Roles and functions of IAV proteins in host immune evasion

Atractylenolide-Ⅲ binds non-structural protein-1 to suppress influenza A by modulating macrophage polarization and alternative polyadenylation

BACKGROUND

Drug-resistant influenza demands novel antiviral treatments. Non-structural protein 1 (NS1) of influenza A virus (IAV) regulates the viral life cycle and host immune response, thus becoming a promising therapeutic target. The atractylenolide (ACT) -Ⅲ exhibits notable anti-IAV efficacy; however, its in vivo anti-IAV activity and the underlying mechanisms need further exploration.

PURPOSE

We explored the binding affinity of ACT-Ⅲ with NS1 and elucidated the in vivo anti-influenza activity and underlying mechanism of ACT-Ⅲ.

STUDY DESIGN AND METHODS

Surface plasmon resonance (SPR) analysis was utilized to determine the binding affinity of ACT-Ⅲ to NS1. The anti-IAV activity of ACT-Ⅲ was further tested in vitro using IAV-infected lung epithelial cells and in vivo in IAV-challenged mice. The evaluation criteria included the assessment of virus-associated cytopathies, viral protein and gene expression, virus titer, mice weight loss, survival curve, and lung pathology. Transcriptomic sequencing was conducted to evaluate the inflammation regulatory function of ACT-Ⅲ in IAV-infected Raw264.7 cells. Quantitative real-time PCR (qRT-PCR) was used to detect the target gene expression. Flow cytometry was utilized to assess macrophages polarization. Co-immunoprecipitation was employed to examine the impact of ACT-Ⅲ on the interaction between NS1 and cleavage and polyadenylation-specific factor 4 (CPSF4).

RESULTS

ACT-Ⅲ exhibited anti-IAV activity in vitro and in vivo, mitigating virus-induced lung injury. Mechanistically, ACT-Ⅲ impeded IAV infection and viral induced inflammation by binding to viral NS1, which reduced the activation of pro-inflammatory signaling, and disrupted the NS1-CPSF4 interaction that mediates alternative polyadenylation (APA).

CONCLUSION

ACT-Ⅲ inhibits IAV replication and viral pneumonia by binding to NS1, showing potential as a therapeutic agent for IAV treatment.

Pathogenesis Induced by Influenza Virus Infection: Role of the Early Events of the Infection and the Innate Immune Response

Infections by influenza A virus (IAV) are a significant cause of global mortality. The pathogenesis of the infection is usually studied in terms of direct viral-induced damage or the overreactive immune response that continues after the virus is cleared. However, factors such as the initial infectious dose, the early response after infection in different cell types, and the presence of autoantibodies for relevant antiviral cytokines like type I IFNs seem to influence the course of the infection and lead to fatal outcomes. In this article, we address the current knowledge about the early events during influenza virus infection, which are important for their participation in influenza-derived pathogenesis.

Plasma nontargeted metabolomics study of H1N1 and H3N2 influenza in children

Background

This study used a nontargeted metabolomic approach to investigate small molecular metabolites in the peripheral blood of pediatric patients with influenza. By comparing these metabolites with those in healthy children, potential biomarkers for the early detection and diagnosis of influenza were explored.

Methods

Plasma samples were collected from 47 children with H1N1 influenza, 40 with H3N2 influenza, and 40 healthy controls at Xi'an Children's Hospital, Xi'an Jiaotong University Second Affiliated Hospital, and Xi'an Central Hospital between May and September 2023. Nontargeted metabolomic detection and analysis were performed.

Results

In the H1N1 group, 14 glycerophospholipid metabolites were significantly altered compared to controls, with 11 (78.5%) markedly downregulated. These downregulated metabolites showed negative correlations with inflammatory markers, including white blood cell (WBC) count, neutrophils, C-reactive protein (CRP), and Procalcitonin (PCT), whereas the upregulated metabolite PC(P-18:1(9Z)/16:0) showed positive correlations with validation markers. In the H3N2 group, 12 glycerophospholipid metabolites were significantly altered, with 9 being downregulated. The downregulated LysoPC(20:0/0:0) showed a positive correlation with alanine aminotransferase (ALT) but a negative correlation with WBC count, while the upregulated metabolite LysoPA(18:1(9Z)0:0) correlated positively with ALT, aspartate aminotransferase (AST), and lactate dehydrogenase (LDH).

