Viruses employ different strategies to circumvent the antiviral actions of the innate immune response. SARS coronavirus (SARS-CoV), a virus that causes severe lung damage, encodes an array of proteins able to inhibit induction and signaling of type-I interferons. However, recent studies have demonstrated that interferons are produced during SARS-CoV infection in humans and macaques. Furthermore, nuclear translocation of activated STAT1 and a range of interferon-stimulated genes could be demonstrated in the lungs of SARS-CoV-infected macaques. In line with these observations, plasmacytoid dendritic cells have been shown to produce interferons upon SARS-CoV infection in vitro. Given the pivotal role of interferons during viral infections, (differential) induction of interferons may affect the outcome of the infection. Therefore, the functional implication of interferon production during SARS-CoV infection remains to be re-investigated. Interferon induction during viral infection Type-I interferons are induced in direct response to viral infection and play an important role in innate immunity. Although most mammalian cells are capable of producing type-I interferons, plasmacytoid dendritic cells, also known as ‘professional’ interferon producers, produce much higher amounts of IFN-α than other cell types. Invading viruses are sensed by the host cell either though a cytoplasmatic pathway, using the RNA helicases RIG-I and MDA-5, or by the endosomal pathway, in which Toll-like receptors are involved. After viral RNA is detected by the host cell, activation of several signaling pathways ultimately leads to phosphorylation of IRF-3 and IRF-7, which are subsequently translocated to the nucleus where they activate the interferon promoter together with other cofactors, resulting in the production of type-I interferons. Interferon induction by SARS-CoV SARS-CoV employs several mechanisms that inhibit induction of type-I interferons. As a result, most cell types do not produce type-I interferons upon SARS-CoV infection. Despite blocks on interferon production, type-I interferons are detected in SARS-CoV-infected macaques and humans. Plasmacytoid dendritic cells are able to produce interferons upon SARS-CoV infection and are a possible source for interferon production in vivo. SARS-CoV blocks interferon signaling When interferons activate the JAK/STAT signaling pathway, more than 300 interferon-stimulated genes are activated. SARS-CoV not only blocks interferon induction but also interferon signaling through the JAK/STAT pathway. Interferons produced during in vivo SARS-CoV infection activate STAT1 in uninfected cells. Future perspective Patients with severe cases of SARS develop pneumonia and acute respiratory distress syndrome (ARDS). Although ARDS-associated mortality remains very high, no successful pharmacological therapies have been developed for ARDS as yet. Insights into the complex regulation of the interferon response during SARS-CoV may provide clues for intervention strategies based on the use of interferons. However, more research in appropriate SARS animal models should be performed to address this issue. Reference & Source information: https://www.futuremedicine.com/ Read More on :

Sequencing almost 60,000 cells, researchers have found that certain cilia progenitor cells have gene transcripts for ACE2 and co-factor TMPRSS2, enabling COVID-19 infection. The researchers are from the Berlin Institute of Health (BIH), Charité – Universitätsmedizin Berlin and the Thorax Clinic at Heidelberg University Hospital, whose collaboration is taking place under the auspices of the German Center for Lung Research (DZL). “We analysed a total of nearly 60,000 cells to determine whether they activated the gene for the receptor and potential co-factors, thus in principle allowing them to be infected by the coronavirus,” said Soeren Lukassen, one of the lead authors of the study. “We only found the gene transcripts for ACE2 and for the co-factor TMPRSS2 in very few cells and only in very small numbers.” According to the researchers, they discovered that the receptor for COVID-19 is expressed in certain progenitor cells. These cells normally develop into respiratory tract cells lined with hair-like projections called cilia that sweep mucus and bacteria out of the lungs. The SARS-CoV-2 pandemic affecting the human respiratory system severely challenges public health and urgently demands for increasing our understanding of COVID-19 pathogenesis, especially host factors facilitating virus infection and replication. SARS-CoV-2 was reported to enter cells via binding to ACE2, followed by its priming by TMPRSS2. Here, we investigate ACE2 and TMPRSS2 expression levels and their distribution across cell types in lung tissue (twelve donors, 39,778 cells) and in cells derived from subsegmental bronchial branches (four donors, 17,521 cells) by single nuclei and single cell RNA sequencing, respectively. While TMPRSS2 is expressed in both tissues, in the subsegmental bronchial branches ACE2 is predominantly expressed in a transient secretory cell type. Interestingly, these transiently differentiating cells show an enrichment for pathways related to RHO GTPase function and viral processes suggesting increased vulnerability for SARS-CoV-2 infection. Our data provide a rich resource for future investigations of COVID-19 infection and pathogenesis. Reference & Source Information: https://www.drugtargetreview.com/, https://www.embopress.org/ Read more on :

