Infectious Progeny of 2009 A (H1N1) Influenza Virus Replicated in and Released from Human Neutrophils

Pandemic influenza A (H1N1) virus causes abortive infection of primary human T cells

Influenza A virus still represents a noticeable epidemic risk to international public health at present, despite the extensive use of vaccines and anti-viral drugs. In the fight against pathogens, the immune defence lines consisting of diverse lymphocytes are indispensable for humans. However, the role of virus infection of lymphocytes and subsequent abnormal immune cell death remains to be explored. Different T cell subpopulations have distinct characterizations and functions, and we reveal the high heterogeneity of susceptibility to viral infection and biological responses such as apoptosis in various CD4+ T and CD8+ T cell subsets through single-cell transcriptome analyses. Effector memory CD8+ T cells (CD8+ TEM) that mediate protective memory are identified as the most susceptible subset to pandemic influenza A virus infection among primary human T cells. Non-productive infection is established in CD8+ TEM and naïve CD8+ T cells, which indicate the mechanism of intracellular antiviral activities for inhibition of virus replication such as abnormal viral splicing efficiency, incomplete life cycles and up-regulation of interferon-stimulated genes in human T cells. These findings provide insights into understanding lymphopenia and the infectious mechanisms of pandemic influenza A virus and broad immune host-pathogen interactional atlas in primary human T cells.

Patient hematology during hospitalization for viral pneumonia caused by SARS-CoV-2 and non-SARS-CoV-2 agents: a retrospective study

Background

Hematological comparison of coronavirus disease (COVID-19) and other viral pneumonias can provide insights into COVID-19 treatment.

Methods

In this retrospective case–control single-center study, we compared the data of 126 patients with viral pneumonia during different outbreaks [severe acute respiratory syndrome (SARS) in 2003, influenza A (H1N1) in 2009, human adenovirus type 7 in 2018, and COVID-19 in 2020].

Results

One of the COVID-19 characteristics was a continuous decline in the hemoglobin level. The neutrophil count was related to the aggravation of COVID-19 and SARS. Thrombocytopenia occurred in patients with SARS and severe COVID-19 even at the recovery stage. Lymphocytes were related to the entire course of adenovirus infection, recovery of COVID-19, and disease development of SARS.

Conclusions

Dynamic changes in hematological counts could provide a reference for the pathogenesis and prognosis of pneumonia caused by respiratory viruses in clinics.

Recent Advances in Quenchbody, a Fluorescent Immunosensor

The detection of viruses, disease biomarkers, physiologically active substances, drugs, and chemicals is of great significance in many areas of our lives. Immunodetection technology is based on the specificity and affinity of antigen–antibody reactions. Compared with other analytical methods such as liquid chromatography coupled with mass spectrometry, which requires a large and expensive instrument, immunodetection has the advantages of simplicity and good selectivity and is thus widely used in disease diagnosis and food/environmental monitoring. Quenchbody (Q-body), a new type of fluorescent immunosensor, is an antibody fragment labeled with fluorescent dyes. When the Q-body binds to its antigen, the fluorescence intensity increases. The detection of antigens by changes in fluorescence intensity is simple, easy to operate, and highly sensitive. This review comprehensively discusses the principle, construction, application, and current progress related to Q-bodies.

Host DNA released by NETosis in neutrophils exposed to seasonal H1N1 and highly pathogenic H5N1 influenza viruses

BACKGROUND

Neutrophil is of the most abundant number in human immune system. During acute influenza virus infection, neutrophils are already active in the early phase of inflammation - a time in which clinical biopsy or autopsy material is not readily available. However, the role of neutrophil in virus infection is not well understood. Here, we studied the role of neutrophil in host defense during influenza A virus infection, specifically assessing if it contributes to the differential pathogenesis in H5N1 disease.

METHODS

Neutrophils were freshly isolated from healthy volunteers and subjected to direct influenza H1N1 and H5N1 virus infection in vitro. The ability of the naïve neutrophils to infiltrate from the basolateral to the apical phase of the influenza virus infected alveolar epithelium was assessed. The viral replication, innate immune responses and Neutrophil extracellular trap (NET) formation of neutrophils upon influenza virus infection were evaluated.

