Immunopathology of Chikungunya Virus Infection: Lessons Learned from Patients and Animal Models

A novel interaction between the 5' untranslated region of the Chikungunya virus genome and Musashi RNA binding protein is essential for efficient virus genome replication

Chikungunya virus (CHIKV) is a re-emerging, pathogenic alphavirus that is transmitted to humans by Aedesspp. mosquitoes-causing fever and debilitating joint pain, with frequent long-term health implications and high morbidity. The CHIKV replication cycle is poorly understood and specific antiviral therapeutics are lacking. In the current study, we identify host cell Musashi RNA binding protein-2 (MSI-2) as a proviral factor. MSI-2 depletion and small molecule inhibition assays demonstrated that MSI-2 is required for efficient CHIKV genome replication. Depletion of both MSI-2 and MSI-1 homologues was found to synergistically inhibit CHIKV replication, suggesting redundancy in their proviral function. Electromobility shift assay (EMSA) competition studies demonstrated that MSI-2 interacts specifically with an RNA binding motif within the 5' untranslated region (5'UTR) of CHIKV and reverse genetic analysis showed that mutation of the binding motif inhibited genome replication and blocked rescue of mutant virus. For the first time, this study identifies the proviral role of MSI RNA binding proteins in the replication of the CHIKV genome, providing important new insight into mechanisms controlling replication of this significant human pathogen and the potential of a novel therapeutic target.

Essential role of the CCL2-CCR2 axis in Mayaro virus-induced disease

Mayaro virus (MAYV) is an emerging arbovirus member of the Togaviridae family and Alphavirus genus. MAYV infection causes an acute febrile illness accompanied by persistent polyarthralgia and myalgia. Understanding the mechanisms involved in arthritis caused by alphaviruses is necessary to develop specific therapies. In this work, we investigated the role of the CCL2/CCR2 axis in the pathogenesis of MAYV-induced disease. For this, wild-type (WT) C57BL/6J and CCR2-/- mice were infected with MAYV subcutaneously and evaluated for disease development. MAYV infection induced an acute inflammatory disease in WT mice. The immune response profile was characterized by an increase in the production of inflammatory mediators, such as IL-6, TNF, and CCL2. Higher levels of CCL2 at the local and systemic levels were followed by the significant recruitment of CCR2+ macrophages and a cellular response orchestrated by these cells. CCR2-/- mice showed an increase in CXCL-1 levels, followed by a replacement of the macrophage inflammatory infiltrate by neutrophils. Additionally, the absence of the CCR2 receptor protected mice from bone loss induced by MAYV. Accordingly, the silencing of CCL2 chemokine expression in vivo and the pharmacological blockade of CCR2 promoted a partial improvement in disease. Cell culture data support the mechanism underlying the bone pathology of MAYV, in which MAYV infection promotes a pro-osteoclastogenic microenvironment mediated by CCL2, IL-6, and TNF, which induces the migration and differentiation of osteoclast precursor cells. Overall, these data contribute to the understanding of the pathophysiology of MAYV infection and the identification future of specific therapeutic targets in MAYV-induced disease.IMPORTANCEThis work demonstrates the role of the CCL2/CCR2 axis in MAYV-induced disease. The infection of wild-type (WT) C57BL/6J and CCR2-/- mice was associated with high levels of CCL2, an important chemoattractant involved in the recruitment of macrophages, the main precursor of osteoclasts. In the absence of the CCR2 receptor, there is a mitigation of macrophage migration to the target organs of infection and protection of these mice against bone loss induced by MAYV infection. Much evidence has shown that host immune response factors contribute significantly to the tissue damage associated with alphavirus infections. Thus, this work highlights molecular and cellular targets involved in the pathogenesis of arthritis triggered by MAYV and identifies novel therapeutic possibilities directed to the host inflammatory response unleashed by MAYV.

