High Viral Titers Research Articles

Rescue of a Live-Attenuated Porcine Epidemic Diarrhea Virus HSGP Strain Using a Virulent Strain and a Partially Attenuated Strain.

In South Korea in 2013, the G1-based vaccine failed to prevent an outbreak of G2b-type porcine epidemic diarrhea virus (PEDV), which is more pathogenic than the traditional G1-type strain, thereby allowing the virus to spread. In 2017 and 2018, field samples were cultured sequentially on Vero cells to isolate HS (virulent) and SGP-M1 (partially attenuated) strains, respectively, of the G2b type. The HS strain harbors a single amino acid (aa) change and two aa deletions in the N-terminal domain of S1 (55I56G57E→55K56Δ57Δ). The SGP-M1 strain harbors a seven aa deletion in the C-terminal domain of S2 (1380~1386ΔFEKVHVQ). By co-infecting various animal cells with these two strains (HS and SGP-M1), we succeeded in cloning strain HSGP, which harbors the mutations present in the two original viruses. The CPE pattern of the HSGP strain was different from that of the HS and SGP-M1 strains, with higher viral titers. Studies in piglets showed attenuated pathogenicity of the HSGP strain, with no clinical symptoms or viral shedding, and histopathologic lesions similar to those in negative controls. These findings confirm that deletion of specific sequences from the S gene attenuates the pathogenicity of PEDV. In addition, HSGP strains created by combining two different strains have the potential for use as novel attenuated live vaccine candidates.

QPCR Assay as a Tool for Examining Cotton Resistance to the Virus Complex Causing CLCuD: Yield Loss Inversely Correlates with Betasatellite, Not Virus, DNA Titer.

Cotton leaf curl disease (CLCuD) is a significant constraint to the economies of Pakistan and India. The disease is caused by different begomoviruses (genus Begomovirus, family Geminiviridae) in association with a disease-specific betasatellite. However, another satellite-like molecule, alphasatellite, is occasionally found associated with this disease complex. A quantitative real-time PCR assay for the virus/satellite components causing CLCuD was used to investigate the performance of selected cotton varieties in the 2014-2015 National Coordinated Varietal Trials (NCVT) in Pakistan. The DNA levels of virus and satellites in cotton plants were determined for five cotton varieties across three geographic locations and compared with seed cotton yield (SCY) as a measure of the plant performance. The highest virus titer was detected in B-10 (0.972 ng·µg-1) from Vehari and the lowest in B-3 (0.006 ng·µg-1) from Faisalabad. Likewise, the highest alphasatellite titer was found in B-1 (0.055 ng·µg-1) from Vehari and the lowest in B-1 and B-2 (0.001 ng·µg-1) from Faisalabad. The highest betasatellite titer was found in B-23 (1.156 ng·µg-1) from Faisalabad and the lowest in B-12 (0.072 ng·µg-1) from Multan. Virus/satellite DNA levels, symptoms, and SCY were found to be highly variable between the varieties and between the locations. Nevertheless, statistical analysis of the results suggested that betasatellite DNA levels, rather than virus or alphasatellite DNA levels, were the important variable in plant performance, having an inverse relationship with SCY (-0.447). This quantitative assay will be useful in breeding programs for development of virus resistant plants and varietal trials, such as the NCVT, to select suitable varieties of cotton with mild (preferably no) symptoms and low (preferably no) virus/satellite. At present, no such molecular techniques are used in resistance breeding programs or varietal trials in Pakistan.

Porcine epidemic diarrhea viruses from Vietnam: isolation, characterization, and neutralizing activity

Porcine epidemic diarrhea (PED) is characterized by acute enteritis, watery diarrhea, weight loss, dehydration, and death, with high mortality in neonatal piglets. In this study, 3 virus isolates collected in Vietnam between 2016 and 2017 were propagated successfully in Vero cells at high virus titers. Sequence analysis of the full-length spike (S) gene showed that all 3 isolates belong to genogroup 2b, which is closely related to other prevalent Asian strains. A comparison of the amino acid sequence revealed a 98.19% to 99.13% homology with the Vietnam isolates circulating during 2013–2015, suggesting that field PED viruses (PEDVs) are evolving continuously. Experiments in animals showed that the antisera from guinea pigs immunized with the vaccine strain resulted in higher levels (5 log2) of neutralizing antibodies against the homologous strain and a relatively moderate level of neutralizing antibodies against the field isolates. This finding would be helpful in selecting a PEDV strain for vaccine development.

