critically ill patients infected with H1N1 influenza virus, which yielded AUC of 0.9510, 0.8951 and 0.8811, respectively. We subsequently constructed an integrative network of miRNA-mediated host-influenza virus protein interactions, wherein we found that miRNAs are involved in regulating important pathways, such as mitogen-activated protein kinase signaling pathway, epidermal growth factor receptor signaling pathway, and Toll-like receptor signaling pathway, during influenza virus infection. Some of differentially expressed miRNAs via in silico analysis targeted mRNAs of several key genes in these pathways. The mRNA expression level of tumor protein T53 and transforming growth factor beta receptor 1 were found significantly reduced in critically ill patients, whereas the expression of Janus kinase 2, caspase 3 apoptosis-related cysteine peptidase, interleukin 10, and myxovirus resistance 1 were extremely increased in critically ill patients.

CONCLUSIONS

Our data suggest that the dysregulation of miRNAs in the PBMCs of H1N1 critically ill patients can regulate a number of key genes in the major signaling pathways associated with influenza virus infection. These differentially expressed miRNAs could be potential therapeutic targets or biomarkers for severe influenza virus infection.

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

Innate and adaptive immune responses play critical roles in the body’s defense against viruses. We investigated the host immune response against the 2009 pandemic H1N1 influenza virus [A(H1N1)pdm09] in patients before and after anti-influenza therapy and found that the numbers of dendritic cells and T cells were significantly reduced compared with those of a healthy control group. In contrast, the frequency of natural killer, γδT and T regulatory (T_reg) cells increased, and the concentrations of plasma interferon (IFN)-α/γ and interleukin (IL-15) were significantly higher than those of the control. Following therapy the frequency of γδT and T_reg cells returned to normal; the counts of myeloid dendritic and plasmacytoid dendritic cells were still lower than the control, while the concentrations of IFN-α/γ and IL-15 remained high. We show that infection with A (H1N1)pdm09 was accompanied by changes in peripheral blood lymphocyte subgroups and cytokine profiles, leading to deleterious imbalances in innate and adaptive immunity.

Microbiota regulates the TLR7 signaling pathway against respiratory tract influenza A virus infection

Although intestinal flora are crucial in maintaining immune homeostasis of the intestine, the role of intestinal flora in immune responses at other mucosal surfaces remains less clear. Here, we show that intestinal flora composition critically regulates the toll-like receptor 7 (TLR7) signaling pathway following respiratory influenza virus infection. TLR7 ligands rescued the immune impairment in antibiotic-treated mice. Intact microbiota provided signals leading to the expression of mRNA for TLR7, MyD88, IRAK4, TRAF6, and NF-κB at steady state. Significant changes in the composition of culturable commensal bacteria reduced the expression levels of components of the TLR7 signaling pathway. Our results reveal the importance of intestinal flora in regulating immunity in the respiratory mucosa through the upregulation of the TLR7 signaling pathway for the proper activation of inflammasomes.

Limited anti-inflammatory role for interleukin-1 receptor like 1 (ST2) in the host response to murine postinfluenza pneumococcal pneumonia

Interleukin-1 receptor like 1 (ST2) is a negative regulator of Toll-like receptor (TLR) signaling. TLRs are important for host defense during respiratory tract infections by both influenza and Streptococcus (S.) pneumoniae. Enhanced susceptibility to pneumococcal pneumonia is an important complication following influenza virus infection. We here sought to determine the role of ST2 in primary influenza A infection and secondary pneumococcal pneumonia. ST2 knockout (st2^−/−) and wild-type (WT) mice were intranasally infected with influenza A virus; in some experiments mice were infected 2 weeks later with S. pneumoniae. Both mouse strains cleared the virus similarly during the first 14 days of influenza infection and had recovered their weights equally at day 14. Overall st2^−/− mice tended to have a stronger pulmonary inflammatory response upon infection with influenza; especially 14 days after infection modest but statistically significant elevations were seen in lung IL-6, IL-1β, KC, IL-10, and IL-33 concentrations and myeloperoxidase levels, indicative of enhanced neutrophil activity. Interestingly, bacterial lung loads were higher in st2^−/− mice during the later stages of secondary pneumococcal pneumonia, which was associated with relatively increased lung IFN-γ levels. ST2 deficiency did not impact on gross lung pathology in either influenza or secondary S. pneumoniae pneumonia. These data show that ST2 plays a limited anti-inflammatory role during both primary influenza and postinfluenza pneumococcal pneumonia.

