Single-cell landscape of peripheral immune responses to fatal SFTS

A viral necrosome mediates direct RIPK3 activation to promote inflammatory necroptosis

Necroptosis is an inflammatory programmed cell death pathway triggered by RIPK3 activation through one of the upstream RHIM-domain-containing proteins including RIPK1, TRIF, and ZBP1. Whether necroptosis can be activated independent of the upstream signaling pathways leading to inflammatory pathogenesis remains ambiguous. Here, we revealed a mechanism in which a viral protein mediates direct RIPK3 activation resulting in severe inflammatory pathogenesis in patients. The nonstructural protein NSs of a pathogenic hemorrhagic virus, SFTSV, interacts with the RIPK3 kinase domain and forms biocondensate to promote RIPK3 autophosphorylation and necroptosis activation in an RHIM-independent manner. In parallel, sequestration of RIPK3 within the NSs-RIPK3 condensate inhibited RIPK3-mediated apoptosis and promoted viral replication. Infection with an SFTSV NSs mutant virus not forming NSs condensate triggered pronounced apoptosis resulting in reduced viral replication and decreased fatality in vivo. Blocking SFTSV-triggered necroptosis through depletion of MLKL or treatment with a RIPK3-kinase inhibitor reduced viral inflammatory pathogenesis and fatality in vivo. In contrast, blocking SFTSV-triggered apoptosis through depletion of RIPK3 resulted in enhanced viral replication and increased fatality in vivo. The virus-triggered necroptosis correlated with severe inflammatory pathogenesis and lethality in virus-infected patients. The NSs-RIPK3 condensate may represent a necroptosis activation mechanism that promotes viral pathogenesis.

Metformin as antiviral therapy protects hyperglycemic and diabetic patients

Viral infections disrupt glucose metabolism; however, their impact on disease prognosis in highly pathogenic viruses remains largely unknown. There is an additional need to investigate the antiviral mechanisms of glucose-lowering therapeutics. Here, our multicenter clinical study shows that hyperglycemia and pre-existing diabetes are independent risk factors for mortality in patients infected with severe fever with thrombocytopenia syndrome virus (SFTSV), an emerging and highly pathogenic bunyavirus. SFTSV infection triggers gluconeogenesis, which, in turn, inhibits AMPK activity and subsequent interferon I (IFN-I) responses, thereby facilitating viral replication. In vitro and animal studies further reveal that metformin inhibits SFTSV replication by suppressing autophagy through the AMPK-mTOR pathway, contributing to protection against lethal SFTSV infection in mice. Importantly, our large cohort study demonstrates that metformin reduces viremia and SFTSV-related mortality in patients with hyperglycemia or pre-existing diabetes, contrasting with the disadvantageous effect of insulin. These findings highlight the promising therapeutic potential of metformin in treating viral infections, particularly among individuals with hyperglycemia or diabetes.

IMPORTANCE

Severe fever with thrombocytopenia syndrome virus (SFTSV), an emerging tick-borne bunyavirus, causes severe hemorrhagic fever with a high mortality rate. Previous studies have shown metabolic disturbances, particularly hyperglycemia, in SFTSV-infected individuals. However, the mechanism underlying this metabolic derangement remains unclear, and further investigation is needed to determine whether glucose-lowering therapeutics could be beneficial for SFTSV-infected patients. In this study, our multicenter clinical data show that hyperglycemia and pre-existing diabetes are independent risk factors for mortality in patients with SFTSV infection. Furthermore, we observed that SFTSV infection triggers gluconeogenesis, which promotes viral replication through the regulation of the AMPK-IFN-I signaling pathway. Notably, metformin significantly reduces viremia and SFTSV-related mortality in patients with hyperglycemia or pre-existing diabetes, attributed to its inhibitory effect on autophagy through the AMPK-mTOR pathway. Therefore, our study uncovers the interaction between SFTSV infection and glucose metabolic disorder and highlights the promising therapeutic potential of metformin for treating SFTSV infection.

Endothelial cell-released mitochondrial DNA promotes B cell differentiation and virus replication during severe fever with thrombocytopenia syndrome virus infection

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease acquired through tick bites. We have previously demonstrated the correlation between SFTSV-induced mitochondrial dysfunction and inflammation induction, disease progression, and fatal outcome. In the current study, our clinical observation study establishes a strong correlation between elevated levels of circulating cell-free mtDNA and poor prognosis. In vivo studies further reveal endothelial cells as an important source responsible for releasing mtDNA into circulation, which promotes B cell activation, migration, and differentiation via Toll-like receptor 9 (TLR9). Notably, TLR9 activation enhances B-cell susceptibility to SFTSV infection. These findings suggest that mtDNA released by injured endothelial cells facilitates B cell differentiation and virus replication, emphasizing the significant role of mitochondrial damage within endothelial cells in contributing to the severity of SFTS outcomes.IMPORTANCESevere fever with thrombocytopenia syndrome (SFTS) is a new acute tick-borne infectious disease with a high fatality rate of 10%-50%. There is a strong correlation between SFTSV-induced mitochondrial dysfunction and inflammation induction, disease progression, and fatal outcome. Our research has revealed the crucial role of mtDNA in predicting the prognosis of SFTS and its impact on vascular endothelial injuries as well as B cell differentiation, two previously unexplored features of SFTSV infection. Moreover, mtDNA could activate the TLR9 signal to induce plasmablast differentiation in B cells and promote SFTSV infection. This study provides valuable mechanistic and clinical insights into the adverse outcomes associated with SFTSV infection.

A Single-Cell Atlas Revealed Altered B Cells and Neutrophils Immune Signatures and Inflammatory Responses in SFTSV Infection

Severe fever with thrombocytopenia syndrome virus (SFTSV) presents an emerging public threat due to its high mortality rate and ever-expanding geographic distribution. However, characterization of SFTSV infection pathogenesis and immunological impact at single-cell level remains underexplored. Here, we employ single-cell transcriptome-wide sequencing in peripheral blood mononuclear cells (PBMCs) from hospitalized SFTSV-infected patients to map the immune landscape across acute and convalescent stages of infection. The results reveal significant alterations in immune cell compositions, along with profound disruption in intercellular crosstalk. B cells and neutrophils appear to be the primary target for SFTSV infection besides monocytes, as evidenced by heightened virus-related pathways in these two cell types during the acute phase. In addition, SFTSV infection induces a substantial inflammatory response, which were prominently reflected in monocytes and neutrophils. These data illustrate the complex immune remodeling and inflammatory cascades triggered by SFTSV, with a particular focus on its effects on B cells and neutrophils, bringing novel insights into future therapeutic developments.

Genome-wide CRISPR screening identifies LRP1 as an entry factor for SFTSV

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne disease caused by the SFTS virus (SFTSV), which has high mortality rates and poses a significant threat to public health. To identify potential therapeutic targets against SFTSV, we conduct genome-wide knockout screening, which identifies the previously known host factor CCR2, and reveals prolow-density lipoprotein receptor-related protein 1 (LRP1) as an entry factor for SFTSV. Knockdown or knockout of LRP1 significantly attenuate SFTSV infection in mouse embryonic fibroblasts (MEFs). Additionally, inhibition of LRP1 suppresses SFTSV pseudovirus infection in MEFs, suggesting its role in viral entry. The interaction between the SFTSV glycoprotein Gn and LRP1 via the CLI and CLII domains is revealed by co-IP and surface plasmon resonance (SPR). Moreover, LRP1 antagonists and neutralizing antibodies effectively attenuate SFTSV infection in MEFs. Administration of an LRP1-neutralizing antibody in a lethal male mouse model reduces the viral load, mitigates tissue damage, and improves survival. This study identifies LRP1 as a host entry receptor for SFTSV, providing a target for therapeutic strategy development.

