How antibodies alter the cell entry pathway of dengue virus particles in macrophages

The antibodies against the A137R protein drive antibody-dependent enhancement of African swine fever virus infection in porcine alveolar macrophages

African swine fever virus (ASFV) is the causative agent of African swine fever (ASF), a highly contagious disease that can kill up to 100% of domestic pigs and wild boars. It has been shown that the pigs inoculated with some ASF vaccine candidates display more severe clinical signs and die earlier than do pigs not immunized. We hypothesize that antibody-dependent enhancement (ADE) of ASFV infection may be caused by the presence of some unidentified antibodies. In this study, we found that the ASFV-encoded structural protein A137R (pA137R) can be recognized by the anti-ASFV positive sera, indicating that the anti-pA137R antibodies are induced in the ASFV-infected pigs. Interestingly, our results demonstrated that the anti-pA137R antibodies produced in rabbits or pigs enhanced viral replication of different ASFV strains in primary porcine alveolar macrophages (PAMs), the target cells of ASFV. Mechanistic investigations revealed that anti-pA137R antibodies were able to promote the attachment of ASFV to PAMs and two types of Fc gamma receptors (FcγRs), FcγRII and FcγRIII, mediated the ADE of ASFV infection. Taken together, anti-pA137R antibodies are able to drive ASFV ADE in PAMs. These findings shed new light on the roles of anti-ASFV antibodies and have implications for the pathophysiology of the disease and the development of ASF vaccines.

Neutralizing and enhancing monoclonal antibodies in SARS-CoV-2 convalescent patients: lessons from early variant infection and impact on shaping emerging variants

Serological studies of COVID-19 convalescent patients have identified polyclonal lineage-specific and cross-reactive antibodies (Abs), with varying effector functions against virus variants. Individual specificities of anti-SARS-CoV-2 Abs and their impact on infectivity by other variants have been little investigated to date. Here, we dissected at a monoclonal level neutralizing and enhancing Abs elicited by early variants and how they affect infectivity of emerging variants. B cells from 13 convalescent patients originally infected by D614G or Alpha variants were immortalized to isolate 445 naturally-produced anti-SARS-CoV-2 Abs. Monoclonal antibodies (mAbs) were tested for their abilities to impact the cytopathic effect of D614G, Delta, and Omicron (BA.1) variants. Ninety-eight exhibited robust neutralization against at least one of the three variant types, while 309 showed minimal or no impact on infectivity. Thirty-eight mAbs enhanced infectivity of SARS-CoV-2. Infection with D614G/Alpha variants generated variant-specific (65 neutralizing Abs, 35 enhancing Abs) and cross-reactive (18 neutralizing Abs, 3 enhancing Abs) mAbs. Interestingly, among the neutralizing mAbs with cross-reactivity restricted to two of the three variants tested, none demonstrated specific neutralization of the Delta and Omicron variants. In contrast, cross-reactive mAbs enhancing infectivity (n = 3) were found exclusively specific to Delta and Omicron variants. Notably, two mAbs that amplified in vitro the cytopathic effect of the Delta variant also exhibited neutralization against Omicron. These findings shed light on functional diversity of cross-reactive Abs generated during SARS-CoV-2 infection and illustrate how the balance between neutralizing and enhancing Abs facilitate variant emergence.

C1q modulation of antibody-dependent enhancement of dengue virus infection in human myeloid cell lines is dependent on cell type and antibody specificity

Antibody-dependent enhancement (ADE) of dengue virus (DENV) infection is one of the mechanisms contributing to increased severity during heterotypic, secondary infection. The complement protein C1q has been shown to reduce the magnitude of ADE in vitro. Therefore, we investigated the mechanisms of C1q modulation of ADE, focusing on processes of viral entry. Using a model of ADE of DENV-1 infection in human myeloid cell lines in the presence of monoclonal antibodies, 4G2 and 2H2, we found that C1q produced nearly a 40-fold reduction of ADE of DENV-1 in K562 cells, but had no effect in U937 cells. In K562 cells, C1q reduced adsorption of DENV-1/4G2 and exerted a dual inhibitory effect on adsorption and internalization of DENV-1/2H2. Distinct endocytic pathways in the presence of antibody corresponded to conditions where C1q produced a differential action. Also, C1q did not affect the intrinsic cell response mediated by FcγR in human myeloid cells. The modulation of ADE of DENV-1 by C1q is dependent on the FcγR expressed on immune cells and the specificity of the antibody comprising the immune complex. Understanding protective and pathogenic mechanisms in the humoral response to DENV infections is crucial for the successful design of antivirals and vaccines.

Functional genomics screens reveal a role for TBC1D24 and SV2B in antibody-dependent enhancement of dengue virus infection

Dengue virus (DENV) can hijack non-neutralizing IgG antibodies to facilitate its uptake into target cells expressing Fc gamma receptors (FcgR) - a process known as antibody-dependent enhancement (ADE) of infection. Beyond a requirement for FcgR, host dependency factors for this non-canonical infection route remain unknown. To identify cellular factors exclusively required for ADE, here, we performed CRISPR knockout screens in an in vitro system permissive to infection only in the presence of IgG antibodies. Validating our approach, a top hit was FcgRIIa, which facilitates binding and internalization of IgG-bound DENV but is not required for canonical infection. Additionally, we identified host factors with no previously described role in DENV infection, including TBC1D24 and SV2B, both of which have known functions in regulated secretion. Using genetic knockout and trans-complemented cells, we validated a functional requirement for these host factors in ADE assays performed with monoclonal antibodies and polyclonal sera in multiple cell lines and using all four DENV serotypes. We show that knockout of TBC1D24 or SV2B impaired binding of IgG-DENV complexes to cells without affecting FcgRIIa expression levels. Thus, we identify cellular factors beyond FcgR that are required for ADE of DENV infection. Our findings represent a first step towards advancing fundamental knowledge behind the biology of ADE that can ultimately be exploited to inform vaccination and therapeutic approaches.