Chikungunya fever

Chikungunya virus is widespread throughout the tropics, where it causes recurrent outbreaks of chikungunya fever. In recent years, outbreaks have afflicted populations in East and Central Africa, South America and Southeast Asia. The virus is transmitted by Aedes aegypti and Aedes albopictus mosquitoes. Chikungunya fever is characterized by severe arthralgia and myalgia that can persist for years and have considerable detrimental effects on health, quality of life and economic productivity. The effects of climate change as well as increased globalization of commerce and travel have led to growth of the habitat of Aedes mosquitoes. As a result, increasing numbers of people will be at risk of chikungunya fever in the coming years. In the absence of specific antiviral treatments and with vaccines still in development, surveillance and vector control are essential to suppress re-emergence and epidemics.

Development and validation of a clinical rule for the diagnosis of chikungunya fever in a dengue-endemic area

Rio de Janeiro is a dengue-endemic city that experienced Zika and chikungunya epidemics between 2015 and 2019. Differential diagnosis is crucial for indicating adequate treatment and assessing prognosis and risk of death. This study aims to derive and validate a clinical rule for diagnosing chikungunya based on 3,214 suspected cases consecutively treated at primary and secondary health units of the sentinel surveillance system (up to 7 days from onset of symptoms) in Rio de Janeiro, Brazil. Of the total sample, 624 were chikungunya, 88 Zika, 51 dengue, and 2,451 were negative for all these arboviruses according to real-time polymerase chain reaction (RT-qPCR). The derived rule included fever (1 point), exanthema (1 point), myalgia (2 points), arthralgia or arthritis (2 points), and joint edema (2 points), providing an AUC (area under the receiver operator curve) = 0.695 (95% CI: 0.662-0.725). Scores of 4 points or more (validation sample) showed 74.3% sensitivity (69.0% - 79.2%) and 51.5% specificity (48.8% - 54.3%). Adding more symptoms improved the specificity at the expense of a lower sensitivity compared to definitions proposed by government agencies based on fever alone (European Center for Disease Control) or in combination with arthralgia (World Health Organization) or arthritis (Pan American Health Organization, Brazilian Ministry of Health). The proposed clinical rule offers a rapid, low-cost, easy-to-apply strategy to differentiate chikungunya fever from other arbovirus infections during epidemics.

UBXN3B Controls Immunopathogenesis of Arthritogenic Alphaviruses by Maintaining Hematopoietic Homeostasis

Ubiquitin regulatory X domain-containing proteins (UBXN) might be involved in diverse cellular processes. However, their in vivo physiological functions remain largely elusive. We recently showed that UBXN3B positively regulated stimulator-of-interferon-genes (STING)-mediated innate immune responses to DNA viruses. Herein, we reported the essential role of UBXN3B in the control of infection and immunopathogenesis of two arthritogenic RNA viruses, Chikungunya (CHIKV) and O'nyong'nyong (ONNV) viruses. Ubxn3b deficient (Ubxn3b-/-) mice presented higher viral loads, more severe foot swelling and immune infiltrates, and slower clearance of viruses and resolution of inflammation than the Ubxn3b+/+ littermates. While the serum cytokine levels were intact, the virus-specific immunoglobulin G and neutralizing antibody levels were lower in the Ubxn3b-/- mice. The Ubxn3b-/- mice had more neutrophils and macrophages, but much fewer B cells in the ipsilateral feet. Of note, this immune dysregulation was also observed in the spleens and blood of uninfected Ubxn3b-/- mice. UBXN3B restricted CHIKV replication in a cell-intrinsic manner but independent of type I IFN signaling. These results demonstrated a dual role of UBXN3B in the maintenance of immune homeostasis and control of RNA virus replication. IMPORTANCE The human genome encodes 13 ubiquitin regulatory X (UBX) domain-containing proteins (UBXN) that might participate in diverse cellular processes. However, their in vivo physiological functions remain largely elusive. Herein, we reported an essential role of UBXN3B in the control of infection and immunopathogenesis of arthritogenic alphaviruses, including Chikungunya virus (CHIKV), which causes acute and chronic crippling arthralgia, long-term neurological disorders, and poses a significant public health problem in the tropical and subtropical regions worldwide. However, there are no approved vaccines or specific antiviral drugs. This was partly due to a poor understanding of the protective and detrimental immune responses elicited by CHIKV. We showed that UBXN3B was critical for the control of CHIKV replication in a cell-intrinsic manner in the acute phase and persistent immunopathogenesis in the post-viremic stage. Mechanistically, UBXN3B was essential for the maintenance of hematopoietic homeostasis during viral infection and in steady-state.

