ABSTRACT
Given the emergence of SARS-CoV-2 virus as a life-threatening pandemic, identification of immunodominant epitopes of the viral structural proteins, particularly the nucleocapsid (NP) protein and receptor-binding domain (RBD) of spike protein, is important to determine targets for immunotherapy and diagnosis. In this study, epitope screening was performed using a panel of overlapping peptides spanning the entire sequences of the RBD and NP proteins of SARS-CoV-2 in the sera from 66 COVID-19 patients and 23 healthy subjects by enzyme-linked immunosorbent assay (ELISA). Our results showed that while reactivity of patients' sera with reduced recombinant RBD protein was significantly lower than the native form of RBD (P < 0.001), no significant differences were observed for reactivity of patients' sera with reduced and non-reduced NP protein. Pepscan analysis revealed weak to moderate reactivity towards different RBD peptide pools, which was more focused on peptides encompassing amino acids (aa) 181-223 of RBD. NP peptides, however, displayed strong reactivity with a single peptide covering aa 151-170. These findings were confirmed by peptide depletion experiments using both ELISA and western blotting. Altogether, our data suggest involvement of mostly conformational disulfide bond-dependent immunodominant epitopes in RBD-specific antibody response, while the IgG response to NP is dominated by linear epitopes. Identification of dominant immunogenic epitopes in NP and RBD of SARS-CoV-2 could provide important information for the development of passive and active immunotherapy as well as diagnostic tools for the control of COVID-19 infection.
Subject(s)
Antibodies, Viral/immunology , COVID-19/immunology , Immunodominant Epitopes/immunology , Nucleocapsid/immunology , Receptors, Virus/immunology , SARS-CoV-2/immunology , Spike Glycoprotein, Coronavirus/immunology , Aged , Amino Acid Motifs , Antibodies, Viral/blood , COVID-19/virology , Enzyme-Linked Immunosorbent Assay/methods , Female , Humans , Immunodominant Epitopes/chemistry , Iran , Male , Middle Aged , Pandemics , Peptides/immunology , Protein Binding , SARS-CoV-2/chemistry , Spike Glycoprotein, Coronavirus/chemistry , Viral Proteins/immunologyABSTRACT
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may lead to severe disease in some cases, leading to acute respiratory distress syndrome, multi-organ failure, and death. This severe phenotype seems to be associated with a cytokine storm and immune dysregulation. Increased pro-inflammatory cytokines and CD14+CD16+ inflammatory monocytes, lymphopenia, and decreased levels of regulatory T cells are some of the immunological features that are seen in patients with SARS-CoV-2. As the outcome of SARS-CoV-2 is influenced by both viral virulence and dysregulated inflammatory response, a combination therapy approach using antiviral drugs plus anti-inflammatory treatments, such as corticosteroids, monoclonal antibodies against the IL-6 and IL-1ß pathways, and JAK inhibitors are under clinical trials.