SFTSV NSs interacts with AGO2 to regulate the RNAi pathway for viral replication

RNA interference (RNAi) is a posttranscriptional gene silencing mechanism acting as an antiviral defense in eukaryotes. During viral replication, intermediate double-stranded RNAs are processed into virus-derived small interfering RNAs (vsiRNAs) by the host enzyme, DICER. These vsiRNAs are incorporated into the RNA-induced silencing complex (RISC), where AGO2 cleaves viral genomic RNAs. However, viruses have evolved mechanisms to suppress this pathway. Here, we report that the nonstructural protein (NSs) of severe fever with thrombocytopenia syndrome virus (SFTSV) interacts with RISC to suppress the RNAi pathway. NSs forms a ternary complex by interacting with both DICER and AGO2 of the RNAi pathway. The interaction between NSs and DICER, facilitated by the two RNase III domains of DICER, is disrupted in the absence of AGO2 or the DICER-interacting domain (PIWI) of AGO2, indicating a direct interaction between NSs and AGO2. Functional assays using shRNA- and siRNA-mediated silencing of GFP signal, along with co-localization studies, demonstrated that NSs competes with siRNA to interact with AGO2, thereby abolishing RNAi activity. Mutational analysis identified an NSs-A26 mutant that no longer interacts with AGO2 and is unable to suppress RNAi activity, suggesting that NSs acts as a viral suppressor of RNAi (VSR) for SFTSV. Viral infection led to the generation of vsiRNA and showed higher replication in AGO2-/- cells compared to wild-type (WT) cells, confirming the antiviral role of the RNAi pathway against SFTSV infection. These data suggest that the NSs-AGO2 interaction suppresses RNAi, counteracting the antiviral RNAi pathway, thereby facilitating SFTSV infection and pathogenesis.IMPORTANCERNA interference (RNAi) is the main antiviral defense pathway in plants and insects but is not predominant in mammals. While RNAi's role in countering severe fever with thrombocytopenia syndrome virus (SFTSV) infection has been studied in ticks, its role in humans is unknown. The SFTSV nonstructural protein (NSs) forms inclusion bodies (IBs) in the host, sequestering multiple antiviral proteins and facilitating pathogenesis, contributing to SFTSV's high mortality rate. Our study found that SFTSV NSs directly interacts with AGO2, a key RNAi protein, hindering its function. A novel NSs mutant failed to interact with AGO2 and lost its RNAi suppression ability, highlighting NSs as a viral suppressor of RNAi (VSR). Infection studies confirmed the RNAi pathway's critical role in combating SFTSV infection. This study demonstrates NSs's role in viral infection and suggests potential therapeutic approaches.

Enhancing Sensitivity in Detecting Severe Fever With Thrombocytopenia Syndrome Virus: Development of a Reverse Transcription-Droplet Digital Polymerase Chain Reaction

Severe fever with thrombocytopenia syndrome (SFTS) is a highly fatal disease. Droplet digital polymerase chain reaction (ddPCR) presents unparalleled sensitivity and enables absolute quantification of viral load. In this prospective study, we enrolled 111 patients with SFTS and collected 259 continuous samples. Our findings unveil a robust reverse transcription (RT)-ddPCR method for SFTS with a limit of detection of 2.46 copies/µL (95% CI, 1.50-11.05), surpassing the sensitivity of RT-quantitative polymerase chain reaction at 103.29 copies/µL (95% CI, 79.69-216.35). Longitudinal cohort analysis revealed significantly higher RT-ddPCR detection rates at days 10 to 11, 13 to 14, and ≥15 of the disease course as compared with RT-quantitative polymerase chain reaction (P < .05). Positive RT-ddPCR results were associated with declined platelet and elevated aspartate aminotransferase and lactate dehydrogenase on the same day vs negative RT-ddPCR samples. RT-ddPCR exhibits commendable diagnostic efficacy in SFTS, and it remains detectable in blood samples from patients with an extended disease course. Furthermore, RT-ddPCR correlates with clinical laboratory tests, furnishing valuable reference data for clinical diagnosis.

Two-transcript signature for differentiation and clinical outcomes in severe fever with thrombocytopenia syndrome (SFTS) patients: a double-blind, multicenter, validation study

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with a high mortality rate that is often underdiagnosed due to the limitations of current laboratory testing. Timely diagnosis and early identification of severe cases are crucial to improving patient outcomes and overall survival rates. This study aimed to evaluate the efficacy of two transcripts, IFI44L and PI3, in the early differentiation between SFTS virus (SFTSV) infection and bacterial sepsis, as well as in the prompt identification of severe cases during epidemic seasons. In a prospective study conducted between 1 May 2021 and 30 September 2022, we enrolled 225 patients who presented with acute fever and thrombocytopenia at four hospitals in Shandong Province, China. The two-transcript signature provided a clear distinction between SFTS and bacterial infection, achieving an area under the receiver operating characteristic curve of 0.961 (95% confidence interval [95% CI] 0.916-0.986), outperforming C-reactive protein (0.810 [95% CI 0.738-0.870]) and procalcitonin (0.764 [95% CI 0.687-0.830]). Importantly, the relative expression of the IFI44L gene was significantly elevated in fatal SFTS cases, with an area under the curve (AUC) of 0.820 (95% CI 0.727-0.914), indicating its potential as an early prognostic marker. Additionally, IFI44L and PI3 were identified as potential biomarkers for distinguishing SFTS patients with and without invasive pulmonary aspergillosis, with AUC values of 0.817 and 0.753, respectively. Our findings demonstrate that the two-transcript signature effectively distinguishes SFTSV infection from bacterial sepsis and helps identify high-risk individuals, guiding appropriate treatment during SFTS outbreak.

Severe fever with thrombocytopenia syndrome complicated with aspergillus endocarditis and multiple organ infarctions after glucocorticoid treatment in an immunocompetent man: a case report

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease characterized by leukopenia and thrombocytopenia, and aspergillosis is a common complication in severe cases. Previous studies have reported cases of SFTS complicated with invasive pulmonary aspergillosis (IPA) and central nervous system aspergillosis. Here, we present the first case of an immunocompetent patient with SFTS who progressed to IPA and Aspergillus endocarditis after glucocorticoid treatment, and embolism of the vegetations from the left ventricle led to multiple infarctions in the brain, kidney, and spleen.

CASE PRESENTATION

A 66-year-old male farmer developed altered mental status during SFTS. His consciousness improved during the treatment of glucocorticoids, intravenous immunoglobulin, and ribavirin, but he developed embolisms in the spleen and right kidney, initially attributed to atrial fibrillation, and the anticoagulant agent was not administered due to the high risk of bleeding. Later, He was diagnosed with SFTS-associated IPA (SAPA), for which voriconazole was administered. However, he subsequently experienced a recurrence of altered mental status, accompanied by headache, blindness, and muscle weakness. Brain magnetic resonance imaging (MRI) revealed multiple cerebral embolisms and abscess. The echocardiography showed the vegetations in the left ventricle, suggesting multi-organ embolism caused by infective endocarditis (IE). Aspergillus fumigatus was confirmed through pathology and culture of the excised vegetations. The patient was eventually discharged with improved consciousness and muscle strength, but his vision showed minimal recovery.

CONCLUSION

Clinicians should be wary of aspergillosis in severe patients with SFTS, particularly those receiving glucocorticoid treatment. In patients with SAPA, cerebral aspergillosis and embolic stroke caused by Aspergillus endocarditis should also be considered when mental status alters. Furthermore, the possibility of Aspergillosis in other organs should be considered in high-risk patients.