DENV-specific IgA contributes protective and non-pathologic function during antibody-dependent enhancement of DENV infection

Dengue represents a growing public health burden worldwide, accounting for approximately 100 million symptomatic cases and tens of thousands of fatalities yearly. Prior infection with one serotype of dengue virus (DENV) is the greatest known risk factor for severe disease upon secondary infection with a heterologous serotype, a risk which increases as serotypes co-circulate in endemic regions. This disease risk is thought to be mediated by IgG-isotype antibodies raised during a primary infection, which poorly neutralize heterologous DENV serotypes and instead opsonize virions for uptake by FcγR-bearing cells. This antibody-dependent enhancement (ADE) of infection leads to a larger proportion of susceptible cells infected, higher viremia and greater immunopathology. We have previously characterized the induction of a serum IgA response, along with the typical IgM and IgG responses, during dengue infection, and have shown that DENV-reactive IgA can neutralize DENV and competitively antagonize IgG-mediated ADE. Here, we evaluate the potential for IgA itself to cause ADE. We show that IgG, but not IgA, mediated ADE of infection in cells expressing both FcαR and FcγRs. IgG-mediated ADE stimulated significantly higher pro-inflammatory cytokine production by primary human macrophages, while IgA did not affect, or slightly suppressed, this production. Mechanistically, we show that DENV/IgG immune complexes bind susceptible cells significantly more efficiently than DENV/IgA complexes or virus alone. Finally, we show that over the course of primary dengue infection, the expression of FcγRI (CD64) increases during the period of acute viremia, while FcγRIIa (CD32) and FcαR (CD89) expression decreases, thereby further limiting the ability of IgA to facilitate ADE in the presence of DENV. Overall, these data illustrate the distinct protective role of IgA during ADE of dengue infection and highlight the potential therapeutic and prognostic value of DENV-specific IgA.

Antibody-Dependent Enhancement with a Focus on SARS-CoV-2 and Anti-Glycan Antibodies

Antibody-dependent enhancement (ADE) is a phenomenon where virus-specific antibodies paradoxically cause enhanced viral replication and/or excessive immune responses, leading to infection exacerbation, tissue damage, and multiple organ failure. ADE has been observed in many viral infections and is supposed to complicate the course of COVID-19. However, the evidence is insufficient. Since no specific laboratory markers have been described, the prediction and confirmation of ADE are very challenging. The only possible predictor is the presence of already existing (after previous infection) antibodies that can bind to viral epitopes and promote the disease enhancement. At the same time, the virus-specific antibodies are also a part of immune response against a pathogen. These opposite effects of antibodies make ADE research controversial. The assignment of immunoglobulins to ADE-associated or virus neutralizing is based on their affinity, avidity, and content in blood. However, these criteria are not clearly defined. Another debatable issue (rather terminological, but no less important) is that in most publications about ADE, all immunoglobulins produced by the immune system against pathogens are qualified as pre-existing antibodies, thus ignoring the conventional use of this term for natural antibodies produced without any stimulation by pathogens. Anti-glycan antibodies (AGA) make up a significant part of the natural immunoglobulins pool, and there is some evidence of their antiviral effect, particularly in COVID-19. AGA have been shown to be involved in ADE in bacterial infections, but their role in the development of ADE in viral infections has not been studied. This review focuses on pros and cons for AGA as an ADE trigger. We also present the results of our pilot studies, suggesting that AGAs, which bind to complex epitopes (glycan plus something else in tight proximity), may be involved in the development of the ADE phenomenon.

A Review: Understanding Molecular Mechanisms of Antibody-Dependent Enhancement in Viral Infections

Antibody Dependent Enhancement (ADE) of an infection has been of interest in the investigation of many viruses. It is associated with the severity of the infection. ADE is mediated by non-neutralizing antibodies, antibodies at sub-neutralizing concentrations, or cross-reactive non-neutralizing antibodies. Treatments like plasma therapy, B cell immunizations, and antibody therapies may trigger ADE. It is seen as an impediment to vaccine development as well. In viruses including the Dengue virus (DENV), severe acute respiratory syndrome (SARS) virus, Middle East respiratory syndrome (MERS) virus, human immunodeficiency virus (HIV), Ebola virus, Zika virus, and influenza virus, the likely mechanisms of ADE are postulated and described. ADE improves the likelihood of productively infecting cells that are expressing the complement receptor or the Fc receptor (FcR) rather than the viral receptors. ADE occurs when the FcR, particularly the Fc gamma receptor, and/or complement system, particularly Complement 1q (C1q), allow the entry of the virus-antibody complex into the cell. Moreover, ADE alters the innate immune pathways to escape from lysis, promoting viral replication inside the cell that produces viral particles. This review discusses the involvement of FcR and the downstream immunomodulatory pathways in ADE, the complement system, and innate antiviral signaling pathways modification in ADE and its impact on facilitating viral replication. Additionally, we have outlined the modes of ADE in the cases of different viruses reported until now.

New Neutralizing Epitope Exposed on the Domain II of Tick-Borne Encephalitis Virus Envelope Glycoprotein E

Orthoflavivirus encephalitidis, formerly tick-borne encephalitis virus (TBEV), belongs to the Orthoflavivirus genus. TBEV is transmitted by tick bites and infection with TBEV can lead to serious disorders of the central nervous system. In this study, a new protective monoclonal mouse antibody (mAb) FVN-32, with high binding activity to glycoprotein E of TBEV, was selected and examined in post exposure prophylaxis in a mouse model of TBEV infection. BALB/c mice were injected mAb FVN-32 at doses of 200 μg, 50 μg, and 12.5 μg per mouse one day after a TBEV challenge. mAb FVN-32 showed 37.5% protective efficacy when administered at doses of 200 μg and 50 μg per mouse. The epitope for protective mAb FVN-32 was localized in TBEV glycoprotein E domain I+II, using a set of truncated fragments of glycoprotein E. Additionally, the target site recognized by mAb FVN-32 was defined using combinatorial libraries of peptides. Three-dimensional modeling revealed that the site is dspatially close to the fusion loop, but does not come into contact with it, and is localized in a region between 247 and 254 amino acid residues on the envelope protein. This region is conserved among TBEV-like orthoflaviviruses.

Dengue virus infection - a review of pathogenesis, vaccines, diagnosis and therapy

The transmission of dengue virus (DENV) from an infected Aedes mosquito to a human, causes illness ranging from mild dengue fever to fatal dengue shock syndrome. The similar conserved structure and sequence among distinct DENV serotypes or different flaviviruses has resulted in the occurrence of cross reaction followed by antibody-dependent enhancement (ADE). Thus far, the vaccine which can provide effective protection against infection by different DENV serotypes remains the biggest hurdle to overcome. Therefore, deep investigation is crucial for the potent and effective therapeutic drugs development. In addition, the cross-reactivity of flaviviruses that leads to false diagnosis in clinical settings could result to delay proper intervention management. Thus, the accurate diagnostic with high specificity and sensitivity is highly required to provide prompt diagnosis in respect to render early treatment for DENV infected individuals. In this review, the recent development of neutralizing antibodies, antiviral agents, and vaccine candidates in therapeutic platform for DENV infection will be discussed. Moreover, the discovery of antigenic cryptic epitopes, principle of molecular mimicry, and application of single-chain or single-domain antibodies towards DENV will also be presented.

