Hide and Seek: The Interplay Between Zika Virus and the Host Immune Response

Cross Talk between MicroRNAs and Dengue Virus

Dengue fever (DF) is an endemic infectious tropical disease and is rapidly becoming a global problem. Dengue fever is caused by one of the four dengue virus (DENV) serotypes and is spread by the female Aedes mosquito. Clinical manifestations of DF may range from asymptomatic to life-threatening severe illness with conditions of hemorrhagic fever and shock. Early and precise diagnosis is vital to avoid mortality from DF. A different approach is required to combat DF because of the challenges with the vaccines currently available, which are nonspecific; each is capable of causing cross-reaction and disease-enhancing antibody responses against the residual serotypes. MicroRNAs (miRNAs) are known to be implicated in DENV infection and are postulated to be involved in most of the host responses. Thus, they might be a suitable target for new strategies against the disease. The involvement of miRNAs in cellular activities and pathways during viral infections has been explored under numerous conditions. Interestingly, miRNAs have also been shown to be involved in viral replication. In this review, we summarize the role of known miRNAs, specifically the role of miRNA Let-7c (miR-Let-7c), miR-133a, miR-30e, and miR-146a, in the regulation of DENV replication and their possible effects on the initial immune reaction.

siRNA lipid nanoparticles for CXCL12 silencing modulate brain immune response during Zika infection

CXCL12 is a key chemokine implicated in neuroinflammation, particularly during Zika virus (ZIKV) infection. Specifically, CXCL12 is upregulated in circulating cells of ZIKV infected patients. Here, we developed a lipid nanoparticle (LNP) to deliver siRNA in vivo to assess the impact of CXCL12 silencing in the context of ZIKV infection. The biodistribution of the LNP was assessed in vivo after intravenous injection using fluorescently tagged siRNA. Next, we investigated the ability of the developed LNP to silence CXCL12 in vivo and assessed the resulting effects in a murine model of ZIKV infection. The LNP encapsulating siRNA significantly inhibited CXCL12 levels in the spleen and induced microglial activation in the brain during ZIKV infection. This activation was evidenced by the enhanced expression of iNOS, TNF-α, and CD206 within microglial cells. Moreover, T cell subsets exhibited reduced secretion of IFN-ɣ and IL-17 following LNP treatment. Despite no observable alteration in viral load, CXCL12 silencing led to a significant reduction in type-I interferon production compared to both ZIKV-infected and uninfected groups. Furthermore, we found grip strength deficits in the group treated with siRNA-LNP compared to the other groups. Our data suggest a correlation between the upregulated pro-inflammatory cytokines and the observed decrease in strength. Collectively, our results provide evidence that CXCL12 silencing exerts a regulatory influence on the immune response in the brain during ZIKV infection. In addition, the modulation of T-cell activation following CXCL12 silencing provides valuable insights into potential protective mechanisms against ZIKV, offering novel perspectives for combating this infection.

ZIKV induction of tristetraprolin in endothelial and Sertoli cells post-transcriptionally inhibits IFNβ/λ expression and promotes ZIKV persistence

IMPORTANCE

Our findings define a novel role for ZIKV-induced TTP expression in regulating IFNβ/IFNλ production in primary hBMECs and Sertoli cells. These cells comprise key physiological barriers subverted by ZIKV to access brain and testicular compartments and serve as reservoirs for persistent replication and dissemination. We demonstrate for the first time that the ARE-binding protein TTP is virally induced and post-transcriptionally regulates IFNβ/IFNλ secretion. In ZIKV-infected hBMEC and Sertoli cells, TTP knockout increased IFNβ/IFNλ secretion, while TTP expression blocked IFNβ/IFNλ secretion. The TTP-directed blockade of IFN secretion permits ZIKV spread and persistence in hBMECs and Sertoli cells and may similarly augment ZIKV spread across IFNλ-protected placental barriers. Our work highlights the importance of post-transcriptional ZIKV regulation of IFN expression and secretion in cells that regulate viral access to protected compartments and defines a novel mechanism of ZIKV-regulated IFN responses which may facilitate neurovirulence and sexual transmission.