Atypical Patients With Severe Fever With Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne disease with a high fatality rate. The clinical diagnosis criteria mainly rely on white blood cell (WBC) and platelet (PLT), which, however, are of limited usage in identifying atypical SFTS. A multicenter study was performed in two hospitals from 2011 to 2023. SFTS patients were categorized as atypical or typical based on the clinical diagnosis criteria. Clinical progress and outcomes were compared between the two groups. A total of 2876 laboratory-confirmed SFTS patients were included in this study, 90.54% (2604/2876) of whom exhibited both thrombocytopenia and leukopenia and were defined as typical SFTS patients, while 9.46% (272/2876) were defined as atypical SFTS patients. Patients with typical SFTS were more likely to develop complications (adjusted odds ratio [OR] = 2.09, 95% confidence interval [CI]:1.48-2.92, p < 0.001) and fatal outcomes (adjusted OR = 2.24, 95% CI: 1.37-3.89, p = 0.002) compared to patients with atypical SFTS. Among atypical patients, those with decreased PLT and normal WBC levels (PLT↓ and WBC→) experienced increased complication rates (adjusted OR = 2.76, 95% CI: 1.30-6.05, p < 0.001) compared to those with decreased WBC and normal PLT (WBC↓ and PLT→). In the typical group, 238 patients developed thrombocytopenia earlier than leukocytopenia (defined as the TL group), while 311 subjects developed leukocytopenia earlier than thrombocytopenia (defined as the LT group). Compared to the LT group, patients in the TL group were more likely to develop fatal outcomes (HR = 1.91, 95% CI: 1.04-3.50). These findings highlight the presence of atypical SFTS cases that did not meet the clinical diagnosis criteria. Clinical profiles and outcomes differed between typical and atypical SFTS patients. A less stringent diagnostic criterion than combined thrombocytopenia and leukopenia is suggested for making clinical diagnoses within 7 days of disease onset.

Evolving therapeutic strategies for severe fever with thrombocytopenia syndrome: from past to future

Severe fever with thrombocytopenia syndrome (SFTS) is a hemorrhagic fever caused by Bandavirus dabieense. SFTS was first identified in China in 2009 and has been reported since then in neighboring countries and regions. The clinical manifestations of SFTS include fever, thrombocytopenia, and leukocytopenia and are often accompanied by gastrointestinal symptoms and bleeding. In severe cases, patients experience life-threatening immune damage and cytokine storms. Despite nearly 15 years since its discovery, no effective vaccine has been approved. However, significant progress has been achieved in elucidating the mechanisms of host immune responses, accompanied by the clinical implementation of various therapeutic agents. This article provides a comprehensive review of commonly utilized treatments supported by current clinical evidence. Favipiravir has advantages over ribavirin in terms of viral clearance and prognosis. Conventional immunomodulators like interferon, intravenous immunoglobulin, and glucocorticoids have limited effects and may even worsen conditions, whereas novel immunomodulators such as tocilizumab and ruxolitinib have shown potential for improving prognosis. Prophylactic platelet transfusions neither prevent bleeding nor improve clinical outcomes. Additionally, plasma exchange, calcium channel blockers, and arginine can improve laboratory values and expedite viral clearance. In the future, screening Food and Drug Administration-approved drugs and conducting multiomics analyses may lead to the discovery of new effective therapeutic options.

Host specific sphingomyelin is critical for replication of diverse RNA viruses

Lipids and lipid metabolism play an important role in RNA virus replication, which typically occurs on host cell endomembrane structures in the cytoplasm through mechanisms that are not yet fully identified. We conducted genome-scale CRISPR screening and identified sphingomyelin synthase 1 (SMS1; encoded by SGMS1) as a critical host factor for infection by severe fever with thrombocytopenia syndrome virus (SFTSV). SGMS1 knockout reduced sphingomyelin (SM) (d18:1/16:1) levels, inhibiting SFTSV replication. A helix-turn-helix motif in SFTSV RNA-dependent RNA polymerase (RdRp) directly binds to SM(d18:1/16:1) in Golgi apparatus, which was also observed in SARS-CoV-2 and lymphocytic choriomeningitis virus (LCMV), both showing inhibited replication in SGMS1-KO cells. SM metabolic disturbance is associated with disease severity of viral infections. We designed a novel SMS1 inhibitor that protects mice against lethal SFTSV infection and reduce SARS-CoV-2 replication and pathogenesis. These findings highlight the critical role of SMS1 and SM(d18:1/16:1) in RNA virus replication, suggesting a broad-spectrum antiviral strategy.

Lactate dehydrogenase to albumin ratio (LAR) is a novel predictor of fatal outcome in patients with SFTS: an observational study

Background

Severe fever with thrombocytopenia syndrome (SFTS) is a serious infectious disease. This study explored the prognostic value of lactate dehydrogenase (LDH) to albumin (ALB) ratio (LAR) levels in fatal outcomes of the disease.

Methods

Two-hundred and nine patients with SFTS were enrolled in this study. Based on the prognosis, patients were divided into survival and deceased groups. Laboratory metrics were compared by univariate Cox regression and multivariate Cox regression analyses. The prognostic risk factors for SFTS disease were discussed, and the receiver operator characteristic (ROC) curve and the Kaplan-Meier survival curve were plotted to analyze the predictive value of independent risk factors on disease prognosis.

Results

A total of 209 patients with SFTS, including 152 in the survival group and 57 in the death group, were enrolled. The median age of 209 SFTS patients was 64 years. Three indicators, age, aspartate aminotransferase (AST), and LAR, were identified as predictors of mortality in patients with SFTS. The area under the ROC curve of LAR was the highest (0.835), followed by that of AST (0.794), and age (0.720). The Kaplan-Meier survival curve showed an increased case fatality rate, of >1.4691, in patients with LAR.

Conclusion

Elevated LAR level on admission is an independent risk factor for fatal outcomes in patients with SFTS; this can help healthcare professionals identify patients with SFTS having a high risk of fatal outcomes.

Transcriptome Profiles Characteristics of the Peripheral Immune in Patients with Severe Fever with Thrombocytopenia Syndrome

Purpose

Severe fever with thrombocytopenia syndrome (SFTS) is an acute viral infection disease with a high mortality, but there are no specific effective drugs or vaccines available for use. To develop effective treatment methods, more basic researches are urgently needed to elucidate the response mechanisms of patients.

Patients and Methods

Here, we conducted the transcriptomic analysis of peripheral immunity in 14 SFTS patients, ranging from moderate infection to severe and fatal disease.

Results

The results showed orderly cytokine signaling pathway modulation in moderate patients, cellular immunosuppression in severe patients, and significant dysregulation of the inflammatory response and coagulation dysfunction characteristic of deceased patients. In addition, WGCNA further showed a significant positive correlation between fatal outcomes and B cell and immunoglobulin mediated immune function modules, as well as a significant negative correlation with coagulation function modules.

Conclusion

Overall, our research findings systematically observed potential immune mechanisms underlying clinical symptom heterogeneity and noteworthily revealed multiple signaling pathways leading to coagulation dysfunction in fatal outcomes, not just related to decreased platelet count, which can further elucidate the interaction between viruses and hosts and contribute to clinical treatment.

Adenovirus type 5-expressing Gn induces better protective immunity than Gc against SFTSV infection in mice

Severe fever with thrombocytopenia syndrome (SFTS) is caused by the SFTS virus (SFTSV) with high morbidity and mortality. The major immunodominant region of SFTSV surface glycoprotein (G) remains unclear. In this study, we constructed adenovirus type 5 (Ad5) vectored vaccine candidates expressing different regions of SFTSV G (Gn, Gc and Gn-Gc) and evaluated their immunogenicity and protective efficacy in mice. In wild-type mice, compared with Ad5-Gc or Ad5-Gn-Gc, Ad5-Gn recruited/activated more dendritic cells and B cells in lymph nodes or peripheral blood, causing Th1-/Th2-mediated responses in splenocytes and triggered a greater level of SFTSV-neutralizing antibodies. In IFNAR Ab-treated mice, immunization of Ad5-Gn exhibited better protection against SFTSV challenge than Ad5-Gc or Ad5-Gn-Gc. Furthermore, passive immunization revealed complete protective immunity of Gn-specific serum rather than Gc. Collectively, our data demonstrated that Gn is the immunodominant fragment of SFTSV G and could be a potential candidate for SFTSV vaccine development.

