Viral interference between severe acute respiratory syndrome coronavirus 2 and influenza A viruses.

Some respiratory viruses can cause a viral interference through the activation of the interferon (IFN) pathway that reduces the replication of another virus. Epidemiological studies of coinfections between SARS-CoV-2 and other respiratory viruses have been hampered by non-pharmacological measures applied to mitigate the spread of SARS-CoV-2 during the COVID-19 pandemic. With the ease of these interventions, SARS-CoV-2 and influenza A viruses can now co-circulate. It is thus of prime importance to characterize their interactions. In this work, we investigated viral interference effects between an Omicron variant and a contemporary influenza A/H3N2 strain, in comparison with an ancestral SARS-CoV-2 strain and the 2009 pandemic influenza A/H1N1 virus. We infected nasal human airway epitheliums with SARS-CoV-2 and influenza, either simultaneously or 24 h apart. Viral load was measured by RT-qPCR and IFN-α/ß/λ1/λ2 proteins were quantified by immunoassay. Expression of four interferon-stimulated genes (ISGs; OAS1/IFITM3/ISG15/MxA) was also measured by RT-droplet digital PCR. Additionally, susceptibility of each virus to IFN-α/ß/λ2 recombinant proteins was determined. Our results showed that influenza A, and especially A/H3N2, interfered with both SARS-CoV-2 viruses, but that SARS-CoV-2 did not significantly interfere with A/H3N2 or A/H1N1. Consistently with these results, influenza, and particularly the A/H3N2 strain, caused a higher production of IFN proteins and expression of ISGs than SARS-CoV-2. SARS-CoV-2 induced a marginal IFN production and reduced the IFN response during coinfections with influenza. All viruses were susceptible to exogenous IFNs, with the ancestral SARS-CoV-2 and Omicron being less susceptible to type I and type III IFNs, respectively. Thus, influenza A causes a viral interference towards SARS-CoV-2 most likely through an IFN response. The opposite is not necessarily true, and a concurrent infection with both viruses leads to a lower IFN response. Taken together, these results help us to understand how SARS-CoV-2 interacts with another major respiratory pathogen.

The impact of trained immunity in respiratory viral infections.

Epidemic peaks of respiratory viruses that co-circulate during the winter-spring seasons can be synchronous or asynchronous. The occurrence of temporal patterns in epidemics caused by some respiratory viruses suggests that they could negatively interact with each other. These negative interactions may result from a programme of innate immune memory, known as trained immunity, which may confer broad protective effects against respiratory viruses. It is suggested that stimulation of innate immune cells by a vaccine or a pathogen could induce their long-term functional reprogramming through an interplay between metabolic and epigenetic changes, which influence the transcriptional response to a secondary challenge. During the coronavirus disease 2019 pandemic, the circulation of most respiratory viruses was prevented by non-pharmacological interventions and then resumed at unusual periods once sanitary measures were lifted. With time, respiratory viruses should find again their own ecological niches. This transition period provides an opportunity to study the interactions between respiratory viruses at the population level.

A protectin DX (PDX) analog with in vitro activity against influenza A(H1N1) viruses.

Antiviral therapy based on neuraminidase (oseltamivir) or polymerase (baloxavir marboxil) inhibitors plays an important role in the management of influenza infections. However, the emergence of drug resistance and the uncontrolled inflammatory response are major limitations in the treatment of severe influenza disease. Protectins D1 (PD1) and DX (PDX), part of a family of pro-resolving mediators, have previously demonstrated anti-influenza activity as well as anti-inflammatory properties in various clinical contexts. Herein, we synthetized a series of simplified PDX analogs and assessed their in vitro antiviral activity against influenza A(H1N1) viruses, including oseltamivir- and baloxavir-resistant variants. In ST6GalI-MDCK cells, the PDX analog AN-137B reduced viral replication in a dose-dependent manner with IC50 values of 23.8 for A/Puerto Rico/8/1934 (H1N1) and between 32.6 and 36.7 µM for susceptible and resistant A(H1N1)pdm09 viruses. In MTS-based cell viability experiments, AN-137B showed a 50% cellular cytotoxicity (CC50 ) of 638.7 µM with a resulting selectivity index of 26.8. Of greater importance, the combination of AN-137B with oseltamivir or baloxavir resulted in synergistic and additive in vitro effects, respectively. Treatment of lipopolysaccharide (LPS)-stimulated macrophages with AN-137B resulted in a decrease of iNOS activity as shown by the reduction of nitrite production, suggesting an anti-inflammatory effect. In conclusion, our results indicate that the protectin analog AN-137B constitutes an interesting therapeutic modality against influenza A virus, warranting further evaluation in animal models.

