SFTSV Infection Induced Interleukin-1ß Secretion Through NLRP3 Inflammasome Activation.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne virus that causes hemorrhagic fever. Previous studies showed that SFTSV-infected patients exhibited elevated levels of pro-inflammatory cytokines like interleukin-1ß (IL-1ß), indicating that SFTSV infection may activate inflammasomes. However, the detailed mechanism remains poorly understood. Herein, we found that SFTSV could stimulate the IL-1ß secretion in the infected human peripheral blood mononuclear cells (PBMCs), human macrophages, and C57/BL6 mice. We demonstrate that the maturation and secretion of IL-1ß during SFTSV infection is mediated by the nucleotide and oligomerization domain, leucine-rich repeat-containing protein family, pyrin-containing domain 3 (NLRP3) inflammasome. This process is dependent on protease caspase-1, a component of the NLRP3 inflammasome complex. For the first time, our study discovered the role of NLRP3 in response to SFTSV infection. This finding may lead to the development of novel drugs to impede the pathogenesis of SFTSV infection.

The Severe Fever with Thrombocytopenia Syndrome Virus NSs Protein Interacts with CDK1 To Induce G2 Cell Cycle Arrest and Positively Regulate Viral Replication.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a newly identified phlebovirus associated with severe hemorrhagic fever in humans. While many viruses subvert the host cell cycle to promote viral growth, it is unknown whether this is a strategy employed by SFTSV. In this study, we investigated how SFTSV manipulates the cell cycle and the effect of the host cell cycle on SFTSV replication. Our results suggest that cells arrest at the G2/M transition following infection with SFTSV. The accumulation of cells at the G2/M transition did not affect virus adsorption and entry but did facilitate viral replication. In addition, we found that SFTSV NSs, a nonstructural protein that forms viroplasm-like structures in the cytoplasm of infected cells and promotes virulence by modulating the interferon response, induces a large number of cells to arrest at the G2/M transition by interacting with CDK1. The interaction between NSs and CDK1, which is inclusion body dependent, inhibits formation and nuclear import of the cyclin B1-CDK1 complex, thereby leading to cell cycle arrest. Expression of a CDK1 loss-of-function mutant reversed the inhibitive effect of NSs on the cell cycle, suggesting that this protein is a potential antiviral target. Our study provides new insight into the role of a specific viral protein in SFTSV replication, indicating that NSs induces G2/M arrest of SFTSV-infected cells, which promotes viral replication.IMPORTANCE Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne pathogen that causes severe hemorrhagic fever. Although SFTSV poses a serious threat to public health and was recently isolated, its pathogenesis remains unclear. In particular, the relationship between SFTSV infection and the host cell cycle has not been described. Here, we show for the first time that both asynchronized and synchronized SFTSV-susceptible cells arrest at the G2/M checkpoint following SFTSV infection and that the accumulation of cells at this checkpoint facilitates viral replication. We also identify a key mechanism underlying SFTSV-induced G2/M arrest, in which SFTSV NSs interacts with CDK1 to inhibit formation and nuclear import of the cyclin B1-CDK1 complex, thus preventing it from regulating cell cycle progression. Our study highlights the key role that NSs plays in SFTSV-induced G2/M arrest.

Serial analysis of cytokine and chemokine profiles and viral load in severe fever with thrombocytopenia syndrome: Case report and review of literature.