Evaluation of Resistance of Oilseed Rape Genotypes to Turnip Yellows Virus

Turnip yellows virus (TuYV), is one of the most important pathogens of oilseed rape, which has caused enormous yield losses in all growing regions of the world in recent years. Therefore, there is a need for resistant varieties for sustainable crop protection. We have investigated the resistance of known varieties and newly developed advanced-breeding lines of oilseed rape to TuYV in greenhouse and field trials. We have analysed the TuYV titre of individual genotypes inoculated with the virus using viruliferous aphids Myzus persicae. The genotypes ‘DK Temptation’ and ‘Rescator’ had the lowest and highest virus titres, respectively, and were used as resistant and susceptible models for comparative analyses with other genotypes. In the greenhouse, the best results were obtained with the genotypes ‘OP-8143 DH’ (2.94 × 105 copies), OP-BN-72 (3.29 × 105 copies), ‘Navajo’ (3.58 × 105 copies) and ‘SG-C 21215’ (4.09 × 105 copies), which reached virus titres about 2 times higher than the minimum virus concentration measured in ‘DK Temptation’ (1.80 × 105 copies). In the field trials, the genotypes ‘Navajo’ (3.39 × 105 copies), ‘OP-8148 DH’ (4.44 × 105 copies), ‘SG-C 21215’ (6.80 × 105 copies) and OP-8480 (7.19 × 105 copies) had the lowest virus titres and reached about 3 times the virus titre of DK Temptation (2.54 × 105 copies). Both trials showed that at least two commercial varieties (e.g., DK Temptation, Navajo) and three advanced breeding lines (e.g., OP-8143 DH, OP-BN-72, SG-C 21215) had low titres of the virus after TuYV infection. This indicates a high level of resistance to TuYV in ‘Navajo’ or the newly developed breeding lines and the basis of resistance is probably different from R54 (as in ‘DK Temptation’). Furthermore, the greenhouse trials together with RT -qPCR-based virus titre analysis could be a cost-effective and efficient method to assess the level of resistance of a given genotype to TuYV infection compared to the field trials. However, further research is needed to identify the underlying mechanisms causing this difference in susceptibility.

Creating the "Dew Drop on a Rose Petal": the Molecular Pathogenesis of Varicella-Zoster Virus Skin Lesions.

Varicella-zoster virus (VZV) is a human alphaherpesvirus that causes varicella (chicken pox) as the primary infection in a susceptible host. Varicella is very contagious through its transmission by direct contact with vesicular skin lesions that contain high titers of infectious virus and respiratory droplets. While the clinical manifestations of primary VZV infection are well recognized, defining the molecular mechanisms that drive VZV pathogenesis in the naive host before adaptive antiviral immunity is induced has been a challenge due to species specificity. This review focuses on advances made in identifying the differentiated human host cells targeted by VZV to cause varicella, the processes involved in viral takeover of these heterogenous cell types, and the host cell countermeasures that typically culminate in a benign illness. This work has revealed many unexpected and multifaceted mechanisms used by VZV to achieve its high prevalence and persistence in the human population.

Chronic allergic asthma induces T-cell exhaustion and impairs virus clearance in mice

BackgroundAllergic asthma, one of the most common types of asthma, is thought to be highly susceptible to respiratory viral infections; however, its pathological mechanism needs to be elucidated. Recent studies have found impaired T-cell function in asthmatic mice. Therefore, we aimed to investigate the way by which asthma induction affects T-cell exhaustion in the lungs and assess the relationship between T-cell exhaustion and influenza viral infection.MethodsChronic allergic asthma mice were induced by intranasal injection of ovalbumin for 6 weeks and asthmatic features and T cell populations in lung or airway were assessed. To determine the influenza virus susceptibility, control and asthma mice were challenged with the human influenza virus strain A/Puerto Rico/8/1934 H1N1 and evaluated the survival rate, lung damage, and virus titer.ResultsSix weeks of OVA sensitization and challenge successfully induced chronic allergic asthma in a mouse model showing significant increase of sera IgE level and broncho-pathological features. A significant decrease in interferon-γ-producing T-cell populations and an increase in exhausted T-cell populations in the lungs of OVA-induced asthmatic mice were observed. Asthmatic mice were more susceptible to influenza virus infection than control mice showing lower survival rate and higher virus titer in lung, and a positive correlation existed between T-cell exhaustion in the lung and virus titer.ConclusionsAsthma induction in mice results in the exhaustion of T-cell immunity, which may contribute to the defective capacity of viral protection. This study demonstrates a correlation between asthma conditions and viral susceptibility by investigating the functional characteristics of T-cells in asthma. Our results provide insights into the development of strategies to overcome the dangers of respiratory viral disease in patients with asthma.