Omicron incidence and seroprevalence among children in Montreal, Canada, in early 2023: final results from the longitudinal EnCORE serology study.

Since early 2022, routine testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) based on symptoms and exposure history has largely ceased in Canada. Consequently, seroprevalence studies, particularly longitudinal studies, have become critical for monitoring the rate of incident SARS-CoV-2 infections and the proportion of the population with evidence of immunity. EnCORE is a longitudinal SARS-CoV-2 seroprevalence study comprising five rounds of serology testing from October 2020 to June 2023, in a sample of 2- to 17-year-olds (at baseline), recruited from daycares and schools in four neighbourhoods of Montreal, Canada. We report on SARS-CoV-2 incidence and seroprevalence among the 509 participants in the fifth and final round of the study. Seroprevalence of antibodies from either infection or vaccination was 98% (95 per cent confidence interval [CI]: 97, 99). The infection-acquired seroprevalence was 78% (95% CI: 73-82), and the incidence rate was 113 per 100 person-years (95% CI: 94-132), compared to the seroprevalence of 58% and the incidence rate of 133 per 100 person-years, respectively, in the fourth round of testing (mid-late 2022). Of the 131 participants newly seropositive for infection in Round 4, only 18 were seronegative for infection in Round 5 (median follow-up: 326 days).

The possibility of spreading herpes simplex virus type 1 via food handling and sharing.

AIMS: Herpes simplex virus type 1 (HSV-1) is an enveloped virus that causes recurrent and incurable diseases in 67% of the world population. Although it is not listed as a foodborne virus, some studies have shown that it can be recovered from surfaces as well as food. METHODS AND RESULTS: We investigated its persistence at -20°C, 4°C, 20°C, or 37°C for up to 7 days on stainless steel, aluminum, glass, polypropylene, cheddar cheese, sliced almond, and apple skin and in cola soft drink, orange juice, coffee, and milk, as well as its transferability from stainless steel to dry or moistened nitrile or latex gloves over time at typical ambient temperatures. Based on the plaque assay on Vero cells, HSV-1 persisted at least 24 h on all surfaces and at least 1 h on food matrices but was inactivated quickly in cola soft drink. Temperature and pH affected HSV-1 infectivity. Transfer of HSV-1 at a contact pressure of 1 kg cm2-1 for 10 s occurred only on latex, especially moistened. CONCLUSIONS: Our data on the persistence of HSV-1 on food-related surfaces suggest that some risk may be associated with sharing foods with infected carriers.

Impact of COVID-19 and Vaccination During Pregnancy on Placenta-Mediated Complications (COVIGRO Study).

OBJECTIVES: COVID-19 has been associated with preterm birth (PTB) and placental-mediated complications, including fetal growth restriction and preeclampsia (PE). This study aimed to estimate the impact of COVID-19 and vaccination on adverse pregnancy outcomes and markers of placental function. METHODS: We performed a study on a prospective cohort of women recruited in the first trimester of pregnancy during the early COVID-19 pandemic period (December 2020 to December 2021). At each trimester of pregnancy, the assessment included a questionnaire on COVID-19 and vaccination status; serological tests for COVID-19 (for asymptomatic infection); measurement of placental growth factor (PlGF) and soluble fms-like tyrosine kinase 1 (sFlt-1) in maternal blood; measurement of mean uterine artery pulsatility index (UtA-PI); and pregnancy outcomes (PTB, PE, birth weight below the fifth and the tenth percentile). RESULTS: Among 788 patients with complete data, we observed 101 (13%) cases of symptomatic infection and 74 (9%) cases of asymptomatic infection with SARS-CoV-2. Most cases (73%) of infection were among women with previous vaccination or COVID-19 infection before pregnancy. COVID-19 infection was not associated with adverse pregnancy outcomes, abnormal fetal growth, sFlt-1/PlGF ratio, or mean UtA-PI. Vaccination during pregnancy did not influence these outcomes either. We observed no case of severe COVID-19 infection requiring respiratory support. CONCLUSION: Mild symptomatic or asymptomatic COVID-19 during pregnancy did not influence the risk of adverse pregnancy outcomes and the markers of placental function in predominantly vaccinated women. Fetal growth monitoring is unlikely to be mandatory in women with mild symptoms of COVID-19.