RATIONALE: Severe fever with thrombocytopenia syndrome (SFTS) is a recently recognized fatal infectious disease caused by the SFTS virus, and severe cases are complicated by the presence of hemophagocytic lymphohistiocytosis (HLH) associated with a cytokine storm. Herein, we report on serial changes of serum cytokine levels and viral load in a severe case of SFTS. PATIENT CONCERNS: A 63-year-old Japanese woman presented with high-grade fever, abdominal pain, diarrhea, impaired consciousness, leukocytopenia, and thrombocytopenia. DIAGNOSIS: SFTS was diagnosed based on a positive serum test for SFTS virus RNA and electroencephalogram (EEG) findings of encephalopathy. INTERVENTIONS: The patient was treated with supportive therapy, including steroid pulse therapy (intravenous methylprednisolone 1 g/d for 3 days) for HLH and intravenous recombinant thrombomodulin 19200 U/d for 7 days for disseminated intravascular coagulation. OUTCOMES: Treatment for 7 days improved both symptoms and abnormal EEG findings, and SFTS virus RNA disappeared from the serum at day 10 from the onset of symptoms. The serum cytokines and chemokines analysis during the clinical course revealed 2 distinct phases: the acute phase and the recovery phase. The cytokines and chemokines elevated in the acute phase included interleukin (IL)-6, IL-10, interferon (IFN)-α2, IFN-γ, tumor necrosis factor-α, interferon-γ-induced protein-10, and fractalkine, while the IL-1ß, IL-12p40, IL-17, and vascular endothelial growth factor levels were higher in the recovery phase. CONCLUSION: These observations suggest that the cytokines and chemokines elevated in the acute phase may reflect the disease severity resulted in a cytokine storm, while those in the recovery phase may be attributed to T-cell activation and differentiation.

Severe Fever with Thrombocytopenia Syndrome Phlebovirus causes lethal viral hemorrhagic fever in cats.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever caused by the SFTS phlebovirus (SFTSV). SFTS patients were first reported in China, followed by Japan and South Korea. In 2017, cats were diagnosed with SFTS for the first time, suggesting that these animals are susceptible to SFTSV. To confirm whether or not cats were indeed susceptible to SFTSV, animal subjects were experimentally infected with SFTSV. Four of the six cats infected with the SPL010 strain of SFTSV died, all showing similar or more severe symptoms than human SFTS patients, such as a fever, leukocytopenia, thrombocytopenia, weight loss, anorexia, jaundice and depression. High levels of SFTSV RNA loads were detected in the serum, eye swab, saliva, rectal swab and urine, indicating a risk of direct human infection from SFTS-infected animals. Histopathologically, acute necrotizing lymphadenitis and hemophagocytosis were prominent in the lymph nodes and spleen. Severe hemorrhaging was observed throughout the gastrointestinal tract. B cell lineage cells with MUM-1 and CD20, but not Pax-5 in the lesions were predominantly infected with SFTSV. The present study demonstrated that cats were highly susceptible to SFTSV. The risk of direct infection from SFTS-infected cats to humans should therefore be considered.

Identification of the amino acid residue important for fusion of severe fever with thrombocytopenia syndrome virus glycoprotein.

Severe fever with thrombocytopenia syndrome (SFTS) is an infectious disease with a high fatality rate, caused by SFTS virus (SFTSV). Because little is known about the nature of SFTSV, basic studies are required for the developments of vaccines and effective therapies. In the present study, we identified the amino acid residue important for membrane fusion induced by the SFTSV glycoprotein (GP). Syncytium formations were observed in cells expressing the GPs of SFTSV Japanese strain (YG-1 and SPL030). In contrast, no or only weak syncytium formations were induced in cells expressing GP of SFTSV Chinese strain (HB29). The replacement of arginine at amino acid residue 962 with serine in HB29 GP (R962S) induced membrane fusion, while the replacement of serine at residue 962 with arginine in YG1 GP (S962R) did not. These data indicate that serine at residue 962 in the SFTSV-GP is critical for inducing membrane fusion and viral infection.

Interferon-γ-Directed Inhibition of a Novel High-Pathogenic Phlebovirus and Viral Antagonism of the Antiviral Signaling by Targeting STAT1.