RESULTS

Our results demonstrated that influenza virus infected alveolar epithelium allowed neutrophil transmigration. Significantly more neutrophils migrated across the H5N1 influenza virus infected the epithelium than the counterpart infected by the seasonal influenza H1N1 virus infected. Neutrophils were equally susceptible to H5N1 and H1N1 virus infection with similar viral gene transcription. Productive replication was observed in H5N1 infected neutrophils. H5N1 induced higher cytokine and chemokine gene transcription than H1N1 infected neutrophils, including TNF-α, IFN-β, CXCL10, MIP-1α and IL-8. This inferred a more intense inflammatory response posed by H5N1 than H1N1 virus. Strikingly, NADPH oxidase-independent NET formation was only observed in H1N1 infected neutrophils at 6 hpi while no NET formation was observed upon H5N1 infection.

CONCLUSION

Our data is the first to demonstrate that NET formation is abrogated in H5N1 influenza virus infection and might contribute to the severity of H5N1 disease.

Pathway mapping of leukocyte transcriptome in influenza patients reveals distinct pathogenic mechanisms associated with progression to severe infection

Background

Influenza infections produce a spectrum of disease severity, ranging from a mild respiratory illness to respiratory failure and death. The host-response pathways associated with the progression to severe influenza disease are not well understood.

Methods

To gain insight into the disease mechanisms associated with progression to severe infection, we analyzed the leukocyte transcriptome in severe and moderate influenza patients and healthy control subjects. Pathway analysis on differentially expressed genes was performed using a topology-based pathway analysis tool that takes into account the interaction between multiple cellular pathways. The pathway profiles between moderate and severe influenza were then compared to delineate the biological mechanisms underpinning the progression from moderate to severe influenza.

Results

107 patients (44 severe and 63 moderate influenza patients) and 52 healthy control subjects were included in the study. Severe influenza was associated with upregulation in several neutrophil-related pathways, including pathways involved in neutrophil differentiation, migration, degranulation and neutrophil extracellular trap (NET) formation. The degree of upregulation in neutrophil-related pathways were significantly higher in severely infected patients compared to moderately infected patients. Severe influenza was also associated with downregulation in immune response pathways, including pathways involved in antigen presentation such as CD4+ T-cell co-stimulation, CD8+ T cell and Natural Killer (NK) cells effector functions. Apoptosis pathways were also downregulated in severe influenza patients compare to moderate and healthy controls.

Conclusions

These findings showed that there are changes in gene expression profile that may highlight distinct pathogenic mechanisms associated with progression from moderate to severe influenza infection.

The Role of Innate Leukocytes during Influenza Virus Infection

Influenza virus infection is a serious threat to humans and animals, with the potential to cause severe pneumonia and death. Annual vaccination strategies are a mainstay to prevent complications related to influenza. However, protection from the emerging subtypes of influenza A viruses (IAV) even in vaccinated individuals is challenging. Innate immune cells are the first cells to respond to IAV infection in the respiratory tract. Virus replication-induced production of cytokines from airway epithelium recruits innate immune cells to the site of infection. These leukocytes, namely, neutrophils, monocytes, macrophages, dendritic cells, eosinophils, natural killer cells, innate lymphoid cells, and γδ T cells, become activated in response to IAV, to contain the virus and protect the airway epithelium while triggering the adaptive arm of the immune system. This review addresses different anti-influenza virus schemes of innate immune cells and how these cells fine-tune the balance between immunoprotection and immunopathology during IAV infection. Detailed understanding on how these innate responders execute anti-influenza activity will help to identify novel therapeutic targets to halt IAV replication and associated immunopathology.

The role of platelets in mediating a response to human influenza infection

Influenza infection increases the incidence of myocardial infarction but the reason is unknown. Platelets mediate vascular occlusion through thrombotic functions but are also recognized to have immunomodulatory activity. To determine if platelet processes are activated during influenza infection, we collected blood from 18 patients with acute influenza infection. Microscopy reveals activated platelets, many containing viral particles and extracellular-DNA associated with platelets. To understand the mechanism, we isolate human platelets and treat them with influenza A virus. Viral-engulfment leads to C3 release from platelets as a function of TLR7 and C3 leads to neutrophil-DNA release and aggregation. TLR7 specificity is confirmed in murine models lacking the receptor, and platelet depletion models support platelet-mediated C3 and neutrophil-DNA release post-influenza infection. These findings demonstrate that the initial intrinsic defense against influenza is mediated by platelet–neutrophil cross-communication that tightly regulates host immune and complement responses but can also lead to thrombotic vascular occlusion.