Chikungunya patient transcriptional signatures faithfully recapitulated in a C57BL/6J mouse model

Introduction

An adult wild-type C57BL/6J mouse model of chikungunya virus (CHIKV) infection and disease has been extensively used to study the alphaviral arthritic immunopathology and to evaluate new interventions. How well mouse models recapitulate the gene expression profiles seen in humans remains controversial.

Methods

Herein we perform a comparative transcriptomics analysis using RNA-Seq datasets from the C57BL/6J CHIKV mouse model with datasets obtained from adults and children acutely infected with CHIKV.

Results

Despite sampling quite different tissues, peripheral blood from humans and feet from mice, gene expression profiles were quite similar, with an overlap of up to ≈50% for up-regulated single copy orthologue differentially expressed genes. Furthermore, high levels of significant concordance between mouse and human were seen for immune pathways and signatures, which were dominated by interferons, T cells and monocyte/macrophages. Importantly, predicted responses to a series of anti-inflammatory drug and biologic treatments also showed cogent similarities between species.

Discussion

Comparative transcriptomics and subsequent pathway analysis provides a detailed picture of how a given model recapitulates human gene expression. Using this method, we show that the C57BL/6J CHIKV mouse model provides a reliable and representative system in which to study CHIKV immunopathology and evaluate new treatments.

Parálisis facial aislada posterior a infección por virus de chikunguña: un nuevo diagnóstico diferencial

En las últimas décadas, se ha incrementado el reporte de manifestaciones neurológicas asociadas con la infección por el virus de chikunguña. Se informa el caso de un adulto joven previamente sano que presentó parálisis facial izquierda aislada después de una infección reciente por el virus de chikunguña en el trópico colombiano. Se describen aspectos importantes de la fisiopatología del virus y su tropismo por el sistema nervioso central y periférico, y se sugiere considerar este virus en el diagnóstico diferencial de la parálisis facial en pacientes con infección confirmada por el virus de chikunguña en regiones tropicales endémicas o en aquellos con antecedente de viajes recientes a dichas regiones.

Regulatory T Cells in acute and chronic human Chikungunya infection

Chikungunya virus (CHIKV) infection generates strong immune responses that are associated with the disease pathophysiology. Regulatory T cells (Treg-cluster of differentiation (CD)-4⁺CD25^highforkhead box P3 (FOXP3⁺)) are essential for the induction and maintenance of peripheral tolerance. Thus, they play key roles in determining the patient prognosis by preventing excessive immune responses via different suppression immune mechanisms. However, the regulatory mechanisms involved in human CHIKV infection are still poorly understood. Here, we characterize for the first time the Treg cell molecule-associated-mechanism during acute and chronic human Chikungunya disease. Here, we assessed the Treg cell population and molecule-associated mechanism in the peripheral blood samples of acute and chronic patients with Chikungunya. Our results indicate that CHIKV infection is associated with reduced frequency of Tregs, along with the impaired expression and production of Treg functional markers, including CD39, CD73, perforin, granzyme, programmed death 1 (PD-1), cytotoxic T lymphocyte antigen (CTLA)-4, and transforming growth factor (TGF)-β. This observation suggests that Treg cells possess poor regulatory capacity in both acute and chronic phases of the disease. Taken together, these data provide significant evidence that the imbalanced response of Treg cells plays an essential role in establishing the pathogenesis of Chikungunya.

Macrodomain Binding Compound MRS 2578 Inhibits Alphavirus Replication

Alphaviruses are positive-strand RNA viruses causing febrile disease. Macrodomain-containing proteins, involved in ADP-ribose-mediated signaling, are encoded by both host cells and several virus groups, including alphaviruses. In this study, compound MRS 2578 that targets the human ADP-ribose glycohydrolase MacroD1 inhibited Semliki Forest virus production as well as viral RNA replication and replicase protein expression. The inhibitor was similarly active in alphavirus trans-replication systems, indicating that it targets the viral RNA replication stage.

