HIV-1 and its gp120 inhibits the influenza A(H1N1)pdm09 life cycle in an IFITM3-dependent fashion

Severe influenza infection is associated with inflammatory programmed cell death in infected macrophages

Introduction

Influenza A virus (IAV) is one of the leading causes of respiratory tract infections in humans, representing a major public health concern. The various types of cell death have a crucial role in IAV pathogenesis because this virus may trigger both apoptosis and necroptosis in airway epithelial cells in parallel. Macrophages play an important role in the clearance of virus particles, priming the adaptive immune response in influenza. However, the contribution of macrophage death to pathogenesis of IAV infection remains unclear.

Methods

In this work, we investigated IAV-induced macrophage death, along with potential therapeutic intervention. We conducted in vitro and in vivo experiments to evaluate the mechanism and the contribution of macrophages death to the inflammatory response induced by IAV infection.

Results

We found that IAV or its surface glycoprotein hemagglutinin (HA) triggers inflammatory programmed cell death in human and murine macrophages in a Toll-like receptor-4 (TLR4)- and TNF-dependent manner. Anti-TNF treatment in vivo with the clinically approved drug etanercept prevented the engagement of the necroptotic loop and mouse mortality. Etanercept impaired the IAV-induced proinflammatory cytokine storm and lung injury.

Conclusion

In summary, we demonstrated a positive feedback loop of events that led to necroptosis and exacerbated inflammation in IAV-infected macrophages. Our results highlight an additional mechanism involved in severe influenza that could be attenuated with clinically available therapies.

The Dual Role of CCR5 in the Course of Influenza Infection: Exploring Treatment Opportunities

Influenza is one of the most relevant respiratory viruses to human health causing annual epidemics, and recurrent pandemics. Influenza disease is principally associated with inappropriate activation of the immune response. Chemokine receptor 5 (CCR5) and its cognate chemokines CCL3, CCL4 and CCL5 are rapidly induced upon influenza infection, contributing to leukocyte recruitment into the airways and a consequent effective antiviral response. Here we discuss the existing evidence for CCR5 role in the host immune responses to influenza virus. Complete absence of CCR5 in mice revealed the receptor’s role in coping with influenza via the recruitment of early memory CD8+ T cells, B cell activation and later recruitment of activated CD4+ T cells. Moreover, CCR5 contributes to inflammatory resolution by enhancing alveolar macrophages survival and reprogramming macrophages to pro-resolving phenotypes. In contrast, CCR5 activation is associated with excessive recruitment of neutrophils, inflammatory monocytes, and NK cells in models of severe influenza pneumonia. The available data suggests that, while CCL5 can play a protective role in influenza infection, CCL3 may contribute to an overwhelming inflammatory process that can harm the lung tissue. In humans, the gene encoding CCR5 might contain a 32-base pair deletion, resulting in a truncated protein. While discordant data in literature regarding this CCR5 mutation and influenza severity, the association of CCR5delta32 and HIV resistance fostered the development of different CCR5 inhibitors, now being tested in lung inflammation therapy. The potential use of CCR5 inhibitors to modulate the inflammatory response in severe human influenza infections is to be addressed.

The Chemokine CCL5 Inhibits the Replication of Influenza A Virus Through SAMHD1 Modulation

