A longitudinal study of SARS-CoV-2-infected patients reveals a high correlation between neutralizing antibodies and COVID-19 severity

Abstract

Understanding the immune responses elicited by SARS-CoV-2 infection is critical in terms of protection against reinfection and, thus, for public health policy and vaccine development for COVID-19. In this study, using either live SARS-CoV-2 particles or retroviruses pseudotyped with the SARS-CoV-2 S viral surface protein (Spike), we studied the neutralizing antibody (nAb) response in serum samples from a cohort of 140 SARS-CoV-2 qPCR-confirmed infections, including patients with mild symptoms and also more severe forms, including those that required intensive care. We show that nAb titers correlated strongly with disease severity and with anti-spike IgG levels. Indeed, patients from intensive care units exhibited high nAb titers; conversely, patients with milder disease symptoms had heterogeneous nAb titers, and asymptomatic or exclusive outpatient-care patients had no or low nAbs. We found that nAb activity in SARS-CoV-2-infected patients displayed a relatively rapid decline after recovery compared to individuals infected with other coronaviruses. Moreover, we found an absence of cross-neutralization between endemic coronaviruses and SARS-CoV-2, indicating that previous infection by human coronaviruses may not generate protective nAbs against SARS-CoV-2. Finally, we found that the D614G mutation in the spike protein, which has recently been identified as the current major variant in Europe, does not allow neutralization escape. Altogether, our results contribute to our understanding of the immune correlates of SARS-CoV-2-induced disease, and rapid evaluation of the role of the humoral response in the pathogenesis of SARS-CoV-2 is warranted.

Keywords: Antibody; COVID-19; Humoral response; Pathogenesis; SARS-CoV-2.

Fig. 1

Serum neutralization of SARS-CoV-2 correlates with the hospitalization units of COVID-19 patients. A Correlation between the ID50 of live virus, as plotted as number of dilutions (twofold dilutions starting from serum diluted at 1/10) with the percentage of neutralization of SARS-CoV-2pp for all tested samples. B Number of patients classified in the indicated groups according to the percentage of neutralization. In white: samples that induced a percentage of neutralization below 90%. C Comparison of the percentage of neutralization with SARS-CoV-2pp (left) or ID50 with live virus (right) for each patient classified according to the hospitalization unit. For patients with serial serum samples, the sera collected at the time closest to twenty days post onset of symptoms were chosen. In light green are asymptomatic patients (ASY) among the EOC patients. D Percentage of neutralization according to the severity of symptoms in HOS patients. The cutoff for neutralization (35%) was set using the mean neutralization of a 1/100 dilution of negative sera + 2 SD for SARS-CoV-2pp. For the wild-type virus, the cutoff for the ID50 was set at the 1/10 dilution (first tested dilution), as all negative sera were below this threshold

Fig. 2

Serum neutralization of SARS-CoV-2 correlates with anti-S antibodies. A Correlation between the percentage of neutralization of SARS-CoV-2pp (left) or ID50 of live virus (right) with seroconversion measured by anti-N antibodies. B Same as A with anti-S antibodies. C Anti-S (left) and anti-N (right) IgG value distributions in the three groups of patients

Fig. 3

Appearance and longevity of neutralizing antibodies. A Seroconversion assessed by anti-S IgGs plotted against the days post-symptoms on which the samples were collected. B Percentage of neutralization of each serum sample assessed with SARS-CoV-2pp plotted against the days post-symptoms on which the samples were collected. The lines show the mean values expected from a second-order polynomial regression; the ribbons indicate the pointwise 95% confidence intervals. C Neutralizing antibody titers (ID50) assessed with SARS-CoV-2pp plotted against the days post-symptoms on which the samples were collected. The lines show the mean values expected from a second-order polynomial regression; the ribbons indicate the pointwise 95% confidence intervals. D Individual kinetics displayed for ICU patients with nAb titers (ID50) below (top) or above (bottom) 2000

Fig. 4

Sera from patients infected by endemic coronaviruses have no cross-neutralizing activity against SARS-CoV-2. A Characteristics of samples from patients infected with other coronaviruses. B Seroconversion assessed by anti-N (left) and anti-S (middle) SARS-CoV-2 or neutralization measured by SARS-CoV-2pp (right). For neutralization assays, a commercial anti-S antibody was used as a positive control (control+) and five prepandemic serum samples were used as a negative control (control−)

Fig. 5

The residue at position 614 of SARS-CoV-2 spike does not influence the activity of nAbs. Percentage of neutralization of SARS-CoV-2pp using the spike protein with either a G or D at position 614