The Putative Roles and Functions of Indel, Repetition and Duplication Events in Alphavirus Non-Structural Protein 3 Hypervariable Domain (nsP3 HVD) in Evolution, Viability and Re-Emergence

Alphavirus non-structural proteins 1–4 (nsP1, nsP2, nsP3, and nsP4) are known to be crucial for alphavirus RNA replication and translation. To date, nsP3 has been demonstrated to mediate many virus–host protein–protein interactions in several fundamental alphavirus mechanisms, particularly during the early stages of replication. However, the molecular pathways and proteins networks underlying these mechanisms remain poorly described. This is due to the low genetic sequence homology of the nsP3 protein among the alphavirus species, especially at its 3′ C-terminal domain, the hypervariable domain (HVD). Moreover, the nsP3 HVD is almost or completely intrinsically disordered and has a poor ability to form secondary structures. Evolution in the nsP3 HVD region allows the alphavirus to adapt to vertebrate and insect hosts. This review focuses on the putative roles and functions of indel, repetition, and duplication events that have occurred in the alphavirus nsP3 HVD, including characterization of the differences and their implications for specificity in the context of virus–host interactions in fundamental alphavirus mechanisms, which have thus directly facilitated the evolution, adaptation, viability, and re-emergence of these viruses.

Construction and Immunogenicity of Recombinant Vaccinia Virus Vaccine Against Japanese Encephalitis and Chikungunya Viruses Infection in Mice

Japanese encephalitis virus (JEV) is recognized as a public health risk by the World Health Organization. In Asia, each year, ∼70,000 people become infected with JEV, which results in ∼10,000 deaths. Chikungunya virus (CHIKV) is an RNA virus, whose infection mainly causes fever, myalgia, and skin rash. Although the mortality rate is low, it seriously affects daily life. JEV and CHIKV infect humans through mosquitoes; therefore, a recombinant vaccinia virus coexpressing JEV E and CHIKV E1 proteins was constructed to prevent their concurrent infection. In this study, after mice first immunization, booster immunization was performed at 21 days postimmunization (dpi). At 35 dpi, mice were challenged with JEV and CHIKV. Specific antibodies significantly increased in the rVTT-CE1-JE-EGFP group, which were significantly (p < 0.01) higher than those of the control groups at 35 dpi. The plaque reduction neutralization tests (JEV) of rVTT-CE1-JE-EGFP group was 1:320 at 35 dpi. Furthermore, cytokine levels and the percentage of CD3⁺CD4⁺ and CD3⁺CD8⁺ T-lymphocytes in the rVTT-CE1-JE-EGFP group were significantly (p < 0.01) higher than those in the control groups at 35 dpi. After challenge, mice body weights in rVTT-CE1-JE-EGFP group were not significantly altered, and the survival rate was 100%. These results showed the rVTT-CE1-JE-EGFP group elicited significant humoral and cellular immune responses, thus indicating that the recombinant vaccine may serve as a candidate for effective prevention of CHIKV and JEV infection.

In-depth characterization of a novel live-attenuated Mayaro virus vaccine candidate using an immunocompetent mouse model of Mayaro disease

Mayaro virus (MAYV) is endemic in South American countries where it is responsible for sporadic outbreaks of acute febrile illness. The hallmark of MAYV infection is a highly debilitating and chronic arthralgia. Although MAYV emergence is a potential threat, there are no specific therapies or licensed vaccine. In this study, we developed a murine model of MAYV infection that emulates many of the most relevant clinical features of the infection in humans and tested a live-attenuated MAYV vaccine candidate (MAYV/IRES). Intraplantar inoculation of a WT strain of MAYV into immunocompetent mice induced persistent hypernociception, transient viral replication in target organs, systemic production of inflammatory cytokines, chemokines and specific humoral IgM and IgG responses. Inoculation of MAYV/IRES in BALB/c mice induced strong specific cellular and humoral responses. Moreover, MAYV/IRES vaccination of immunocompetent and interferon receptor-defective mice resulted in protection from disease induced by the virulent wt MAYV strain. Thus, this study describes a novel model of MAYV infection in immunocompetent mice and highlights the potential role of a live-attenuated MAYV vaccine candidate in host's protection from disease induced by a virulent MAYV strain.