Methods Plasma collected from 175 COVID-19 recovered patients with mild symptoms were 32 screened using a safe and sensitive pseudotyped-lentiviral-vector-based neutralization 33 assay. Spike-binding antibody in plasma were determined by ELISA using RBD, S1, 34 and S2 proteins of SARS-CoV-2. The levels and the time course of SARS-CoV-2-35 specific NAbs and the spike-binding antibodies were monitored at the same time. Findings 38 SARS-CoV-2 NAbs were unable to cross-reactive with SARS-CoV virus. SARS-CoV-39 2-specific NAbs were detected in patients from day 10-15 after the onset of the disease 40 and remained thereafter. The titers of NAb among these patients correlated with the 41 spike-binding antibodies targeting S1, RBD, and S2 regions. The titers of NAbs were 42 variable in different patients. Elderly and middle-age patients had significantly higher 43 plasma NAb titers (P<0.0001) and spike-binding antibodies (P=0.0003) than young 44 patients. Notably, among these patients, there were ten patients whose NAb titers were 45 under the detectable level of our assay (ID50: < 40); while in contrast, two patients, 46 showed very high titers of NAb, with ID50 :15989 and 21567 respectively. The NAb 47 titers were positive correlated with plasma CRP levels but negative correlated with the 48 lymphocyte counts of patients at the time of admission, indicating an association 49 between humoral response and cellular immune response. Interpretation 52 The variations of SARS-CoV-2 specific NAbs in recovered COVID-19 patients may 53 raise the concern about the role of NAbs on disease progression. The correlation of 54 NAb titers with age, lymphocyte counts, and blood CRP levels suggested that the 55 interplay between virus and host immune response in coronavirus infections should be 56 further explored for the development of effective vaccine against SARS-CoV-2 virus. 57 Furthermore, titration of NAb is helpful prior to the use of convalescent plasma for 58 prevention or treatment Red and Source of Information https://www.medrxiv.org/content/10.1101/2020.03.30.20047365v1.full.pdf

Many viruses induce hepatitis in humans, highlighting the need to understand the underlying mechanisms of virus-induced liver pathology. Themurine coronavirus,mouse hepatitis virus(MHV), causes acute hepatitis in its natural host and provides a useful model for understanding virus interaction with liver cells. The MHV accessory protein,ns2, antagonizes thetype I interferonresponse and promotes hepatitis. We show that ns2 has 2′,5′-phosphodiesterase activity, which blocks the interferon inducible 2′,5′-oligoadenylate synthetase (OAS)-RNase L pathway to facilitate hepatitis development. Ns2 cleaves 2′,5′-oligoadenylate, the product of OAS, to prevent activation of the cellular endoribonuclease RNase L and consequently block viralRNA degradation. An ns2mutant viruswas unable to replicate in the liver or induce hepatitis in wild-type mice, but was highly pathogenic in RNase L deficient mice. Thus, RNase L is a critical cellular factor for protection against viral infection of the liver and the resulting hepatitis. Our results underscore the important role of RNase L in host restriction of viral infection of the liver. The success of IFN-α treatment of chronichepatitis C virus(HCV) may depend in part on the susceptibility of viral RNA genome to degradation by RNase L, which cleaves single-stranded viral RNA on the 3′ sides of UU and UA dinucleotides. Cleavage of HCV genome RNA by RNase L releases a small RNA that is recognized byRIG-Iand thus serves to enhance IFN induction (Malathi et al., 2010). Indeed, the strains of HCV that are most susceptible to IFN-α treatment are those strains with genomes predicted to be most vulnerable to RNase L-mediated degradation (Han et al., 2004,Washenberger et al., 2007). Thus, enhancement of the activity of the OAS-RNase L pathway may have potential for antiviral therapy for liver infections. A possible approach to enhancing RNase L mediated viral RNA genome degradation might be to limit activities of enzymes that degrade 2-5A; treatment with an inhibitor for 2′-PDE was shown to decrease vaccinia virus replication in vitro (Kubota et al., 2004). In this regard, inhibitors of virus-encoded phosphodiesterases that degrade 2′,5′-oligoadenylates could provide an avenue for development of targeted antiviral drugs. Reference & Source Information: https://www.sciencedirect.com/ Read More on :

