The Receptor Binding Domain (RBD) of the SARS-CoV-2 Spike (S) protein is a major target for the antibody response, including Immunoglobulin G. Also, the recombinant SARS-CoV-2 RBD antigen was found to be highly sensitive (98%) and specific (100%) for antibodies induced by SARS-CoVs (i).
The presence of antibodies against a SARS-CoV-2 RBD pathogen in blood indicates an adaptive immune response to SARS-CoV-2 due to vaccination or prior infection. After exposure to pathogen, the anti-RBD IgG levels start gradually rising to reach their maximum within the period of 3–4 weeks (ii). As a result of vaccination, the antibodies can be detected from one week after the first dose of vaccination and start to decrease after 25 days (iii).
Current SARS-CoV-2 mRNA vaccines, such as Comirnaty (Pfizer-BioNTech) (iv) and Moderna (v) are based on SARS-CoV-2 S protein vector, which contains RBD. Thus, these vaccines trigger the immune system to produce antibodies against SARS-CoV-2 RBD. Antibodies against SARS-CoV-2 RBD are also formed as a result of native SARS-CoV-2 infection.
(i) Premkumar L. et al. 2020. The receptor binding domain of the viral spike protein is an immunodominant and highly specific target of antibodies in SARS-CoV-2 patients. Sci Immunol. 5: eabc8413.
(ii) Peng Z. et al. 2020. A pneumonia outbreak associated with a new coronavirus of probable bat origin. Nature 579;270–273.
(iii) Pang, N.YL. et al. 2021. Understanding neutralising antibodies against SARS- CoV-2 and their implications in clinical practice. Military Medical Research 8.
(iv) WHO, World Health Organization. 2020.Transmission of SARS-CoV-2. https://www.who.int/news-room/commentaries/detail/transmission-of-sars-cov-2-implications-for-infection-prevention-precautions.
(v) (WHO, World Health Organization. 2021. COVID-19 vaccines. https://www.who.int/emergencies/diseases/novel-coronavirus-2019/covid-19-vaccines.
