Early Humoral Response Correlates with Disease Severity and Outcomes in COVID-19 Patients

Abstract

The Coronavirus Disease 2019 (COVID-19), caused by SARS-CoV-2, continues to spread globally with significantly high morbidity and mortality rates. Antigen-specific responses are of unquestionable value for clinical management of COVID-19 patients. Here, we investigated the kinetics of IgM, IgG against the spike (S) and nucleoproteins (N) proteins and their neutralizing capabilities in hospitalized COVID-19 patients with different disease presentations (i.e., mild, moderate or severe), need for intensive care units (ICU) admission or outcomes (i.e., survival vs death). We show that SARS-CoV-2 specific IgG, IgM and neutralizing antibodies (nAbs) were readily detectable in almost all COVID-19 patients with various clinical presentations. Interestingly, significantly higher levels of nAbs as well as anti-S1 and -N IgG and IgM antibodies were found in patients with more severe symptoms, patients requiring admission to ICU or those with fatal outcomes. More importantly, early after symptoms onset, we found that the levels of anti-N antibodies correlated strongly with disease severity. Collectively, these findings provide new insights into the kinetics of antibody responses in COVID-19 patients with different disease severity.

Keywords: COVID19; SARS-CoV-2; anti-N antibodies; neutralizing antibodies.

Figure 1

Kinetics of SARS-CoV-2 specific antibodies over time based on disease severity. (a) Neutralizing antibodies (nAbs) titers (IC₅₀) and OD values of (b) S1-specific IgG and IgM and (c) N-specific IgG and IgM are plotted against the days post disease onset. The line and the ribbon show the mean expected from a locally estimated scatterplot smoothing (LOESS) regression model with 95% confidence interval. The colored circles indicate disease severity with green circles represent mild cases, blue circles represent moderate cases, and red circles represent severe cases. OD = optical density. Changes in (d) nAbs titers (IC₅₀) and OD values of (e) S1-specific IgG and (f) N-specific IgG for each patient are shown over time. Data from first sample and last collected sample are shown for patients with samples that were at least 7 days apart.

Figure 2

Relationship between S1 and N-specific IgG and IgM and neutralizing titer based on disease severity. (a) Pearson’s correlation between S1-IgG, N-IgG, S1-IgM, and N-IgM and neutralizing titer based on disease severity. Scatter plots were generated using OD values (y-axis) versus IC₅₀ (x-axis) from each individual serum sample with colored circles indicate disease severity. (b) Pearson’s correlation between IgG response against S1 and N proteins and IgM response against S1 and N proteins based on disease severity. Scatter plots were generated using anti-N OD values (y-axis) versus anti-S1 OD values (x-axis) from each individual serum sample with colored circles indicate disease severity. Pearson’s correlation between (c) IgG response against S1 and N proteins and (d) IgM response against S1 and N proteins based on neutralizing titer. Colored circles indicate neutralizing titers (IC₅₀). The dotted lines represent the cut-off of each assay. OD = optical density.

Figure 3

Overall impact of disease severity on antibody responses against SARS-CoV-2. Comparison of neutralizing titer (IC₅₀) and OD values of S1-IgG, N-IgG, S1-IgM, and N-IgM for (a) individuals from the different disease severity categories; (b) individuals who survived or died; and (c) individuals who required intensive care units (ICU) admission or not. Statistical significance was determined using one-way analysis of variance with Tukey post-hoc test in (a) and using Student’s t test in (b) and (c). Mean with SD are shown, and statistical significance is represented as *, p ≤ 0.05; **, p ≤ 0.01; ***; p ≤ 0.001; and ****, p ≤ 0.0001.

Figure 4

Impact of disease severity on kinetics of antibody responses against SARS-CoV-2. Comparison of neutralizing titer (IC₅₀) and OD values of S1-IgG, N-IgG, S1-IgM, and N-IgM for (a) individuals from the different disease severity categories; (b) individuals who survived or died; and (c) individuals who required ICU admission or not. Data are shown based on time post disease onset. Statistical significance was determined using one-way analysis of variance with Tukey post-hoc test in (a) and using Student’s t test in (b) and (c). Mean with SD are shown, and statistical significance is represented as *, p ≤ 0.05; **, p ≤ 0.01; and ****, p ≤ 0.0001.