Longitudinal monitoring of SARS-CoV-2 spike protein-specific antibody responses in Lower Austria

Abstract

The Lower Austrian Wachau region was an early COVID-19 hotspot of infection. As previously reported, in June 2020, after the first peak of infections, we determined that 8.5% and 9.0% of the participants in Weißenkirchen and surrounding communities in the Wachau region were positive for immunoglobulin G (IgG) and immunoglobulin A (IgA) antibodies against the receptor-binding domain of the spike protein of SARS-CoV-2, respectively. Here, we present novel data obtained eight months later (February 2021) from Weißenkirchen, after the second peak of infection, with 25.0% (138/552) and 23.6% (130/552) of participants that are positive for IgG and IgA, respectively. In participants with previous IgG/IgA positivity (June 2020), we observed a 24% reduction in IgG levels, whereas the IgA levels remained stable in February 2021. This subgroup was further analyzed for SARS-CoV-2 induced T cell activities. Although 76% (34/45) and 76% (34/45) of IgG positive and IgA positive participants, respectively, showed specific T cell activities (upon exposure to SARS-CoV-2 spike protein-derived peptides), those were not significantly correlated with the levels of IgG or IgA. Thus, the analyses of antibodies cannot surrogate the measurement of T cell activities. For a comprehensive view on SARS-CoV-2-triggered immune responses, the measurement of different classes of antibodies should be complemented with the determination of T cell activities.

Fig 1. Immunoglobulin titers measured in June 2020 and February 2021.

Table depicting numbers of participants with above-threshold titers for respective Igs (A). Vertical scatter plots of IgG (B) and IgA (C) titers derived from all participants at two time points, and of IgG (D) and IgA (E) titers from participants who tested positive in June 2020. Plots depicting IgG (F) and IgA (G) titers as in (D,E) but with lines connecting data points of each individual. Statistical analysis was performed using Student’ s t-test (**p < 0.01, ****p < 0.0001).

Fig 2. Venn diagram depicting numbers of participants of the test cohort in February 2021 who had all three parameters (IgA, IgG and IGRA) measured (N = 78).

Fig 3. Correlation of immunoglobulin titers with IGRA response.

Plot of interferon release as a function of IgG (A) and IgA (B) titers derived from serum taken in February 2021.