Serum lipidome reveals lipid metabolic dysregulation in severe fever with thrombocytopenia syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a rapidly progressing infectious disease with a high fatality rate caused by a novel bunyavirus (SFTSV). The role of lipids in viral infections is well-documented; however, the specific alterations in lipid metabolism during SFTSV infection remain elusive. This study aims to elucidate the lipid metabolic dysregulations in the early stages of SFTS patients.

METHODS

This study prospectively collected peripheral blood sera from 11 critical SFTS patients, 37 mild SFTS patients, and 23 healthy controls during the early stages of infection for lipidomics analysis. A systematic bioinformatics analysis was conducted from three aspects integrating lipid differential expressions, lipid differential correlations, and lipid-clinical indices correlations to reveal the serum lipid metabolic dysregulation in SFTSV-infected individuals.

RESULTS

Our findings reveal significant lipid metabolic dysregulation in SFTS patients. Specifically, compared to healthy controls, SFTS patients exhibited three distinct modes of lipid differential expression: increased levels of lipids including phosphatidylserine (PS), hexosylceramide (HexCer), and triglycerides (TG); decreased levels of lipids including lysophosphatidylcholine (LPC), acylcarnitine (AcCa), and cholesterol esters (ChE); and lipids showing "dual changes" including phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Finally, based on lipid metabolic pathways and literature analysis, we systematically elucidated the potential mechanisms underlying lipid metabolic dysregulation in the early stage of SFTSV infection.

CONCLUSIONS

Our study presents the first global serum lipidome profile and reveals the lipid metabolic dysregulation patterns in the early stage of SFTSV infection. These findings provide a new basis for the diagnosis, treatment, and further investigation of the disease.

Taurolithocholic acid protects against viral haemorrhagic fever via inhibition of ferroptosis

Bile acids are microbial metabolites that can impact infection of enteric and hepatitis viruses, but their functions during systemic viral infection remain unclear. Here we show that elevated levels of the secondary bile acid taurolithocholic acid (TLCA) are associated with reduced fatality rates and suppressed viraemia in patients infected with severe fever with thrombocytopenia syndrome virus (SFTSV), an emerging tick-borne haemorrhagic fever virus. TLCA inhibits viral replication and mitigates host inflammation during SFTSV infection in vitro, and indirectly suppresses SFTSV-mediated induction of ferroptosis by upregulating fatty acid desaturase 2 via the TGR5-PI3K/AKT-SREBP2 axis. High iron and ferritin serum levels during early infection were correlated with decreased TLCA levels and fatal outcomes in SFTSV-infected patients, indicating potential biomarkers. Furthermore, treatment with either ferroptosis inhibitors or TLCA protected mice from lethal SFTSV infection. Our findings highlight the therapeutic potential of bile acids to treat haemorrhagic fever viral infection.

Recent research advances in the development of Dabie Banda virus vaccines

Severe fever with thrombocytopenia syndrome (SFTS) is a newly identified tick-borne viral hemorrhagic fever caused by Dabie Banda virus (DBV). The virus was first discovered in eastern China in 2009 and is now considered an infectious disease with a mortality rate ranging from 6.3% to 30%. The best strategy for controlling SFTS is to develop effective vaccines. However, no approved vaccines are currently available to prevent this disease, despite the number of extensive and in-depth studies conducted on DBV in the past few years. This review focuses on the structure of DBV and the induced host immune responses which are the fundamental factors in vaccine development, and thoroughly summarizes the current research progress on DBV vaccines. The developing DBV vaccines include protein subunit vaccines, live attenuated vaccines, recombinant virus vector vaccines, and DNA vaccines. At present, almost all candidate vaccines for DBV are in the laboratory development or preclinical stages. There remain challenges in successfully developing clinically approved DBV vaccines.

RVFV virulence factor NSs triggers the mitochondrial MCL-1-BAK axis to activate pathogenic NLRP3 pyroptosis

Infection of Rift Valley fever virus (RVFV), a highly pathogenic mosquito-borne zoonotic virus, triggers severe inflammatory pathogenesis but the underlying mechanism of inflammation activation is currently unclear. Here, we report that the non-structural protein NSs of RVFV triggers mitochondrial damage to activate the NLRP3 inflammasome leading to viral pathogenesis in vivo. It is found that the host transcription inhibition effect of NSs causes rapid down-regulation of myeloid cell leukemia-1(MCL-1), a pro-survival member of the Bcl-2 (B-cell lymphoma protein 2) protein family. MCL-1 down-regulation led to BAK activation in the mitochondria, which triggered mtROS production and release of oxidized mitochondrial DNA (ox-mtDNA) into the cytosol. Cytosolic ox-mtDNA binds and activates the NLRP3 inflammasome triggering NLRP3-GSDMD pyroptosis in RVFV infected cells. A NSs mutant virus (RVFV-NSsRM) that is compromised in inducing transcription inhibition did not trigger MCL-1 down-regulation nor NLRP3-GSDMD pyroptosis. RVFV infection of the Nlrp3-/- mouse model demonstrated that the RVFV-triggered NLRP3 pyroptosis contributed to RVFV inflammatory pathogenesis and fatal infection in vivo. Infection with the RVFV-NSsRM mutant virus similarly showed alleviated inflammatory pathogenesis and reduced fatality rate. Taken together, these results revealed a mechanism by which a virulence factor activates the mitochondrial MCL-1-BAK axis through inducing host transcription inhibition to trigger NLRP3-dependent inflammatory pathogenesis.

Microheterogeneity in the Kinetics and Sex-Specific Response to Type I IFN

The response to type I IFNs involves the rapid induction of prototypical IFN signature genes (ISGs). It is not known whether the tightly controlled ISG expression observed at the cell population level correctly represents the coherent responses of individual cells or whether it masks some heterogeneity in gene modules and/or responding cells. We performed a time-resolved single-cell analysis of the first 3 h after in vivo IFN stimulation in macrophages and CD4+ T and B lymphocytes from mice. All ISGs were generally induced in concert, with no clear cluster of faster- or slower-responding ISGs. Response kinetics differed between cell types: mostly homogeneous for macrophages, but with far more kinetic diversity among B and T lymphocytes, which included a distinct subset of nonresponsive cells. Velocity analysis confirmed the differences between macrophages in which the response progressed throughout the full 3 h, versus B and T lymphocytes in which it was rapidly curtailed by negative feedback and revealed differences in transcription rates between the lineages. In all cell types, female cells responded faster than their male counterparts. The ISG response thus seems to proceed as a homogeneous gene block, but with kinetics that vary between immune cell types and with sex differences that might underlie differential outcomes of viral infections.

Effect of tocilizumab plus corticosteroid on clinical outcome in patients hospitalized with severe fever with thrombocytopenia syndrome: A randomized clinical trial

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging viral hemorrhagic fever with high fatality rates. The blockade of pro-inflammatory cytokines presents a promising therapeutic strategy.

METHODS

We conducted a randomized clinical trial at the 154th hospital, Xinyang, Henan Province. Eligible patients with severe SFTS disease were randomly assigned in a 1:2 ratio to receive either a single intravenous infusion of tocilizumab plus usual care; or usual care only. The primary outcome was the clinical status of death/survival at day 14, while secondary outcomes included improvement from baseline in liver and kidney damage and time required for hospital discharge. The efficacy of tocilizumab plus corticosteroid was compared to those receiving corticosteroid alone. The trial is registered with the Chinese Clinical Trial Registry website (ChiCTR2300076317).

