ABSTRACT
SARS-CoV-2 infection elicits varying degrees of protective immunity conferred by neutralizing antibodies (nAbs). Here we report the persistence of nAb responses over 12 months after infection despite its decreasing trend noticed from 6 months. The study included sera from 358 individuals who had been infected with SARS-CoV-2 between January and May 2020. Samples were collected at 6 and 12 months after onset. The titers of IgG to the viral nucleocapsid protein (NP) and receptor-binding domain of the spike protein (RBD) were measured by CLEIA. The nAb titer was determined using lentivirus-based pseudovirus or authentic virus. Antibody titers of NP-IgG, RBD-IgG, and nAbs were higher in severe and moderate cases than in mild cases at 12 months after onset. While the nAb levels were likely to confer adequate protection against wild-type viral infection, the neutralization activity to recently circulating variants in some of the mild cases ([~]30%) was undermined, implying the susceptibility of reinfection to the variants of concerns (VOCs). COVID-19 convalescent individuals have robust humoral immunity even at 12 months after infection albeit that the medical history and background of patients could affect the function and dynamics of antibody response to the VOCs.
Subject(s)
COVID-19ABSTRACT
The ongoing COVID-19 pandemic is a major global public health concern. Although rapid point of care testing for detecting viral antigen is important for management the outbreak, none of current antigen detection kits provide a reliable diagnosis due to the lack of a specific monoclonal antibody (mAb) against SARS-CoV-2. In our current study, we produced mAbs exclusively react with SARS-CoV-2 and exhibited no cross-reactivity with other human coronaviruses including SARS-CoV. Molecular modeling revealed that the mAbs bound to epitopes present on the exterior surface of the nucleocapsid, encompassing their scope for detecting SARS-CoV-2 in clinical samples. We further selected the optimal pair of anti-SARS-CoV-2 NP mAbs for designing ELISA and immunochromatographic assay. An integrated bioinformatics analysis revealed that our mAbs could comprehensively detect divergent strains of SARS-CoV-2. Due to the high redundancy and absence of cross-reactivity, our newly developed mAbs would be instrumental for developing reliable diagnosis kits for COVID-19.Funding: This work was supported in part by Japan Agency for Medical Research and Development (AMED, Grant number: JP19fk0108110 and JP20he0522001), and by Health Labour Sciences research grant from The Ministry of Health Labour and Welfare.Conflict of Interest: The authors have no conflicts of interest directly relevant to the content of this article. YY, SK, KS and DA is a current employee of Kanto Chemical Co., Inc.Ethical Approval: This study was approved by the Institutional Review Board of Yokohama City University (IRB No. B200800106), and the protocols used in the study were approved by the ethicscommittee.