Influenza A virus (IAV) is the main etiological agent of acute respiratory tract infections. During IAV infection, interferon triggers the overexpression of restriction factors (RFs), the intracellular antiviral branch of the innate immune system. Conversely, severe influenza is associated with an unbalanced pro-inflammatory cytokine release. It is unclear whether other cytokines and chemokines released during IAV infection modulate RFs to control virus replication. Among the molecules enhanced in the infected respiratory tract, ligands of the CCR5 receptor play a key role, as they stimulate the migration of inflammatory cells to the alveoli. We investigated here whether ligands of the CCR5 receptor could enhance RFs to levels able to inhibit IAV replication. For this purpose, the human alveolar basal epithelial cell line (A549) was treated with endogenous (CCL3, CCL4 and CCL5) or exogenous (HIV-1 gp120) ligands prior to IAV infection. The three CC-chemokines tested reduced infectious titers between 30% to 45% upon 24 hours of infection. Eploying RT-PCR, a panel of RF mRNA levels from cells treated with CCR5 agonists was evaluated, which showed that the SAMHD1 expression was up-regulated four times over control upon exposure to CCL3, CCL4 and CCL5. We also found that IAV inhibition by CCL5 was dependent on PKC and that SAMHD1 protein levels were also increased after treatment with CCL5. In functional assays, we observed that the knockdown of SAMHD1 resulted in enhanced IAV replication in A549 cells and abolished both CCL5-mediated inhibition of IAV replication and CCL5-mediated cell death inhibition. Our data show that stimuli unrelated to interferon may trigger the upregulation of SAMHD1 and that this RF may directly interfere with IAV replication in alveolar epithelial cells.

Platelet function in HIV plus dengue coinfection associates with reduced inflammation and milder dengue illness

HIV-infected subjects under virological control still exhibit a persistent proinflammatory state. Thus, chronic HIV infection changes the host homeostasis towards an adapted immune response that may affect the outcome of coinfections. However, little is known about the impact of HIV infection on inflammatory amplification and clinical presentation in dengue. Platelets have been shown to participate in immune response in dengue and HIV. We hypothesized that altered platelet responses in HIV-infected subjects may contribute to altered inflammatory milieu and disease progression in dengue. We prospectively followed a cohort of 84 DENV-infected patients of whom 29 were coinfected with HIV under virological control. We report that dengue and HIV coinfection progress with reduced inflammation and milder disease progression with lower risk of vascular instability. Even though the degree of thrombocytopenia and platelet activation were similar between dengue-infected and HIV plus dengue-coinfected patients, plasma levels of the platelet-derived chemokines RANTES/CCL5 and PF4/CXCL4 were lower in coinfection. Consistently, platelets from coinfected patients presented defective secretion of the stored-chemokines PF4 and RANTES, but not newly synthesized IL-1β, when cultured ex vivo. These data indicate that platelets from HIV-infected subjects release lower levels of chemokines during dengue illness, which may contribute to milder clinical presentation during coinfection.

Influenza virus RNA polymerase may be activated inside the virion

Influenza A and B virions are packaged with their polymerases to catalyse RNA-dependent RNA polymerase activity. Since there is no evidence to rule in or out the permissiveness of influenza virions to triphosphate ribonucleotides, we functionally evaluated this. We found the means to stimulate influenza A and B RNA polymerase activity inside the virion, called natural endogenous RNA polymerase (NERP) activity. Stimulation of NERP activity increased up to 3 log10 viral RNA content, allowing the detection of influenza virus in otherwise undetectable clinical samples. NERP activation also improved our capacity to sequence misidentified regions of the influenza genome from clinical samples. By treating the samples with the ribavirin triphosphate we inhibited NERP activity, which confirms our hypothesis and highlights that this assay could be used to screen antiviral drugs. Altogether, our data show that NERP activity could be explored to increase molecular diagnostic sensitivity and/or to develop antiviral screening assays.

Inhibitory effect of microalgae and cyanobacteria extracts on influenza virus replication and neuraminidase activity

Background

The influenza virus can cause seasonal infections with mild to severe symptoms, circulating worldwide, and it can affect people in any age group. Therefore, this infection is a serious public health problem that causes severe illness and death in high-risk populations. Every year, 0.5% of the world’s population is infected by this pathogen. This percentage can increase up to ten times during pandemics. Influenza vaccination is the most effective way to prevent disease. In addition, anti-influenza drugs are essential for prophylactic and therapeutic interventions. The oseltamivir (OST, a neuraminidase inhibitor) is the primary antiviral used in clinics during outbreaks. However, OST resistant viruses may emerge naturally or due to antiviral pressure, with a prevalence of 1–2% worldwide. Thus, the search for new anti-influenza drugs is extremely important. Currently, several groups have been developing studies describing the biotechnological potential of microalgae and cyanobacteria, including antiviral activity of their extracts. In Brazil, this potential is poorly known and explored.