Viral Innate Immune Evasion and the Pathogenesis of Emerging RNA Virus Infections

Positive-sense single-stranded RNA (+ssRNA) viruses comprise many (re-)emerging human pathogens that pose a public health problem. Our innate immune system and, in particular, the interferon response form the important first line of defence against these viruses. Given their genetic flexibility, these viruses have therefore developed multiple strategies to evade the innate immune response in order to optimize their replication capacity. Already many molecular mechanisms of innate immune evasion by +ssRNA viruses have been identified. However, research addressing the effect of host innate immune evasion on the pathology caused by viral infections is less prevalent in the literature, though very relevant and interesting. Since interferons have been implicated in inflammatory diseases and immunopathology in addition to their protective role in infection, antagonizing the immune response may have an ambiguous effect on the clinical outcome of the viral disease. Therefore, this review discusses what is currently known about the role of interferons and host immune evasion in the pathogenesis of emerging coronaviruses, alphaviruses and flaviviruses.

Mayaro Virus Replication Restriction and Induction of Muscular Inflammation in Mice Are Dependent on Age, Type-I Interferon Response, and Adaptive Immunity

Mayaro virus (MAYV) is an emergent arbovirus first described in forest regions of the American continent, with recent and increasing notification of urban area circulation. Similar to Chikungunya (CHIKV) and other arthritogenic Alphavirus, MAYV-induced disease shows a high prevalence of persistent arthralgia, and myalgia. Despite this, knowledge regarding pathogenesis and characteristics of host immune response of MAYV infections are still limited. Here, using different ages of wild-type (WT), adult Type I Interferon receptor deficient (IFNAR^-/-), and adult recombination activation gene-1 deficient (RAG^-/-) mice, we have investigated the dependence of age, innate and adaptive immunity for the control of MAYV replication, tissue damage, and inflammation in mice. We have found that MAYV induces clinical signal and replicates in young WT mice, which gain the ability to restrict MAYV replication with aging. In addition, we observed that mice age and type I interferon response are related to restriction of MAYV infection and muscular inflammation in mice. Moreover, MAYV continues to replicate persistently in RAG^-/- mice, being detected at blood and tissues 40 days post infection, indicating that adaptive immunity is essential to MAYV clearance. Despite chronic replication, infected adult RAG^-/- mice did not develop an apparent signal of muscle damage in early and late infection. On the other hand, MAYV infection in young WT and adult IFNAR-/- mice triggers an increase in the expression of pro-inflammatory mediators, such as TNF, IL-6, KC, IL-1β, MCP-1, and RANTES, in muscle tissue, and decreases TGF-β expression, that were not significantly modulated in adult WT and RAG^-/- mice. Taken together, our data demonstrated that age, innate and adaptive immunity are important to restrict MAYV replication and that adaptive immunity is also involved in MAYV-induced tissue damage. These results contribute to the comprehension of MAYV pathogenesis, and describe translational mice models for further studies of MAYV infection, vaccine tests, and therapeutic strategies against this virus.

Chikungunya virus modulates the miRNA expression patterns in human synovial fibroblasts

Chikungunya virus (CHIKV) is an alphavirus transmitted by mosquitoes. CHIKV infection leads to polyarthritis and polyarthralgia among patients. The synovial fibroblasts are the primary target for CHIKV. The microRNAs (miRNAs) are the small endogenous noncoding RNAs which posttranscriptionally regulate the expression of genes by binding to their target messenger RNAs (mRNAs) through their 3'-untranslated regions. The miRNAs are the key regulators for various pathological processes including viral infection, cancer, cardiovascular disease, and neurodegeneration. This study was designed to dissect out the roles of miRNAs during CHIKV (Ross Strain E1: A226V) infection in primary human synovial fibroblasts. The miRNA microarray profiling was performed on the primary human synovial fibroblasts infected by CHIKV. The gene target prediction analysis, enrichment, and network analysis were performed by various bioinformatics analyses. The subset of 26 differentially expressed microRNAs (DEMs) were identified through microarray profiling and were further screened for gene predictions, Gene Ontology, pathway enrichment, and miRNA-mRNA network using various bioinformatics tools. The bioinformatics analysis indicates the role of DEMs by suppressing the immune response which may contribute to CHIKV persistence in human primary synovial fibroblasts. Our study provides the plausible roles of DEMs, miRNAs, and mRNA interactions and pathways involved in the molecular pathogenesis of CHIKV.

