Soroprevalência de anticorpos do vírus SARS-CoV-2 em escolares no município de São Paulo, 2020

OBJECTIVE: To estimate seroprevalence of SARS-CoV-2 antibodies in schoolchildren aged 4 to 14 years living in the city of São Paulo, according to clinical, demographic, epidemiological, and social variables, during the school closure period as a measure against covid-19 spread. METHODS: A serological survey was made in September 2020 with a random sample stratified by school system (municipal public, state public and private) type. A venous blood sample was collected using the Wondfo SARS-CoV-2 Antibody Test (lateral flow method) for detection of total SARS-CoV-2 virus antibodies. Semi-structured questionnaires were applied to collect clinical, demographic, social, and epidemiological data. RESULTS: Seroprevalence of SARS-CoV-2 antibodies in schoolchildren was of 16.6% (95%CI 15.4–17.8). The study found higher seroprevalence in the municipal (18.5%; 95%CI 16.6–20.6) and state (16.2%; 95%CI 14.4–18.2) public school systems compared to the private school system (11.7; 95%CI 10.0–13.7), among black and brown students (18.4%; 95%CI 16.8–20.2) and in the most vulnerable social stratum (18.5 %;95%CI 16.9–20.2). Lower seroprevalence was identified in schoolchildren who reported following the recommended protective measures against covid-19. CONCLUSION: Seroprevalence of SARS-CoV-2 antibodies is found mainly in the most socially vulnerable schoolchildren. This study can contribute to support public policies that reinforce the importance of suspending face-to-face classes and developing strategies aimed at protective measures and monitoring of the serological status of those who have not yet been included in the vaccination schedule.OBJETIVO: Estimar a soroprevalência de anticorpos do vírus SARS-CoV-2 em escolares de quatro a 14 anos de idade residentes no município de São Paulo, segundo variáveis clínicas, demográficas, epidemiológicas e sociais, durante o período de fechamento das escolas como medida de controle da covid-19. MÉTODOS: Realizou-se um inquérito sorológico em setembro de 2020 com amostra aleatória estratificada por tipo de rede de ensino (pública municipal, pública estadual e privada). Foi coletada amostra de sangue venoso utilizando-se o teste de imunoensaio de fluxo lateral da fabricante Wondfo para detecção de anticorpos totais contra o vírus SARS-CoV-2. Aplicaram-se questionários semiestruturados para o levantamento de dados clínicos, demográficos, sociais e epidemiológicos. RESULTADOS: A soroprevalência de anticorpos do vírus SARS-CoV-2 em escolares foi de 16,6% (IC95% 15,4–17,8). O estudo encontrou soroprevalências mais elevadas na rede pública municipal (18,5%; IC95% 16,6–20,6) e estadual (16,2%; IC95% 14,4–18,2) em relação à rede privada (11,7; IC95% 10,0–13,7) e entre escolares da raça/cor preta e parda (18,4%; IC95% 16,8–20,2) e no estrato social mais vulnerável (18,5%; IC95% 16,9–20,2). A pesquisa identificou menores soroprevalências nos escolares que relataram seguir as medidas recomendadas de proteção contra a covid-19. CONCLUSÃO: A soroprevalência de anticorpos contra o vírus SARS-CoV-2 atinge principalmente os escolares socialmente mais vulneráveis. Este estudo pode contribuir para embasar políticas públicas que reforcem a importância da suspensão das aulas presenciais e da necessidade de estratégias de medidas de proteção e acompanhamento do status sorológico daqueles que ainda não foram contemplados no calendário vacinal

Analysis of High Affinity Self-Association by Fluorescence Optical Sedimentation Velocity Analytical Ultracentrifugation of Labeled Proteins: Opportunities and Limitations

<div><p>Sedimentation velocity analytical ultracentrifugation (SV) is a powerful first-principle technique for the study of protein interactions, and allows a rigorous characterization of binding stoichiometry and affinities. A recently introduced commercial fluorescence optical detection system (FDS) permits analysis of high-affinity interactions by SV. However, for most proteins the attachment of an extrinsic fluorophore is an essential prerequisite for analysis by FDS-SV. Using the glutamate receptor GluA2 amino terminal domain as a model system for high-affinity homo-dimerization, we demonstrate how the experimental design and choice of fluorescent label can impact both the observed binding constants as well as the derived hydrodynamic parameter estimates for the monomer and dimer species. Specifically, FAM (5,6-carboxyfluorescein) was found to create different populations of artificially high-affinity and low-affinity dimers, as indicated by both FDS-SV and the kinetics of dimer dissociation studied using a bench-top fluorescence spectrometer and Förster Resonance Energy Transfer. By contrast, Dylight488 labeled GluA2, as well as GluA2 expressed as an EGFP fusion protein, yielded results consistent with estimates for unlabeled GluA2. Our study suggests considerations for the choice of labeling strategies, and highlights experimental designs that exploit specific opportunities of FDS-SV for improving the reliability of the binding isotherm analysis of interacting systems.</p></div

Total sedimentation boundary signals as determined from integration of the <i>c</i>(<i>s</i>) distribution, divided by the loaded protein concentration for GluA2 ATD labeled with Dylight488 at labeling ratio 1.43 (black), FAM at labeling ratio 1.32 (grey), and expressed as an EGFP fusion protein (red).

<p>Data were acquired at a constant PMT voltage of 36% (Dylight488 and FAM), or 38% (EGFP fusion protein) and signals were divided by the gain factor.</p

Dilution series with different fluorescent labels for the GluA2 ATD.

<p>Sedimentation coefficient distributions <i>c</i>(<i>s</i>) (Panels A, C, and E) and the resulting <i>s_w</i> isotherms (Panels B, D, and F) from integration of <i>c</i>(<i>s</i>) for Dylight488-GluA2 ATD (first row), EGFP-GluA2 ATD (second row) and FAM-GluA2 ATD (third row). In the <i>c</i>(<i>s</i>) plots, the distributions were normalized with respect to the loading concentrations indicated. In the isotherm plots, solid circles are the <i>s_w</i> data from the dilution series, and the solid line is the best-fit isotherm with a monomer-dimer model, resulting in best-fit estimates of <i>K_D</i> 20.5 nM (95% CI 15.9 – 26.4), <i>s</i>₁ = 3.52 S (95% CI 3.47 – 3.56), and <i>s</i>₂ = 5.21 S (95% CI 5.15 – 5.28) for Dylight488-GluA2 ATD; <i>K_D</i> = 25.4 nM (95% CI 20.1 – 31.9), <i>s</i>₁ = 4.26 S (95% CI 4.22 – 4.30), and <i>s</i>₂ = 6.44 S (95% CI 6.35 – 6.53) for EGFP-GluA2 ATD; and <i>K_D</i> = 2.3 nM (95% CI 0.99 – 5.0), <i>s</i>₁ = 3.52 S (95% CI 3.22 – 3.72), and <i>s</i>₂ = 5.04 S (95% CI 4.95 – 5.14) for FAM-GluA2 ATD.</p

Dilution series for FAM-GluA2 ATD at different labeling ratios.

<p>Shown are the sedimentation coefficient distribution distributions <i>c</i>(<i>s</i>) (Panels A, C, and E) and the resulting <i>s_w</i> isotherms (Panels B, D, and F) from integration of <i>c</i>(<i>s</i>) for FAM-GluA2 ATD at labeling ratios of 0.68 (first row), 1.05 (second row) and 2.26 (third row). Analogous to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0083439#pone-0083439-g003" target="_blank">Figure 3</a>, in the <i>c</i>(<i>s</i>) plots the distributions were normalized with respect to the loading concentrations indicated, and in the isotherm plots, solid circles are the <i>s_w</i> data from the dilution series, and the solid line is the best-fit isotherm with a monomer-dimer model. This resulted in best-fit values at the labeling ratio of 0.68 (Panel B) of <i>K_D</i> = 3.1 nM (95% CI 0.16 – 30.5), <i>s</i>₁ = 3.43 S (95% CI 2.53 – 3.82), and <i>s</i>₂ = 5.01 S (95% CI 4.60 – 5.51); for the labeling ratio of 1.05 (Panel D) the best-fit values were <i>K_D</i> = 2.6 nM (95% CI 1.1 – 5.9), <i>s</i>₁ = 3.42 S (95% CI 3.27 – 3.56), and <i>s</i>₂ = 5.00 S (95% CI 4.88 – 5.14); and for the labeling ratio of 2.26 (Panel F) the best-fit values were <i>K_D</i> = 4.7 nM (95% CI 3.0 – 7.3), <i>s</i>₁ = 3.57 S (95% CI 3.49 – 3.63), and <i>s</i>₂ = 5.03 S (95% CI 4.96 – 5.11).</p