ABSTRACT
Intranasal vaccination is an attractive strategy for preventing COVID-19 disease as it stimulates the production of multimeric secretory immunoglobulin A (IgAs), the predominant antibody isotype in the mucosal immune system, at the target site of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) entry. Currently, the evaluation of intranasal vaccine efficacy is based on the measurement of polyclonal antibody titers in nasal lavage fluid. However, how individual multimeric secretory IgA protects the mucosa from SARS-CoV-2 infection remains to be elucidated. To understand the precise contribution and molecular nature of multimeric secretory IgAs induced by intranasal vaccines, we developed 99 monoclonal IgAs from nasal mucosa and 114 monoclonal IgAs or IgGs from nonmucosal tissues of mice that were intranasally immunized with the SARS-CoV-2 spike protein. The nonmucosal IgAs exhibited shared origins and both common and unique somatic mutations with the related nasal IgA clones, indicating that the antigen-specific plasma cells in the nonmucosal tissues originated from B cells stimulated at the nasal mucosa. Comparing the spike protein binding reactivity, angiotensin-converting enzyme-2-blocking and SARS-CoV-2 virus neutralization of monomeric and multimeric IgA pairs recognizing different epitopes showed that even nonneutralizing monomeric IgA, which represents 70% of the nasal IgA repertoire, can protect against SARS-CoV-2 infection when expressed as multimeric secretory IgAs. Our investigation is the first to demonstrate the function of nasal IgAs at the monoclonal level, showing that nasal immunization can provide effective immunity against SARS-CoV-2 by inducing multimeric secretory IgAs at the target site of virus infection.
Subject(s)
Coronavirus Infections , Tumor Virus Infections , COVID-19ABSTRACT
Background The rapid and accurate diagnosis of individuals with SARS-CoV-2 infection is an effective way to prevent and control the spread of COVID-19. Although the detection of SARS-CoV‐2 viral RNA by RT‐qPCR is the gold standard for COVID‐19 testing, the use of antigen-detecting rapid diagnostic tests (Ag-RDTs) is emerging as a complementary surveillance tool as Omicron case numbers skyrocket worldwide. However, the results from Ag-RDTs are less accurate for individuals with low viral loads.Methods To develop a more sensitive and accurate Ag-RDT, we screened a total of 90 candidate monoclonal antibodies (mAbs) obtained from guinea pigs immunized with SARS-CoV-2 nucleocapsid protein (CoV-2-NP), and a highly specific epitope-characterized mAb set suitable for detecting the antigen was selected. By applying the mAb set to an automated chemiluminescence flow-through membrane immunoassay device, we developed a highly sensitive and quantitative Ag-RDT, CoV-2-POCube.Results CoV-2-POCube exclusively recognizes a variety of CoV-2-NP variants but not the nucleocapsid proteins of SARS-CoV and other human coronaviruses. CoV-2-POCube achieved a limit of detection sensitivity of 0.20 ~ 0.66 pg/mL of a variety of CoV-2-NP variants, showing over 100 times greater sensitivity than commercially airable SARS-CoV-2 Ag-RDTs.Conclusion CoV-2-POCube is a promising alternative to currently available diagnostic devices for faster clinical decision-making in individuals with suspected COVID-19 in limited-resource settings.