High neutralizing antibody titer in intensive care unit patients with COVID-19

Abstract

Coronavirus disease 2019 (COVID-19) has a wide spectrum of disease severity from mild upper respiratory symptoms to respiratory failure. The role of neutralizing antibody (NAb) response in disease progression remains elusive. This study determined the seroprevalence of 733 non-COVID-19 individuals from April 2018 to February 2020 in the Hong Kong Special Administrative Region and compared the neutralizing antibody (NAb) responses of eight COVID-19 patients admitted to the intensive care unit (ICU) with those of 42 patients not admitted to the ICU. We found that NAb against SARS-CoV-2 was not detectable in any of the anonymous serum specimens from the 733 non-COVID-19 individuals. The peak serum geometric mean NAb titer was significantly higher among the eight ICU patients than the 42 non-ICU patients (7280 [95% confidence interval (CI) 1468-36099]) vs (671 [95% CI, 368-1223]). Furthermore, NAb titer increased significantly at earlier infection stages among ICU patients than among non-ICU patients. The median number of days to reach the peak Nab titers after symptoms onset was shorter among the ICU patients (17.6) than that of the non-ICU patients (20.1). Multivariate analysis showed that oxygen requirement and fever during admission were the only clinical factors independently associated with higher NAb titers. Our data suggested that SARS-CoV-2 was unlikely to have silently spread before the COVID-19 emergence in Hong Kong. ICU patients had an accelerated and augmented NAb response compared to non-ICU patients, which was associated with disease severity. Further studies are required to understand the relationship between high NAb response and disease severity.

Keywords: COVID19; ICU patient; SARS-CoV-2; disease severity; neutralizing antibody.

Figure 1.

(A) Entry assay of pseudotyped virus. 50 μl pseudovirus was used to infect 2 × 10⁴ HEK293-ACE2, Huh7, Vero-E6 and HEK-293T cells, respectively. Luciferase activity was measured 48 h postinfection using the Promega kit. Triplicates were tested in each experiment. The average values and standard error bars are presented. The experiment was repeated three times with similar results obtained. (B) Comparison of pseudotyped neutralization assay with the live SARS-CoV-2 based MN assay. Log-transformed NAb titers (IC₅₀) are presented in the plot. Pearson correlation test results demonstrated a significant positive correlation (p < 0.0001) between two assays.

Figure 2.

Neutralizing antibody profiles of patients determined by pseudotyped neutralization assay. (A) Proportion of patients with low neutralizing antibody titer. Error bar indicates 95% confidence interval. (B) Peak levels of neutralizing antibodies in patients at different time points after symptoms onset. Dots represent the NAb titer in patient serum. Geometric mean of the NAb titer is shown by a line. Error bar indicates 95%.

Figure 3.

Differences of neutralizing antibody titers between ICU and non-ICU patients. (A) Comparison of peak geometric mean titers between ICU and non-ICU patients. (B) Comparison of geometric mean titers between ICU and non-ICU patients at weekly intervals after symptoms onset. The highest titer during each weekly period was presented. (C) Comparison of seropositive rates between ICU and non-ICU patients. A serum specimen is considered to be seropositive if the defined 50% inhibitory concentration (IC₅₀) value was above 1:50. (D) Comparison of Nab titer change between ICU and non-ICU patients at weekly intervals after symptoms onset. Fold change was calculated using the highest titer from each time period against the highest titer from prior week. The error bar indicates 95% confidence interval. Unpaired student’s t-test was used. *P < 0.05, **P < 0.01, ***P < 0.001.