Ecological drivers of sustained enzootic yellow fever virus transmission in Brazil, 2017-2021.

Beginning December 2016, sylvatic yellow fever (YF) outbreaks spread into southeastern Brazil, and Minas Gerais state experienced two sylvatic YF waves (2017 and 2018). Following these massive YF waves, we screened 187 free-living non-human primate (NHPs) carcasses collected throughout the state between January 2019 and June 2021 for YF virus (YFV) using RTqPCR. One sample belonging to a Callithrix, collected in June 2020, was positive for YFV. The viral strain belonged to the same lineage associated with 2017-2018 outbreaks, showing the continued enzootic circulation of YFV in the state. Next, using data from 781 NHPs carcasses collected in 2017-18, we used generalized additive mixed models (GAMMs) to identify the spatiotemporal and host-level drivers of YFV infection and intensity (an estimation of genomic viral load in the liver of infected NHP). Our GAMMs explained 65% and 68% of variation in virus infection and intensity, respectively, and uncovered strong temporal and spatial patterns for YFV infection and intensity. NHP infection was higher in the eastern part of Minas Gerais state, where 2017-2018 outbreaks affecting humans and NHPs were concentrated. The odds of YFV infection were significantly lower in NHPs from urban areas than from urban-rural or rural areas, while infection intensity was significantly lower in NHPs from urban areas or the urban-rural interface relative to rural areas. Both YFV infection and intensity were higher during the warm/rainy season compared to the cold/dry season. The higher YFV intensity in NHPs in warm/rainy periods could be a result of higher exposure to vectors and/or higher virus titers in vectors during this time resulting in the delivery of a higher virus dose and higher viral replication levels within NHPs. Further studies are needed to better test this hypothesis and further compare the dynamics of YFV enzootic cycles between different seasons.

Low Replication Efficiency of a Japanese Rabbit Hepatitis E Virus Strain in the Human Hepatocarcinoma Cell Line PLC/PRF/5.

A Japanese rabbit hepatitis E virus (HEV) strain, JP-59, has been identified in a feral rabbit. When this virus was transmitted to a Japanese white rabbit, it caused persistent HEV infection. The JP-59 strain shares an <87.5% nucleotide sequence identity with other rabbit HEV strains. Herein, to isolate JP-59 by cell culture, we used a 10% stool suspension recovered from a JP-59-infected Japanese white rabbit and contained 1.1 × 107 copies/mL of the viral RNA and using it to infect a human hepatocarcinoma cell line, PLC/PRF/5. No sign of virus replication was observed. Although long-term virus replication was observed in PLC/PRF/5 cells inoculated with the concentrated and purified JP-59 containing a high titer of viral RNA (5.1 × 108 copies/mL), the viral RNA of JP-59c that was recovered from the cell culture supernatants was <7.1 × 104 copies/mL during the experiment. The JP-59c strain did not infect PLC/PRF/5 cells, but its intravenous inoculation caused persistent infection in rabbits. The nucleotide sequence analyses of the virus genomes demonstrated that a total of 18 nucleotide changes accompanying three amino acid mutations occurred in the strain JP-59c compared to the original strain JP-59. These results indicate that a high viral RNA titer was required for JP-59 to infect PLC/PRF/5 cells, but its replication capability was extremely low. In addition, the ability of rabbit HEVs to multiply in PLC/PRF/5 cells varied depending on the rabbit HEV strains. The investigations of cell lines that are broadly susceptible to rabbit HEV and that allow the efficient propagation of the virus are thus needed.

Transcriptomic Responses Underlying the High Virulence of Black Queen Cell Virus and Sacbrood Virus following a Change in Their Mode of Transmission in Honey Bees (Apis mellifera).

