ABSTRACT
SARS-CoV-2 specific IgG responses play critical roles for patients to recover from COVID-19, in-depth dissecting of the IgG responses on systems level is of great interest. Herein, we adopted a newly developed high-throughput epitope mapping technology (AbMap), analyzed 55 COVID-19 convalescent sera and 226 antibody samples enriched by specific proteins or peptides from these sera. We revealed three areas that are rich of IgG epitopes, two are on Spike protein but outside of RBD, and one is on Nucleocapsid protein. We identified 29 significant epitopes on Spike protein, from two of these significant epitopes, two critical epitope residues were found, i. e., D936 and P1263, which are highly related to the infectivity of SARS-CoV-2 In summary, we provided the first global map of IgG binding epitopes for SARS-CoV-2 at single amino acid resolution. This map will facilitate the precise development of therapeutic antibodies and vaccines. HIGHLIGHTSO_LIA map of SARS-CoV-2 specific IgG binding epitopes at single amino acid resolution C_LIO_LITwo areas outside of RBD that are rich of significant epitopes were identified C_LIO_LIOne area rich of significant epitopes was determined on Nucleocapsid protein C_LIO_LITwo critical epitope residues (D936 and P1263) on Spike protein are highly related to the infectivity of SARS-CoV-2 C_LI
ABSTRACT
ImportanceAsymptomatic COVID-19 infections have a long duration of viral shedding and contribute substantially to disease transmission. However, the missing asymptomatic cases have been significantly overlooked because of imperfect sensitivity of nucleic acid testing. We aimed to investigate the humoral immunity in asymptomatics, which will help us develop serological tests and improve early identification, understand the humoral immunity to COVID-19, and provide more rational control strategies for the pandemic. ObjectiveTo better control the pandemic of COVID-19, dynamics of IgM and IgG responses to 23 proteins of SARS-CoV-2 and neutralizing antibody in asymptomatic COVID-19 infections after exposure time were investigated. Design, setting, and participants63 asymptomatic individuals were screened by RT-qPCR and ELISA for IgM and IgG from 11,776 personnel returning to work, and close contacts with the confirmed cases in different communities of Wuhan by investigation of clusters and tracing infectious sources. 63 healthy contacts with both negative results for NAT and antibodies were selected as negative controls. 51 mild patients without any preexisting conditions were also screened as controls from 1056 patients during hospitalization in Tongji Hospital. A total of 177 participants were enrolled in this study and serial serum samples (n=213) were collected. The research was conducted between 17 February 2020 and 28 April 2020. Serum IgM and IgG profiles of 177 participants were further probed using a SARS-CoV-2 proteome microarray. Neutralizing antibody responses in different population were detected by a pseudotyped virus neutralization assay system. The dynamics of IgM and IgG antibodies and neutralizing antibodies were analyzed with exposure time or symptoms onset. ResultsAsymptomatics were classified into four subgroups based on NAT and serological tests. In particular, only 19% had positive NAT results while approximately 81% detected positive IgM/IgG responses. Comparative SARS-CoV-2 proteome microarray further demonstrated that there was a significantly difference of antibody dynamics responding to S1 or N proteins among three populations, although IgM and IgG profiles could not be used to differentiate them. S1 specific IgM responses were elicited in asymptomatic individuals as early to the seventh day after exposure and peaked on days from 17d to 25d, which might be used as an early diagnostic biomarker and give an additional 36.5% seropositivity. Mild patients produced stronger both S1 specific IgM and neutralizing antibody responses than asymptomatic individuals. Most importantly, S1 specific IgM/IgG responses and the titers of neutralizing antibody in asymptomatic individuals gradually vanished in two months. Conclusions and relevanceOur findings might have important implications for the definition of asymptomatic COVID-19 infections, diagnosis, serological survey, public health and immunization strategies.