Conclusions

Distinct metabolomic profiles were identified in pediatric H1N1 and H3N2 influenza cases compared to healthy controls. Specific glycerophospholipid metabolites were closely associated with inflammatory and liver function markers, highlighting their potential as biomarkers for disease monitoring and early diagnosis.

Emergence, migration and spreading of the high pathogenicity avian influenza virus H5NX of the Gs/Gd lineage into America

The high pathogenicity avian influenza virus H5N1, which first emerged in the winter of 2021, has resulted in multiple outbreaks across the American continent through the summer of 2023 and they continue based on early 2025 records, presenting significant challenges for global health and food security. The viruses causing the outbreaks belong to clade 2.3.4.4b, which are descendants of the lineage A/Goose/Guangdong/1/1996 (Gs/Gd) through genetic reassortments with several low pathogenicity avian influenza viruses present in populations of Anseriformes and Charadriiformes orders. This review addresses these issues by thoroughly analysing available epidemiological databases and specialized literature reviews. This project explores the mechanisms behind the resurgence of the H5N1 virus. It provides a comprehensive overview of the origin, timeline and factors contributing to its prevalence among wild bird populations on the American continent.

Antiviral strategies against influenza virus: an update on approved and innovative therapeutic approaches

Influenza viruses still represent a great concern for Public Health by causing yearly seasonal epidemics and occasionally worldwide pandemics. Moreover, spillover events at the animal-human interface are becoming more frequent nowadays, also involving animal species not previously found as reservoirs. To restrict the effects of influenza virus epidemics, especially in at-risk population, and to prepare a drug arsenal for possible future pandemics, researchers worldwide have been working on the development of antiviral strategies since the 80's of the last century. One of the main obstacles is the considerable genomic variability of influenza viruses, which constantly poses the issues of drug-resistance emergence and immune evasion. This review summarizes the approved therapeutics for clinical management of influenza, promising new anti-flu compounds and monoclonal antibodies currently undergoing clinical evaluation, and molecules with efficacy against influenza virus in preclinical studies. Moreover, we discuss some innovative anti-influenza therapeutic approaches such as combination therapies and targeted protein degradation. Given the limited number of drugs approved for influenza treatment, there is a still strong need for novel potent anti-influenza drugs endowed with a high barrier to drug resistance and broad-spectrum activity against influenza viruses of animal origin that may be responsible of future large outbreaks and pandemics.

The PB1 protein of H9N2 influenza A virus inhibits antiviral innate immunity by targeting MAVS for TRIM25-mediated autophagic degradation

The proteins encoded by Influenza A virus (IAV) evade the innate immune system through diverse strategies to facilitate their replication. However, the regulatory mechanisms remain not fully understood. In this study, we identified that the H9N2 PB1 protein suppressed the activities of the IFN-β, ISRE, and NF-κB promoters. Furthermore, H9N2 PB1 inhibited the phosphorylation of IRF3, IκBα, and TBK1 and the secretion of IFN-β. The results demonstrated H9N2 PB1 as a negative regulator of the RIG-I signaling pathway. Subsequent investigations revealed a specific interaction between H9N2 PB1 and MAVS, which disturbed the stability of MAVS. Notably, we discovered that H9N2 PB1 exploited the function of TRIM25, leading to the autophagic degradation of MAVS through K48-linked polyubiquitination. In conclusion, we uncovered a negative regulatory axis consisting of H9N2 PB1-TRIM25-MAVS-IFN-I. These findings provide valuable insights into the molecular interactions involved in the regulation of the host's innate immune antiviral response by IAV.

Functional Involvement of Signal Transducers and Activators of Transcription in the Pathogenesis of Influenza A Virus

Signal transducers and activators of transcription (STATs) function both as signal transducers and transcription regulators. STAT proteins are involved in the signaling pathways of cytokines and growth factors; thus, they participate in various life activities and play especially critical roles in antiviral immunity. Convincing evidence suggests that STATs can establish innate immune status through multiple mechanisms, efficiently eliminating pathogens. STAT1 and STAT2 can activate the antiviral status by regulating the interferon (IFN) signal. In turn, suppressor of cytokine signaling-1 (SOCS1) and SOCS3 can modulate the activation of STATs and suppress the excessive antiviral immune response. STAT3 not only regulates the IFN signal, but also transduces Interleukin-6 (IL-6) to stimulate the host antiviral response. The function of STAT4 and STAT5 is related to CD4+ T helper (Th) cells, and the specific mechanism of STAT5 remains to be studied. STAT6 mainly exerts antiviral effects by mediating IL-4 and IL-13 signaling. Here, we reviewed the recent findings regarding the critical roles of STATs in the interactions between the host and viral infection, especially influenza A virus (IAV) infection. We also discuss the molecular mechanisms underlying their functions in antiviral responses.