Over the last two decades, honey bees (Apis mellifera) have suffered high rates of colony losses that have been attributed to a variety of factors, chief among which are viral pathogens, such as deformed wing virus (DWV), whose virulence has increased because of vector-based transmission by the invasive, ectoparasitic varroa mite (Varroa destructor). A shift in the experimental mode of transmission of the black queen cell virus (BQCV) and sacbrood virus (SBV) from fecal/food-oral (direct horizontal) to vector-mediated (indirect horizontal) transmission also results in high virulence and viral titers in pupal and adult honey bees. Agricultural pesticides represent another factor that acts independently or in interaction with pathogens, and they are also thought to cause colony loss. Understanding the molecular mechanisms underlying the higher virulence following a vector-based mode of transmission provides deeper insight into honey bee colony losses, as does determining whether or not host-pathogen interactions are modulated by exposure to pesticides. Through an experimental design with controlled laboratory, we investigated the effects of the modes of transmission of BQCV and SBV (feeding vs. vector-mediated via injection) alone or in combination with chronic exposure to sublethal and field-realistic concentrations of flupyradifurone (FPF), a novel agricultural insecticide, on honey bee survival and transcription responses by using high-throughput RNA sequencing (RNA-seq) analysis. Co-exposure to viruses via feeding (VF) or injection (VI) and FPF insecticide had no statistically significant interactive effect on their survival compared to, respectively, VF or VI treatments alone. Transcriptomic analysis revealed a distinct difference in the gene expression profiles of bees inoculated with viruses via injection (VI) and exposed to FPF insecticide (VI+FPF). The number of differentially expressed genes (DEGs) at log2 (fold-change) > 2.0 in VI bees (136 genes) or/and VI+FPF insecticide (282 genes) was very high compared to that of VF bees (8 genes) or the VF+FPF insecticide treatment (15 genes). Of these DEGs, the expression in VI and VI+FPF bees of some immune-related genes, such as those for antimicrobial peptides, Ago2, and Dicer, was induced. In short, several genes encoding odorant binding proteins, chemosensory proteins, odor receptors, honey bee venom peptides, and vitellogenin were downregulated in VI and VI+FPF bees. Given the importance of these suppressed genes in honey bees' innate immunity, eicosanoid biosynthesis, and olfactory associative function, their inhibition because of the change in the mode of infection with BQCV and SBV to vector-mediated transmission (injection into haemocoel) could explain the high virulence observed in these viruses when they were experimentally injected into hosts. These changes may help explain why other viruses, such as DWV, represent such a threat to colony survival when transmitted by varroa mites.

Coinfection with porcine epidemic diarrhea virus and Clostridium perfringens type A enhances disease severity in weaned pigs.

Clostridium perfringens is a constituent of the normal gut microbiome in pigs; however, it can potentially cause pre- and post-weaning diarrhea. Nevertheless, the importance of this bacterium as a primary pathogen of diarrhea in piglets needs to be better understood, and the epidemiology of C. perfringens in Korean pig populations is unknown. To study the prevalence and typing of C. perfringens, 203 fecal samples were collected from diarrheal piglets on 61 swine farms during 2021-2022 and examined for the presence of C. perfringens and enteric viruses, including porcine epidemic diarrhea virus (PEDV). We determined that the most frequently identified type of C. perfringens was C. perfringens type A (CPA; 64/203, 31.5%). Among the CPA infections, single infections with CPA (30/64, 46.9%) and coinfections with CPA and PEDV (29/64, 45.3%) were the most common in diarrheal samples. Furthermore, we conducted animal experiments to investigate the clinical outcome of single infections and coinfections with highly pathogenic (HP)-PEDV and CPA in weaned piglets. The pigs infected with HP-PEDV or CPA alone showed mild or no diarrhea, and none of them died. However, animals that were co-inoculated with HP-PEDV and CPA showed more-severe diarrheal signs than those of the singly infected pigs. Additionally, CPA promoted PEDV replication in coinfected piglets, with high viral titers in the feces. A histopathological examination revealed more-severe villous atrophy in the small intestine of coinfected pigs than in singly infected pigs. This indicates a synergistic effect of PEDV and CPA coinfection on clinical disease in weaned piglets.