Impaired dendritic cell maturation in response to pandemic H1N109 influenza virus

BACKGROUND

Infection with pandemic A/H1N1/2009 influenza virus led to hospitalisation of patients not expected to be at risk of severe disease from seasonal influenza infection.

OBJECTIVES

We sought to establish whether (i) DC maturation was compromised in patients experiencing severe pandemic influenza infection, (ii) the pandemic virus differed from seasonal influenza virus in its ability to induce DC maturation and (iii) there was an associated inability to activate memory B cells or induce antibody.

STUDY DESIGN

Peripheral blood mononuclear (PBMCs) cells were sampled from individuals with confirmed acute pandemic A/H1N1/2009 influenza infection or from healthy vaccinated controls. DCs were differentiated from the PBMC and tested for their ability to mature following stimulation with pandemic virus, seasonal H3N2 influenza virus or LPS. Serum samples from the patients were used to assess seroconversion to influenza and the levels of influenza specific memory B cells in PBMC were also determined.

RESULTS

DCs obtained from all individuals exhibited negligible maturation marker upregulation when exposed to pandemic A/H1N1/2009 virus but showed a strong response to the seasonal H3N2 virus and LPS. Robust levels of memory B cell were obtained in both groups and patients seroconverted to the virus.

CONCLUSIONS

Overall, the ability of patient's DC to mature in response to different stimuli was no different to that of control subjects DCs. Importantly, panH1N109 virus failed to induce substantial DC maturation in any individual, contrasting with seasonal virus, but this did not result in failure to mount memory B cell and antibody responses to the virus.

Review on the impact of pregnancy and obesity on influenza virus infection

A myriad of risk factors have been linked to an increase in the severity of the pandemic H1N1 2009 influenza A virus [A(H1N1)pdm09] including pregnancy and obesity where death rates can be elevated as compared to the general population. The goal of this review is to provide an overview of the influence of pregnancy and obesity on the reported cases of A(H1N1)pdm09 virus infection and of how the concurrent presence of these factors may have an exacerbating effect on infection outcome. Also, the hypothesized immunologic mechanisms that contribute to A(H1N1)pdm09 virus severity during pregnant or obese states are outlined. Identifying the mechanisms underlying the increased disease severity in these populations may result in improved therapeutic approaches and future pandemic preparedness.

Two years after pandemic influenza A/2009/H1N1: what have we learned?

The world had been anticipating another influenza pandemic since the last one in 1968. The pandemic influenza A H1N1 2009 virus (A/2009/H1N1) finally arrived, causing the first pandemic influenza of the new millennium, which has affected over 214 countries and caused over 18,449 deaths. Because of the persistent threat from the A/H5N1 virus since 1997 and the outbreak of the severe acute respiratory syndrome (SARS) coronavirus in 2003, medical and scientific communities have been more prepared in mindset and infrastructure. This preparedness has allowed for rapid and effective research on the epidemiological, clinical, pathological, immunological, virological, and other basic scientific aspects of the disease, with impacts on its control. A PubMed search using the keywords "pandemic influenza virus H1N1 2009" yielded over 2,500 publications, which markedly exceeded the number published on previous pandemics. Only representative works with relevance to clinical microbiology and infectious diseases are reviewed in this article. A significant increase in the understanding of this virus and the disease within such a short amount of time has allowed for the timely development of diagnostic tests, treatments, and preventive measures. These findings could prove useful for future randomized controlled clinical trials and the epidemiological control of future pandemics.

Type I interferon signaling regulates the composition of inflammatory infiltrates upon infection with Listeria monocytogenes

Type I IFN is key to the immune response to viral pathogens, however its role in bacterial infections is less well understood. Mice lacking the type I IFN receptor (IFNAR-/-) demonstrate enhanced resistance to infection with Listeriamonocytogenes. We have now determined that following infection with Listeria, the composition of innate cells recruited to the peritoneal cavity of IFNAR-/- mice reflects an increase in the frequency of neutrophils and a decrease in monocyte frequency compared to WT controls. These differences in inflammatory infiltrates could not be attributed to distinct bone marrow composition prior to infection or to level of apoptosis. We also observed no differences in neutrophil oxidative burst. However, blocking CXCR2 prevented enhanced neutrophil influx and hampered bacterial clearance. Taken together, these studies highlight a novel mechanism by which type I interferon signaling regulates the immune response to Listeria, through negative regulation of chemokines driving neutrophil recruitment.