Antibody-Dependent Enhancement: ″Evil″ Antibodies Favorable for Viral Infections

The pandemics caused by emerging viruses such as severe acute respiratory syndrome coronavirus 2 result in severe disruptions to public health. Vaccines and antibody drugs play essential roles in the control and prevention of emerging infectious diseases. However, in contrast with the neutralizing antibodies (NAbs), sub- or non-NAbs may facilitate the virus to enter the cells and enhance viral infection, which is termed antibody-dependent enhancement (ADE). The ADE of most virus infections is mediated by the Fc receptors (FcRs) expressed on the myeloid cells, while others are developed by other mechanisms, such as complement receptor-mediated ADE. In this review, we comprehensively analyzed the characteristics of the viruses inducing FcRs-mediated ADE and the new molecular mechanisms of ADE involved in the virus entry, immune response, and transcription modulation, which will provide insights into viral pathogenicity and the development of safer vaccines and effective antibody drugs against the emerging viruses inducing ADE.

Peculiarities of Zika Immunity and Vaccine Development: Lessons from Dengue and the Contribution from Controlled Human Infection Model

The Zika virus (ZIKV) was first isolated from a rhesus macaque in the Zika forest of Uganda in 1947. Isolated cases were reported until 2007, when the first major outbreaks of Zika infection were reported from the Island of Yap in Micronesia and from French Polynesia in 2013. In 2015, ZIKV started to circulate in Latin America, and in 2016, ZIKV was considered by WHO to be a Public Health Emergency of International Concern due to cases of Congenital Zika Syndrome (CZS), a ZIKV-associated complication never observed before. After a peak of cases in 2016, the infection incidence dropped dramatically but still causes concern because of the associated microcephaly cases, especially in regions where the dengue virus (DENV) is endemic and co-circulates with ZIKV. A vaccine could be an important tool to mitigate CZS in endemic countries. However, the immunological relationship between ZIKV and other flaviviruses, especially DENV, and the low numbers of ZIKV infections are potential challenges for developing and testing a vaccine against ZIKV. Here, we discuss ZIKV vaccine development with the perspective of the immunological concerns implicated by DENV-ZIKV cross-reactivity and the use of a controlled human infection model (CHIM) as a tool to accelerate vaccine development.

Role of Clathrin and Dynamin in Clathrin Mediated Endocytosis/Synaptic Vesicle Recycling and Implications in Neurological Diseases

Endocytosis is a process essential to the health and well-being of cell. It is required for the internalisation and sorting of “cargo”—the macromolecules, proteins, receptors and lipids of cell signalling. Clathrin mediated endocytosis (CME) is one of the key processes required for cellular well-being and signalling pathway activation. CME is key role to the recycling of synaptic vesicles [synaptic vesicle recycling (SVR)] in the brain, it is pivotal to signalling across synapses enabling intracellular communication in the sensory and nervous systems. In this review we provide an overview of the general process of CME with a particular focus on two key proteins: clathrin and dynamin that have a central role to play in ensuing successful completion of CME. We examine these two proteins as they are the two endocytotic proteins for which small molecule inhibitors, often of known mechanism of action, have been identified. Inhibition of CME offers the potential to develop therapeutic interventions into conditions involving defects in CME. This review will discuss the roles and the current scope of inhibitors of clathrin and dynamin, providing an insight into how further developments could affect neurological disease treatments.

Recent Development of Ruminant Vaccine Against Viral Diseases

Pathogens of viral origin produce a large variety of infectious diseases in livestock. It is essential to establish the best practices in animal care and an efficient way to stop and prevent infectious diseases that impact animal husbandry. So far, the greatest way to combat the disease is to adopt a vaccine policy. In the fight against infectious diseases, vaccines are very popular. Vaccination's fundamental concept is to utilize particular antigens, either endogenous or exogenous to induce immunity against the antigens or cells. In light of how past emerging and reemerging infectious diseases and pandemics were handled, examining the vaccination methods and technological platforms utilized for the animals may provide some useful insights. New vaccine manufacturing methods have evolved because of developments in technology and medicine and our broad knowledge of immunology, molecular biology, microbiology, and biochemistry, among other basic science disciplines. Genetic engineering, proteomics, and other advanced technologies have aided in implementing novel vaccine theories, resulting in the discovery of new ruminant vaccines and the improvement of existing ones. Subunit vaccines, recombinant vaccines, DNA vaccines, and vectored vaccines are increasingly gaining scientific and public attention as the next generation of vaccines and are being seen as viable replacements to conventional vaccines. The current review looks at the effects and implications of recent ruminant vaccine advances in terms of evolving microbiology, immunology, and molecular biology.

Dengue Virus Infection: A Tale of Viral Exploitations and Host Responses

Dengue is a mosquito-borne viral disease (arboviral) caused by the Dengue virus. It is one of the prominent public health problems in tropical and subtropical regions with no effective vaccines. Every year around 400 million people get infected by the Dengue virus, with a mortality rate of about 20% among the patients with severe dengue. The Dengue virus belongs to the Flaviviridae family, and it is an enveloped virus with positive-sense single-stranded RNA as the genetic material. Studies of the infection cycle of this virus revealed potential host targets important for the virus replication cycle. Here in this review article, we will be discussing different stages of the Dengue virus infection cycle inside mammalian host cells and how host proteins are exploited by the virus in the course of infection as well as how the host counteracts the virus by eliciting different antiviral responses.

Human plasmacytoid dendritic cells at the crossroad of type I interferon-regulated B cell differentiation and antiviral response to tick-borne encephalitis virus

The Tick-borne encephalitis virus (TBEV) causes different disease symptoms varying from asymptomatic infection to severe encephalitis and meningitis suggesting a crucial role of the human host immune system in determining the fate of the infection. There is a need to understand the mechanisms underpinning TBEV-host interactions leading to protective immunity. To this aim, we studied the response of human peripheral blood mononuclear cells (PBMC) to the whole formaldehyde inactivated TBEV (I-TBEV), the drug substance of Encepur, one of the five commercially available vaccine. Immunophenotyping, transcriptome and cytokine profiling of PBMC revealed that I-TBEV generates differentiation of a sub-population of plasmacytoid dendritic cells (pDC) that is specialized in type I interferon (IFN) production. In contrast, likely due to the presence of aluminum hydroxide, Encepur vaccine was a poor pDC stimulus. We demonstrated I-TBEV-induced type I IFN together with Interleukin 6 and BAFF to be critical for B cell differentiation to plasmablasts as measured by immunophenotyping and immunoglobulin production. Robust type I IFN secretion was induced by pDC with the concerted action of both viral E glycoprotein and RNA mirroring previous data on dual stimulation of pDC by both S. aureus and influenza virus protein and nucleic acid that leads to a type I IFN-mediated sustained immune response. E glycoprotein neutralization or high temperature denaturation and inhibition of Toll-like receptor 7 signalling confirmed the importance of preserving the functional integrity of these key viral molecules during the inactivation procedure and manufacturing process to produce a vaccine able to stimulate strong immune responses.