RESULTS

63 eligible patients were assigned to the tocilizumab group and 126 to the control group. The addition of tocilizumab to usual care was associated with a reduced death rate (9.5%) compared to those received only usual care (23.0%), with an adjusted hazard ratio (aHR) of 0.37 (95% confidence interval [CI], 0.15 to 0.91, P = 0.029). Combination therapy of tocilizumab and corticosteroids was associated with a significantly reduced fatality (aHR, 0.21; 95% CI, 0.08 to 0.56; P = 0.002) compared to those receiving corticosteroids alone.

CONCLUSIONS

A significant benefit of reducing fatality in severe SFTS patients was observed by using tocilizumab. A combined therapy of tocilizumab plus corticosteroids was recommended for the therapy of severe SFTS.

N-glycosylation of viral glycoprotein is a novel determinant for the tropism and virulence of highly pathogenic tick-borne bunyaviruses

Severe fever with thrombocytopenia syndrome (SFTS) virus, a tick-borne bunyavirus, causes a severe/fatal disease termed SFTS; however, the viral virulence is not fully understood. The viral non-structural protein, NSs, is the sole known virulence factor. NSs disturbs host innate immune responses and an NSs-mutant SFTS virus causes no disease in an SFTS animal model. The present study reports a novel determinant of viral tropism as well as virulence in animal models, within the glycoprotein (GP) of SFTS virus and an SFTS-related tick-borne bunyavirus. Infection with mutant SFTS viruses lacking the N-linked glycosylation of GP resulted in negligible usage of calcium-dependent lectins in cells, less efficient infection, high susceptibility to a neutralizing antibody, low cytokine production in macrophage-like cells, and reduced virulence in Ifnar-/- mice, when compared with wildtype virus. Three SFTS virus-related bunyaviruses had N-glycosylation motifs at similar positions within their GP and a glycan-deficient mutant of Heartland virus showed in vitro and in vivo phenotypes like those of the SFTS virus. Thus, N-linked glycosylation of viral GP is a novel determinant for the tropism and virulence of SFTS virus and of a related virus. These findings will help us understand the process of severe/fatal diseases caused by tick-borne bunyaviruses.

Dynamic immune status analysis of peripheral blood mononuclear cells in patients with Klebsiella pneumoniae bloodstream infection sepsis using single-cell RNA sequencing

Background

Klebsiella pneumoniae is a common Gram-negative bacterium. Blood infection caused by K. pneumoniae is one of the most common causes of human sepsis, which seriously threatens the life of patients. The immune status of peripheral blood mononuclear cells (PBMCs) based on single-cell RNA sequencing (scRNA-seq) in acute stage and recovery stage of sepsis caused by K. pneumoniae bloodstream infection has not been studied.

Methods

A total of 13 subjects were included in this study, 3 healthy controls, 7 patients with K. pneumoniae bloodstream infection in the acute stage (4 patients died), and 3 patients in the recovery stage. Peripheral blood of all patients was collected and PBMCs were isolated for scRNA-seq analysis. We studied the changes of PBMCs components, signaling pathways, differential genes, and cytokines in acute and recovery stages.

Results

During K. pneumoniae acute infection we observed a decrease in the proportion of T cells, most probably due to apoptosis and the function of T cell subtypes was disorder. The proportion of monocytes increased in acute stage. Although genes related to their phagocytosis function were upregulated, their antigen presentation capacity-associated genes were downregulated. The expression of IL-1β, IL-18, IFNGR1 and IFNGR2 genes was also increased in monocytes. The proportion of DCs was depleted during the acute stage and did not recover during sepsis recovery. DCs antigen presentation was weakened during the acute stage but recovered fast during the recovery stage. pDCs response to MCP-1 chemokine was weakened, they recovered it quickly during the recovery stage. B cells showed apoptosis both in the acute stage and recovery stage. Their response to complement was weakened, but their antigen presentation function was enhanced. The proportion of NK cells stable during all disease's stages, and the expression of IFN-γ gene was upregulated.

Conclusion

The proportion of PBMCs and their immune functions undergo variations throughout the course of the disease, spanning from the acute stage to recovery. These findings provide new insights into the mechanism of PBMCs immune function during K. pneumoniae bloodstream infection sepsis and recovery and sets the basis for further understanding and treatment.

Ruxolitinib plus standard of care in severe hospitalized adults with severe fever with thrombocytopenia syndrome (SFTS): an exploratory, single-arm trial

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease, and its morbidity and mortality are increasing. At present, there is no specific therapy available. An exacerbated IFN-I response and cytokine storm are related to the mortality of patients with SFTS. Ruxolitinib is a Janus kinase (JAK) 1/2 inhibitor that can block proinflammatory cytokines and inhibit the type I IFN pathway. We aimed to explore the use of ruxolitinib plus standard of care for severe SFTS.

METHODS

We conducted a prospective, single-arm study of severe SFTS. We recruited participants aged 18 years or older who were admitted to the hospital with laboratory-confirmed severe SFTS and whose clinical score exceeded 8 points within 6 days of symptom onset. Participants received oral ruxolitinib (10 mg twice a day) for up to 10 days. The primary endpoint was 28-day overall survival. The secondary endpoints included the proportion of participants who needed intensive care unit (ICU) admission, total cost, changes in neurologic symptoms and clinical laboratory parameters, and adverse events (AEs) within 28 days. A historical control group (HC group, n = 26) who met the upper criteria for inclusion and hospitalized from April 1, 2021, to September 16, 2022, was selected and 1:1 matched for baseline characteristics by propensity score matching.

RESULTS

Between Sep 16, 2022, and Sep 16, 2023, 26 participants were recruited into the ruxolitinib treatment group (RUX group). The 28-day overall mortality was 7.7% in the RUX group and 46.2% in the HC group (P = 0.0017). There was a significantly lower proportion of ICU admissions (15.4% vs 65.4%, p < 0.001) and total hospitalization cost in the RUX group. Substantial improvements in neurologic symptoms, platelet counts, hyperferritinemia, and an absolute decrease in the serum SFTS viral load were observed in all surviving participants. Treatment-related adverse events were developed in 6 patients (23.2%) and worsened in 8 patients (30.8%), and no treatment-related serious adverse events were reported.

CONCLUSIONS

Our findings indicate that ruxolitinib has the potential to increase the likelihood of survival as well as reduce the proportion of ICU hospitalization and being tolerated in severe SFTS. Further trials are needed.

TRAIL REGISTRATION

ChiCTR2200063759, September 16, 2022.

MCP-3 as a prognostic biomarker for severe fever with thrombocytopenia syndrome: a longitudinal cytokine profile study

Introduction

Severe fever with thrombocytopenia syndrome (SFTS) is characterized by a high mortality rate and is associated with immune dysregulation. Cytokine storms may play an important role in adverse disease regression, this study aimed to assess the validity of MCP-3 in predicting adverse outcomes in SFTS patients and to investigate the longitudinal cytokine profile in SFTS patients.

Methods

The prospective study was conducted at Yantai Qishan Hospital from May to November 2022. We collected clinical data and serial blood samples during hospitalization, patients with SFTS were divided into survival and non-survival groups based on the clinical prognosis.