Immunologic changes during Pandemic (H1N1) 2009, China

We analyzed changes in immunologic values over time for 28 hospitalized patients with pandemic (H1N1) 2009. Levels of interleukin-6, interferon-y, and interleukin-10 increased 1 day after illness onset and then decreased to baseline levels. Levels of virus-specific antibody were undetectable 1 day after illness onset and peaked 36 days later.

Immunologic changes during Pandemic (H1N1) 2009, China

We analyzed changes in immunologic values over time for 28 hospitalized patients with pandemic (H1N1) 2009. Levels of interleukin-6, interferon-γ, and interleukin-10 increased 1 day after illness onset and then decreased to baseline levels. Levels of virus-specific antibody were undetectable 1 day after illness onset and peaked 36 days later.

Cytokine response patterns in severe pandemic 2009 H1N1 and seasonal influenza among hospitalized adults

Background

Studying cytokine/chemokine responses in severe influenza infections caused by different virus subtypes may improve understanding on pathogenesis.

Methods

Adults hospitalized for laboratory-confirmed seasonal and pandemic 2009 A/H1N1 (pH1N1) influenza were studied. Plasma concentrations of 13 cytokines/chemokines were measured at presentation and then serially, using cytometric-bead-array with flow-cytometry and ELISA. PBMCs from influenza patients were studied for cytokine/chemokine expression using ex-vivo culture (Whole Blood Assay,±PHA/LPS stimulation). Clinical variables were prospectively recorded and analyzed.

Results

63 pH1N1 and 53 seasonal influenza patients were studied. pH1N1 patients were younger (mean±S.D. 42.8±19.2 vs 70.5±16.7 years), and fewer had comorbidities. Respiratory/cardiovascular complications were common in both groups (71.4% vs 81.1%), although severe pneumonia with hypoxemia (54.0% vs 28.3%) and ICU admissions (25.4% vs 1.9%) were more frequent with pH1N1. Hyperactivation of the proinflammatory cytokines IL-6, CXCL8/IL-8, CCL2/MCP-1 and sTNFR-1 was found in pH1N1 pneumonia (2–15 times normal) and in complicated seasonal influenza, but not in milder pH1N1 infections. The adaptive-immunity (Th1/Th17)-related CXCL10/IP-10, CXCL9/MIG and IL-17A however, were markedly suppressed in severe pH1N1 pneumonia (2–27 times lower than seasonal influenza; P−values<0.01). This pattern was further confirmed with serial measurements. Hypercytokinemia tended to be sustained in pH1N1 pneumonia, associated with a slower viral clearance [PCR-negativity: day 3–4, 55% vs 85%; day 6–7, 67% vs 100%]. Elevated proinflammatory cytokines, particularly IL-6, predicted ICU admission (adjusted OR 12.6, 95%CI 2.6–61.5, per log₁₀unit increase; P = 0.002), and correlated with fever, tachypnoea, deoxygenation, and length-of-stay (Spearman's rho, P-values<0.01) in influenza infections. PBMCs in seasonal influenza patients were activated and expressed cytokines ex vivo (e.g. IL-6, CXCL8/IL-8, CCL2/MCP-1, CXCL10/IP-10, CXCL9/MIG); their ‘responsiveness’ to stimuli was shown to change dynamically during the illness course.

Conclusions

A hyperactivated proinflammatory, but suppressed adaptive-immunity (Th1/Th17)-related cytokine response pattern was found in severe pH1N1 pneumonia, different from seasonal influenza. Cytokine/immune-dysregulation may be important in its pathogenesis.

Severe Necrotizing Pneumonia Complicating Influenza A (H1N1): The Role of Immunologic Interaction

This report describes the successful management of a documented necrotizing pneumonia due to Streptococcus pneumoniae in a child with pandemic influenza A (H1N1). The importance of early recognition of bacterial superinfection in patients with influenza and the immunologic interactive mechanisms between viruses and bacteria in determining respiratory diseases are highlighted. The role of modern molecular techniques in improving diagnostic microbiology sensitivity and informing consequent clinical care is emphasized.