B-arrestin deletion abrogates the innate immune response in murine CVB3 myocarditis

β-arrestins (βarrs), initially discovered as desensitizers of GPCR signaling, are now known to function as intracellular scaffolds and signaling transducers mediating a wide array of signaling cascades including immune responses to inflammatory stimuli. An important cause of immune cell infiltration and cardiac inflammation are viral pathogens such as enterovirus coxsackievirus B3 (CVB3) induced myocarditis. While viral myocarditis is a leading cause of dilated cardiomyopathy, the precise molecular mechanisms for the acute immune response to CVB3 infection are not well understood. Given the important role for βarrs in the acute immune response, we tested the hypothesis that βarrs are necessary for the activation of the acute immune response and mediate the progression and severity of cardiotropic CVB3-induced myocarditis in mice. Five to 7-week-old mice devoid of βarr1 (βarr1 KO) or βarr2 (βarr2 KO) were infected intraperitoneally with 1x103-1x104 plaque forming units (PFU) of CVB3 per animal. Wild type (WT) C57BL/6 mice infected with CVB3 were used as controls. The survival rate 7 days post infection (dpi) was significantly improved in male βarr1 KOs (80%) and βarr2 KOs (75%) compared to male WT control mice (35%, p=0.013). Female WT, βarr1 KO, and βarr2 KO mice showed similar survival rates 7 dpi., ranging from 70% to 80%. Early mortality among all groups before 5 dpi was associated with high viral titers (~6.0 ± 0.5 log10PFU/mg) in the liver compared to mortality after 5 dpi (~2.4 ± 1.7 log10PFU/mg) as determined by plaque assay. Viral titers in the heart (WT=3.7 ± 0.9 log10PFU/mg, βarr1KO=3.6 ± 1.3 log10PFU/mg, βarr2KO=3.5 ± 1.2log10PFU/mg) were similar among all groups suggesting that βarrs are not involved in viral replication. Morphometric analysis showed similar weight loss (~18%) across all groups at 7 dpi corroborated by viral cardiac PFU. Immunofluorescent staining of the heart with the pan-inflammatory marker, CD45, revealed high immune cell infiltration in infected WT mice (34.2% ± 4.5%), whereas immune cell infiltration was significantly blunted in infected βarr1 KO (6.0% ± 1.1%; p&lt;0.0001) and βarr2 KO (8.5% ± 0.9%; p&lt;0.0001) mice. The degree of immune cell infiltration in hearts of infected WT mice was directly correlated with an increase in heart viral titer, whereas immune cell infiltration remained blunted across a broad range of heart viral titers in both βarr1 and 2 KO mice. The blunted immune response in both βarr KOs compared to WT infected controls was consistent across multiple immune cell markers including CD4 for helper T cells and CD11b for innate immune cells. In conclusion, we demonstrate that βarrs are necessary for immune cell recruitment to the heart in CVB3 myocarditis and deletion of βarrs in male mice may be cardioprotective as indicated by an increase in survival rate. These data suggest that βarrs may serve as potential therapeutic targets in the treatment of acute viral myocarditis. This work was supported by the National Institutes of Health Grants HL056687 (to H.A.R.). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Unraveling the cell death induced by SARS-CoV-2 in lung epithelial cells

Abstract The COVID-19 pandemic has continued to affect people’s lives worldwide, and SARS-CoV-2, the pathogen that causes the pandemic, has infected over 100 million people and claimed over 10 million lives globally. There is strong evidence that lung damage contributes to the inflammatory responses against SARS-CoV-2, and that diverse forms of cell death occur in myeloid cells upon infection. However, less is known about the cell death pathways activated in the primary cell target of SARS-CoV-2, lung epithelial cells. Previously, we showed that conventional pyroptosis was activated in bystander myeloid cells. Using a human epithelial cell line with the ACE2 receptor and primary human airway epithelial culture, we analyzed the impact of SARS-CoV-2 infection on cell death. The latter is grown at an air-liquid interface (ALI) and is used to model airway pseudostratified epithelium. SARS-CoV-2 infection of these cells triggers lytic cell death. Pathway analysis shows that biomarkers of necroptosis, apoptosis, and pyroptosis are activated and increase with time, but some forms of cell death are limited predominantly to cells that are co-stained with SARS-CoV-2 viral antigens while others are not. RT-PCR and single-cell RNAseq analysis revealed that cell death genes increase with high viral titer and severity of disease in patients. R56 AI158314, R01 AI158314, AI029564, AI141333, CA232109

Dysregulated myeloid cell activity is associated with fatal disease in SARS-CoV-2 infected aged mice