Identification of alpha-linolenic acid as a broad-spectrum antiviral against zika, dengue, herpes simplex, influenza virus and SARS-CoV-2 infection

Zika virus (ZIKV) has garnered global attention due to its association with severe congenital defects including microcephaly. However, there are no licensed vaccines or drugs against ZIKV infection. Pregnant women have the greatest need for treatment, making drug safety crucial. Alpha-linolenic acid (ALA), a polyunsaturated ω-3 fatty acid, has been used as a health-care product and dietary supplement due to its potential medicinal properties. Here, we demonstrated that ALA inhibits ZIKV infection in cells without loss of cell viability. Time-of-addition assay revealed that ALA interrupts the binding, adsorption, and entry stages of ZIKV replication cycle. The mechanism is probably that ALA disrupts the membrane integrity of the virions to release ZIKV RNA, inhibiting viral infectivity. Further examination revealed that ALA inhibits DENV-2, HSV-1, influenza virus and SARS-CoV-2 infection dose-dependently. ALA is a promising broad-spectrum antiviral agent.

Comparative Infections of Zika, Dengue, and Yellow Fever Viruses in Human Cytotrophoblast-Derived Cells Suggest a Gating Role for the Cytotrophoblast in Zika Virus Placental Invasion

The Zika virus (ZIKV) is teratogenic and considered a TORCH pathogen (toxoplasmosis [Toxoplasma gondii], rubella, cytomegalovirus, herpes simplex virus [HSV], and other microorganisms capable of crossing the blood-placenta barrier). In contrast, the related flavivirus dengue virus (DENV) and the attenuated yellow fever virus vaccine strain (YFV-17D) are not. Understanding the mechanisms used by ZIKV to cross the placenta is necessary. In this work, parallel infections with ZIKV of African and Asian lineages, DENV, and YFV-17D were compared for kinetics and growth efficiency, activation of mTOR pathways, and cytokine secretion profile using cytotrophoblast-derived HTR8 cells and monocytic U937 cells differentiated to M2 macrophages. In HTR8 cells, ZIKV replication, especially the African strain, was significantly more efficient and faster than DENV or YFV-17D. In macrophages, ZIKV replication was also more efficient, although differences between strains were reduced. Greater activation of the mTORC1 and mTORC2 pathways in HTR8 cells infected with ZIKV than with DENV or YFV-17D was observed. HTR8 cells treated with mTOR inhibitors showed a 20-fold reduction in ZIKV yield, versus 5- and 3.5-fold reductions for DENV and YFV-17D, respectively. Finally, infection with ZIKV, but not DENV or YFV-17D, efficiently inhibited the interferon (IFN) and chemoattractant responses in both cell lines. These results suggest a gating role for the cytotrophoblast cells in favoring entry of ZIKV, but not DENV and YFV-17D, into the placental stroma. IMPORTANCE Zika virus acquisition during pregnancy is associated with severe fetal damage. The Zika virus is related to dengue virus and yellow fever virus, yet fetal damage has not been related to dengue or inadvertent vaccination for yellow fever during pregnancy. Mechanisms used by the Zika virus to cross the placenta need to be deciphered. By comparing parallel infections of Zika virus strains belonging to the African and Asian lineages, dengue virus, and the yellow fever vaccine virus strain YFV-17D in placenta-derived cytotrophoblast cells and differentiated macrophages, evidence was found that Zika virus infections, especially by the African strains, were more efficient in cytotrophoblast cells than dengue virus or yellow fever vaccine virus strain infections. Meanwhile, no significant differences were observed in macrophages. Robust activation of the mTOR signaling pathways and inhibition of the IFN and chemoattractant response appear to be related to the better growth capacity of the Zika viruses in the cytotrophoblast-derived cells.