Immunoglobulin Therapy in a Patient With Severe Chikungunya Fever and Vesiculobullous Lesions

Chikungunya virus (CHIKV) is an emerging arbovirus whose transmission has already been reported in several countries. Although the majority of individuals acutely infected with CHIKV appear to become asymptomatic, reports showing the occurrence of atypical and severe forms of the disease are increasing. Among them, the neurological and skin manifestations require medical attention. Treatment of CHIKV infection is almost symptomatic. In this sense, we report the case of a 56-years-old man who presented fever, headaches, paresthesia and pain in the right arm with visible red spots on the skin starting 30 days before Hospital admission. Tests determined Chikungunya infection and excluded other co-morbidities. Disease evolved with edema in hands and feet and extensive hemorrhagic bullous lesions on the skin of upper and lower limbs. Variations in hematological counts associated with liver dysfunction determined this patient's admission to the Intensive Care Unit. Then, he received intravenous antibiotic and immunoglobulin therapy (400 mg/Kg/day for the period of 5 days) with total recovery from the lesions after 10 days of follow-up. A general improvement in blood cell count and successful wound healing was observed. After discharge, no other clinical sign of the disease was reported until nowadays. This case reports for the first time the successful administration of intravenous immunoglobulin therapy to a patient with severe atypical dermatological form of Chikungunya Fever without any associated comorbidity.

Design, Synthesis, and Anti-RNA Virus Activity of 6'-Fluorinated-Aristeromycin Analogues

The 6'-fluorinated aristeromycins were designed as dual-target antiviral compounds aimed at inhibiting both the viral RNA-dependent RNA polymerase (RdRp) and the host cell S-adenosyl-l-homocysteine (SAH) hydrolase, which would indirectly target capping of viral RNA. The introduction of a fluorine at the 6'-position enhanced the inhibition of SAH hydrolase and the activity against RNA viruses. The adenosine and N⁶-methyladenosine analogues 2a-e showed potent inhibition against SAH hydrolase, while only the adenosine derivatives 2a-c exhibited potent antiviral activity against all tested RNA viruses such as Middle East respiratory syndrome-coronavirus (MERS-CoV), severe acute respiratory syndrome-coronavirus, chikungunya virus, and/or Zika virus. 6',6'-Difluoroaristeromycin (2c) showed the strongest antiviral effect for MERS-CoV, with a ∼2.5 log reduction in infectious progeny titer in viral load reduction assay. The phosphoramidate prodrug 3a also demonstrated potent broad-spectrum antiviral activity, possibly by inhibiting the viral RdRp. This study shows that 6'-fluorinated aristeromycins can serve as starting points for the development of broad-spectrum antiviral agents that target RNA viruses.

Characterization of antibody response in patients with acute and chronic chikungunya virus disease

BACKGROUND

Chikungunya virus (CHIKV) is a re-emerging arbovirus capable of causing chronic arthralgia, which can last for months to years. Although neutralizing antibodies have been shown to be important for viral clearance, is it not clear whether the quantitative and qualitative nature of antibodies play a role in progression to chronic disease.

OBJECTIVES

To characterize and compare the antibody responses in acute and chronic patients in a prospective observational CHIKV study in Curaçao during the 2014-2015 outbreak.

STUDY DESIGN

We performed virus neutralization tests and ELISA on plasma samples collected from a prospective observational chikungunya study in Curaçao to compare the complement-dependent and -independent neutralization capacity, as well as the antibody avidity index of acute and chronic patients.

RESULTS

We found that there was no significant difference in the virus neutralization titers between patients with acute and chronic chikungunya infection. Furthermore, we found that complement increased the neutralization capacity when large amounts of virus was used. Moreover, we found that patients with acute chikungunya disease had a significantly higher antibody avidity index compared to those with chronic disease.