Though vaccination is generally considered effective in reducing tick-borne encephalitis (TBE) incidence, several studies have shown that the antibody response to TBEV vaccination declines with age resulting in more frequent TBE cases among 50+ year-old vaccinees. These observations together with the lack of a specific antiviral drug impose to pinpoint novel host- and pathogen-directed therapies and to improve the control of vaccine efficacy. Thus, we interrogated in vitro human PBMC, whose response to TBEV may provide a picture closer to what occurs in vivo in humans after vaccination or natural infection compared to animal models. The role of E glycoprotein and viral RNA in promoting antiviral and B cell-mediated responses was investigated. Thus, these key viral molecules should be considered, in future, for novel subunit vaccine formulations than the current whole inactivated TBEV-based vaccines, which require laborious manipulation in biosafety level-3 laboratory and animal testing for manufacturing and batch release.

Dissecting strategies to tune the therapeutic potential of SARS-CoV-2-specific monoclonal antibody CR3022

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), coupled with a lack of therapeutics, has paralyzed the globe. Although significant effort has been invested in identifying antibodies that block infection, the ability of antibodies to target infected cells through Fc interactions may be vital to eliminate the virus. To explore the role of Fc activity in SARS-CoV-2 immunity, the functional potential of a cross–SARS-reactive antibody, CR3022, was assessed. CR3022 was able to broadly drive antibody effector functions, providing critical immune clearance at entry and upon egress. Using selectively engineered Fc variants, no protection was observed after administration of WT IgG1 in mice or hamsters. Conversely, the functionally enhanced Fc variant resulted in increased pathology in both the mouse and hamster models, causing weight loss in mice and enhanced viral replication and weight loss in the more susceptible hamster model, highlighting the pathological functions of Fc-enhancing mutations. These data point to the critical need for strategic Fc engineering for the treatment of SARS-CoV-2 infection.

Intrinsic ADE: The Dark Side of Antibody Dependent Enhancement During Dengue Infection

Dengue fever is an Aedes mosquito-borne illness caused by any one of the four different dengue virus (DENV) serotypes (1–4) and manifests in the form of symptoms ranging from mild or asymptomatic to severe disease with vascular leakage, leading to shock, and viral hemorrhagic syndrome. Increased risk of severe disease occurs during secondary infection with a virus serotype distinct from that of prior dengue infection. This occurs by antibody dependent enhancement (ADE) of infection, wherein sub-neutralizing antibodies against the virus particles opsonize dengue virus entry via formation of immune complexes that interact with fragment crystallizable gamma receptors (FcγR) on monocytes, dendritic cells, and macrophages. The ADE phenomenon has two components: Extrinsic and Intrinsic ADE. While extrinsic ADE contributes to enhanced virus entry, intrinsic ADE results in heightened virus production by inhibition of type1 interferon and activation of interleukin-10 biosynthesis, thereby favoring a Th2 type immune response. Intrinsic ADE has greater contribution in enhancing Dengue replication as compared to extrinsic ADE. Detailed elucidation of intrinsic ADE during secondary dengue infection can increase our understanding of DENV-pathogenesis and aid in the development of host-targeting antivirals. Here we review literature focusing on intrinsic factors contributing to severe dengue pathology and suggest possible avenues for further research.

Oxygen: viral friend or foe?

The oxygen levels organ and tissue microenvironments vary depending on the distance of their vasculature from the left ventricle of the heart. For instance, the oxygen levels of lymph nodes and the spleen are significantly lower than that in atmospheric air. Cellular detection of oxygen and their response to low oxygen levels can exert a significant impact on virus infection. Generally, viruses that naturally infect well-oxygenated organs are less able to infect cells under hypoxic conditions. Conversely, viruses that infect organs under lower oxygen tensions thrive under hypoxic conditions. This suggests that in vitro experiments performed exclusively under atmospheric conditions ignores oxygen-induced modifications in both host and viral responses. Here, we review the mechanisms of how cells adapt to low oxygen tensions and its impact on viral infections. With growing evidence supporting the role of oxygen microenvironments in viral infections, this review highlights the importance of factoring oxygen concentrations into in vitro assay conditions. Bridging the gap between in vitro and in vivo oxygen tensions would allow for more physiologically representative insights into viral pathogenesis.

Serotonergic Drugs Inhibit Chikungunya Virus Infection at Different Stages of the Cell Entry Pathway

Chikungunya virus (CHIKV) is an important reemerging human pathogen transmitted by mosquitoes. The virus causes an acute febrile illness, chikungunya fever, which is characterized by headache, rash, and debilitating (poly)arthralgia that can reside for months to years after infection. Currently, effective antiviral therapies and vaccines are lacking. Due to the high morbidity and economic burden in the countries affected by CHIKV, there is a strong need for new strategies to inhibit CHIKV replication. The serotonergic drug 5-nonyloxytryptamine (5-NT) was previously identified as a potential host-directed inhibitor for CHIKV infection. In this study, we determined the mechanism of action by which the serotonin receptor agonist 5-NT controls CHIKV infection. Using time-of-addition and entry bypass assays, we found that 5-NT predominantly inhibits CHIKV in the early phases of the replication cycle, at a step prior to RNA translation and genome replication. Intriguingly, however, no effect was seen during virus-cell binding, internalization, membrane fusion and genomic RNA (gRNA) release into the cell cytosol. In addition, we show that the serotonin receptor antagonist methiothepin mesylate (MM) also has antiviral properties toward CHIKV and specifically interferes with the cell entry process and/or membrane fusion. Taken together, pharmacological targeting of 5-HT receptors may represent a potent way to limit viral spread and disease severity.IMPORTANCE The rapid spread of mosquito-borne viral diseases in humans puts a huge economic burden on developing countries. For many of these infections, including those caused by chikungunya virus (CHIKV), there are no specific treatment possibilities to alleviate disease symptoms. Understanding the virus-host interactions that are involved in the viral replication cycle is imperative for the rational design of therapeutic strategies. In this study, we discovered an antiviral compound, elucidated its mechanism of action, and propose serotonergic drugs as potential host-directed antivirals for CHIKV.

