Antibodies to the Spike Protein Receptor-Binding Domain of SARS-CoV-2 at 4–13 Months after COVID-19

Abstract

Identification of factors behind the level and duration of persistence of the SARS-CoV-2 antibodies in the blood is assumed to set the direction for studying humoral immunity mechanisms against COVID-19, optimizing the strategy for vaccine use, antibody-based drugs, and epidemiological control of COVID-19. Objective: This study aimed to study the relationship between clinical and demographic characteristics and the level of IgG antibodies to the RBD of SARS-CoV-2 spike protein after COVID-19 in the long term. Residents of the Altai Region of Western Siberia of Russia, Caucasians, aged from 27 to 93 years (median 53.0 years), who recovered from COVID-19 between May 2020 and February 2021 (n = 44) took part in this prospective observational study. The titer of IgG antibodies to the RBD of SARS-CoV-2 spike protein was measured repeatedly in the blood at 4–13 months from the beginning of the clinical manifestation of COVID-19 via the method of enzyme-linked immunosorbent assay. The antibody titer positively correlated with age (p = 0.013) and COVID-19 pneumonia (p = 0.002) at 20–40 and 20–24 weeks from the onset of COVID-19 symptoms, respectively. Age was positively associated with antibody titer regardless of history of COVID-19 pneumonia (beta regression coefficient p = 0.009). The antibody titer decreased in 15 (34.1%) patients, increased in 10 (22.7%) patients, and did not change in 19 (43.2%) patients from the baseline to 48–49 weeks from the onset of COVID-19 symptoms, with seropositivity persisting in all patients. Age and COVID-19 pneumonia are possibly associated with higher IgG antibodies to the spike protein RBD of SARS-CoV-2 following COVID-19 in the long term. Divergent trends of anti-RBD IgG levels in adults illustrate inter-individual differences at 4–13 months from the onset of COVID-19 symptoms.

Natural IgG against S-Protein and RBD of SARS-CoV-2 Do Not Bind and Hydrolyze DNA and Are Not Autoimmune

“…The RBD fragment of S-protein was prepared in a CHO-K1 cell line containing the RBD coding fragment of the S-protein coding part of the Wuhan-1 SARS-CoV-2 strain (GenBank: MN908947) with codon-optimization for expression in mammalian cells as in [69][70][71]. The synthesized RBD sequence was cloned into the pVEAL2 transposon plasmid in frame with the N-terminal spike signal sequence (MFVFLVLLPLVSSQC) and the Cterminal 10×His-tag.…”

Catalase Activity of IgGs of Patients Infected with SARS-CoV-2

“…The specific antibodies of COVID-19 patients are anti-S-IgGs and anti-RBD-IgGs. The levels of anti-S-IgGs and anti-RBD-IgGs are considered to be one of the main measured indicators of the level of immunity to SARS-CoV-2 [ 57 , 58 ]. Antibodies to the SARS-CoV-2 RBD of the S-protein inhibit the interaction of the virion with target cells, thereby being able to prevent infection [ 59 ].…”

“…Antibodies to the SARS-CoV-2 RBD of the S-protein inhibit the interaction of the virion with target cells, thereby being able to prevent infection [ 59 ]. These factors determined the choice of the RBD S-protein as a priority target for vaccines against COVID-19 [ 57 ]. Despite the physiological importance of anti-S-IgGs and anti- RBD-IgGs, the plasma content of both COVID-19 and Sputnik V vaccinated patients were quite low: 1.1–1.4% for anti-RBD-IgGs and 0.2–0.6% for other fragments of the S-protein [ 46 ].…”