Results

The levels of serum 48 cytokines were measured using Luminex assays. Compared to healthy controls, SFTS patients exhibited higher levels of most cytokines. The non-survival group had significantly higher levels of 32 cytokines compared to the survival group. Among these cytokines, MCP-3 was ranked as the most significant variable by the random forest (RF) model in predicting the poor prognosis of SFTS patients. Additionally, we validated the predictive effects of MCP-3 through receiver operating characteristic (ROC) curve analysis with an AUC of 0.882 (95% CI, 0.787-0.978, P <0.001), and the clinical applicability of MCP-3 was assessed favorably based on decision curve analysis (DCA). The Spearman correlation analysis indicated that the level of MCP-3 was positively correlated with ALT, AST, LDH, α-HBDH, APTT, D-dimer, and viral load (P<0.01).

Discussion

For the first time, our study identified and validated that MCP-3 could serve as a meaningful biomarker for predicting the fatal outcome of SFTS patients. The longitudinal cytokine profile analyzed that abnormally increased cytokines were associated with the poor prognosis of SFTS patients. Our study provides new insights into exploring the pathogenesis of cytokines with organ damage and leading to adverse effects.

Antiviral immunity of severe fever with thrombocytopenia syndrome: current understanding and implications for clinical treatment

Dabie Banda virus (DBV), a tick-borne pathogen, was first identified in China in 2009 and causes profound symptoms including fever, leukopenia, thrombocytopenia and multi-organ dysfunction, which is known as severe fever with thrombocytopenia syndrome (SFTS). In the last decade, global incidence and mortality of SFTS increased significantly, especially in East Asia. Though previous studies provide understandings of clinical and immunological characteristics of SFTS development, comprehensive insight of antiviral immunity response is still lacking. Here, we intensively discuss the antiviral immune response after DBV infection by integrating previous ex- and in-vivo studies, including innate and adaptive immune responses, anti-viral immune responses and long-term immune characters. A comprehensive overview of potential immune targets for clinical trials is provided as well. However, development of novel strategies for improving the prognosis of the disease remains on challenge. The current review may shed light on the establishment of immunological interventions for the critical disease SFTS.

Inhibition of SFTSV replication in humanized mice by a subcutaneously administered anti-PD1 nanobody

Severe fever with thrombocytopenia syndrome (SFTS) is a life-threatening disease caused by a novel bunyavirus (SFTSV), mainly transmitted by ticks. With no effective therapies or vaccines available, understanding the disease's mechanisms is crucial. Recent studies found increased expression of programmed cell death-1 (PD-1) on dysfunctional T cells in SFTS patients. However, the role of the PD-1/programmed cell death-ligand 1 (PD-L1) pathway in SFTS progression remains unclear. We investigated PD-1 blockade as a potential therapeutic strategy against SFTSV replication. Our study analyzed clinical samples and performed in vitro experiments, revealing elevated PD-1/PD-L1 expression in various immune cells following SFTSV infection. An anti-PD-1 nanobody, NbP45, effectively inhibited SFTSV infection in peripheral blood mononuclear cells (PBMCs), potentially achieved through the mitigation of apoptosis and the augmentation of T lymphocyte proliferation. Intriguingly, subcutaneous administration of NbP45 showed superior efficacy compared to a licensed anti-PD-1 antibody in an SFTSV-infected humanized mouse model. These findings highlight the involvement of the PD-1/PD-L1 pathway during acute SFTSV infection and suggest its potential as a host target for immunotherapy interventions against SFTSV infection.

A model based on meta-analysis to evaluate poor prognosis of patients with severe fever with thrombocytopenia syndrome

Background

Early identification of risk factors associated with poor prognosis in Severe fever with thrombocytopenia syndrome (SFTS) patients is crucial to improving patient survival.

Method

Retrieve literature related to fatal risk factors in SFTS patients in the database, extract the risk factors and corresponding RRs and 95% CIs, and merge them. Statistically significant factors were included in the model, and stratified and assigned a corresponding score. Finally, a validation cohort from Yantai Qishan Hospital in 2021 was used to verify its predictive ability.

Result

A total of 24 articles were included in the meta-analysis. The model includes six risk factors: age, hemorrhagic manifestations, encephalopathy, Scr and BUN. The analysis of lasso regression and multivariate logistic regression shows that model score is an independent risk factor (OR = 1.032, 95% CI 1.002-1.063, p = 0.034). The model had an area under the curve (AUC) of 0.779 (95% CI 0.669-0.889, P<0.001). The validation cohort was divided into four risk groups with cut-off values. Compared with the low-medium risk group, the mortality rate of high-risk and very high-risk patients was more significant (RR =5.677, 95% CI 4.961-6.496, P<0.001).

Conclusion

The prediction model for the fatal outcome of SFTS patients has shown positive outcomes.Systematic review registration:https://www.crd.york.ac.uk/prospero/ (CRD42023453157).

CCR2 is a host entry receptor for severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne bunyavirus causing a high fatality rate of up to 30%. To date, the receptor mediating SFTSV entry remained uncharacterized, hindering the understanding of disease pathogenesis. Here, C-C motif chemokine receptor 2 (CCR2) was identified as a host receptor for SFTSV based on a genome-wide CRISPR-Cas9 screen. Knockout of CCR2 substantially reduced viral binding and infection. CCR2 enhanced SFTSV binding through direct binding to SFTSV glycoprotein N (Gn), which is mediated by its N-terminal extracellular domain. Depletion of CCR2 in C57BL/6J mouse model attenuated SFTSV replication and pathogenesis. The peripheral blood primary monocytes from elderly individuals or subjects with underlying diabetes mellitus showed higher CCR2 surface expression and supported stronger binding and replication of SFTSV. Together, these data indicate that CCR2 is a host entry receptor for SFTSV infection and a novel target for developing anti-SFTSV therapeutics.

Dabie bandavirus infection induces macrophagic pyroptosis and this process is attenuated by platelets

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infection with a high mortality rate in humans, which is caused by Dabie bandavirus (DBV), formerly known as SFTS virus. Clinical manifestations of SFTS are characterized by high fever, thrombocytopenia, leukopenia, hemorrhage, gastrointestinal symptoms, myalgia and local lymph node enlargement with up to 30% case fatality rates in human. Macrophage depletion in secondary lymphoid organs have important roles in the pathogenic process of fatal SFTS, but its exact cell death mechanism remains largely unknown. Here, we showed for the first time that DBV infection induced macrophagic pyroptosis, as evidenced by swollen cells, pore-forming structures, accumulation of gasdermin D N-terminal (GSDMD-NT) as well as the release of lactate dehydrogenase (LDH) and IL-1β in human macrophages. In addition to the upregulation of pyronecrosis genes, the expressions of pyroptosis-related proteins (GSDMD, caspase-1 and IL-1β) were also elevated. To be noted, platelets were found to play a protective role in DBV-derived pyroptosis. Transcriptome analysis and in vitro studies demonstrated that platelets significantly reduced the gene expressions and protein production of pro-pyroptotic markers and inflammatory cytokines in macrophages, whereas platelets conferred a propagation advantage for DBV. Collectively, this study demonstrates a novel mechanism by which DBV invasion triggers pyroptosis as a host defense to remove replication niches in human macrophages and platelets provide an additional layer to reduce cellular death. These findings may have important implications to the pathogenesis of lethal DBV, and provide new ideas for developing novel therapeutics to combat its infection.

COVID-19 Disease in Pediatric Solid Organ Transplantation from Alpha to Omicron: A High Monocyte Count in the Preceding Three Months Portends a Risk for Severe Disease

IMPORTANCE

Planning for future resurgences in SARS-CoV-2 infection is necessary for providers who care for immunocompromised patients.

OBJECTIVE

to determine factors associated with COVID-19 disease severity in immunosuppressed children.

DESIGN

a case series of children with solid organ transplants diagnosed with SARS-CoV-2 infection between 15 March 2020 and 31 March 2023.

SETTING

a single pediatric transplant center.

PARTICIPANTS

all children with a composite transplant (liver, pancreas, intestine), isolated intestine transplant (IT), isolated liver transplant LT), or simultaneous liver kidney transplant (SLK) with a positive PCR for SARS-CoV-2.