Characterization of neutralizing monoclonal antibody against tick-borne encephalitis virus in vivo

Tick-borne encephalitis virus (TBEV) is the most important tick-transmitted pathogen in the family Flaviviridae and causes one of the most severe human neuroinfections. In this study, a neutralizing mouse mAb 14D5, which was previously shown to have cross-reactive binding to several flaviviruses belonging to the TBEV group, was examined for its prophylactic and therapeutic effects in BALB/c mice infected with TBEV. Before and after infection, mice were administrated mAb 14D5 at doses 100 μg and 10 μg per mouse. mAb 14D5 showed clear protective efficacy when injected at the high dose one day after infection, with survival rates that were TBEV dose-dependent. Prophylactic administration of mAb 14D5 was more effective than post-exposure administration and complete protection was documented when the mAb was administered one day before infection. The protective efficacy of mAb 14D5 was significantly higher than that of the anti-TBE serum immunoglobulin. However, no protection was observed in mice received the low dose of mAb 14D5 independent of the timing of mAb injection and TBEV dose. The ability of species-matched mAb 14D5 to mediate TBEV infection in mice was also investigated, and the results indicated that mAb 14D5 did not augment TBEV infection independent of the time of mAb administration. The neutralizing epitope for mAb 14D5 was localized in domain III of glycoprotein E of TBEV in a region between residues 301-339, which is conserved among flaviviruses from the TBEV group.

Antibody-Dependent Dengue Virus Entry Modulates Cell Intrinsic Responses for Enhanced Infection

Dengue is caused by infection with any one of four dengue viruses (DENV); the risk of severe disease appears to be enhanced by the cross-reactive or subneutralizing levels of antibody from a prior DENV infection. These antibodies opsonize DENV entry through the activating Fc gamma receptors (FcγR), instead of infection through canonical receptor-mediated endocytosis, to result in higher levels of DENV replication. However, whether the enhanced replication is solely due to more efficient FcγR-mediated DENV entry or is also through FcγR-mediated alteration of the host transcriptome response to favor DENV infection remains unclear. Indeed, more efficient viral entry through activation of the FcγR can result in an increased viral antigenic load within target cells and confound direct comparisons of the host transcriptome response under antibody-dependent and antibody-independent conditions. Herein, we show that, despite controlling for the viral antigenic load in primary monocytes, the antibody-dependent and non-antibody-dependent routes of DENV entry induce transcriptome responses that are remarkably different. Notably, antibody-dependent DENV entry upregulated DENV host dependency factors associated with RNA splicing, mitochondrial respiratory chain complexes, and vesicle trafficking. Additionally, supporting findings from other studies, antibody-dependent DENV entry impeded the downregulation of ribosomal genes caused by canonical receptor-mediated endocytosis to increase viral translation. Collectively, our findings support the notion that antibody-dependent DENV entry alters host responses that support the viral life cycle and that host responses to DENV need to be defined in the context of its entry pathway.IMPORTANCE Dengue virus is the most prevalent mosquito-borne viral infection globally, resulting in variable manifestations ranging from asymptomatic viremia to life-threatening shock and multiorgan failure. Previous studies have indicated that the risk of severe dengue in humans can be increased by a specific range of preexisting anti-dengue virus antibody titers, a phenomenon termed antibody-dependent enhancement. There is hence a need to understand how antibodies augment dengue virus infection compared to the alternative canonical receptor-mediated viral entry route. Herein, we show that, besides facilitating viral uptake, antibody-mediated entry increases the expression of early host dependency factors to promote viral infection; these factors include RNA splicing, mitochondrial respiratory chain complexes, vesicle trafficking, and ribosomal genes. These findings will enhance our understanding of how differences in entry pathways can affect host responses and offer opportunities to design therapeutics that can specifically inhibit antibody-dependent enhancement of dengue virus infection.

Amplificación de la infección dependiente de anticuerpos en la inmunopatogénesis del dengue grave, implicaciones para el desarrollo y uso de las vacunas

Actualmente, la infección por el virus de dengue (DENV) es uno de los problemas más importantes de salud pública en países tropicales y endémicos como Colombia, pues en tanto puede ser producida por cuatro diferentes serotipos virales, durante las infecciones secundarias se presentan frecuentemente cuadros más severos que incluso pueden llevar a desenlaces fatales. El centro de la fisiopatología del dengue grave es el daño producido al endotelio, que se traduce en un aumento en la permeabilidad vascular que se evidencia como fuga plasmática, descontrol en la coagulación y daño de órganos. Aunque hay varias teorías que explican la enfermedad severa, el fenómeno denominado amplificación de la infección dependiente de anticuerpos (antibody dependent enhancement, ADE) es el más conocido. En este, se postula que el virus causante de una infección secundaria es reconocido, pero no neutralizado, por anticuerpos generados en la infección previa e internalizado en las células susceptibles usando receptores Fc-gamma, lo cual aumenta la replicación viral e induce modificaciones en la respuesta inmune celular que contribuyen al desarrollo de dengue grave. En este escrito, se realiza una revisión de los hallazgos sobre los mecanismos involucrados en el fenómeno de ADE y cómo pueden contribuir a la progresión hacia dengue grave, describiendo los conceptos de ADE extrínseco e intrínseco, además de como este fenómeno debe ser tenido en cuenta para el diseño, desarrollo e implementación de una vacuna para dengue, en tanto es capaz de afectar su eficacia y seguridad.

Human Schwann cells are susceptible to infection with Zika and yellow fever viruses, but not dengue virus

Zika virus (ZIKV) is a re-emerged flavivirus transmitted by Aedes spp mosquitoes that has caused outbreaks of fever and rash on islands in the Pacific and in the Americas. These outbreaks have been associated with neurologic complications that include congenital abnormalities and Guillain-Barré syndrome (GBS). The pathogenesis of ZIKV-associated GBS, a potentially life-threatening peripheral nerve disease, remains unclear. Because Schwann cells (SCs) play a central role in peripheral nerve function and can be the target for damage in GBS, we characterized the interactions of ZIKV isolates from Africa, Asia and Brazil with human SCs in comparison with the related mosquito-transmitted flaviviruses yellow fever virus 17D (YFV) and dengue virus type 2 (DENV2). SCs supported sustained replication of ZIKV and YFV, but not DENV. ZIKV infection induced increased SC expression of IL-6, interferon (IFN)β1, IFN-λ, IFIT-1, TNFα and IL-23A mRNAs as well as IFN-λ receptors and negative regulators of IFN signaling. SCs expressed baseline mRNAs for multiple potential flavivirus receptors and levels did not change after ZIKV infection. SCs did not express detectable levels of cell surface Fcγ receptors. This study demonstrates the susceptibility and biological responses of SCs to ZIKV infection of potential importance for the pathogenesis of ZIKV-associated GBS.