Severe fever with thrombocytopenia syndrome (SFTS) is a life-threatening infectious disease caused by a novel phlebovirus, SFTS virus (SFTSV). Currently, there is no vaccine or antiviral available and the viral pathogenesis remains largely unknown. In this study, we demonstrated that SFTSV infection results in substantial production of serum interferon-γ (IFN-γ) in patients and then that IFN-γ in turn exhibits a robust anti-SFTSV activity in cultured cells, indicating the potential role of IFN-γ in anti-SFTSV immune responses. However, the IFN-γ anti-SFTSV efficacy was compromised once viral infection had been established. Consistently, we found that viral nonstructural protein (NSs) expression counteracts IFN-γ signaling. By protein interaction analyses combined with mass spectrometry, we identified the transcription factor of IFN-γ signaling pathway, STAT1, as the cellular target of SFTSV for IFN-γ antagonism. Mechanistically, SFTSV blocks IFN-γ-triggered STAT1 action through (1) NSs-STAT1 interaction-mediated sequestration of STAT1 into viral inclusion bodies and (2) viral infection-induced downregulation of STAT1 protein level. Finally, the efficacy of IFN-γ as an anti-SFTSV drug in vivo was evaluated in a mouse infection model: IFN-γ pretreatment but not posttreatment conferred significant protection to mice against lethal SFTSV infection, confirming IFN-γ's anti-SFTSV effect and viral antagonism against IFN-γ after the infection establishment. These findings present a picture of virus-host arm race and may promote not only the understanding of virus-host interactions and viral pathogenesis but also the development of antiviral therapeutics.

Higher Fatality for Severe Fever with Thrombocytopenia Syndrome Complicated by Hemophagocytic Lymphohistiocytosis.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious zoonosis caused by the SFTS virus. Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening syndrome associated with excessive immune activation. Cytokine storms are often seen in both SFTS and HLH, resulting in rapid disease progression and poor prognosis. The aim of this study was to identify whether SFTS cases complicated by HLH are related to higher rates of mortality. Descriptive analysis of the frequency of clinical and laboratory data, complications, treatment outcomes, and HLH-2004 criteria was performed. Cases presenting with five or more clinical or laboratory findings corresponding to the HLH-2004 diagnostic criteria were defined as SFTS cases complicated by HLH. Eighteen cases of SFTS were identified during a 2-year study period, with a case-fatality proportion of 22.2% (4 among 18 cases, 95% confidence interval 9%-45.2%). SFTS cases complicated by HLH were identified in 33.3% (6 among 18 cases). A mortality rate of 75% (3 among 4 cases) was recorded among SFTS cases complicated by HLH. Although there were no statistically significant differences in outcomes, fatal cases exhibited more frequent correlation with HLH-2004 criteria than non-fatal cases [3/14 (21.4%) vs. 3/4 (75%), p=0.083]. In conclusion, the present study suggests the possibility that SFTS cases complicated by HLH are at higher risk of poor prognosis.

Targeting of severe fever with thrombocytopenia syndrome virus structural proteins to the ERGIC (endoplasmic reticulum Golgi intermediate compartment) and Golgi complex.

Severe fever with thrombocytopenia syndrome phlebovirus (SFTSV) is a newly emerged phlebovirus identified in China, Japan, and South Korea. Phlebovirus glycoproteins (GP) play a key role in targeting viral structural components to the budding compartments in the ER-Golgi intermediate compartment (ERGIC) and Golgi complex. However, the role of SFTSV GP in targeting structural proteins to the ERGIC and Golgi complex remains unresolved. In this study, we show that SFTSV GP plays a significant role in targeting RNA-dependent RNA polymerase (L) and nucleocapsid protein (NP) to the budding sites. Confocal microscopy was used to investigate the subcellular localization of SFTSV structural proteins. In SFTSV-infected cells, GP and L localized to the ER, ERGIC and Golgi complex, whereas NP localized to the ERGIC and Golgi complex. In addition, GP colocalized with L and NP in infected cells. In cells singly transfected with GP, L or NP, GP localized to the same subcellular compartments as in infected cells. However, L or NP alone did not localize to the ER, ERGIC, or Golgi complex. Cotransfection experiments showed that GP altered the localization of L to the ERGIC and Golgi complex but not that of NP. Interestingly, plasmid-expressed NP fused with a hemagglutinin tag localized to the ERGIC and Golgi complex when expressed in SFTSV-infected cells and colocalised with GP, suggesting that GP plays a role in the subcellular localization of L and NP in infected cells. Thus, the SFTSV structural components start to assemble at the ERGIC to Golgi complex. GP is required for transporting L and NP to the ERGIC and Golgi complex. In addition, targeting of NP requires interaction with other factors besides GP.

Kinetics of viral load and cytokines in severe fever with thrombocytopenia syndrome.