Methods

With the aim of increasing the knowledge on this topic, 38 extracts from microalgae and cyanobacteria isolated from marine and freshwater biomes in Brazil were tested against: cellular toxicity; OST-sensitive and resistant influenza replications; and neuraminidase activity.

Results

For this purpose, Madin-Darby Canine Kidney (MDCK)-infected cells were treated with 200 μg/mL of each extract. A total of 17 extracts (45%) inhibited influenza A replication, with seven of them resulting in more than 80% inhibition. Moreover, functional assays performed with viral neuraminidase revealed two extracts (from Leptolyngbya sp. and Chlorellaceae) with IC₅₀ mean < 210 μg/mL for influenza A and B, and also OST-sensitive and resistant strains. Furthermore, MDCK cells exposed to 1 mg/mL of all the extracts showed viability higher than 80%.

Discussion

Our results suggest that extracts of microalgae and cyanobacteria have promising anti-influenza properties. Further chemical investigation should be conducted to isolate the active compounds for the development of new anti-influenza drugs. The data generated contribute to the knowledge of the biotechnological potential of Brazilian biomes that are still little explored for this purpose.

Aureonitol, a Fungi-Derived Tetrahydrofuran, Inhibits Influenza Replication by Targeting Its Surface Glycoprotein Hemagglutinin

The influenza virus causes acute respiratory infections, leading to high morbidity and mortality in groups of patients at higher risk. Antiviral drugs represent the first line of defense against influenza, both for seasonal infections and pandemic outbreaks. Two main classes of drugs against influenza are in clinical use: M2-channel blockers and neuraminidase inhibitors. Nevertheless, because influenza strains that are resistant to these antivirals have been described, the search for novel compounds with different mechanisms of action is necessary. Here, we investigated the anti-influenza activity of a fungi-derived natural product, aureonitol. This compound inhibited influenza A and B virus replication. This compound was more effective against influenza A(H3N2), with an EC₅₀ of 100 nM. Aureonitol cytoxicity was also very low, with a CC₅₀ value of 1426 μM. Aureonitol inhibited influenza hemagglutination and, consequently, significantly impaired virus adsorption. Molecular modeling studies revealed that aureonitol docked in the sialic acid binding site of hemagglutinin, forming hydrogen bonds with highly conserved residues. Altogether, our results indicate that the chemical structure of aureonitol is promising for future anti-influenza drug design.

Intranasal Immunization with Pressure Inactivated Avian Influenza Elicits Cellular and Humoral Responses in Mice

Influenza viruses pose a serious global health threat, particularly in light of newly emerging strains, such as the avian influenza H5N1 and H7N9 viruses. Vaccination remains the primary method for preventing acquiring influenza or for avoiding developing serious complications related to the disease. Vaccinations based on inactivated split virus vaccines or on chemically inactivated whole virus have some important drawbacks, including changes in the immunogenic properties of the virus. To induce a greater mucosal immune response, intranasally administered vaccines are highly desired as they not only prevent disease but can also block the infection at its primary site. To avoid these drawbacks, hydrostatic pressure has been used as a potential method for viral inactivation and vaccine production. In this study, we show that hydrostatic pressure inactivates the avian influenza A H3N8 virus, while still maintaining hemagglutinin and neuraminidase functionalities. Challenged vaccinated animals showed no disease signs (ruffled fur, lethargy, weight loss, and huddling). Similarly, these animals showed less Evans Blue dye leakage and lower cell counts in their bronchoalveolar lavage fluid compared with the challenged non-vaccinated group. We found that the whole inactivated particles were capable of generating a neutralizing antibody response in serum, and IgA was also found in nasal mucosa and feces. After the vaccination and challenge we observed Th1/Th2 cytokine secretion with a prevalence of IFN-γ. Our data indicate that the animals present a satisfactory immune response after vaccination and are protected against infection. Our results may pave the way for the development of a novel pressure-based vaccine against influenza virus.