SARS-CoV-2 enters host cells via cell receptor ACE II (ACE2) and the transmembrane serine protease 2 (TMPRSS2). In order to identify possible prime target cells of SARS-CoV-2 by comprehensive dissection of ACE2 and TMPRSS2 coexpression pattern in different cell types, five datasets with single-cell transcriptomes of lung, oesophagus, gastric mucosa, ileum and colon were analysed. Design Five datasets were searched, separately integrated and analysed. Violin plot was used to show the distribution of differentially expressed genes for different clusters. The ACE2-expressing and TMPRRSS2-expressing cells were highlighted and dissected to characterise the composition and proportion. Results Cell types in each dataset were identified by known markers. ACE2 and TMPRSS2 were not only coexpressed in lung AT2 cells and oesophageal upper epithelial and gland cells but also highly expressed in absorptive enterocytes from the ileum and colon. Additionally, among all the coexpressing cells in the normal digestive system and lung, the expression of ACE2 was relatively highly expressed in the ileum and colon. This study provides the evidence of the potential route of SARS-CoV-2 in the digestive system along with the respiratory tract based on single-cell transcriptomic analysis. This finding may have a significant impact on health policy setting regarding the prevention of SARS-CoV-2 infection. Our study also demonstrates a novel method to identify the prime cell types of a virus by the coexpression pattern analysis of single-cell sequencing data. Conclusion This single-cell transcriptomic study provides the evidence of the potential route of SARS-CoV-2 in the digestive system along with the respiratory tract. It may have a significant impact to health policy setting regarding the prevention of SARS-CoV-2 infection. In addition, our study provides a novel method to guide identification of prime cell types of a virus by the coexpression pattern analysis of single-cell sequencing data. Reference & Source information: https://gut.bmj.com/ Read More on :

Investigate the possible effect of chloroquine/hydroxychloroquine against SARS-CoV-2 since this molecule was previously described as a potent inhibitor of most coronaviruses, including SARS-CoV-1. Preliminary trials of chloroquine repurposing in the treatment of COVID-19 in China have been encouraging, leading to several new trials. Here we discuss the possible mechanisms of chloroquine interference with the SARS-CoV-2 replication cycle. Conclusion Chloroquine has been shown to be capable of inhibiting the in vitro replication of several coronaviruses. Recent publications support the hypothesis that chloroquine can improve the clinical outcome of patients infected by SARS-CoV-2. The multiple molecular mechanisms by which chloroquine can achieve such results remain to be further explored. Since SARS-CoV-2 was found a few days ago to utilise the same cell surface receptor ACE2 (expressed in lung, heart, kidney and intestine) as SARS-CoV-1 [85,86] (Table 1), it may be hypothesised that chloroquine also interferes with ACE2 receptor glycosylation thus preventing SARS-CoV-2 binding to target cells. Wang and Cheng reported that SARS-CoV and MERS-CoV upregulate the expression of ACE2 in lung tissue, a process that could accelerate their replication and spread [85]. Although the binding of SARS-CoV to sialic acids has not been reported so far (it is expected that Betacoronavirus adaptation to humans involves progressive loss of hemagglutinin-esterase lectin activity), if SARS-CoV-2 like other coronaviruses targets sialic acids on some cell subtypes, this interaction will be affected by chloroquine treatment [87,88]. Today, preliminary data indicate that chloroquine interferes with SARS-CoV-2 attempts to acidify the lysosomes and presumably inhibits cathepsins, which require a low pH for optimal cleavage of SARS-CoV-2 spike protein [89], a prerequisite to the formation of the autophagosome [49]. Obviously, it can be hypothesised that SARS-CoV-2 molecular crosstalk with its target cell can be altered by chloroquine through inhibition of kinases such as MAPK. Chloroquine could also interfere with proteolytic processing of the M protein and alter virion assembly and budding (Fig. 1). Finally, in COVID-19 disease this drug could act indirectly through reducing the production of pro-inflammatory cytokines and/or by activating anti-SARS-CoV-2 CD8+ T-cells. Reference & Source information: https://www.sciencedirect.com/ Read more on:

As one would expect of a newly characterized disease, much knowledge about the microbiology, pathogenesis, natural history, and epidemiology of SARS remains to be discovered. For example, scientists have not yet identified the animal source of the infectious agent and have not determined whether a persistent animal reservoir of the infectious agent exists. It is also unclear whether SARS, like influenza, is a seasonal disease that would have receded on its own. Along the same lines, it remains to be seen whether SARS will reemerge on a seasonal basis, and if so, how virulent future manifestations of SCoV will be. These and other unanswered scientific questions, listed in , were a prominent theme of workshop presentations and discussions. Answers to these questions would certainly advance the world’s ability to predict and prepare for a resurgence of SARS. https://www.ncbi.nlm.nih.gov/books/NBK92490/