Abstract Covid-19 caused by recently emerged SARS-CoV-2 is a significant threat to global public health. Although SARS-CoV-2 efficiently infects individuals of all age groups, the aged population exhibit poor clinical outcome as demonstrated by high rates of morbidity and mortality. However, the underlying mechanism driving severe pneumonia and lethal disease in the elderly is not well defined. SARS-CoV-2-induced excessive inflammation and impaired antiviral response (collectively referred to as ‘dysregulated immunity’) is believed to cause acute lung injury (ALI) and fatal pneumonia. In this study, using a novel mouse-adapted SARS-CoV-2, we evaluated disease severity in young and aged mice, and examined the mechanistic basis for age-related severe disease caused by SARS-COV-2. Similar to Covid-19, our results showed increased morbidity and mortality in the aged compared to young mice. Further examination of SARS-CoV-2 infected lungs from young and aged mice demonstrated high lung viral titers, dysregulated inflammatory cytokine expression, and downregulation of interferon (IFN) expression in aged mice compared to young cohorts. Our results also showed elevated inflammatory monocyte macrophage (IMM) and neutrophil accumulation in the aged lungs compared to young mice. To conclusively establish if robust myeloid cell activity causes severe disease, we depleted monocytes and neutrophils and found that combined depletion delayed mortality and alleviated disease severity in mice infected with a lethal dose of SARS-CoV-2. Collectively, our results establish that impaired innate antiviral response along with a robust accumulation of inflammatory myeloid cells cause severe disease in the aged hosts. This study was supported in part by institutional research funds from Oklahoma State University—Stillwater and NIA 5P20GM103648-10 2R.C.

Differential role of TLR7 signaling in SARS-CoV-2-induced antiviral and inflammatory responses

Abstract Since its emergence in 2019, SARS-CoV-2 has caused significant morbidity and mortality in humans. SARS-CoV-2-induced impaired antiviral and excessive inflammatory responses drive acute lung injury and severe pneumonia. However, the key pattern recognition receptors that elicit effective antiviral and pathogenic inflammatory responses are not well defined. Since CoVs are single-stranded RNA (ssRNA) viruses that make double-stranded RNA (dsRNA) intermediates during replication, we assessed the antiviral and pro-inflammatory roles of ssRNA and dsRNA mimics in mouse macrophages. We show that R837-TLR7 signaling induced excessive inflammation, while PolyIC-TLR3/MDA activation caused robust IFN production. Since R837-TLR7 induced high levels of inflammatory cytokines, using a novel mouse-adapted SARS-COV-2, we examined the role of TLR7 signaling in COVID-19 pathogenesis. Our results show that TLR7 KO mice were more susceptible to SARS-CoV-2 infection as compared to WT mice. Further investigation of SARS-CoV-2 infected lungs showed significantly reduced mRNA levels of antiviral interferons (IFNα/β/λ), ISGs (ISG15 and CXCL10), and several pro-inflammatory cytokine/chemokines in TLR7 KO lungs compared to WT. Interestingly, immunolabelling of cells isolated from infected WT and TLR7 KO lungs showed a high neutrophil count in TLR7 KO mice compared to WT mice. Furthermore, reduced lung IFN levels and increased mortality correlated with high lung viral titer in TLR7 KO mice. In summary, our findings conclusively establish that TLR7 signaling is protective during SARS-CoV-2 infection, and despite TLR7-mediated robust inflammatory cytokine production, TLR7-induced IFN and ISG responses play a key role in host protection.

Bystander CD8+ T cells are Important Antiviral Effectors in the Brain

Abstract The central nervous system (CNS) presents a unique immunological environment with restricted infiltration of immune cells from the periphery. Since much is unknown about CNS-infiltrating immune cells during infection, we utilized the attenuated Venezuelan equine encephalitis virus vaccine strain TC83 (VEEV-TC83) to study T cell responses to this viral infection. VEEV-TC83 intracranial (IC) infection of wild-type mice produces high viral titers in the brain without lethality, enabling the study of the complete antiviral immune response in the CNS. Many T cells rapidly (5dpi) infiltrate the CNS, in a seemingly antigen-independent manner, upon IC VEEV-TC83 infection. During infection, CD8+ T cells (~40% of CNS-infiltrating T cells) in the brain express high levels of innate-memory markers. These bystander CD8+ T cells can produce IFNγ when treated with IL-12 and IL-18, cytokines known to induce innate signaling. IL-12, IL-18, and IL-15 (another innate-memory T cell supporter) are upregulated upon IC VEEV-TC83 infection. IC infection of IL-15 knockout (KO) mice results in decreased CNS infiltration by bystander CD8+ T cells. CD8+ T cells that do infiltrate the brains of IL-15 KO mice express fewer activation markers and cytokines, and are therefore likely not fully functional. Additionally, microglia express innate-memory cytokines during infection and likely support the recruitment and function of bystander CD8+ T cells in the CNS during infection. Data deposited in GEO indicate that infection with many neurotropic viruses induces Il15, Il12, and Il18 expression in CNS cells and tissues. Bystander CD8+ T cells are likely an important first line of defense during viral infection of the CNS. Supported by grants from the NIH (Training grant T32 AI07405 and RO1 NS123431)

