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Protein sensors based on allosteric enzymes responding to target binding with rapid changes in enzymatic activity are potential tools for homogeneous assays. However, a high signal-to-noise ratio (S/N) is difficult to achieve in their construction. A high S/N is critical to discriminate signals from the background, a phenomenon that might largely vary among serum samples from different individuals. Herein, based on the modularized luciferase NanoLuc, we designed a novel biosensor called NanoSwitch. This sensor allows direct detection of antibodies in 1 μl serum in 45 min without washing steps. In the detection of Flag and HA antibodies, NanoSwitches respond to antibodies with S/N ratios of 33-fold and 42-fold, respectively. Further, we constructed a NanoSwitch for detecting SARS-CoV-2-specific antibodies, which showed over 200-fold S/N in serum samples. High S/N was achieved by a new working model, combining the turn-off of the sensor with human serum albumin and turn-on with a specific antibody. Also, we constructed NanoSwitches for detecting antibodies against the core protein of hepatitis C virus (HCV) and gp41 of the human immunodeficiency virus (HIV). Interestingly, these sensors demonstrated a high S/N and good performance in the assays of clinical samples; this was partly attributed to the combination of off-and-on models. In summary, we provide a novel type of protein sensor and a working model that potentially guides new sensor design with better performance., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Objective: Few studies have explored the clinical features in children infected with SARS-CoV-2 and other common respiratory viruses, including respiratory syncytial virus (RSV), Influenza virus (IV), and adenovirus (ADV). Herein, we reported the clinical characteristics and cytokine profiling in children with COVID-19 or other acute respiratory tract infections (ARTI)., Methods: We enrolled 20 hospitalized children confirmed as COVID-19 positive, 58 patients with ARTI, and 20 age and sex-matched healthy children. The clinical information and blood test results were collected. A total of 27 cytokines and chemokines were measured and analyzed., Results: The median age in the COVID-19 positive group was 14.5 years, which was higher than that of the ARTI groups. Around one-third of patients in the COVID-19 group experienced moderate fever, with a peak temperature of 38.27°C. None of the patients displayed wheezing or dyspnea. In addition, patients in the COVID-19 group had lower white blood cells, platelet counts as well as a neutrophil-lymphocyte ratio. Lower serum concentrations of 14 out of 27 cytokines were observed in the COVID-19 group than in healthy individuals. Seven cytokines (IL-1Ra, IL-1β, IL-9, IL-10, TNF-α, MIP-1α, and VEGF) changed serum concentration in COVID-19 compared with other ARTI groups., Conclusion: Patients with COVID-19 were older and showed milder symptoms and a favorable prognosis than ARTI caused by RSV, IV, and ADV. There was a low grade or constrained innate immune reaction in children with mild COVID-19., (© 2021 Wiley Periodicals LLC.)

Background: Coronavirus disease 2019 (COVID-19) is a global pandemic with no licensed vaccine or specific antiviral agents for therapy. Little is known about the longitudinal dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific neutralizing antibodies (NAbs) in patients with COVID-19., Methods: Blood samples (n = 173) were collected from 30 patients with COVID-19 over a 3-month period after symptom onset and analyzed for SARS-CoV-2-specific NAbs using the lentiviral pseudotype assay, coincident with the levels of IgG and proinflammatory cytokines., Results: SARS-CoV-2-specific NAb titers were low for the first 7-10 days after symptom onset and increased after 2-3 weeks. The median peak time for NAbs was 33 days (interquartile range [IQR], 24-59 days) after symptom onset. NAb titers in 93.3% (28/30) of the patients declined gradually over the 3-month study period, with a median decrease of 34.8% (IQR, 19.6-42.4%). NAb titers increased over time in parallel with the rise in immunoglobulin G (IgG) antibody levels, correlating well at week 3 (r = 0.41, P < .05). The NAb titers also demonstrated a significant positive correlation with levels of plasma proinflammatory cytokines, including stem cell factor (SCF), TNF-related apoptosis-inducing ligand (TRAIL), and macrophage colony-stimulating factor (M-CSF)., Conclusions: These data provide useful information regarding dynamic changes in NAbs in patients with COVID-19 during the acute and convalescent phases., (© The Author(s) 2020. Published by Oxford University Press for the Infectious Diseases Society of America.)