Anti-spike, Anti-nucleocapsid and Neutralizing Antibodies in SARS-CoV-2 Inpatients and Asymptomatic Individuals

Abstract

A better understanding of the anti-SARS-CoV-2 immune response is necessary to finely evaluate commercial serological assays but also to predict protection against reinfection and to help the development of vaccines. For this reason, we monitored the anti-SARS-CoV-2 antibody response in infected patients. In order to assess the time of seroconversion, we used 151 samples from 30 COVID-19 inpatients and monitored the detection kinetics of anti-S1, anti-S2, anti-RBD and anti-N antibodies with in-house ELISAs. We observed that specific antibodies were detectable in all inpatients 2 weeks post-symptom onset and that the detection of the SARS-CoV-2 Nucleocapsid and RBD was more sensitive than the detection of the S1 or S2 subunits. Using retroviral particles pseudotyped with the spike of the SARS-CoV-2, we also monitored the presence of neutralizing antibodies in these samples as well as 25 samples from asymptomatic individuals that were shown SARS-CoV-2 seropositive using commercial serological tests. Neutralizing antibodies reached a plateau 2 weeks post-symptom onset and then declined in the majority of inpatients but they were undetectable in 56% of asymptomatic patients. Our results indicate that the SARS-CoV-2 does not induce a prolonged neutralizing antibody response. They also suggest that induction of neutralizing antibodies is not the only strategy to adopt for the development of a vaccine. Finally, they imply that anti-SARS-CoV-2 neutralizing antibodies should be titrated to optimize convalescent plasma therapy.

Keywords: COVID-19; SARS-CoV-2; convalescent plasma therapy; neutralizing antibodies; nucleocapsid; spike; vaccine.

FIGURE 1

Antibody response in SARS-CoV-2 infected inpatients. (A) Kinetics of anti-S1, anti-S2, anti-RBD, anti-N and NAb detection in 30 COVID-19 inpatients post-symptom onset. (B) Evolution of the anti-S1, anti-S2, anti-RBD, and anti-N antibody levels during the first month post-symptom onset.

FIGURE 2

Temporal profiles of anti-S1, anti-S2, anti-RBD, and anti-N antibody levels. Inpatients samples were divided into three periods groups (day 0–7, day 8–14, and day > 14). (A) The temporal profiles are presented according to the severity of the disease (SD, severe disease requiring intensive care; MD, mild disease requiring non-intensive care). (B) The temporal profiles are presented according to the sex (M, male; F, female). (C) The temporal profiles are presented according to the age (< or >60 years old). Dashed lines indicate assays cut-offs for positivity and lines indicate the median for each assay. OD, optical density. NS, not significant; *p < 0.05; **p < 0.01.

FIGURE 3

(A) Evolution of the NAb titer in 30 COVID-19 inpatients during the first month post-symptom onset. (B) Evolution of the NAb titer in 11 COVID-19 inpatients after more than 40 days post-symptom onset. The dashed line indicates the cut-off of the assay. (C–F) Correlations between NAb titers and anti-S1 (C), anti-S2 (D), anti-RBD (E), and anti-N (F) antibody levels. Dashed lines indicate assay cut-offs for positivity. OD, optical density.

FIGURE 4

Temporal profiles of NAb titers. Inpatients samples were divided into three periods groups (day 0–7, day 8–14, and day >14). (A) The temporal profiles are presented according to the severity of the disease (SD, severe disease requiring intensive care; MD, mild disease requiring non-intensive care). (B) The temporal profiles are presented according to the sex (M, male; F, female). (C) The temporal profiles are presented according to the age (< or >60 years old). Dashed lines indicate assays cut-offs for positivity and lines indicate the median for each assay. NS, not significant; *p < 0.05.

FIGURE 5

SARS-CoV-2 NAbs in asymptomatic individual samples. (A) SARS-CoV-2pp were pre-incubated with serially diluted plasma obtained from 25 asymptomatic patients that were seropositive with commercial serological assays (AP1 to AP25). Dose response curves represent the means of normalized infectivity (%) from two independent experiments performed in duplicate. Error bars have been omitted for clarity. (B) Determination of the NAb titer in plasma samples from 25 asymptomatic patients.