Impact of temperature on the affinity of SARS-CoV-2 Spike glycoprotein for host ACE2.

The seasonal nature of outbreaks of respiratory viral infections with increased transmission during low temperatures has been well established. Accordingly, temperature has been suggested to play a role on the viability and transmissibility of SARS-CoV-2, the virus responsible for the COVID-19 pandemic. The receptor-binding domain (RBD) of the Spike glycoprotein is known to bind to its host receptor angiotensin-converting enzyme 2 (ACE2) to initiate viral fusion. Using biochemical, biophysical, and functional assays to dissect the effect of temperature on the receptor-Spike interaction, we observed a significant and stepwise increase in RBD-ACE2 affinity at low temperatures, resulting in slower dissociation kinetics. This translated into enhanced interaction of the full Spike glycoprotein with the ACE2 receptor and higher viral attachment at low temperatures. Interestingly, the RBD N501Y mutation, present in emerging variants of concern (VOCs) that are fueling the pandemic worldwide (including the B.1.1.7 (α) lineage), bypassed this requirement. This data suggests that the acquisition of N501Y reflects an adaptation to warmer climates, a hypothesis that remains to be tested.

Viral Interference between Respiratory Viruses.

Multiple respiratory viruses can concurrently or sequentially infect the respiratory tract and lead to virus‒virus interactions. Infection by a first virus could enhance or reduce infection and replication of a second virus, resulting in positive (additive or synergistic) or negative (antagonistic) interaction. The concept of viral interference has been demonstrated at the cellular, host, and population levels. The mechanisms involved in viral interference have been evaluated in differentiated airway epithelial cells and in animal models susceptible to the respiratory viruses of interest. A likely mechanism is the interferon response that could confer a temporary nonspecific immunity to the host. During the coronavirus disease pandemic, nonpharmacologic interventions have prevented the circulation of most respiratory viruses. Once the sanitary restrictions are lifted, circulation of seasonal respiratory viruses is expected to resume and will offer the opportunity to study their interactions, notably with severe acute respiratory syndrome coronavirus 2.

In Vitro Selection of Remdesivir-Resistant SARS-CoV-2 Demonstrates High Barrier to Resistance.

In vitro selection of remdesivir-resistant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) revealed the emergence of a V166L substitution, located outside of the polymerase active site of the Nsp12 protein, after 9 passages of a single lineage. V166L remained the only Nsp12 substitution after 17 passages (10 µM remdesivir), conferring a 2.3-fold increase in 50% effective concentration (EC50). When V166L was introduced into a recombinant SARS-CoV-2 virus, a 1.5-fold increase in EC50 was observed, indicating a high in vitro barrier to remdesivir resistance.

Single-cell transcriptomics of the ventral posterolateral nucleus-enriched thalamic regions from HSV-1-infected mice reveal a novel microglia/microglia-like transcriptional response.

BACKGROUND: Microglia participate in the immune response upon central nervous system (CNS) infections. However, the role of these cells during herpes simplex encephalitis (HSE) has not been fully characterized. We sought to identify different microglia/microglia-like cells and describe the potential mechanisms and signaling pathways involved during HSE. METHODS: The transcriptional response of CD11b+ immune cells, including microglia/microglia-like cells, was investigated using single-cell RNA sequencing (scRNA-seq) on cells isolated from the ventral posterolateral nucleus (VPL)-enriched thalamic regions of C57BL/6 N mice intranasally infected with herpes simplex virus-1 (HSV-1) (6 × 105 PFUs/20 µl). We further performed scanning electronic microscopy (SEM) analysis in VPL regions on day 6 post-infection (p.i.) to provide insight into microglial functions. RESULTS: We describe a novel microglia-like transcriptional response associated with a rare cell population (7% of all analyzed cells), named "in transition" microglia/microglia-like cells in HSE. This new microglia-like transcriptional signature, found in the highly infected thalamic regions, was enriched in specific genes (Retnlg, Cxcr2, Il1f9) usually associated with neutrophils. Pathway analysis of this cell-type transcriptome showed increased NLRP3-inflammasome-mediated interleukin IL-1ß production, promoting a pro-inflammatory response. These cells' increased expression of viral transcripts suggests that the distinct "in transition" transcriptome corresponds to the intrinsic antiviral immune signaling of HSV-1-infected microglia/microglia-like cells in the thalamus. In accordance with this phenotype, we observed several TMEM119+/IBA-I+ microglia/microglia-like cells immunostained for HSV-1 in highly infected regions. CONCLUSIONS: A new microglia/microglia-like state may potentially shed light on how microglia could react to HSV-1 infection. Our observations suggest that infected microglia/microglia-like cells contribute to an exacerbated CNS inflammation. Further characterization of this transitory state of the microglia/microglia-like cell transcriptome may allow the development of novel immunomodulatory approaches to improve HSE outcomes by regulating the microglial immune response.

Fitness of influenza A and B viruses with reduced susceptibility to baloxavir: A mini-review.

Neuraminidase inhibitors (NAIs), that currently include oseltamivir (Tamiflu® ), zanamivir (Relenza® ), peramivir (Rapivab® ) and laninamivir (Inavir® ), constitute an important class of antivirals recommended against seasonal influenza A and B infections. NAIs target the surface NA protein whose sialidase activity is responsible for virion release from infected cells. Because of their pivotal role in the transcription/translation process, the polymerase acidic (PA) and polymerase basic 1 and 2 (PB1 and PB2, respectively) internal proteins also constitute targets of interest for the development of additional anti-influenza agents. Baloxavir marboxil (BXM), an inhibitor of the cap-dependent endonuclease activity of the influenza PA protein, was approved in the United States and Japan in 2018. Baloxavir acid (BXA), the active compound of BXM, demonstrated a potent in vitro activity against different types/subtypes of influenza viruses including seasonal influenza A/B strains as well as avian influenza A viruses with a pandemic potential. A single oral dose of BXM provided virological and clinical benefits that were respectively superior or equal to those displayed by the standard (5 days, twice daily) oseltamivir regimen. Nevertheless, BXM-resistant variants have emerged at relatively high rates in BXM-treated children and adults. Consequently, there is a need to study the fitness (virulence and transmissibility) characteristics of mutants with a high potential to emerge as such variants can compromise the clinical usefulness of BXM. The purpose of this manuscript is to review the fitness properties of influenza A and B isolates harbouring mutations of reduced susceptibility to BXA.

Low and high temperatures decrease the mating success of an egg parasitoid and the proportion of females in the population.

Temperature influences all aspects of insect physiology and behaviour, including reproduction. Adverse temperatures can decrease mating success and sperm transfer, leading to increased sex ratio (more males) in populations of haplodiploid organisms. We tested the effect of five temperatures on the reproduction of the egg parasitoid Anaphes listronoti. Temperatures above and below 24.5°C decreased mating success by 30%-80%. Mating failures can arise from lack of encounters between sexes, absence of courting by the male, or the female refusing to mate. Both courtship and copulation duration decreased with increasing temperature. For mated females, there was no effect of mating temperature on offspring number and sex ratio. However, the increased number of virgin females at adverse temperatures did modify the simulated population sex ratio of the next generation, which increased from 0.2 at 24.5°C to 0.4, 0.5, 0.4 and 0.8 at 15.7°C, 20°C and 30°C and 35°C, respectively. The effect of temperature on courtship and copulation success of A. listronoti could lead to a decrease of the number of females in the population.

Immunomodulatory Strategies in Herpes Simplex Virus Encephalitis.

Herpes simplex virus 1 (HSV-1) can be responsible for life-threatening HSV encephalitis (HSE). The mortality rate of patients with HSE who do not receive antiviral treatment is 70%, with most survivors suffering from permanent neurological sequelae. The use of intravenous acyclovir together with improved diagnostic technologies such as PCR and magnetic resonance imaging has resulted in a reduction in the mortality rate to close to 20%. However, 70% of surviving patients still do not recover complete neurological functions. Thus, there is an urgent need to develop more effective treatments for a better clinical outcome. It is well recognized that cerebral damage resulting from HSE is caused by viral replication together with an overzealous inflammatory response. Both of these processes constitute potential targets for the development of innovative therapies against HSE. In this review, we discuss recent progress in therapy that may be used to ameliorate the outcome of patients with HSE, with a particular emphasis on immunomodulatory agents. Ideally, the administration of adjunctive immunomodulatory drugs should be initiated during the rise of the inflammatory response, and its duration should be limited in time to reduce undesired effects. This critical time frame should be optimized by the identification of reliable biomarkers of inflammation.

Human Respiratory Syncytial Virus-Induced Immune Signature of Infection Revealed by Transcriptome Analysis of Clinical Pediatric Nasopharyngeal Swab Samples.

Human respiratory syncytial virus (HRSV) constitutes one the main causes of respiratory infection in neonates and infants worldwide. Transcriptome analysis of clinical samples using high-throughput technologies remains an important tool to better understand virus-host complex interactions in the real-life setting but also to identify new diagnosis/prognosis markers or therapeutics targets. A major challenge when exploiting clinical samples such as nasal swabs, washes, or bronchoalveolar lavages is the poor quantity and integrity of nucleic acids. In this study, we applied a tailored transcriptomics workflow to exploit nasal wash samples from children who tested positive for HRSV. Our analysis revealed a characteristic immune signature as a direct reflection of HRSV pathogenesis and highlighted putative biomarkers of interest such as IP-10, TMEM190, MCEMP1, and TIMM23.

Impact of Amino Acid Substitutions in Region II and Helix K of Herpes Simplex Virus 1 and Human Cytomegalovirus DNA Polymerases on Resistance to Foscarnet.

Amino acid substitutions conferring resistance of herpes simplex virus 1 (HSV-1) and human cytomegalovirus (HCMV) to foscarnet (PFA) are located in the genes UL30 and UL54, respectively, encoding the DNA polymerase (pol). In this study, we analyzed the impact of substitutions located in helix K and region II that are involved in the conformational changes of the DNA pol. Theoretical substitutions were identified by sequences alignment of the helix K and region II of human herpesviruses (susceptible to PFA) and bacteriophages (resistant to PFA) and introduced in viral genomes by recombinant phenotyping. We characterized the susceptibility of HSV-1 and HCMV mutants to PFA. In UL30, the substitutions I619K (helix K), V715S, and A719T (both in region II) increased mean PFA 50% effective concentrations (EC50s) by 2.5-, 5.6-, and 2.0-fold, respectively, compared to the wild type (WT). In UL54, the substitution Q579I (helix K) conferred hypersusceptibility to PFA (0.17-fold change), whereas the substitutions Q697P, V715S, and A719T (all in region II) increased mean PFA EC50s by 3.8-, 2.8- and 2.5-fold, respectively, compared to the WT. These results were confirmed by enzymatic assays using recombinant DNA pol harboring these substitutions. Three-dimensional modeling suggests that substitutions conferring resistance/hypersusceptibility to PFA located in helix K and region II of UL30 and UL54 DNA pol favor an open/closed conformation of these enzymes, resulting in a lower/higher drug affinity for the proteins. Thus, this study shows that both regions of UL30 and UL54 DNA pol are involved in the conformational changes of these proteins and can influence the susceptibility of both viruses to PFA.

Replication and transmission of an influenza A(H3N2) virus harboring the polymerase acidic I38T substitution, in guinea pigs.

The polymerase acidic (PA) I38T substitution is a dominant marker of resistance to baloxavir. We evaluated the impact of I38T on the fitness of a contemporary influenza A(H3N2) virus. Influenza A/Switzerland/9715293/2013 (H3N2) wild-type (WT) virus and its I38T mutant were rescued by reverse genetics. Replication kinetics were compared using ST6GalI-MDCK and A549 cells and infectivity/contact transmissibility were evaluated in guinea pigs. Nasal wash (NW) viral titres were determined by TCID50 ml-1 in ST6GalI-MDCK cells. Competition experiments were performed and the evolution of viral population was assessed by droplet digital RT-PCR. I38T did not alter in vitro replication. I38T induced comparable titres vs the WT in guinea pigs NWs and the two viruses transmitted equally by direct contact. However, a 50 %:50 % mixture inoculum evolved to mean WT/I38T ratios of 71 %:29 % and 66.4 %:33.6 % on days 4 and 6 p.i., respectively. Contemporary influenza A(H3N2)-I38T PA variants may conserve a significant level of viral fitness.

Microglia are involved in phagocytosis and extracellular digestion during Zika virus encephalitis in young adult immunodeficient mice.

BACKGROUND: Zika virus (ZIKV) has been associated with several neurological complications in adult patients. METHODS: We used a mouse model deficient in TRIF and IPS-1 adaptor proteins, which are involved in type I interferon production, to study the role of microglia during brain infection by ZIKV. Young adult mice were infected intravenously with the contemporary ZIKV strain PRVABC59 (1 × 105 PFUs/100 µL). RESULTS: Infected mice did not present overt clinical signs of the disease nor body weight loss compared with noninfected animals. However, mice exhibited a viremia and a brain viral load that were maximal (1.3 × 105 genome copies/mL and 9.8 × 107 genome copies/g of brain) on days 3 and 7 post-infection (p.i.), respectively. Immunohistochemistry analysis showed that ZIKV antigens were distributed in several regions of the brain, especially the dorsal hippocampus. The number of Iba1+/TMEM119+ microglia remained similar in infected versus noninfected mice, but their cell body and arborization areas significantly increased in the stratum radiatum and stratum lacunosum-moleculare layers of the dorsal hippocampus cornu ammoni (CA)1, indicating a reactive state. Ultrastructural analyses also revealed that microglia displayed increased phagocytic activities and extracellular digestion of degraded elements during infection. Mice pharmacologically depleted in microglia with PLX5622 presented a higher brain viral load compared to untreated group (2.8 × 1010 versus 8.5 × 108 genome copies/g of brain on day 10 p.i.) as well as an increased number of ZIKV antigens labeled with immunogold in the cytoplasm and endoplasmic reticulum of neurons and astrocytes indicating an enhanced viral replication. Furthermore, endosomes of astrocytes contained nanogold particles together with digested materials, suggesting a compensatory phagocytic activity upon microglial depletion. CONCLUSIONS: These results indicate that microglia are involved in the control of ZIKV replication and/or its elimination in the brain. After depletion of microglia, the removal of ZIKV-infected cells by phagocytosis could be partly compensated by astrocytes.

An Early Microglial Response Is Needed To Efficiently Control Herpes Simplex Virus Encephalitis.