A Ferritin Nanoparticle-Based Zika Virus Vaccine Candidate Induces Robust Humoral and Cellular Immune Responses and Protects Mice from Lethal Virus Challenge

The severe consequences of the Zika virus (ZIKV) infections resulting in congenital Zika syndrome in infants and the autoimmune Guillain-Barre syndrome in adults warrant the development of safe and efficacious vaccines and therapeutics. Currently, there are no approved treatment options for ZIKV infection. Herein, we describe the development of a bacterial ferritin-based nanoparticle vaccine candidate for ZIKV. The viral envelope (E) protein domain III (DIII) was fused in-frame at the amino-terminus of ferritin. The resulting nanoparticle displaying the DIII was examined for its ability to induce immune responses and protect vaccinated animals upon lethal virus challenge. Our results show that immunization of mice with a single dose of the nanoparticle vaccine candidate (zDIII-F) resulted in the robust induction of neutralizing antibody responses that protected the animals from the lethal ZIKV challenge. The antibodies neutralized infectivity of other ZIKV lineages indicating that the zDIII-F can confer heterologous protection. The vaccine candidate also induced a significantly higher frequency of interferon (IFN)-γ positive CD4 T cells and CD8 T cells suggesting that both humoral and cell-mediated immune responses were induced by the vaccine candidate. Although our studies showed that a soluble DIII vaccine candidate could also induce humoral and cell-mediated immunity and protect from lethal ZIKV challenge, the immune responses and protection conferred by the nanoparticle vaccine candidate were superior. Further, passive transfer of neutralizing antibodies from the vaccinated animals to naïve animals protected against lethal ZIKV challenge. Since previous studies have shown that antibodies directed at the DIII region of the E protein do not to induce antibody-dependent enhancement (ADE) of ZIKV or other related flavivirus infections, our studies support the use of the zDIII-F nanoparticle vaccine candidate for safe and enhanced immunological responses against ZIKV.

Zika virus non-structural protein 4B interacts with DHCR7 to facilitate viral infection

Zika virus (ZIKV) evolves non-structural proteins to evade immune response and ensure efficient replication in the host cells. Cholesterol metabolic enzyme 7-dehydrocholesterol reductase (DHCR7) was recently reported to impact innate immune responses in ZIKV infection. However, the vital non-structural protein and mechanisms involved in DHCR7-mediated viral evasion are not well elucidated. In this study, we demonstrated that ZIKV infection facilitated DHCR7 expression. Notably, the upregulated DHCR7 in turn facilitated ZIKV infection and blocking DHCR7 suppressed ZIKV infection. Mechanically, ZIKV non-structural protein 4B (NS4B) interacted with DHCR7 to induce DHCR7 expression. Moreover, DHCR7 inhibited TANK-binding kinase 1 (TBK1) and interferon regulatory factor 3 (IRF3) phosphorylation, which resulted in the reduction of interferon-beta (IFN-β) and interferon-stimulated genes (ISGs) productions. Therefore, we propose that ZIKV NS4B binds to DHCR7 to repress TBK1 and IRF3 activation, which in turn inhibits IFN-β and ISGs, and thereby facilitating ZIKV evasion. This study broadens the insights on how viral non-structural proteins antagonize innate immunity to facilitate viral infection via cholesterol metabolic enzymes and intermediates.

A novel IFNbeta-induced long non-coding RNA ZAP-IT1 interrupts Zika virus replication in A549 cells

Zika virus (ZIKV) infection can cause severe neurological diseases including neonatal microcephaly and Guillain-Barre syndrome. Long noncoding RNAs (lncRNAs) are the by-products of the transcription process, which are considered to affect viral infection. However, it remains largely unexplored whether host lncRNAs play a role in ZIKV infection. Here, we identified a group of human lncRNAs that were up-regulated upon ZIKV infection and were dependent on the type I interferon (IFN) signaling. Overexpression of lncRNA ZAP-IT1 leads to an impairment of ZIKV infection. Correspondently, deficiency of ZAP-IT1 led to an enhancement of ZIKV infection. We further confirmed that ZAP-IT1, an intronic lncRNA with total 551 ​nt in length, is mainly located in the nuclear upon ZIKV infection. Knockout of ZAP-IT1 also led to the increase of dengue virus (DENV), Japanese encephalitis virus (JEV), or vesicular stomatitis virus (VSV) infection. Mechanically, we found that the antiviral effect of ZAP-IT1 was independent of the type I IFN signaling pathway. Therefore, our data unveiled that host lncRNA ZAP-IT1 induced by the type I IFN signaling, showed robust restriction on ZIKV infection, and even on DENV, JEV, and VSV infection, which may benefit the development of antiviral therapeutics.

