As pointed out by the authors, detection and measurement of antibodies generated by SARS-CoV-2 infection should be extended over a longer period of time. Moreover, neutralizing antibody titers still correlated with neutralizing antibody titers at Day 148. 1 Notably, specific antibodies were maintained for at least 5 months, showing a modest decrease over time (particularly at initial titers of 1:960 to ≥1:2880). 2 In addition, the Science paper also examined longevity of IgG antibodies specific for the SARS-CoV-2 S protein in 121 volunteers over a period of around 5 months, separated by three mean time points (30, 82, and 148 days after symptom onset). The data from this study are consistent with those from previous studies on SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV), other coronaviruses with high fatality rates in humans the latter studies show that, virus-specific antibodies, particularly those targeting S proteins and/or RBD fragments, correlate positively with neutralizing antibody titers. Overall, these results indicate that SARS-CoV-2 S-targeting IgG antibodies in SARS-CoV-2-infected patients neutralized authentic SARS-CoV-2 infection, and that the induced IgG antibody titer correlated with the neutralizing antibody titer. Plasma with IgG titers of 1:320, 1:960, or ≥1:2880 corresponded to neutralizing antibody titers of 1:30, 1:75, and 1:550, respectively, and all samples with IgG titers ranging from 1:960 to ≥1:2880 neutralized SARS-CoV-2 infection. They then selected 120 plasma samples with IgG titers varying from non-detectable to ≥1:2880 and examined neutralizing activity against authentic SARS-CoV-2 infection. This figure was prepared using BioRender ( ) and UCSF ChimeraX ( ) SARS-CoV-2 S NTD is colored in orange, RBD in green, and the rest part of S protein in light blue. The following PDB entries are used for structural illustrations: 7C2L (structure of SARS-CoV-2 S in complex with NTD-targeting mAb 4A8), 7K4N (structure of SARS-CoV-2 S in complex with RBD-targeting mAb S2E12), 7KKK (structure of SARS-CoV-2 S in complex with RBD-targeting nanobody Nb6), and 6VW1 (structure of SARS-CoV-2 RBD in complex with human ACE2). RBD-targeting neutralizing mAbs or nanobodies (Nbs), on the other hand, bind directly to SARS-CoV-2 S protein RBD and compete with the cellular receptor, angiotensin converting enzyme 2 (ACE2), resulting in neutralization of viral infection and clearance of the virus. Monoclonal antibodies (mAbs) targeting S protein NTD prevent conformational changes of the S protein that are required for S2-mediated membrane fusion, and hence inhibit viral entry into host cells. b Mode of action of SARS-CoV-2 S-specific neutralizing antibodies. NTD, N-terminal domain RBD, receptor-binding domain FP, fusion peptide HR1 and HR2, heptad region 1 and 2 TM, transmembrane domain IC, intracellular tail. a Schematic structures of SARS-CoV-2 virion and its S protein. SARS-CoV-2 spike (S) protein is a key target for eliciting neutralizing antibodies. In general, antibodies targeting the viral RBD are more potent than the antibodies targeting other regions (such as NTD) of S protein, but they might be less broad in inhibiting multiple virus strains. Thus, understanding the aforementioned mechanism underlying SARS-CoV-2 infection and the mode of action of anti-SARS-CoV-2-S antibodies will help elucidate the kinetics of antibody production in SARS-CoV-2-infected individuals, and facilitate the development of effective countermeasures. By contrast, RBD-targeting antibodies such as mAbs and nanobodies (Nbs) form RBD/mAb or RBD/Nb complexes that inhibit binding of the RBD to ACE2, thereby preventing entry of SARS-CoV-2 into target cells (Fig. For example, NTD-targeting antibodies (monoclonal antibodies (mAbs) or their fragments) bind the NTD to form an NTD/mAb complex, thereby preventing conformational changes in the S protein and blocking membrane fusion and viral entry (Fig. Antibodies targeting various regions of S protein have different mechanisms in inhibiting SARS-CoV-2 infection. Different from other structural proteins, the S protein is a critical target for the induction of antibodies, particularly neutralizing antibodies, specific for SARS-CoV-2. This triggers conformational changes in the S protein, leading to membrane fusion mediated via HR1 and HR2 this process culminates in viral entry into target cells (Fig. SARS-CoV-2 infection undergoes a series of processes: the RBD first binds its receptor, angiotensin converting enzyme 2 (ACE2), to form an RBD/ACE2 complex. 2 It comprises subunits S1 and S2: S1 harbors the N-terminal domain (NTD) and the receptor-binding domain (RBD), whereas S2 harbors heptad repeat 1 (HR1) and HR2 (Fig. ![]() The S protein plays a key role in viral infection and pathogenesis. The SARS-CoV-2 genome encodes spike (S), nucleocapsid, membrane, and envelope structural proteins.
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