The Environmental Stability of SARS-CoV-2 Variants Omicron BA.1 and BA.5 on the Surfaces of Widely Used Transport Packaging Materials.

The increased transmissibility of SARS-CoV-2 variants of concern (VOCs) has raised questions regarding the environmental stability of these viruses. Although a prolonged survival time has been reported for SARS-CoV-2, how long new variants can persist on contaminated surfaces and how environmental factors affect the persistence time are not fully characterized. The present study provides a comprehensive assessment of the stability of Omicron variants BA.1 and BA.5, which are currently circulating strains, on the surfaces of widely used transport packaging materials. By monitoring viable virus detection over a 7-day period under different environmental conditions, it was found that the environmental stability of SARS-CoV-2 Omicron variants depended heavily on the surface type, temperature, and virus concentration. In addition, virus nucleic acid exhibited high stability on the material surface independent of whether viable virus was detected. These findings provide useful information for logistics practitioners and the general public to appropriately deal with transport items under different conditions to minimize the risk of epidemic transmission. IMPORTANCE This study shows the environmental stability of SARS-CoV-2 Variants Omicron BA.1 and BA.5 on surfaces of widely used transport packaging materials. The findings demonstrate that the environmental stability of the SARS-CoV-2 Omicron variants varies based on material type. The viability of SARS-CoV-2 on material surfaces depends heavily on temperature and viral titer. Low temperatures and high viral titers promote virus survival. Moreover, in contrast to virus viability, virus nucleic acid exhibits high stability on the surfaces of widely used materials, making the detection of virus nucleic acid unsuitable for evaluating the risk of epidemic transmission.

Coxsackievirus B3 infects and disrupts human induced-pluripotent stem cell derived brain-like endothelial cells.

Coxsackievirus B3 (CVB3) is a significant human pathogen that is commonly found worldwide. CVB3 among other enteroviruses, are the leading causes of aseptic meningo-encephalitis which can be fatal especially in young children. How the virus gains access to the brain is poorly-understood, and the host-virus interactions that occur at the blood-brain barrier (BBB) is even less-characterized. The BBB is a highly specialized biological barrier consisting primarily of brain endothelial cells which possess unique barrier properties and facilitate the passage of nutrients into the brain while restricting access to toxins and pathogens including viruses. To determine the effects of CVB3 infection on the BBB, we utilized a model of human induced-pluripotent stem cell-derived brain-like endothelial cells (iBECs) to ascertain if CVB3 infection may alter barrier cell function and overall survival. In this study, we determined that these iBECs indeed are susceptible to CVB3 infection and release high titers of extracellular virus. We also determined that infected iBECs maintain high transendothelial electrical resistance (TEER) during early infection despite possessing high viral load. TEER progressively declines at later stages of infection. Interestingly, despite the high viral burden and TEER disruptions at later timepoints, infected iBEC monolayers remain intact, indicating a low degree of late-stage virally-mediated cell death, which may contribute to prolonged viral shedding. We had previously reported that CVB3 infections rely on the activation of transient receptor vanilloid potential 1 (TRPV1) and found that inhibiting TRPV1 activity with SB-366791 significantly limited CVB3 infection of HeLa cervical cancer cells. Similarly in this study, we observed that treating iBECs with SB-366791 significantly reduced CVB3 infection, which suggests that not only can this drug potentially limit viral entry into the brain, but also demonstrates that this infection model could be a valuable platform for testing antiviral treatments of neurotropic viruses. In all, our findings elucidate the unique effects of CVB3 infection on the BBB and shed light on potential mechanisms by which the virus can initiate infections in the brain.

Astrocytes derived from neural progenitor cells are susceptible to Zika virus infection.