EXPOSURE

SARS-CoV-2 infection.

MAIN OUTCOME AND MEASURES

We hypothesized that children on the most immunosuppression, defined by the number of immunosuppressive medications and usage of steroids, would have the most severe disease course and that differential white blood cell count in the months preceding infection would be associated with likelihood of having severe disease. The hypothesis being tested was formulated during data collection. The primary study outcome measurement was disease severity defined using WHO criteria.

RESULTS

77 children (50 LT, 24 intestine, 3 SLK) were infected with SARS-CoV-2, 57.4 months from transplant (IQR 19.7-87.2). 17% were ≤1 year post transplant at infection. 55% were male, 58% were symptomatic and ~29% had severe disease. A high absolute lymphocyte count at diagnosis decreased the odds of having severe COVID-19 disease (OR 0.29; CI 0.11-0.60; p = 0.004). Conversely, patients with a high absolute monocyte count in the three months preceding infection had increased odds of having severe disease (OR 30.49; CI 1.68-1027.77; p = 0.033). Steroid use, higher tacrolimus level, and number of immunosuppressive medications at infection did not increase the odds of having severe disease.

CONCLUSIONS AND RELEVANCE

The significance of a high monocyte count as predictor of severe disease potentially confirms the importance of monocytic inflammasome-driven inflammation in COVID-19 pathogenesis. Our data do not support reducing immunosuppression in the setting of infection. Our observations may have important ramifications in resource management as vaccine- and infection-induced immunity wanes.

SFTSV infection is associated with transient overproliferation of monoclonal lambda-type plasma cells

The impairment of antibody-mediated immunity is a major factor associated with fatal cases of severe fever with thrombocytopenia syndrome (SFTS). By collating the clinical diagnosis reports of 30 SFTS cases, we discovered the overproliferation of monoclonal plasma cells (MCP cells, CD38⁺cLambda⁺cKappa^-) in bone marrow, which has only been reported previously in multiple myeloma. The ratio of CD38⁺cLambda⁺ versus CD38⁺cKappa⁺ in SFTS cases with MCP cells was significantly higher than that in normal cases. MCP cells presented transient expression in the bone marrow, which was distinctly different from multiple myeloma. Moreover, the SFTS patients with MCP cells had higher clinical severity. Further, the overproliferation of MCP cells was also observed in SFTS virus (SFTSV)-infected mice with lethal infectious doses. Together, SFTSV infection induces transient overproliferation of monoclonal lambda-type plasma cells, which have important implications for the study of SFTSV pathogenesis, prognosis, and the rational development of therapeutics.

The clinical and immunological characteristics in fatal severe fever with thrombocytopenia syndrome virus (SFTSV) infection

OBJECTIVE

This study aimed to make a comprehensive evaluation of peripheral immune profiles for further understanding the immunopathogenesis of severe fever with thrombocytopenia syndrome (SFTS).

METHODS

Forty-seven patients with SFTS virus infection were included, of which 24 were deceased. The percentages, absolute numbers, phenotype of lymphocyte subsets were detected by flow cytometry.

RESULTS

In patients with SFTS, the numbers of CD3+T, CD4+T, CD8+T and NKT cells were decreased compared with healthy controls (HCs), accompanied with highly active and exhausted phenotypes for T cells, and overproliferating plasmablasts. High inflammatory status, dysregulation of coagulation and host immune response were more obvious in deceased patients than that of survivors. Higher levels of PCT, IL-6, IL-10, TNF-α, APTT, TT and the occurrence of hemophagocytic lymphohistiocytosis were poor prognostic indicators of SFTS.

CONCLUSIONS

The evaluation of immunological markers in combination with laboratory tests has critical value for selecting prognostic markers and potential treatment target.

Longitudinal analysis of immunocyte responses and inflammatory cytokine profiles in SFTSV-infected rhesus macaques

Severe fever with thrombocytopenia syndrome virus (SFTSV), an emerging bunyavirus, causes severe fever with thrombocytopenia syndrome (SFTS), with a high fatality rate of 20%-30%. At present, however, the pathogenesis of SFTSV remains largely unclear and no specific therapeutics or vaccines against its infection are currently available. Therefore, animal models that can faithfully recapitulate human disease are important to help understand and treat SFTSV infection. Here, we infected seven Chinese rhesus macaques (Macaca mulatta) with SFTSV. Virological and immunological changes were monitored over 28 days post-infection. Results showed that mild symptoms appeared in the macaques, including slight fever, thrombocytopenia, leukocytopenia, increased aspartate aminotransferase (AST) and creatine kinase (CK) in the blood. Viral replication was persistently detectable in lymphoid tissues and bone marrow even after viremia disappeared. Immunocyte detection showed that the number of T cells (mainly CD8⁺ T cells), B cells, natural killer (NK) cells, and monocytes decreased during infection. In detail, effector memory CD8⁺ T cells declined but showed increased activation, while both the number and activation of effector memory CD4⁺ T cells increased significantly. Furthermore, activated memory B cells decreased, while CD80⁺/CD86⁺ B cells and resting memory B cells (CD27⁺CD21⁺) increased significantly. Intermediate monocytes (CD14⁺CD16⁺) increased, while myeloid dendritic cells (mDCs) rather than plasmacytoid dendritic cells (pDCs) markedly declined during early infection. Cytokines, including interleukin-6 (IL-6), interferon-inducible protein-10 (IP-10), and macrophage inflammatory protein 1 (MCP-1), were substantially elevated in blood and were correlated with activated CD4⁺ T cells, B cells, CD16⁺CD56⁺ NK cells, CD14⁺CD16⁺ monocytes during infection. Thus, this study demonstrates that Chinese rhesus macaques infected with SFTSV resemble mild clinical symptoms of human SFTS and provides detailed virological and immunological parameters in macaques for understanding the pathogenesis of SFTSV infection.

CD8+ T cells mediate antiviral response in severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS), which is caused by a novel Bunyavirus, has gradually become a threatening infectious disease in rural areas of Asia. Studies have identified a severe cytokine storm and impaired humoral immune response in SFTS. However, the cellular immune response to SFTS virus (SFTSV) infection remains largely unknown. Here we report that SFTS patients had a cytokine storm accompanied by high levels of chemokines. CD8⁺ T cells in peripheral blood mononuclear cells of SFTS patients exhibited a more activated phenotype and enhanced the antiviral responses. They increased the expression of CD69 and CD25, secreted a higher level of IFN-γ and granzyme, and had a stronger proliferative ability than in healthy controls. In convalescent SFTS patients, the expression of CD69 and CD25 on CD8⁺ T cells was reduced. In addition, we found the ratio and cellularity of CD14⁺ CD16⁺ intermediate monocytes were increased in peripheral blood of SFTS patients. Both the expression of C-X-C motif chemokine ligand 10 (CXCL10) on CD14⁺ CD16⁺ intermediate monocytes and the expression of C-X-C motif chemokine receptor 3 (CXCR3) on CD8⁺ T cells increased dramatically in SFTS patients. Our studies reveal a potential pathway that CD8⁺ T cells rapidly activate and are mostly recruited by intermediate monocytes through CXCL10 in SFTSV infection. Our results may be of clinical relevance for further treatment and discharge instructions in SFTSV infections.