BACKGROUND: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease in China, Japan, and Korea, which is characterized by high fever, thrombocytopenia, and high mortality. It is hypothesized that a cytokine storm plays an important role in the pathophysiology of SFTS. However, limited data have been published on the detailed kinetics of the viral load and cytokine profiles throughout the course of this disease. OBJECTIVES: We investigated the patterns of changes in cytokines and viral load in SFTS patients. STUDY DESIGN: During the admission period of patients, RNA was extracted from plasma and quantified by reverse transcription polymerase chain reaction. In addition, cytokine bead arrays were performed for the 18 cytokines and chemokines selected for testing. RESULTS: The median time from admission to the negative conversion of SFTS viremia was 17.0 days. When censored patients were found to be negative for viral load at discharge, the median duration of viral shedding was 13.0 days (95% CI, 5.4-20.6). Interferon (IFN)-α, interleukin (IL)-10, and IFN-γ-induced protein (IP)-10 concentrations significantly increased in the early course of disease and then decreased during the hospital stay. However, the concentrations of tumor necrosis factor-α, IL-1ß, IL-12p40, IL-13, IL-17A, Regulated on Activation and Normally T-cell Expressed and Secreted (RANTES), and vascular endothelial growth factor (VEGF) increased during the late course of disease. Initial IP-10 levels during hospital days 1-4 were the most significantly correlated with initial viral load (r = 0.88, P < .01). CONCLUSION: SFTS viremia persisted until weeks 2-3 and was highly correlated with initial plasma IP-10 levels. In addition, IFN-α, IL-10, and IP-10 were associated with the initial cytokine storm in SFTS.

The amino acid at position 624 in the glycoprotein of SFTSV (severe fever with thrombocytopenia virus) plays a critical role in low-pH-dependent cell fusion activity.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel phlebovirus responsible for causing an emerging zoonotic disease. We previously established subclones from SFTSV strain YG1 based on differences in low-pH-dependent cell fusion activities and found two amino acid substitutions, Y328H and R624W, in the envelope glycoprotein (GP) of high fusion subclones. In this study, we show that transiently expressed GP with the R624W mutation, but not the Y328H mutation, induced cell fusion under acidic conditions. GP possessing either tryptophan, serine, glycine or aspartic acid at position 624 induced cell fusion, whereas GP possessing basic amino acids such as arginine or lysine did not induce cell fusion. These results indicated that the amino acid at position 624 has an important role for inducing low-pH-dependent cell fusion.

Identification of a candidate standard strain of severe fever with thrombocytopenia syndrome virus for vaccine quality control in China using a cross-neutralization assay.

Severe fever with thrombocytopenia syndrome (SFTS) is caused by a phlebovirus of the Bunyaviridae family, which is designated as SFTS virus (SFTSV). To our knowledge, no efficient SFTSV vaccine exists. Here, we report the identification of a standard virus strain for the eight major SFTSV strains circulating in China for use in evaluating the SFTSV vaccine. Rabbits were immunized with the SFTSV strains and the cross-neutralization capacities of SFTSV anti-sera were determined in microculture cytopathic effect (CPE)-inhibition assays. The mean cross-neutralization capacity of the eight SFTSV anti-sera ranged from 62.4 to 142.6%, compared to autologous strains. The HB29 strain demonstrated strong cross-reactivity with heterologous antibodies, and 33 serum samples from SFTS patients efficiently neutralized HB29, suggesting its broad cross-reactivity. In addition, HB29 demonstrated good replication in Vero and MRC-5 cells (8.0 and 6.0 lg 50% cell culture-infectious dose/mL, respectively) and significant CPE, which satisfied the requirements for a standard virus strain. The HB29 isolate was proven identical to the reported HB29 strain by DNA sequencing, and showed high homology in the S segments with other SFTSV strains (94.8-99.7%). Our results suggest that HB29 may be the best candidate standard strain for use in SFTS vaccine development in China.

Establishment of Subclones of the Severe Fever with Thrombocytopenia Syndrome Virus YG1 Strain Selected Using Low pH-Dependent Cell Fusion Activity.