Influenza viremia is rare in human blood and not well studied. Here, the authors show that influenza can be found in human platelets and that platelet engulfment of influenza A results in TLR7-dependent C3 release, which in turn promotes neutrophil-DNA release and formation of platelet-DNA aggregates.

Single-Step Detection of the Influenza Virus Hemagglutinin Using Bacterially-Produced Quenchbodies

We have successfully generated a Quenchbody that enables the detection of the influenza virus hemagglutinin (HA), in a simple and convenient manner. By two-site labeling of the bacterially-produced anti-HA Fab with ATTO520, its fluorescence intensity was increased to 4.4-fold, in the presence of a nanomolar concentration of H1N1 HA. Our results indicate the potential use of this Quenchbody, as a sensor for the simple in situ detection of influenza A virus.

Differential Ability of Pandemic and Seasonal H1N1 Influenza A Viruses To Alter the Function of Human Neutrophils

A long-standing notion is that IAV inhibits normal neutrophil function and thereby predisposes individuals to secondary bacterial infections. Here we report that seasonal H1N1 IAV primes human neutrophils for enhanced killing of Staphylococcus aureus. Moreover, we provide a comprehensive view of the changes in neutrophil gene expression during interaction with seasonal or pandemic IAV and report how these changes relate to functions such as bactericidal activity. This study expands our knowledge of IAV interactions with human neutrophils.

Neutrophils are essential cells of host innate immunity. Although the role of neutrophils in defense against bacterial and fungal infections is well characterized, there is a relative paucity of information about their role against viral infections. Influenza A virus (IAV) infection can be associated with secondary bacterial coinfection, and it has long been posited that the ability of IAV to alter normal neutrophil function predisposes individuals to secondary bacterial infections. To better understand this phenomenon, we evaluated the interaction of pandemic or seasonal H1N1 IAV with human neutrophils isolated from healthy persons. These viruses were ingested by human neutrophils and elicited changes in neutrophil gene expression that are consistent with an interferon-mediated immune response. The viability of neutrophils following coculture with either pandemic or seasonal H1N1 IAV was similar for up to 18 h of culture. Notably, neutrophil exposure to seasonal (but not pandemic) IAV primed these leukocytes for enhanced functions, including production of reactive oxygen species and bactericidal activity. Taken together, our results are at variance with the universal idea that IAV impairs neutrophil function directly to predispose individuals to secondary bacterial infections. Rather, we suggest that some strains of IAV prime neutrophils for enhanced bacterial clearance.

IMPORTANCE A long-standing notion is that IAV inhibits normal neutrophil function and thereby predisposes individuals to secondary bacterial infections. Here we report that seasonal H1N1 IAV primes human neutrophils for enhanced killing of Staphylococcus aureus. Moreover, we provide a comprehensive view of the changes in neutrophil gene expression during interaction with seasonal or pandemic IAV and report how these changes relate to functions such as bactericidal activity. This study expands our knowledge of IAV interactions with human neutrophils.

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.

The inflammatory response triggered by Influenza virus: a two edged sword

Influenza A virus (IAV) is a relevant respiratory tract pathogen leading to a great number of deaths and hospitalizations worldwide. Secondary bacterial infections are a very common cause of IAV associated morbidity and mortality. The robust inflammatory response that follows infection is important for the control of virus proliferation but is also associated with lung damage, morbidity and death. The role of the different components of immune response underlying protection or disease during IAV infection is not completely elucidated. Overall, in the context of IAV infection, inflammation is a 'double edge sword' necessary to control infection but causing disease. Therefore, a growing number of studies suggest that immunomodulatory strategies may improve disease outcome without affecting the ability of the host to deal with infection. This review summarizes recent aspects of the inflammatory responses triggered by IAV that are preferentially involved in causing severe pulmonary disease and the anti-inflammatory strategies that have been suggested to treat influenza induced immunopathology.