The possible role of cross-reactive dengue virus antibodies in Zika virus pathogenesis

Zika virus (ZIKV) has been known for decades to circulate in Africa and Asia. However, major complications of a ZIKV infection have recently become apparent for reasons that are still not fully elucidated. One of the hypotheses for the seemingly increased pathogenicity of ZIKV is that cross-reactive dengue antibodies can enhance a ZIKV infection through the principle of antibody-dependent enhancement (ADE). Recently, ADE in ZIKV infection has been studied, but conclusive evidence for the clinical importance of this principle in a ZIKV infection is lacking. Conversely, the widespread circulation of ZIKV in dengue virus (DENV)-endemic regions raises new questions about the potential contribution of ZIKV antibodies to DENV ADE. In this review, we summarize the results of the evidence to date and elaborate on other possible detrimental effects of cross-reactive flavivirus antibodies, both for ZIKV infection and the risk of ZIKV-related congenital anomalies, DENV infection, and dengue hemorrhagic fever.

Antibody-Dependent Cellular Phagocytosis in Antiviral Immune Responses

Antiviral activities of antibodies may either be dependent only on interactions between the antibody and cognate antigen, as in binding and neutralization of an infectious virion, or instead may require interactions between antibody-antigen immune complexes and immunoproteins or Fc receptor expressing immune effector cells. These Fc receptor-dependent antibody functions provide a direct link between the innate and adaptive immune systems by combining the potent antiviral activity of innate effector cells with the diversity and specificity of the adaptive humoral response. The Fc receptor-dependent function of antibody-dependent cellular phagocytosis (ADCP) provides mechanisms for clearance of virus and virus-infected cells, as well as for stimulation of downstream adaptive immune responses by facilitating antigen presentation, or by stimulating the secretion of inflammatory mediators. In this review, we discuss the properties of Fc receptors, antibodies, and effector cells that influence ADCP. We also provide and interpret evidence from studies that support a potential role for ADCP in either inhibiting or enhancing viral infection. Finally, we describe current approaches used to measure antiviral ADCP and discuss considerations for the translation of studies performed in animal models. We propose that additional investigation into the role of ADCP in protective viral responses, the specific virus epitopes targeted by ADCP antibodies, and the types of phagocytes and Fc receptors involved in ADCP at sites of virus infection will provide insight into strategies to successfully leverage this important immune response for improved antiviral immunity through rational vaccine design.

An "on-matrix" digestion procedure for AP-MS experiments dissects the interplay between complex-conserved and serotype-specific reactivities in Dengue virus-human plasma interactome

The interactions between the four Dengue virus (DENV) serotypes and plasma proteins are crucial in the initial steps of viral infection to humans. Affinity purification combined with quantitative mass spectrometry analysis, has become one of the most powerful tools for the investigation on novel protein-protein interactions. Using this approach, we report here that a significant number of bait-interacting proteins do not dissociate under standard elution conditions, i.e. acid pH and chaotropic agents, and that this problem can be circumvented by using the "on-matrix" digestion procedure described here. This procedure enabled the identification of 16 human plasma proteins interacting with domain III from the envelope protein of DENV serotypes 1, 3 and 4 that would have not been detected otherwise and increased the known DIIIE interactors in human plasma to 59 proteins. Selected Reaction Monitoring analysis evidenced DENV interactome in human plasma is rather conserved although significant differences on the reactivity of viral serotypes with specific proteins do exist. A comparison between the serotype-dependent profile of reactivity and the conservation pattern of amino acid residues suggests an evolutionary selection of highly conserved interactions with the host and other interactions mediated for surface regions of higher variability. SIGNIFICANCE: False negative results on the identification of interacting proteins in pull-down experiments compromise the subsequent interpretation of results and the formulation of a working hypothesis for the derived future work. In this study we demonstrate the presence of bait-interacting proteins reluctant to dissociate under elution conditions of acid pH and presence of chaotropics. We propose the direct proteolytic digestion of proteins while still bound to the affinity matrix ("on-matrix" digestion) and evaluate the impact of this methodology in the comparative study of the interactome of the four serotypes of Dengue virus mediated by the domain III of the viral envelope glycoprotein. Fifty nine proteins were identified as putative interaction partners of Dengue virus (IPs) either due to direct binding or by co-isolation with interacting proteins. Collectively the IPs identified from the pull-down with the recombinant domain III proteins representing the four viral serotypes, 29% were identified only after "on-matrix" digestion which demonstrate the usefulness of this method of recovering bait-bound proteins. Results highlight a particular importance of "on-matrix" digestion procedure for comparative studies where a stronger interaction with one of the interest baits could prevent a bound protein to elute under standard conditions thus leading to misinterpretation as absent in the interactome of this particular bait. The analysis of the Interaction Network indicates that Dengue virus interactome mediated by the domain III of the envelope protein is rather conserved in the viral complex suggesting a key role of these interactions for viral infection thus making candidates to explore for potential biomarkers of clinical outcome in DENV-caused disease. Interestingly, some particular IPs exhibit significant differences in the strength of the interaction with the viral serotypes representing interactions that involve more variable regions in the surface of the domain III. Since such variable regions are the consequence of the interaction with antibodies generated by human immune response; this result relates the interaction with proteins from human plasma with the interplay of the virus and the human immune system.

Role of IgG3 in Infectious Diseases

IgG3 comprises only a minor fraction of IgG and has remained relatively understudied until recent years. Key physiochemical characteristics of IgG3 include an elongated hinge region, greater molecular flexibility, extensive polymorphisms, and additional glycosylation sites not present on other IgG subclasses. These characteristics make IgG3 a uniquely potent immunoglobulin, with the potential for triggering effector functions including complement activation, antibody (Ab)-mediated phagocytosis, or Ab-mediated cellular cytotoxicity (ADCC). Recent studies underscore the importance of IgG3 effector functions against a range of pathogens and have provided approaches to overcome IgG3-associated limitations, such as allotype-dependent short Ab half-life, and excessive proinflammatory activation. Understanding the molecular and functional properties of IgG3 may facilitate the development of improved Ab-based immunotherapies and vaccines against infectious diseases.

The Role of Host Cytoskeleton in Flavivirus Infection

The family of flaviviruses is one of the most medically important groups of emerging arthropod-borne viruses. Host cell cytoskeletons have been reported to have close contact with flaviviruses during virus entry, intracellular transport, replication, and egress process, although many detailed mechanisms are still unclear. This article provides a brief overview of the function of the most prominent flaviviruses-induced or -hijacked cytoskeletal structures including actin, microtubules and intermediate filaments, mainly focus on infection by dengue virus, Zika virus and West Nile virus. We suggest that virus interaction with host cytoskeleton to be an interesting area of future research.

