SARS-CoV-2 antibodies, serum inflammatory biomarkers and clinical severity of hospitalized COVID-19 patients

Abstract

Background: The involvement of SARS-CoV-2 antibodies in mediating immunopathogenetic events in COVID-19 patients has been suggested. By using several experimental approaches, we investigated the potential association between SARS-CoV-2 IgGs recognizing the spike (S) protein receptor-binding domain (RBD), neutralizing antibodies (NtAb) targeting S, and COVID-19 severity.

Patients and methods: This unicenter, retrospective, observational study included 51 hospitalized patients (24 at the intensive care unit; ICU). A total of 93 sera from these patients collected at different time points from the onset of symptoms were analyzed. SARS-CoV-2 RBD IgGs were quantitated by ELISA and NtAb50 titers were measured in a GFP reporterbased pseudotyped virus platform. Demographic and clinical data, complete blood counts, as well as serum levels of ferritin, Dimer-D, C reactive protein (CRP), lactose dehydrogenase (LDH), and interleukin-6 (IL-6) were retrieved from clinical charts.

Results: The overall correlation between levels of both antibody measurements was good (Rho = 0.82; P = 0 < 0.001). SARS-CoV-2 RBD IgG and NtAb50 levels in sera collected up to day 30 after the onset of symptoms were comparable between ICU and non-ICU patients (P=>0.1). Four ICU patients died; two of these achieved NtAb50 titers ≥1/160 while the other two exhibited a 1/80 titer. Very weak (Rho=>0.0-<0.2) or weak (Rho=>0.2-<0.4) correlations were observed between anti-RBD IgGs, NtAb50, and serum levels pro-inflammatory biomarkers.

Conclusions: The data presented herein do not support an association between SARS-CoV-2 RBD IgG or NtAb50 levels and COVID-19 severity.

Keywords: COVID-19; Inflammatory biomarkers; Neutralizing antibodies; SARS-CoV-2.

Fig. 1

Correlation between SARS-CoV-2 RBD IgG levels quantitated by ELISA and NtAb₅₀ titers measured by a reporter-based pseudotype (VSV-S) neutralization assay in sera from COVID-19 patients. Rho and P values are shown.

Fig. 2

SARS-CoV-2 RBD IgG levels (A) and NtAb₅₀ titers (B) at different time points after the onset of symptoms in patients with COVID-19.

Fig. 3

Kinetics patterns of SARS-CoV-2 RBD IgGs (A,B,C) and NtAb (D,E,F) in 20 COVID-19 patients (17 admitted to the intensive care unit).

Fig. 4

SARS-CoV-2 RBD IgG avidity indices (AIs) of serial sera from COVID-19 patients collected at different times following the onset of symptoms.

Fig. 5

SARS-CoV-2 RBD IgG levels (A) and NtAb₅₀ titers (B) at different time points after the onset of symptoms in patients with COVID-19 either admitted to the intensive care unit or the pneumology ward. P values for comparisons are shown.

Fig. 6

Correlation between SARS-CoV-2 RBD IgG levels and NtAb₅₀ titers with serum levels of C-reactive protein (CRP), Dimer-D, ferritin, lactate dehydrogenase (LDH), interleukin-6 (IL-6) and absolute lymphocyte counts. Rho and P values are shown.