Development of specific antivirals is an urgent unmet need for SARS-coronavirus 2 (SARS-CoV-2) infections. This study focuses on host proteases that proteolytically activate the SARS-CoV-2 spike protein, critical for its fusion after binding to angiotensin-converting enzyme 2 (ACE2), as antiviral targets. We first validated cleavage at a putative furin substrate motif at SARS-CoV-2 spike by expressing it in VeroE6 cells and found prominent syncytium formation. Both cleavage and syncytium were abolished by treatment with furin inhibitors decanoyl-RVKR-chloromethylketone (CMK) and naphthofluorescein but not by transmembrane protease serine 2 (TMPRSS2) inhibitor camostat. CMK and naphthofluorescein showed antiviral effects in SARS-CoV-2-infected cells by decreasing viral production and cytopathic effects. Further analysis revealed that, similar to camostat, CMK blocks virus entry, but it further suppresses the cleavage of spike and syncytium. Naphthofluorescein instead acts primarily by suppressing viral RNA transcription. Therefore, furin inhibitors may become promising antivirals for prevention and treatment of SARS-CoV-2 infections.

SummaryThe elicitation of large amount inflammatory cytokine in serum has been developed as the cause of the plasma leakage in dengue fever (DF)/dengue haemorrhagic fever (DHF) infection. Virus recognition in innate immunity is the key. The Toll-like receptors (TLRs) play an important role in pathogen recognition towards cytokine induction among several viruses; however, the role of TLRs on innate immune recognition against DENV remains unclear. This study aims at the interaction between dengue virus (DENV) and human TLRs at the incipient stage of infection in vitro. Our experiment reveals that stably expression of TLR3, 7, 8 on HEK293 enables IL-8 secretion after DENV recognition. By the model of human monocytic cells U937, we demonstrated the trigger of IL-8 after viral recognition of human monocytic cell is primary through TLR3 following endosomal acidification. Silencing of TLR3 in U937 cells significantly blocks the DENV-induced IL-8 production. Besides, the interaction is further corroborated by colocalization of TLR3 and DENV RNA upon DENV internalization. Furthermore, in this study we found the expression of TLR3 can mediate strong IFN-a/b release and inhibit DENV viral replication significantly, thus limit the cytopathic effect.

Objective: This study aimed to investigate the clinical characteristics of COVID-19 patients with recurrent SARS-CoV-2 positivity after hospital discharge. Methods: This retrospective study included COVID-19 patients who were readmitted for recurrence of positive SARS-CoV-2 RNA. Univariate and multivariate analyses were performed to assess the risk factors associated to the duration of recurrent RNA positivity. Results: Among the 287 discharged COVID-19 patients, 33 (11.5%) patients with recurrent PCR positivity were included. Among these patients, 21 (63.7%) patients were female, their mean age was 48.7 (±19.7) years old. 22 (66.7%) patients were asymptomatic. The following clinical features were presented in other patients: cough, fatigue, sore throat, fever and expectoration. The chest CT ndings revealed that 8 (24.2%) patients were characterized by deterioration compared to the previous results. The median duration of recurrent RNA positivity was 9.0 days (IQR, 6.0, 15.0). We found that increased serum SARS-CoV-2-speci c IgG antibody titer, elevated serum creatinine level, and female gender were the risk factors for the prolonged duration of recurrent RNA positivity. Conclusion: SARS-CoV-2 turned positive in a minority of discharged patients with COVID-19. Most patients experienced mild clinical course. Increased IgG antibody titer, creatinine and female gender were correlated to the prolonged RNA clearance time.