Viral Factors in Modulation of Host Immune Response: A Route to Novel Antiviral Agents and New Therapeutic Approaches

Viruses utilize host cells at all stages of their life cycle, from the transcription of genes and translation of viral proteins to the release of viral copies. The human immune system counteracts viruses through a variety of complex mechanisms, including both innate and adaptive components. Viruses have an ability to evade different components of the immune system and affect them, leading to disruption. This review covers contemporary knowledge about the virus-induced complex interplay of molecular interactions, including regulation of transcription and translation in host cells resulting in the modulation of immune system functions. Thorough investigation of molecular mechanisms and signaling pathways that are involved in modulating of host immune response to viral infections can help to develop novel approaches for antiviral therapy. In this review, we consider new therapeutic approaches for antiviral treatment. Modern therapeutic strategies for the treatment and cure of human immunodeficiency virus (HIV) are considered in detail because HIV is a unique example of a virus that leads to host T lymphocyte deregulation and significant modulation of the host immune response. Furthermore, peculiarities of some promising novel agents for the treatment of various viral infections are described.

Host Innate Antiviral Response to Influenza A Virus Infection: From Viral Sensing to Antagonism and Escape

Influenza virus possesses an RNA genome of single-stranded, negative-sensed, and segmented configuration. Influenza virus causes an acute respiratory disease, commonly known as the "flu" in humans. In some individuals, flu can lead to pneumonia and acute respiratory distress syndrome. Influenza A virus (IAV) is the most significant because it causes recurring seasonal epidemics, occasional pandemics, and zoonotic outbreaks in human populations, globally. The host innate immune response to IAV infection plays a critical role in sensing, preventing, and clearing the infection as well as in flu disease pathology. Host cells sense IAV infection through multiple receptors and mechanisms, which culminate in the induction of a concerted innate antiviral response and the creation of an antiviral state, which inhibits and clears the infection from host cells. However, IAV antagonizes and escapes many steps of the innate antiviral response by different mechanisms. Herein, we review those host and viral mechanisms. This review covers most aspects of the host innate immune response, i.e., (1) the sensing of incoming virus particles, (2) the activation of downstream innate antiviral signaling pathways, (3) the expression of interferon-stimulated genes, (4) and viral antagonism and escape.

Avian flu: «for whom the bell tolls»?

The family Orthomyxoviridae consists of 9 genera, including Alphainfluenzavirus, which contains avian influenza viruses. In two subtypes H5 and H7 besides common low-virulent strains, a specific type of highly virulent avian virus have been described to cause more than 60% mortality among domestic birds. These variants of influenza virus are usually referred to as «avian influenza virus». The difference between high (HPAI) and low (LPAI) virulent influenza viruses is due to the structure of the arginine-containing proteolytic activation site in the hemagglutinin (HA) protein. The highly virulent avian influenza virus H5 was identified more than 100 years ago and during this time they cause outbreaks among wild and domestic birds on all continents and only a few local episodes of the disease in humans have been identified in XXI century. Currently, a sharp increase in the incidence of highly virulent virus of the H5N1 subtype (clade h2.3.4.4b) has been registered in birds on all continents, accompanied by the transmission of the virus to various species of mammals. The recorded global mortality rate among wild, domestic and agricultural birds from H5 subtype is approaching to the level of 1 billion cases. A dangerous epidemic factor is becoming more frequent outbreaks of avian influenza with high mortality among mammals, in particular seals and marine lions in North and South America, minks and fur-bearing animals in Spain and Finland, domestic and street cats in Poland. H5N1 avian influenza clade h2.3.4.4b strains isolated from mammals have genetic signatures of partial adaptation to the human body in the PB2, NP, HA, NA genes, which play a major role in regulating the aerosol transmission and the host range of the virus. The current situation poses a real threat of pre-adaptation of the virus in mammals as intermediate hosts, followed by the transition of the pre-adapted virus into the human population with catastrophic consequences.