CONCLUSIONS

This study suggests that virus neutralization titers in late convalescent sera do not play a role in chronic chikungunya. However, the median antibody avidity was lower in these patients and may therefore suggest a role for antibody avidity in the development of chronic disease.

An overview of the immune response and Arginase I on CHIKV immunopathogenesis

Chikungunya virus (CHIKV) is mosquito-borne alphavirus that has caused epidemics around the world. Many individuals affected by the disease may experience joint pain that persists for months after the acute phase. The pathophysiology of viral arthritis is not completely elucidated. And it is important to emphasize that the effects of the viral infection in each host may depend on host factors that include immune response, as well as factors specific to the virus as tissue tropism. The main pathway for the response against viral infection is through induction of type I interferon (IFN-I), whose function is important to control viral replication. Beside this, T cell and macrophage mediated immunopathology in CHIKV infections has been reported. It has been demonstrated that some association with the Arginase I and macrophages type II are involved in the infection profile along with myeloid-derived suppressor cells (MDSC) that are responsible for T cell suppression. Therefore, in this review, will be discuss an overview on CHIKV immunopathogenesis and the importance of Arginase I.

Animal model of arthritis and myositis induced by the Mayaro virus

BACKGROUND

The Mayaro virus (MAYV) is an endemic arbovirus in South American countries, where it is responsible for sporadic outbreaks of Mayaro fever. Clinical manifestations include fever, headache, ocular pain, rash, myalgia, and debilitating and persistent polyarthralgia. Understanding the mechanisms associated with MAYV-induced arthritis is of great importance due to the potential for its emergence, urbanization and dispersion to other regions.

METHODS

15-day old Balb/c mice were infected by two distinct pathways, below the forelimb and in the rear footpad. Animals were observed for a period of 21 days. During this time, they were monitored every 24 hours for disease signs, such as weight loss and muscle weakness. Histological damage in the muscles and joints was evaluated 3, 7, 10, 15 and 20 days post-infection. The cytokine profile in serum and muscles during MAYV infection was evaluated by flow cytometry at different post-infection times. For pain analysis, the animals were submitted to the von Frey test and titre in different organs was evaluated throughout the study to obtain viral kinetics.

FINDINGS

Infection by two distinct pathways, below the forelimb and in the rear footpad, resulted in a homogeneous viral spread and the development of acute disease in animals. Clinical signs were observed such as ruffled fur, hunched posture, eye irritation and slight gait alteration. In the physical test, both groups presented loss of resistance, which was associated with histopathological damage, including myositis, arthritis, tenosynovitis and periostitis. The immune response was characterized by a strong inflammatory response mediated by the cytokines TNF-α, IL-6 and INF-γ and chemokine MCP-1, followed by the action of IL-10 and IL-4 cytokines.

INTERPRETATION

The results showed that Balb/c mice represent a promising model to study mechanisms involved in MAYV pathogenesis and for future antiviral testing.

ZIKV Demonstrates Minimal Pathologic Effects and Mosquito Infectivity in Viremic Cynomolgus Macaques

To evaluate the effects of ZIKV infection on non-human primates (NHPs), as well as to investigate whether these NHPs develop sufficient viremia to infect the major urban vector mosquito, Aedes aegypti, four cynomolgus macaques (Macaca fascicularis) were subcutaneously infected with 5.0 log₁₀ focus-forming units (FFU) of DNA clone-derived ZIKV strain FSS13025 (Asian lineage, Cambodia, 2010). Following infection, the animals were sampled (blood, urine, tears, and saliva), underwent daily health monitoring, and were exposed to Ae. aegypti at specified time points. All four animals developed viremia, which peaked 3⁻4 days post-infection at a maximum value of 6.9 log₁₀ genome copies/mL. No virus was detected in urine, tears, or saliva. Infection by ZIKV caused minimal overt disease: serum biochemistry and CBC values largely fell within the normal ranges, and cytokine elevations were minimal. Strikingly, the minimally colonized population of Ae. aegypti exposed to viremic animals demonstrated a maximum infection rate of 26% during peak viremia, with two of the four macaques failing to infect a single mosquito at any time point. These data indicate that cynomolgus macaques may be an effective model for ZIKV infection of humans and highlights the relative refractoriness of Ae. aegypti for ZIKV infection at the levels of viremia observed.