Novel influenza A (H1N1) infection vs. common influenza-like illness: a prospective study

Background

On June 11^th, 2009 the World Health Organization (WHO) declared the first influenza pandemic of the 21^st century. Data regarding the clinical characteristics and course of this viral infectious disease are still being assessed. The aim of this study was to investigate and compare the possible differences in clinical course and outcome between H1N1-positive [H1N1(+)] and negative [H1N1(−)] patients.

Material/Methods

This prospective study was conducted between July 2009 and January 2010 in a regional hospital in Greece. The study population consisted of 165 patients aged 14 years or older, with influenza-like illness (ILI) who, according to CDC recommendations, fulfilled the criteria for diagnostic influenza testing. Enrolled patients underwent a detailed diagnostic work-up. Infection by the H1N1 virus was diagnosed using real-time reverse transcriptase polymerase chain reaction, from pharyngeal swab specimens.

Results

We identified 81 H1N1 (+) (49%) patients. Statistical analysis revealed that H1N1(+) patients were significantly younger (median age 27 vs. 35 years, p<0.05), had a decreased white blood cell count (median 7.200 vs. 8.415, p<0.05) and an increased percentage of monocytes (55.6% vs. 27.4%, p<0.05) compared to the H1N1(−) patients. The clinical presentation at the emergency department, as well as the hospital admission and disease complication rate, were not significantly different between the 2 groups.

Conclusions

The clinical characteristics of the new influenza virus appear to be mild and to resemble those of common influenza-like illnesses (ILI). The patients who tested positive for the H1N1 virus were younger and had an increased percentage of monocytes compared to the H1N1-negative patients.

CD4+/CD8+ T lymphocytes imbalance in children with severe 2009 pandemic influenza A (H1N1) pneumonia

Purpose

This study was conducted to investigate the immune responses of children with moderate and severe novel influenza A virus (H1N1) pneumonia, and to compare their clinical and immunological findings with those of control subjects.

Methods

Thirty-two admitted patients with H1N1 pneumonia were enrolled in the study. The clinical profiles, humoral and cell-mediated immune responses of the 16 H1N1 pneumonia patients who were admitted to the pediatric intensive care unit (severe pneumonia group), 16 H1N1 pneumonia patients admitted to the pediatric general ward (moderate pneumonia group) and 13 control subjects (control group) were measured.

Results

Total lymphocyte counts were significantly lower in patients with H1N1 pneumonia than in the control group (P=0.02). The number of CD4+ T lymphocytes was significantly lower in the severe pneumonia group (411.5±253.5/µL) than in the moderate pneumonia (644.9±291.1/µL, P=0.04) and control (902.5±461.2/µL, P=0.01) groups. However, the number of CD8+ T lymphocytes was significantly higher in the severe pneumonia group (684.2±420.8/µL) than in the moderate pneumonia (319.7±176.6/µL, P=0.02) and control (407.2±309.3/µL, P=0.03) groups. The CD4+/CD8+ T lymphocytes ratio was significantly lower in the severe pneumonia group (0.86±0.24) than in the moderate pneumonia (1.57±0.41, P=0.01) and control (1.61±0.49, P=0.01) groups. The serum levels of IgG, IgM and IgE were significantly higher in the severe pneumonia group than in the 2 other groups.

Conclusion

The results of this study suggest that increased humoral immune responses and the differences in the CD4+ and CD8+ T lymphocyte profiles, and imbalance of their ratios may be related to the severity of H1N1 pneumonia in children.

Severe and persistent depletion of circulating plasmacytoid dendritic cells in patients with 2009 pandemic H1N1 infection

Background

Dysregulation of host immune responses plays a critical role in the pathogenesis of severe 2009 pandemic H1N1 infection. Whether H1N1 virus could escape innate immune defense in vivo remains to be investigated. The aim of this study was to evaluate the pattern of innate immune response during human 2009 H1N1 infection. We performed the enumeration of circulating myeloid dendritic cells (mDC) and plasmacytoid DC (pDC) in blood from patients with H1N1 pneumonia shortly after the onset of symptoms and during follow-up at different intervals of time. The analysis of CD4 and CD8 count, CD38 T-cell activation marker and serum cytokine/chemokine plasma levels was also done.