Modulation of dynamin function by small molecules

Dynamins are essential as membrane remodelers in various cellular processes, like receptor-mediated endocytosis, synaptic vesicle recycling and spermatogenesis. Moreover, dynamin is involved in the internalization of numerous viruses and in the motility of several cancer cell lines. As tools for dissecting the underlying mechanisms of these important biological processes and as potential future therapeutics, small molecules have been developed in the last two decades that modulate the functions of dynamin. In this review we give an overview of the compound classes that are currently in use and describe how they affect dynamin function.

Blockade of dengue virus entry into myeloid cells by endocytic inhibitors in the presence or absence of antibodies

Background

Dengue is the most prevalent arthropod-borne viral human disease in tropical and subtropical regions, caused by four dengue virus (DENV) serotypes. In spite of the increasing global incidence, no specific antiviral therapy is available. Cells of the mononuclear phagocyte lineage are the main targets either for direct antibody (Ab)-independent or Ab-mediated human DENV infection, usually associated to the severe forms of disease. Since the virus entry may be a convenient therapeutic alternative, this study aimed to investigate the mode of DENV internalization into myeloid cells in the absence and presence of DENV Ab and evaluate the inhibitory activity of diverse biochemical inhibitors of endocytosis.

Methodology/principal findings

By infectivity assays and quantitative RT-PCR determinations, it was demonstrated that DENV-2 entry into U937 and K562 cells in the absence of Ab was highly inhibited by the early treatment with ammonium chloride, chlorpromazine and dynasore, but it was not affected by methyl-β-cyclodextrin, indicating that DENV-2 utilizes a low pH-dependent, clathrin- and dynamin-mediated endocytic infectious pathway for the direct entry into both human myeloid cells. To study the Ab-mediated entry of DENV, the experimental conditions for enhancement of infection were established by inoculating immune complexes formed with DENV-2 and the Ab 2H2 or 3H5. The internalization of DENV-2-2H2 or DENV-2-3H5 complexes in both myeloid cells was also dependent on acid pH and dynamin but a differential requirement of the clathrin-mediated endocytic route was observed depending on the FcγR involved in the complex uptake: the infection through FcγRII was dependent on clathrin-coated vesicles whereas the internalization pathway mediated by FcγRI was independent of clathrin. This property was not serotype-specific.

Conclusions/significance

DENV entry into myeloid cells in the absence or presence of Ab can be blocked by diverse biochemical inhibitors affecting the cellular factors involved in endocytosis. The identification of the virus-host interactions involved in virus penetration may allow the finding of host-targeted antivirals widely active against diverse pathogenic flaviviruses with similar requirements for virus entry.

Dengue is currently a widespread viral disease transmitted to human by mosquitoes, with very high prevalence in tropical and subtropical regions of América and Asia. Approximately 2.5 billion people are living in endemic areas and it is estimated that 350 million apparent and inapparent infections occur each year. There is no specific antiviral for treatment of dengue patients. On this basis, the search of antiviral agents is an urgent need. Dengue virus (DENV) entry is an attractive alternative for chemotherapeutic intervention since it represents a barrier to block the beginning of infection. We intended to evaluate the antiviral activity of diverse biochemical inhibitors of endocytosis against DENV in human myeloid cells. Results showed that DENV entry into these cells can be blocked by diverse biochemical inhibitors affecting the cellular factors involved in endocytosis such as intravesicular pH, clathrin-coated vesicles and dynamin, although the presence of non neutralizing antibodies, as can occur in secondary human infections, may alter the entry pathway under certain conditions. Then, the blockade of virus entry with host-targeted inhibitors may be a promising strategy for the development of safe antiviral agents with wide spectrum of activity against DENV and other related pathogenic flaviviruses.

Modulation of Dengue/Zika Virus Pathogenicity by Antibody-Dependent Enhancement and Strategies to Protect Against Enhancement in Zika Virus Infection

Antibody-dependent enhancement (ADE) is a phenomenon in which preexisting poorly neutralizing antibodies leads to enhanced infection. It is a serious concern with mosquito-borne flaviviruses such as Dengue virus (DENV) and Zika virus (ZIKV). In vitro experimental evidences have indicated the preventive, as well as a pathogenicity-enhancing role, of preexisting DENV antibodies in ZIKV infections. ADE has been confirmed in DENV but not ZIKV infections. Principally, the Fc region of the anti-DENV antibody binds with the fragment crystallizable gamma receptor (FcγR), and subsequent C1q interactions and immune effector functions are responsible for the ADE. In contrast to normal DENV infections, with ADE in DENV infections, inhibition of STAT1 phosphorylation and a reduction in IRF-1 gene expression, NOS2 levels, and RIG-1 and MDA-5 expression levels occurs. FcγRIIA is the most permissive FcγR for DENV-ADE, and under hypoxic conditions, hypoxia-inducible factor-1 alpha transcriptionally enhances expression levels of FcγRIIA, which further enhances ADE. To produce therapeutic antibodies with broad reactivity to different DENV serotypes, as well as to ZIKV, bispecific antibodies, Fc region mutants, modified Fc regions, and anti-idiotypic antibodies may be engineered. An in-depth understanding of the immunological and molecular mechanisms of DENV-ADE of ZIKV pathogenicity will be useful for the design of common and safe therapeutics and prophylactics against both viral pathogens. The present review discusses the role of DENV antibodies in modulating DENV/ZIKV pathogenicity/infection and strategies to counter ADE to protect against Zika infection.

Beyond binding: antibody effector functions in infectious diseases

Antibodies play an essential role in host defence against pathogens by recognizing microorganisms or infected cells. Although preventing pathogen entry is one potential mechanism of protection, antibodies can control and eradicate infections through a variety of other mechanisms. In addition to binding and directly neutralizing pathogens, antibodies drive the clearance of bacteria, viruses, fungi and parasites via their interaction with the innate and adaptive immune systems, leveraging a remarkable diversity of antimicrobial processes locked within our immune system. Specifically, antibodies collaboratively form immune complexes that drive sequestration and uptake of pathogens, clear toxins, eliminate infected cells, increase antigen presentation and regulate inflammation. The diverse effector functions that are deployed by antibodies are dynamically regulated via differential modification of the antibody constant domain, which provides specific instructions to the immune system. Here, we review mechanisms by which antibody effector functions contribute to the balance between microbial clearance and pathology and discuss tractable lessons that may guide rational vaccine and therapeutic design to target gaps in our infectious disease armamentarium.