The current practice for diagnosis of COVID-19, based on SARS-CoV-2 PCR testing of pharyngeal or respiratory specimens in a symptomatic patient at high epidemiologic risk, likely underestimates the true prevalence of infection. Serologic methods can more accurately estimate the disease burden by detecting infections missed by the limited testing performed to date. We describe the validation of a coronavirus antigen microarray containing immunologically significant antigens from SARS-CoV-2, in addition to SARS-CoV, MERS-CoV, common human coronavirus strains, and other common respiratory viruses. A comparison of antibody profiles detected on the array from control sera collected prior to the SARS-CoV-2 pandemic versus convalescent blood specimens from virologically confirmed COVID-19 cases demonstrates near-complete discrimination of these two groups, with improved performance from the use of antigen combinations that include both spike protein and nucleoprotein. This array can be used as a diagnostic tool, as an epidemiologic tool to more accurately estimate the disease burden of COVID-19, and as a research tool to correlate antibody responses with clinical outcome. The antibody profiles of naïve individuals include high IgG reactivity to common cold coronaviruses with low-level cross-reactivity with S2 domains from SARS-CoV-2 and other epidemic coronaviruses, which is not surprising given the high degree of sequence homology and previously observed serologic cross-reactivity15 between S2 domains of betacoronaviruses, a group that includes SARS-CoV-2, SARS-CoV, MERS, and common cold coronaviruses HKU1 and OC43. This low-level cross-reactivity occurs in approximately 7% of unexposed individuals which leads to hypotheses regarding whether these individuals differ in COVID-19 susceptibility and outcomes. However, naïve individuals do not show cross-reactivity to other SARS-CoV-2 antigens. Even for the nucleocapsid protein, which also has high sequence homology between betacoronaviruses, cross-reactivity is only seen between SARS-CoV-2 and SARS-CoV and not with MERS-CoV or common cold coronaviruses. In addition, the quantitative difference between high antibody reactivity to SARS-CoV-2 S2 in the positive group and low-level antibody cross-reactivity in the negative group is large enough that these antigens still discriminate these groups with high significance. This study also informs antigen selection and design for population surveillance and clinical diagnostic assays and vaccine development. The optimal assay to discriminate SARS-CoV-2 convalescent sera from pre-pandemic sera is a combination of 2 antigens that includes S2 and NP. As an individual antigen, the S2 demonstrates cross-reactivity with negative control sera which leads to low specificity, but this antigen adds predictive power when combined with the more specific NP antigen. The observation that unexposed individuals with antibodies to common cold coronaviruses do not show cross-reactivity to SARS-CoV-2 NP dispels concerns that the high sequence homology of this protein across betacoronaviruses would impair its performance as a diagnostic antigen. The low-level antibody cross-reactivity of a subset of unexposed ndividuals for SARS-CoV-2 spike protein containing S2 domain may not preclude its use as a diagnostic antigen given the large quantitative difference in antibody reactivity between positive and negative groups, but this cross-reactivity may influence response to vaccination with spike protein antigens containing the S2 domain in this subset of individuals. A coronavirus antigen microarray containing a panel of antigens from SARS-CoV-2 in addition to other human coronaviruses was able to reliably distinguish convalescent plasma of PCR-positive COVID-19 cases from negative control sera collected prior to the pandemic. Antigen combinations including both spike protein and nucleoprotein demonstrated improved performance compared to each individual antigen. Reference & Source information: https://www.biorxiv.org Read More on

A novel coronavirus [severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2)] outbreak has caused a global coronavirus disease 2019 (COVID-19) pandemic, resulting in tens of thousands of infections and thousands of deaths worldwide. The RNA-dependent RNA polymerase [(RdRp), also named nsp12] is the central component of coronaviral replication and transcription machinery, and it appears to be a primary target for the antiviral drug remdesivir. We report the cryo–electron microscopy structure of COVID-19 virus full-length nsp12 in complex with cofactors nsp7 and nsp8 at 2.9-angstrom resolution. In addition to the conserved architecture of the polymerase core of the viral polymerase family, nsp12 possesses a newly identified β-hairpin domain at its N terminus. A comparative analysis model shows how remdesivir binds to this polymerase. The structure provides a basis for the design of new antiviral therapeutics that target viral RdRp. Reference & Source information: https://science.sciencemag.org/ Read More on: