Abstract
SARS-CoV-2 is considered a global emergency, resulting in an exacerbated crisis in the health public in the world. Although there are advances in vaccine development, it is still limited for many countries. On the other hand, an immunological response that mediates protective immunity or indicates that predict disease outcome in SARS-CoV-2 infection remains undefined. This work aimed to assess the antibody levels, avidity, and subclasses of IgG to RBD protein, in symptomatic patients with severe and mild forms of COVID-19 in Brazil using an adapted in-house RBD-IgG ELISA. The RBD IgG-ELISA showed 100% of specificity and 94.3% of sensibility on detecting antibodies in the sera of hospitalized patients. Patients who presented severe COVID-19 had higher anti-RBD IgG levels compared to patients with mild disease. Additionally, most patients analyzed displayed low antibody avidity, with 64.4% of the samples of patients who recovered from the disease and 84.6% of those who died in this avidity range. Our data also reveals an increase of IgG1 and IgG3 levels since the 8th day after symptoms onset, while IgG4 levels maintained less detectable during the study period. Surprisingly, patients who died during 8–14 and 15–21 days also showed higher anti-RBD IgG4 levels in comparison with the recovered (P < 0.05), suggesting that some life-threatening patients can elicit IgG4 to RBD antibody response in the first weeks of symptoms onset. Our findings constitute the effort to clarify IgG antibodies' kinetics, avidity, and subclasses against SARS-CoV-2 RBD in symptomatic patients with COVID-19 in Brazil, highlighting the importance of IgG antibody avidity in association with IgG4 detection as tool laboratory in the follow-up of hospitalized patients with more significant potential for life-threatening.
Highlights
COVID-19 (Coronavirus disease 2019), the most recent pandemic caused by severe acute respiratory syndromerelated coronavirus 2 (SARS-CoV-2), resulting in an exacerbated crisis in the health public, declared as a global emergency by World Health Organization (WHO)[1] in March 2020
The S glycoprotein is a transmembrane protein with a molecular weight of 150 kDa that binds to the angiotensin-converting enzyme 2 (ACE2) or other candidate receptors expressed on the host cells surface through receptor binding domain (RBD) presented in the S1 subunit of S p rotein[11,12]
Forty-seven symptomatic patients tested positive for SARS-CoV-2 infection admitted at the Institute of Infectology Emilio Ribas (IIER; São Paulo, Brazil), between March and June 2020, enrolled in this study
Summary
COVID-19 (Coronavirus disease 2019), the most recent pandemic caused by severe acute respiratory syndromerelated coronavirus 2 (SARS-CoV-2), resulting in an exacerbated crisis in the health public, declared as a global emergency by World Health Organization (WHO)[1] in March 2020. Brazil became the epicenter of COVID-19 in June of 2020 and nowadays Brazil has experienced a rise in the number of cases and deaths associated with SARS-CoV-2 infection[5,6] This scenario may impose new challenges to health services shortly, including the requirement for novel rapid diagnostic tools to interrupt the COVID-19 epidemiological c hain[7,8]. RBD domain from SARS-CoV-2 spike protein is highly immunogenic and induces IgG antibody response in acutely and convalescent infected patients, it is considered a potential target for serological a ssays[22,24,25,26,27,28] and vaccine development[10,29,30,31,32]. IgG2 and IgG4 are less detectable in patients s era[41,43,44], suggesting IgG subclasses as an important marker to distinguish disease time-point and, perhaps, disease severity
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