Longitudinal Antibody Dynamics Against Structural Proteins of SARS-CoV-2 in Three COVID-19 Patients Shows Concurrent Development of IgA, IgM, and IgG

Abstract

Background: Dynamics and persistence of neutralizing and non-neutralizing antibodies can give us the knowledge required for serodiagnosis, disease management, and successful vaccine design and development. The disappearance of antibodies, absence of humoral immunity activation, and sporadic reinfection cases emphasize the importance of longitudinal antibody dynamics against variable structural antigens.

Methods: In this study, twenty-five healthy subjects working in a SARS-COV-2 serodiagnostic assay development project were enrolled, and their sign and symptoms were followed up to six months. Three subjects showed COVID-19-like symptoms, and three subjects' antibody dynamics were followed over 120 days by analyzing 516 samples. We have developed 12 different types of in-house ELISAs to observe the kinetics of IgG, IgM, and IgA against four SARS-CoV-2 proteins, namely nucleocapsid, RBD, S1, and whole spike (S1+S2). For the development of these assays, 30-104 pre-pandemic samples were taken as negative controls and 83 RT-qPCR positive samples as positive ones.

Results: All three subjects presented COVID-19-like symptoms twice, with mild symptoms in the first episode were severe in the second, and RT-qPCR confirmed the latter. The initial episode did not culminate with any significant antibody development, while a multifold increase in IgG antibodies characterized the second episode. Interestingly, IgG antibody development concurrent with IgM and IgA and persisted, whereas the latter two weans off rather quickly if appeared.

Conclusion: Antibody kinetics observed in this study can provide a pathway to the successful development of sero-diagnostics and epidemiologists to predict the fate of vaccination currently in place.

Keywords: COVID-19; SARS-CoV-2; antibody dynamics; reinfection; vaccination.

Figure 1

Antibody dynamic of IgA, IgM, and IgG of the three subjects (S01, S02, S03) against SARS-CoV-2 nucleocapsid (N), receptor-binding domain (RBD), N-terminal of spike protein (S1), and spike protein (S1+S2) (A–L). Figure (A, E and I) represents antibody dynamics against nucleocapsid; (B, G, and J) against RBD; (C, G, and K) against S1; whereas (D, H, and L) against S1+S2 in S01, S02, and S03, respectively. IgG’s increase was consistent in all three subjects though there were some dissimilarities in the IgM and IgA antibody titer among them. However, the second exposure led to a multifold increase of IgG against all four SARS-CoV-2 proteins. In contrast, S01 failed to elicit an increase in IgA against SARS-CoV-2 proteins except for a four-fold increase against whole spike protein. Similarly, S03 failed to elicit IgM response against all four antigens.

Figure 2

Antibody expression during symptomatic episode 1 and symptomatic episode 2. IgG expression during symptomatic episode 2 was higher when compared to symptomatic episode 1 in all the subjects studied. The higher levels of antibodies correlate with the severity of the symptoms of the subjects.

Figure 3

Correlation of the anti-RBD antibody compared with anti-NCP, anti-S1, and anti-S1+S2 in S01, S02, and S03. In all the subjects, the increase in anti-RBD correlated with the increase in anti-S1. The first episode in all the graphs is signified with the cluster formed at the lower end of the x- and y-axis.

Figure 4

Probable causes for two episodes of symptoms. The first episode did not present a significant antibody increase. The symptoms presentation during the first episode may be due to cross-reacting coronavirus infection. Medication may have resulted in the suppression of antibody development during the first episode. In addition to it, lack of Th2 cell-mediated immunity activation in the first episode may cause the lack of antibody development. This, in turn, may lead to virus persistence or viral reinfection, resulting in a second episode of the presentation of the symptoms, which may have led to activation of Th2 cell-mediated immunity.