Akkermansia muciniphila protects mice against an emerging tick-borne viral pathogen

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne disease caused by a phlebovirus in the Bunyaviridae family. Infection can result in systemic inflammatory response syndrome with a high fatality rate, and there are currently no treatments or vaccines available. The microbiota has been implicated in host susceptibility to systemic viral infection and disease outcomes, but whether the gut microbiota is implicated in severe fever with thrombocytopenia syndrome virus (SFTSV) infection is unknown. Here, we analysed faecal and serum samples from patients with SFTS using 16S ribosomal RNA-sequencing and untargeted metabolomics, respectively. We found that the gut commensal Akkermansia muciniphila increased in relative abundance over the course of infection and was reduced in samples from deceased patients. Using germ-free or oral antibiotic-treated mice, we found that A. muciniphila produces the β-carboline alkaloid harmaline, which protects against SFTSV infection by suppressing NF-κB-mediated systemic inflammation. Harmaline indirectly modulated the virus-induced inflammatory response by specifically enhancing bile acid-CoA: amino acid N-acyltransferase expression in hepatic cells to increase conjugated primary bile acids, glycochenodeoxycholic acid and taurochenodeoxycholic acid. These bile acids induced transmembrane G-protein coupled receptor-5-dependent anti-inflammatory responses. These results indicate the probiotic potential of A. muciniphila in mitigating SFTSV infection.

Ruxolitinib for severe fever with thrombocytopenia syndrome (SFTS)

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with high mortality. A 73-year-old woman presented to the hospital with fever after being bitten by ticks and was diagnosed with SFTS. Three days after treatment with high-flow oxygen and supportive therapy, her condition deteriorated to septic shock and multiple organ failure. Ruxolitinib, a JAK1/2 inhibitor, was used for the treatment of cytokine release syndrome, and the patient finally recovered. Ruxolitinib and other host-based immunomodulatory drugs may be potential treatments for fatal SFTS.

Effect of genomic variations in severe fever with thrombocytopenia syndrome virus on the disease lethality

Severe fever with thrombocytopenia syndrome virus (SFTSV), an emerging tick-borne bunyavirus, causes mild-to-moderate infection to critical illness or even death in human patients. The effect of virus variations on virulence and related clinical significance is unclear. We prospectively recruited SFTSV-infected patients in a hotspot region of SFTS endemic in China from 2011 to 2020, sequenced whole genome of SFTSV, and assessed the association of virus genomic variants with clinical data, viremia, and inflammatory response. We identified seven viral clades (I-VII) based on phylogenetic characterization of 805 SFTSV genome sequences. A significantly increased case fatality rate (32.9%) was revealed in one unique clade (IV) that possesses a specific co-mutation pattern, compared to other three common clades (I, 16.7%; II, 13.8%; and III, 11.8%). The phenotype-genotype association (hazard ratios ranged 1.327-2.916) was confirmed by multivariate regression adjusting age, sex, and hospitalization delay. We revealed a pronounced inflammation response featured by more production of CXCL9, IL-10, IL-6, IP-10, M-CSF, and IL-1β, in clade IV, which was also related to severe complications. We observed enhanced cytokine expression from clade IV inoculated PBMCs and infected mice. Moreover, the neutralization activity of convalescent serum from patients infected with one specified clade was remarkably reduced to other viral clades. Together, our findings revealed a significant association between one specific viral clade and SFTS fatality, highlighting the need for molecular surveillance for highly lethal strains in endemic regions and unravelled the importance of evaluating cross-clade effect in development of vaccines and therapeutics.

Antiviral Treatment Options for Severe Fever with Thrombocytopenia Syndrome Infections

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne virus that produces severe fever with thrombocytopenia syndrome (SFTS). It is widespread in Japan, South Korea, and Central and Eastern China. The epidemic has developed rapidly through China in recent years. SFTS cases have been reported in 25 provinces in China, mainly distributed in rural areas in mountainous and hilly areas. The infection has a high case fatality rate and no specific treatments or vaccinations. Therefore, early diagnosis and treatment of SFTS infection is important to survival and disease control. In this article, we provide an overview on different aspects of SFTS with an emphasis on management, to explore the current treatment and prophylactic measures further.

Immune escape mechanisms of severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome (SFTS), which is caused by SFTS virus (SFTSV), poses a serious threat to global public health, with high fatalities and an increasing prevalence. As effective therapies and prevention strategies are limited, there is an urgent need to elucidate the pathogenesis of SFTS. SFTSV has evolved several mechanisms to escape from host immunity. In this review, we summarize the mechanisms through which SFTSV escapes host immune responses, including the inhibition of innate immunity and evasion of adaptive immunity. Understanding the pathogenesis of SFTS will aid in the development of new strategies for the treatment of this disease.

Single-cell RNA sequencing of mitotic-arrested prospermatogonia with DAZL::GFP chickens and revealing unique epigenetic reprogramming of chickens

Background

Germ cell mitotic arrest is conserved in many vertebrates, including birds, although the time of entry or exit into quiescence phase differs. Mitotic arrest is essential for the normal differentiation of male germ cells into spermatogonia and accompanies epigenetic reprogramming and meiosis inhibition from embryonic development to post-hatch. However, mitotic arrest was not well studied in chickens because of the difficulty in obtaining pure germ cells from relevant developmental stage.

Results

We performed single-cell RNA sequencing to investigate transcriptional dynamics of male germ cells during mitotic arrest in DAZL::GFP chickens. Using differentially expressed gene analysis and K-means clustering to analyze cells at different developmental stages (E12, E16, and hatch), we found that metabolic and signaling pathways were regulated, and that the epigenome was reprogrammed during mitotic arrest. In particular, we found that histone H3K9 and H3K14 acetylation (by HDAC2) and DNA demethylation (by DNMT3B and HELLS) led to a transcriptionally permissive chromatin state. Furthermore, we found that global DNA demethylation occurred gradually after the onset of mitotic arrest, indicating that the epigenetic-reprogramming schedule of the chicken genome differs from that of the mammalian genome. DNA hypomethylation persisted after hatching, and methylation was slowly re-established 3 weeks later.

Conclusions

We found a unique epigenetic-reprogramming schedule of mitotic-arrested chicken prospermatogonia and prolonged hypomethylation after hatching. This will provide a foundation for understanding the process of germ-cell epigenetic regulation in several species for which this process is not clearly described. Our findings on the biological processes related to sex-specific differentiation of prospermatogonia could help studying germline development in vitro more elaborately.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00712-4.

Revealing the Immune Heterogeneity between Systemic Lupus Erythematosus and Rheumatoid Arthritis Based on Multi-Omics Data Analysis

The pathogenesis of systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) are greatly influenced by different immune cells. Nowadays both T-cell receptor (TCR) and B-cell receptor (BCR) sequencing technology have emerged with the maturity of NGS technology. However, both SLE and RA peripheral blood TCR or BCR repertoire sequencing remains lacking because repertoire sequencing is an expensive assay and consumes valuable tissue samples. This study used computational methods TRUST4 to construct TCR repertoire and BCR repertoire from bulk RNA-seq data of both SLE and RA patients’ peripheral blood and analyzed the clonality and diversity of the immune repertoire between the two diseases. Although the functions of immune cells have been studied, the mechanism is still complicated. Differentially expressed genes in each immune cell type and cell–cell interactions between immune cell clusters have not been covered. In this work, we clustered eight immune cell subsets from original scRNA-seq data and disentangled the characteristic alterations of cell subset proportion under both SLE and RA conditions. The cell–cell communication analysis tool CellChat was also utilized to analyze the influence of MIF family and GALECTIN family cytokines, which were reported to regulate SLE and RA, respectively. Our findings correspond to previous findings that MIF increases in the serum of SLE patients. This work proved that the presence of LGALS9, PTPRC and CD44 in platelets could serve as a clinical indicator of rheumatoid arthritis. Our findings comprehensively illustrate dynamic alterations in immune cells during pathogenesis of SLE and RA. This work identified specific V genes and J genes in TCR and BCR that could be used to expand our understanding of SLE and RA. These findings provide a new insight inti the diagnosis and treatment of the two autoimmune diseases.