A novel mechanism of antibody-mediated enhancement of flavivirus infection

Antibody-dependent enhancement of viral infection is a well-described phenomenon that is based on the cellular uptake of infectious virus-antibody complexes following their interaction with Fcγ receptors expressed on myeloid cells. Here we describe a novel mechanism of antibody-mediated enhancement of infection by a flavivirus (tick-borne encephalitis virus) in transformed and primary human cells, which is independent of the presence of Fcγ receptors. Using chemical cross-linking and immunoassays, we demonstrate that the monoclonal antibody (mab) A5, recognizing an epitope at the interface of the dimeric envelope protein E, causes dimer dissociation and leads to the exposure of the fusion loop (FL). Under normal conditions of infection, this process is triggered only after virus uptake by the acidic pH in endosomes, resulting in the initiation of membrane fusion through the interaction of the FL with the endosomal membrane. Analysis of virus binding and cellular infection, together with inhibition by the FL-specific mab 4G2, indicated that the FL, exposed after mab A5- induced dimer-dissociation, mediated attachment of the virus to the plasma membrane also at neutral pH, thereby increasing viral infectivity. Since antibody-induced enhancement of binding was not only observed with cells but also with liposomes, it is likely that increased infection was due to FL-lipid interactions and not to interactions with cellular plasma membrane proteins. The novel mechanism of antibody-induced infection enhancement adds a new facet to the complexity of antibody interactions with flaviviruses and may have implications for yet unresolved effects of polyclonal antibody responses on biological properties of these viruses.

Rab5 Enhances Classical Swine Fever Virus Proliferation and Interacts with Viral NS4B Protein to Facilitate Formation of NS4B Related Complex

Classical swine fever virus (CSFV) is a fatal pig pestivirus and causes serious financial losses to the pig industry. CSFV NS4B protein is one of the most important viral replicase proteins. Rab5, a member of the small Rab GTPase family, is involved in infection and replication of numerous viruses including hepatitis C virus and dengue virus. Until now, the effects of Rab5 on the proliferation of CSFV are poorly defined. In the present study, we showed that Rab5 could enhance CSFV proliferation by utilizing lentivirus-mediated constitutive overexpression and eukaryotic plasmid transient overexpression approaches. On the other hand, lentivirus-mediated short hairpin RNA knockdown of Rab5 dramatically inhibited virus production. Co-immunoprecipitation, glutathione S-transferase pulldown and laser confocal microscopy assays further confirmed the interaction between Rab5 and CSFV NS4B protein. In addition, intracellular distribution of NS4B-Red presented many granular fluorescent signals (GFS) in CSFV infected PK-15 cells. Inhibition of basal Rab5 function with Rab5 dominant negative mutant Rab5S34N resulted in disruption of the GFS. These results indicate that Rab5 plays a critical role in facilitating the formation of the NS4B related complexes. Furthermore, it was observed that NS4B co-localized with viral NS3 and NS5A proteins in the cytoplasm, suggesting that NS3 and NS5A might be components of the NS4B related complex. Taken together, these results demonstrate that Rab5 positively modulates CSFV propagation and interacts with NS4B protein to facilitate the NS4B related complexes formation.

The role of autophagy in asparaginase-induced immune suppression of macrophages

Erwinia asparaginase, a bacteria-derived enzyme drug, has been used in the treatment of various cancers, especially acute lymphoblastic leukemia (ALL). One of the most significant side effects associated with asparaginase administration is immune suppression, which limits its application in clinic. Macrophages are phagocytic immune cells and have a central role in inflammation and host defense. We reported here that asparaginase disturbed the function of macrophages including phagocytosis, proliferation, ROS and nitric oxide secretion, interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) secretion, and major histocompatibility complex II (MHC-II) molecule expression, thus induced immune suppression in interferon-γ and lipopolysaccharide-stimulated macrophages. We also observed that asparaginase inhibited autophagy in macrophages via activating Akt/mTOR and suppressing Erk1/2 signaling pathway as evidenced by less formation of autophagosomes, downregulation of autophagy-related protein LC3-II, and decreased number of autophagy-like vacuoles. Further study discovered that treatment with autophagy inhibitor 3-MA in place of asparaginase on activated macrophages could also downregulate phagocytosis, cytokine secretion, and MHC-II expression. Moreover, incubation with autophagy inducer trehalose restored the capacity of phagocytosis, IL-6 and TNF-α secretion, and MHC-II expression in macrophages. These results prove the important role of autophagy in the function of macrophages, and activation of autophagy can overcome asparaginase-induced immune suppression in macrophages.

Hypoxia enhances antibody-dependent dengue virus infection

Dengue virus (DENV) has been found to replicate in lymphoid organs such as the lymph nodes, spleen, and liver in post‐mortem analysis. These organs are known to have low oxygen levels (~0.5–4.5% O₂) due to the vascular anatomy. However, how physiologically low levels of oxygen affect DENV infection via hypoxia‐induced changes in the immune response remains unknown. Here, we show that monocytes adapted to 3% O₂ show greater susceptibility to antibody‐dependent enhancement of DENV infection. Low oxygen level induces HIF1α‐dependent upregulation of fragment crystallizable gamma receptor IIA (FcγRIIA) as well as HIF1α‐independent alterations in membrane ether lipid concentrations. The increased FcγRIIA expression operates synergistically with altered membrane composition, possibly through increase membrane fluidity, to increase uptake of DENV immune complexes for enhanced infection. Our findings thus indicate that the increased viral burden associated with secondary DENV infection is antibody‐dependent but hypoxia‐induced and suggest a role for targeting hypoxia‐induced factors for anti‐dengue therapy.

The mechanistic role of antibodies to dengue virus in protection and disease pathogenesis

INTRODUCTION

Dengue is a prevalent disease in tropical and subtropical countries with an estimated 400 million people infected annually. While significant advancement has been made in the chase for an effective dengue vaccine, the recently licensed Sanofi vaccine was, in contrast to in vitro data, only partially protective. Areas covered: This suggests that our understanding of the serological correlates for dengue is currently inadequate. With growing evidence supporting the role of fragment crystalizable gamma receptors (FcγRs) in antibody-mediated neutralization or antibody-dependent enhancement (ADE) of dengue virus (DENV) infection, FcγR-expressing cells have been increasingly used for measuring neutralizing antibody responses elicited by dengue vaccines. Here, we review the mechanisms of how FcγRs modulates both DENV neutralization and enhanced infections via its interactions with antibodies. Expert commentary: This review provides insights on the importance of factoring FcγRs for in vitro neutralization assays. Bridging the gap between in vitro and clinical observations would allow researchers to more accurately predict in vivo vaccine efficacy.