Immunomodulatory drug methotrexate used to treat patients with chronic inflammatory rheumatisms post-chikungunya does not impair the synovial antiviral and bone repair responses

Chikungunya virus (CHIKV) is a mosquito-transmitted RNA alphavirus causing major outbreaks of infectious chronic inflammatory rheumatisms (CIR). Recently, methotrexate (MTX), a disease modifying anti-rheumatic drug has been used successfully to treat patients suffering from rheumatoid-like arthritis post-CHIK but its immunomodulatory activity in the context of viral persistence has been a matter of concerns. We herein used a model of primary human synovial fibroblasts (HSF) and the synthetic molecule polyriboinosinic:polyribocytidylic acid (PIC) to mimic chronic infectious settings in the joints of CHIKV infected patients. The innate antiviral immune and inflammatory responses were investigated in response to MTX used at the therapeutic concentration of 1 μM. We found that MTX did not affect cellular viability as indicated by the LDH release assay. By quantitative RT-PCR, we observed that HSF responded robustly to PIC by increasing ISG15 and IFNβ mRNA levels. Furthermore, PIC upregulated the mRNA expression of two of the major pattern recognition receptors, RIG-I and MDA5 involved in the innate immune detection of viral RNA. MTX did not impact the antiviral response of PIC on ISG15, IFNβ, RIG-I and MDA5 mRNA expressions. MTX alone or combined with PIC did not affect the expression of proinflammatory CCL2 and CXCL8 chemokines. PIC strongly upregulated the mRNA and protein expression of osteoclastogenic factors (IL-6, GM-CSF but not RANKL). Critically, MTX treatment alone or combined with PIC did not affect the expression of all three tested osteoclastogenic cytokines. We found that MTX alone did not increase the capacity of CHIKV to infect and replicate in HSF. In conclusion, our study argues for a beneficial effect of MTX to treat CIR post-CHIKV given that it does not critically impact the antiviral, the proinflammatory and the bone tissue remodeling responses of synovial cells.

Chikungunya is a mosquito-borne virus (CHIKV) and has been incriminated in the development of arthralgia (pain of the joint) and arthritis particularly in elderly patients. Methotrexate (MTX) has been used widely to effectively treat these chronic rheumatic symptoms. Using a model of primary human joint fibroblasts (HSF), we investigated the capacity of the MTX immunosuppressive drug to affect the immune antiviral and inflammatory responses essential to clear the virus while allowing bone tissue repair. This study is important given that CHIKV and its RNA were shown to persist in the joint for months to years post infection and leading to injuries through ill-characterized mechanisms. The molecule PIC was used to mimic the effect of viral RNA. Interestingly, we found that MTX did not affect the expression of several proinflammatory and bone repair factors by HSF. Remarkably, MTX did not also impair the antiviral response of synovial fibroblasts. Our study revealed for the first time that MTX treatment should be considered as safe even in the context of viral persistence associated with chronic inflammation. MTX will not affect the capacity of the synovial tissue to maintain antiviral mechanism, to control inflammation and to promote bone tissue repair.

The Enigmatic Alphavirus Non-Structural Protein 3 (nsP3) Revealing Its Secrets at Last

Alphaviruses encode 4 non-structural proteins (nsPs), most of which have well-understood functions in capping and membrane association (nsP1), polyprotein processing and RNA helicase activity (nsP2) and as RNA-dependent RNA polymerase (nsP4). The function of nsP3 has been more difficult to pin down and it has long been referred to as the more enigmatic of the nsPs. The protein comprises three domains, an N-terminal macro domain, a central zinc-binding domain and a C-terminal hypervariable domain (HVD). In this article, we review old and new literature about the functions of the three domains. Much progress in recent years has contributed to a picture of nsP3, particularly through its HVD as a hub for interactions with host cell molecules, with multiple effects on the biology of the host cell at early points in infection. These and many future discoveries will provide targets for anti-viral therapies as well as strategies for modification of vectors for vaccine and oncolytic interventions.