The first clinical case of the YG1 strain of the severe fever with thrombocytopenia syndrome virus (SFTSV) has been isolated in Japan. We found that only some of the cells underwent low pH-dependent cell fusion, although all of the cells were confirmed to have been infected with the virus. This suggested that the YG1 strain consists of a heterogeneous mixture of related viruses. Here, we established 3 subclones (termed E3, A4, and B7) from the YG1 strain, using the limiting dilution method with the pH-dependent cell fusion activity. Subclone E3 showed weak fusion activity and cytopathic effects (CPE) in Vero E6 cells. The amino acid sequence of E3 was identical to the published sequence for the YG1 strain, and it likely comprises a subpopulation of the YG1 strain. Subclone A4 displayed strong fusion activity under acidic conditions. In contrast, subclone B7 showed strong fusion activity and CPE under neutral and acidic conditions. Two amino acid differences shared between B7 and A4 were found in the envelope glycoproteins. In addition, an amino acid variant of the RNA-dependent RNA polymerase was found only in B7. These subclones will be valuable tools to elucidate cell fusion mechanisms of SFTSV and the relationship between viral proteins and their functions.

Decreased myeloid dendritic cells indicate a poor prognosis in patients with severe fever with thrombocytopenia syndrome.

OBJECTIVES: Severe fever with thrombocytopenia syndrome (SFTS) is a newly emerging infectious disease caused by a novel bunyavirus in which host immune system suppression is thought to be crucial in the development of disease. This study was designed to study the frequencies and activation status of dendritic cells (DCs) at different stages of SFTS and their association with disease severity. METHODS: All confirmed SFTS patients (N=115) were recruited from the Wuhan Union Hospital in 2015; routine laboratory parameters were collected. The frequencies, phenotypes, and subsets of circulating DCs, including myeloid and plasmacytoid dendritic cells (mDCs and pDCs), were analyzed by flow cytometry. Serum levels of interleukin (IL)-6, IL-10, and tumor necrosis factor alpha (TNF-α) were detected by ELISA. The laboratory parameters and other clinical events related to mortality were assessed by multivariate logistic regression analysis and receiver operating characteristic (ROC) curves. RESULTS: The frequency of circulating mDCs, especially from day 9 after disease onset, could serve as a valuable prognostic biomarker for the outcome in SFTS patients (area under the curve=0.929, p<0.0001). In addition, persistent down-regulation of the co-stimulatory molecules CD80/CD86 on the mDCs was observed during the disease process. Moreover, levels of mDCs were inversely correlated with the production of IL-6, IL-10, and TNF-α and with viral load at admission. CONCLUSIONS: The present results indicate that DCs might be functionally impaired in SFTS. A decreased level of circulating mDCs was closely correlated with the severity of SFTS.

Evidence that Processing of the Severe Fever with Thrombocytopenia Syndrome Virus Gn/Gc Polyprotein Is Critical for Viral Infectivity and Requires an Internal Gc Signal Peptide.

The severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging, highly pathogenic bunyavirus against which neither antivirals nor vaccines are available. The SFTSV glycoproteins, Gn and Gc, facilitate viral entry into host cells. Gn and Gc are generated from a precursor protein, Gn/Gc, but it is currently unknown how the precursor is converted into the single proteins and whether this process is required for viral infectivity. Employing a rhabdoviral pseudotyping system, we demonstrate that a predicted signal sequence at the N-terminus of Gc is required for Gn/Gc processing and viral infectivity while potential proprotein convertase cleavage sites in Gc are dispensable. Moreover, we show that expression of Gn or Gc alone is not sufficient for host cell entry while particles bearing both proteins are infectious, and we provide evidence that Gn facilitates Golgi transport and virion incorporation of Gc. Collectively, these results suggest that signal peptidase liberates mature Gc from the Gn/Gc precursor and that this process is essential for viral infectivity and thus constitutes a potential target for antiviral intervention.

The Role of Phlebovirus Glycoproteins in Viral Entry, Assembly and Release.