The role of a signaling pathway through macrophage colony-stimulating factor (MCSF) and its receptor, macrophage colony-stimulating factor 1 receptor (CSF1R), during experimental herpes simplex virus 1 (HSV-1) encephalitis (HSE) was studied by two different approaches. First, we evaluated the effect of stimulation of the MCSF/CSF1R axis before infection. Exogenous MCSF (40 µg/kg of body weight intraperitoneally [i.p.]) was administered once daily to BALB/c mice on days 4 and 2 before intranasal infection with 2,500 PFU of HSV-1. MCSF treatment significantly increased mouse survival compared to saline (50% versus 10%; P = 0.0169). On day 6 postinfection (p.i.), brain viral titers were significantly decreased, whereas beta interferon (IFN-ß) was significantly increased in mice treated with MCSF compared to mice treated with saline. The number of CD68+ (a phagocytosis marker) microglial cells was significantly increased in MCSF-treated mice compared to the saline-treated group. Secondly, we conditionally depleted CSF1R on microglial cells of CSF1R-loxP-CX3CR1-cre/ERT2 mice (in a C57BL/6 background) through induction with tamoxifen. The mice were then infected intranasally with 600,000 PFU of HSV-1. The survival rate of mice depleted of CSF1R (knockout [KO] mice) was significantly lower than that of wild-type (WT) mice (0% versus 67%). Brain viral titers and cytokine/chemokine levels were significantly higher in KO than in WT animals on day 6 p.i. Furthermore, increased infiltration of monocytes into the brains of WT mice was seen on day 6 p.i., but not in KO mice. Our results suggest that microglial cells are essential to control HSE at early stages of the disease and that the MCSF/CSF1R axis could be a therapeutic target to regulate their response to infection.IMPORTANCE Microglia appear to be one of the principal regulators of neuroinflammation in the central nervous system (CNS). An increasing number of studies have demonstrated that the activation of microglia could result in either beneficial or detrimental effects in different CNS disorders. Hence, the role of microglia during herpes simplex virus encephalitis (HSE) has not been fully characterized. Using experimental mouse models, we showed that an early activation of the MCSF/CSF1R axis improved the outcome of the disease, possibly by inducing a proliferation of microglia. In contrast, depletion of microglia before HSV-1 infection worsened the prognosis of HSE. Thus, an early microglial response followed by sustained infiltration of monocytes and T cells into the brain seem to be key components for a better clinical outcome. These data suggest that microglia could be a potential target for immunomodulatory strategies combined with antiviral therapy to better control the outcome of this devastating disease.

Human metapneumovirus activates NOD-like receptor protein 3 inflammasome via its small hydrophobic protein which plays a detrimental role during infection in mice.

NOD-like receptor protein 3 (NLRP3) inflammasome activation triggers caspase-1 activation-induced maturation of interleukin (IL)-1ß and IL-18 and therefore is important for the development of the host defense against various RNA viral diseases. However, the implication of this protein complex in human metapneumovirus (HMPV) disease has not been fully studied. Herein, we report that NLRP3 inflammasome plays a detrimental role during HMPV infection because NLRP3 inflammasome inhibition protected mice from mortality and reduced weight loss and inflammation without impacting viral replication. We also demonstrate that NLRP3 inflammasome exerts its deleterious effect via IL-1ß production since we observed reduced mortality, weight loss and inflammation in IL-1ß-deficient (IL-1ß-/-) mice, as compared to wild-type animals during HMPV infection. Moreover, the effect on these evaluated parameters was not different in IL-1ß-/- and wild-type mice treated with an NLRP3 inflammasome inhibitor. The production of IL-1ß was also abrogated in bone marrow derived macrophages deficient for NLRP3. Finally, we show that small hydrophobic protein-deleted recombinant HMPV (HMPV ΔSH) failed to activate caspase-1, which is responsible for IL-1ß cleavage and maturation. Furthermore, HMPV ΔSH-infected mice had less weight loss, showed no mortality and reduced inflammation, as compared to wild-type HMPV-infected mice. Thus, NLRP3 inflammasome activation seems to be triggered by HMPV SH protein in HMPV disease. In summary, once activated by the HMPV SH protein, NLRP3 inflammasome promotes the maturation of IL-1ß, which exacerbates HMPV-induced inflammation. Therefore, the blockade of IL-1ß production by using NLRP3 inflammasome inhibitors might be a novel potential strategy for the therapy and prevention of HMPV infection.

Herpes simplex encephalitis in adult patients with MASP-2 deficiency.

We report here two cases of Herpes simplex virus encephalitis (HSE) in adult patients with very rare, previously uncharacterized, non synonymous heterozygous G634R and R203W substitution in mannan-binding lectin serine protease 2 (MASP2), a gene encoding a key protease of the lectin pathway of the complement system. None of the 2 patients had variants in genes involved in the TLR3-interferon signaling pathway. Both MASP2 variants induced functional defects in vitro, including a reduced (R203W) or abolished (G634R) protein secretion, a lost capability to cleave MASP-2 precursor into its active form (G634R) and an in vivo reduced antiviral activity (G634R). In a murine model of HSE, animals deficient in mannose binding lectins (MBL, the main pattern recognition molecule associated with MASP-2) had a decreased survival rate and an increased brain burden of HSV-1 compared to WT C57BL/6J mice. Altogether, these data suggest that MASP-2 deficiency can increase susceptibility to adult HSE.