Methodology/Principal Findings

Blood samples were collected from 13 hospitalized patients with confirmed H1N1-related pneumonia at time of admission and at weeks 1, 4, and 16 of follow-up. 13 healthy donors were enrolled as controls. In the acute phase of the disease, H1N1-infected patients exhibited a significant depletion in both circulating pDC and mDC in conjunction with a decrease of CD4 and CD8 T cell count. In addition, we found plasmatic hyperproduction of IP-10 and RANTES, whereas increase in T-cell immune activation was found at all time points. When we assessed the changes in DC count over time, we observed a progressive normalization of mDC number. On the contrary, H1N1-infected patients did not achieve a complete recovery of pDC count as values remained lower than healthy controls even after 16 weeks of follow-up.

Conclusions

H1N1 disease is associated with a profound depletion of DC subsets. The persistence of pDC deficit for several weeks after disease recovery could be due to H1N1 virus itself or to a preexisting impairment of innate immunity.

Dynamic variations in the peripheral blood lymphocyte subgroups of patients with 2009 pandemic H1N1 swine-origin influenza A virus infection

Background

Novel Influenza A (H1N1) is an acute respiratory infectious disease. Animal experiments indicated that when H1N1 virus infected early hosts, it showed strong CD4⁺, CD8⁺, and CD4⁺CD25⁺ T cell reactions. The aim of this study was to investigate the dynamic fluctuations of the peripheral blood lymphocyte subgroups in patients infected with H1N1 swine-origin influenza A virus (S-OIV).

Methods

The frequency of T cells, B cells, natural killer (NK) cells, and regulatory T cells (Treg) in 36 severe H1N1 and 40 moderate H1N1 patients were detected at different periods by flow cytometry. In parallel, serum cytokines were detected by enzyme-linked immunosorbent assay and C-reactive protein (CRP) was analyzed through an image-type automatic biochemical analyzer. In addition, 20 healthy volunteers, who were not infected with 2009 H1N1 virus, were selected as controls.

Results

The frequency of NK cells were decreased in all cases and CD19⁺ B cells were increased in severe cases than those of the controls. At 1-2d from onset, the frequency of CD4⁺ and CD4⁺CD25⁺ T cells in moderate cases was higher than in the severe cases. Serum cytokines, specifically IL-2, IL-4, IL-6, IL-10, and IFN-γ exhibited no significant change both in the moderate and the severe cases during the whole monitoring process. In the early stage of the disease, serum CRP levels in the severe and moderate groups were significantly higher than that in the control group.

Conclusions

Patients showed different lymphocyte subgroup distributions between mild and severe cases, which might affect the incidence and development of 2009 H1N1.

Pandemic (H1N1) 2009 influenza virus induces weaker host immune responses in vitro: a possible mechanism of high transmissibility

BACKGROUND

The world has recently overcome the first influenza pandemic of the 21st century caused by a novel H1N1 virus (pH1N1) which is a triple reassortant comprising genes derived from avian, human, and swine influenza viruses and antigenically quite different from seasonal H1N1 strains. Although the case fatality rates have decreased in many developed countries, the situation is still alarming in many developing countries including India where considerable numbers of new cases are appearing everyday. There is still a high morbidity and mortality of susceptible adult as well as young population without having underlying health issues due to the influenza infection.

RESULTS

To achieve a better understanding of the risk posed by the pH1N1 and to understand its pathogenicity, we studied the host gene expression response to Indian isolate of pH1N1 infection and compared it with seasonal H1N1 infection. The response was studied at four different time points (4, 8, 16 and 24 h) post infection (hpi) in A549 cells using microarray platform. We found that pH1N1 induces immune response earlier than seasonal H1N1 viruses, but at the later stages of infection there is a suppression of host immune responses. The infection with pH1N1 resulted in considerable decrease in the expression of cytokine and other immune genes namely IL8, STAT1, B2 M and IL4 compared to seasonal H1N1.

CONCLUSION

We propose that the inability to induce strong innate immune response could be a reason for the high transmissibility, pathogenicity and mortality caused by pH1N1 virus.