Bunyaviruses are enveloped viruses with a tripartite RNA genome that can pose a serious threat to animal and human health. Members of the Phlebovirus genus of the family Bunyaviridae are transmitted by mosquitos and ticks to humans and include highly pathogenic agents like Rift Valley fever virus (RVFV) and severe fever with thrombocytopenia syndrome virus (SFTSV) as well as viruses that do not cause disease in humans, like Uukuniemi virus (UUKV). Phleboviruses and other bunyaviruses use their envelope proteins, Gn and Gc, for entry into target cells and for assembly of progeny particles in infected cells. Thus, binding of Gn and Gc to cell surface factors promotes viral attachment and uptake into cells and exposure to endosomal low pH induces Gc-driven fusion of the viral and the vesicle membranes. Moreover, Gn and Gc facilitate virion incorporation of the viral genome via their intracellular domains and Gn and Gc interactions allow the formation of a highly ordered glycoprotein lattice on the virion surface. Studies conducted in the last decade provided important insights into the configuration of phlebovirus Gn and Gc proteins in the viral membrane, the cellular factors used by phleboviruses for entry and the mechanisms employed by phlebovirus Gc proteins for membrane fusion. Here, we will review our knowledge on the glycoprotein biogenesis and the role of Gn and Gc proteins in the phlebovirus replication cycle.

[Inclusion Bodies are Formed in SFTSV-infected Human Macrophages].

The severe fever with thrombocytopenia syndrome virus (SFTSV) is a new member in the genus Phlebovirus of the family Bunyaviridae identified in China. The SFTSV is also the causative pathogen of an emerging infectious disease: severe fever with thrombocytopenia syndrome. Using immunofluorescent staining and confocal microscopy, the intracellular distribution of nucleocapsid protein (NP) in SFTSV-infected THP-1 cells was investigated with serial doses of SFTSV at different times after infection. Transmission electron microscopy was used to observe the ultrafine intracellular structure of SFTSV-infected THP-1 cells at different times after infection. SFTSV NP could form intracellular inclusion bodies in infected THP-1 cells. The association between NP-formed inclusion bodies and virus production was analyzed: the size of the inclusion body formed 3 days after infection was correlated with the viral load in supernatants collected 7 days after infection. These findings suggest that the inclusion bodies formed in SFTSV-infected THP-1 cells could be where the SFTSV uses host-cell proteins and intracellular organelles to produce new viral particles.

Characterization of Glycoprotein-Mediated Entry of Severe Fever with Thrombocytopenia Syndrome Virus.

UNLABELLED: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever with a high case fatality rate caused by SFTS virus (SFTSV). Effective vaccines and specific therapies for SFTS are urgently sought, and investigation into virus-host cell interactions is expected to contribute to the development of antiviral strategies. In this study, we have developed a pseudotype vesicular stomatitis virus (VSV) bearing the unmodified Gn/Gc glycoproteins (GPs) of SFTSV (SFTSVpv). We have analyzed the host cell entry of this pseudotype virus and native SFTSV. Both SFTSVpv and SFTSV exhibited high infectivity in various mammalian cell lines. The use of lysosomotropic agents indicated that virus entry occurred via pH-dependent endocytosis. SFTSVpv and SFTSV infectivity was neutralized by serial dilutions of convalescent-phase patient sera. Entry of SFTSVpv and growth of SFTSV were increased in Raji cells expressing not only the C-type lectin dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) but also DC-SIGN-related (DC-SIGNR) and liver and lymph node sinusoidal endothelial cell C-type lectin (LSECtin). 25-Hydroxycholesterol (25HC), a soluble oxysterol metabolite, inhibited the cell entry of SFTSVpv and the membrane fusion of SFTSV. These results indicate that pH-dependent endocytosis of SFTSVpv and SFTSV is enhanced by attachment to certain C-type lectins. SFTSVpv is an appropriate model for the investigation of SFTSV-GP-mediated cell entry and virus neutralization at lower biosafety levels. Furthermore, 25HC may represent a potential antiviral agent against SFTS. IMPORTANCE: SFTSV is a recently discovered bunyavirus associated with SFTS, a viral hemorrhagic fever with a high case fatality rate endemic to China, South Korea, and Japan. Because little is known about the characteristics of the envelope protein and entry mechanisms of SFTSV, further studies will be required for the development of a vaccine or effective therapies. In this study, we investigated the mechanism of SFTSV cell entry using SFTSVpv and the native virus. SFTSV can grow in nonsusceptible cell lines in the presence of certain C-type lectins. Moreover, 25HC, an oxysterol metabolite, may represent a potential therapeutic inhibitor of SFTSV infection.