Serum Cytokines Predict Neurological Damage in Genetically Diverse Mouse Models

Viral infections contribute to neurological and immunological dysfunction driven by complex genetic networks. Theiler's murine encephalomyelitis virus (TMEV) causes neurological dysfunction in mice and can model human outcomes to viral infections. Here, we used genetically distinct mice from five Collaborative Cross mouse strains and C57BL/6J to demonstrate how TMEV-induced immune responses in serum may predict neurological outcomes in acute infection. To test the hypothesis that serum cytokine levels can provide biomarkers for phenotypic outcomes of acute disease, we compared cytokine levels at pre-injection, 4 days post-injection (d.p.i.), and 14 d.p.i. Each strain produced unique baseline cytokine levels and had distinct immune responses to the injection procedure itself. Thus, we eliminated the baseline responses to the injection procedure itself and identified cytokines and chemokines induced specifically by TMEV infection. Then, we identified strain-specific longitudinal cytokine profiles in serum during acute disease. Using stepwise regression analysis, we identified serum immune markers predictive for TMEV-induced neurological phenotypes of the acute phase, e.g., IL-9 for limb paralysis; and TNF-α, IL-1β, and MIP-1β for limb weakness. These findings indicate how temporal differences in immune responses are influenced by host genetic background and demonstrate the potential of serum biomarkers to track the neurological effects of viral infection.

γδ T Cells in Emerging Viral Infection: An Overview

New emerging viruses belonging to the Coronaviridae, Flaviviridae, and Filoviridae families are serious threats to public health and represent a global concern. The surveillance to monitor the emergence of new viruses and their transmission is an important target for public health authorities. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is an excellent example of a pathogen able to cause a pandemic. In a few months, SARS-CoV-2 has spread globally from China, and it has become a world health problem. Gammadelta (γδ) T cell are sentinels of innate immunity and are able to protect the host from viral infections. They enrich many tissues, such as the skin, intestines, and lungs where they can sense and fight the microbes, thus contributing to the protective immune response. γδ T cells perform their direct antiviral activity by cytolytic and non-cytolytic mechanisms against a wide range of viruses, and they are able to orchestrate the cellular interplay between innate and acquired immunity. For their pleiotropic features, γδ T cells have been proposed as a target for immunotherapies in both cancer and viral infections. In this review, we analyzed the role of γδ T cells in emerging viral infections to define the profile of the response and to better depict their role in the host protection.

Host Molecules Regulating Neural Invasion of Zika Virus and Drug Repurposing Strategy

Zika virus (ZIKV) is a mosquito-borne, single-stranded RNA virus belonging to the genus Flavivirus. Although ZIKV infection is usually known to exhibit mild clinical symptoms, intrauterine ZIKV infections have been associated with severe neurological manifestations, including microcephaly and Guillain Barre syndrome (GBS). Therefore, it is imperative to understand the mechanisms of ZIKV entry into the central nervous system (CNS) and its effect on brain cells. Several routes of neuro-invasion have been identified, among which blood–brain barrier (BBB) disruption is the commonest mode of access. The molecular receptors involved in viral entry remain unknown; with various proposed molecular ZIKV-host interactions including potential non-receptor mediated cellular entry. As ZIKV invade neuronal cells, they trigger neurotoxic mechanisms via cell-autonomous and non-cell autonomous pathways, resulting in neurogenesis dysfunction, viral replication, and cell death, all of which eventually lead to microcephaly. Together, our understanding of the biological mechanisms of ZIKV exposure would aid in the development of anti-ZIKV therapies targeting host cellular and/or viral components to combat ZIKV infection and its neurological manifestations. In this present work, we review the current understanding of ZIKV entry mechanisms into the CNS and its implications on the brain. We also highlight the status of the drug repurposing approach for the development of potential antiviral drugs against ZIKV.