Zika virus (ZIKV) was first isolated in 1947. From its isolation until 2007, symptoms of ZIKV-caused disease were limited (e.g., fever, hives, and headache); however, during the epidemic in Brazil in 2014, ZIKV infection caused Guillain-Barré syndrome in adults and microcephaly in fetuses and infants of women infected during pregnancy. The neurovirulence of ZIKV has been studied using neural progenitor cells (NPCs), brain organoids, neurons, and astrocytes. NPCs and astrocytes appear to be the most susceptible cells of the Central Nervous System to ZIKV infection. In this work, we aimed to develop a culture of astrocytes derived from a human NPC cell line. We analyze how ZIKV affects human astrocytes and demonstrate that 1) ZIKV infection reduces cell viability, increases the production of Reactive Oxygen Species (ROS), and results in high viral titers; 2) there are changes in the expression of genes that facilitate the entry of the virus into the cells; 3) there are changes in the expression of genes involved in the homeostasis of the glutamatergic system; and 4) there are ultrastructural changes in mitochondria and lipid droplets associated with production of virions. Our findings reveal new evidence of how ZIKV compromises astrocytic functionality, which may help understand the pathophysiology of ZIKV-associated congenital disease.

Development and evaluation of a mouse model susceptible to severe fever with thrombocytopenia syndrome virus by rAAV-based exogenous human DC-SIGN expression

Experimental animal model is indispensable to evaluate the prophylactic and therapeutic candidates against severe fever with thrombocytopenia syndrome virus (SFTSV). To develop a suitable mouse model for SFTSV infection, we delivered human dendritic cell–specific ICAM-3-grabbing non-integrin (hDC-SIGN) by adeno-associated virus (AAV2) and validated its susceptibility for SFTSV infection. Western blot and RT-PCR assays confirmed the expression of hDC-SIGN in transduced cell lines and a significantly increased viral infectivity was observed in cells expressing hDC-SIGN. The C57BL/6 mice transduced with AAV2 exhibited a stable hDC-SIGN expression in the organs for 7 days. Upon SFTSV challenge with 1 × 105 FAID50, the mice transduced with rAAV-hDC-SIGN showed a 12.5% mortality and reduced platelet and white blood cell count in accordance with higher viral titer than control group. Liver and spleen samples collected from the transduced mice had pathological signs similar to the IFNAR−/− mice with severe SFTSV infection. Collectively, the rAAV-hDC-SIGN transduced mouse model can be used as an accessible and promising tool for studying the SFTSV pathogenesis and pre-clinical evaluation of vaccines and therapeutics against the SFTSV infection.

Deletion of pentad residues in the N-terminal domain of spike protein attenuates porcine epidemic diarrhea virus in piglets

Our previous study revealed that tissue culture-adapted porcine epidemic diarrhea virus (PEDV) strains, namely KNU-141112-S DEL2/ORF3 and -S DEL5/ORF3, were attenuated to different extents in vivo, suggesting that their independent deletion (DEL) signatures, including 2-amino acid (aa; residues 56–57) or 5-aa (residues 56–60) DEL in the N-terminal domain (NTD) of the spike (S) protein, may contribute to the reduced virulence of each strain. To investigate whether each DEL in the NTD of the S1 subunit is a determinant for the virulence of PEDV, we generated two mutant viruses, named icS DEL2 and icS DEL5, by introducing the identical double or quintuple aa DEL into S1 using reverse genetics with an infectious cDNA clone of KNU-141112 (icKNU-141112). We then orally inoculated conventional suckling piglets with icKNU-141112, icS DEL2, or icS DEL5 to compare their pathogenicities. The virulence of both DEL mutant viruses was significantly diminished compared to that of icKNU-141112, which causes severe clinical signs and 100 % mortality. Interestingly, the degree of attenuation differed between the two mutant viruses: icS DEL5 caused neither diarrhea nor mortality, whereas icS DEL2 caused mild to moderate diarrhea, higher viral titers in feces and intestinal tissues, and 25 % mortality. Furthermore, the icS DEL5-infected piglets displayed no remarkable macroscopic and microscopic intestinal lesions, while the icS DEL2-infected piglets showed histopathological changes in small intestine tissues, including moderate-to-severe villous atrophy. Our data indicate that the loss of the pentad (56GENQG60) residues in S alone can be sufficient to give rise to an attenuated phenotype of PEDV.