Design, antiviral and cytostatic properties of isoxazolidine-containing amonafide analogues.

A novel series of 5-arylcarbamoyl- and 5-arylmethyl-2-methylisoxazolidin-3-yl-3-phosphonates have been synthesized via cycloaddition of N-methyl-C-(diethoxyphosphoryl)nitrone with N-substituted naphthalimide acrylamides and N-allylnaphthalimides. All cis- and trans-isoxazolidine phosphonates obtained herein were assessed for antiviral activity against a broad range of DNA and RNA viruses. Isoxazolidines trans-9d and trans-9f exhibited the highest activity (EC50=8.9µM) toward cytomegalovirus. Compounds cis- and trans-9d as well as cis- and trans-9f were found potent against HSV and Vaccinia viruses (EC50 in the 45-58µM range), whereas isoxazolidines 10a and 10d suppressed replication of Coxsackie B4 and Punta Toro viruses (EC50 in the 45-73µM range). Antiproliferative evaluation of all obtained isoxazolidines revealed the promising activity of cis-9b, cis-9d, trans-9d, cis-9e, trans-9e, cis-9f and trans-9f toward tested cancer cell lines with IC50 in the 1.1-19µM range.

Cytokine and chemokine levels in patients with severe fever with thrombocytopenia syndrome virus.

BACKGROUND: Severe fever with thrombocytopenia syndrome virus (SFTSV), which can cause hemorrhagic fever-like illness, is a newly discovered bunyavirus in China. The pathogenesis of SFTSV infection is poorly understood. However, it has been suggested that immune mechanisms, including cytokines and chemokines, play an important role in disease pathogenesis. In the present study, we investigated host cytokine and chemokine profiles in serum samples of patients with SFTSV infection from Northeast China and explored a possible correlation between cytokine levels and disease severity. METHODS AND PRINCIPAL FINDINGS: Acute phase serum samples from 40 patients, diagnosed with SFTSV infection were included. Patients were divided into two groups--severe or non-severe--based on disease severity. Levels of tumor necrosis factor (TNF)-α, transforming growth factor (TGF)-ß, interleukin-6, interferon (IFN)-γ, IFN- γ-induced protein (IP)-10 and RANTES were measured in the serum samples with commercial ELISAs. Statistical analysis showed that increases in TNF-α, IP-10 and IFN-γ were associated with disease severity. CONCLUSIONS: We suggest that a cytokine-mediated inflammatory response, characterized by cytokine and chemokine production imbalance, might be in part responsible for the disease progression of patients with SFTSV infection.

Characterization of cell-death pathways in Punta Toro virus-induced hepatocyte injury.

Punta Toro virus (PTV; genus Phlebovirus, family Bunyaviridae) causes apoptosis of hepatocytes in vivo in experimentally infected hamsters and in vitro in cultured HepG2 cells. Screening for expression of apoptosis-related genes has shown alterations in the genes for tumour necrosis factor-alpha (TNF-alpha) and the TNF receptor family. This study examined the roles of the TNF receptor-related extrinsic pathway and the Bcl-2 family-associated mitochondrial pathway in PTV-induced cell death. The effects of caspase inhibitors (caspIs) and TNF on cellular viability, virus replication, and morphological and biochemical changes in apoptosis were examined in HepG2 cells at different time points after infection with PTV (Adames strain). The results showed that caspIs dampened the virus-induced reduction in cellular viability, partially suppressed and delayed viral titres and antigen expression, and partially decreased the expression of apoptotic genes, caspase activities and DNA fragmentation. TNF treatment further decreased cellular viability after PTV infection and increased the level of apoptosis, whilst caspIs partially inhibited these effects. These findings indicate that TNF, caspase-8 and caspase-9 contribute to PTV-induced hepatocytic apoptosis and that additional mediators are probably also involved in this process. These mediators from different pathways correlated with one another and may be interlinked.