ACE2 Serum Levels as Predictor of Infectability and Outcome in COVID-19

Abstract

Background: COVID-19 can generate a broad spectrum of severity and symptoms. Many studies analysed the determinants of severity but not among some types of symptoms. More importantly, very few studies analysed patients highly exposed to the virus that nonetheless remain uninfected.

Methods: We analysed serum levels of ACE2, Angiotensin II and anti-Spike antibodies in 2 different cohorts at high risk of viral exposure, highly exposed but uninfected subjects, either high risk health care workers or persons cohabiting with infected close relatives and seropositive patients with symptoms. We tested the ability of the sera of these subjects to neutralize lentivirus pseudotyped with the Spike-protein.

Results: We found that the serum levels of ACE2 are significantly higher in highly exposed but uninfected subjects. Moreover, sera from this seronegative persons can neutralize SARS-CoV-2 infection in cellular assays more strongly that sera from non-exposed negative controls eventhough they do not have anti-CoV-2 IgG antibodies suggesting that high levels of ACE2 in serum may somewhat protect against an active infection without generating a conventional antibody response. Finally, we show that among patients with symptoms, ACE2 levels were significantly higher in infected patients who developed cutaneous as compared with respiratory symptoms and ACE2 was also higher in those with milder symptoms.

Conclusions: These findings suggest that soluble ACE2 could be used as a potential biomarker to predict SARS-CoV-2 infection risk and to discriminate COVID-19 disease subtypes.

Keywords: ACE2; COVID-19; antibodies; biomarker; neutralization.

Figure 1

Serum ACE2 levels and susceptibility to infection. (A) ACE2 serum levels determined by ELISA in the indicated patient groups, ***p<0.0001. (B) Detection of anti-S protein IgG1 antibodies in human patient sera by flow cytometry of Jurkat cells stably expressing the full-length native S protein of SARS-CoV-2. (C) Anti-S IgG1 antibody is negatively related with ACE2 serum level, p<0.0000001. (D) The percentage of patients with low (ACE2<7.3, lowest 25% of all samples) and high levels of ACE2 (ACE2>12.3, highest 25% of all samples), ***p<0.0001.

Figure 2

Neutralization of SARS-CoV-2. (A) Neutralization of a recombinant virus pseudotyped with the Spike protein and at ¼ dilution of all sera. Values are the mean of 2 different experiments. Neutralization versus subjects group, ***p<0.001 among the 3 groups. (B) ACE2 serum levels for the same samples. (C) Neutralization by soluble hACE2 of a recombinant virus pseudotyped with the Spike protein (C1) and authentic SARS-CoV2 (C2). (D) There is a significant positive correlation between neutralization and ACE2 (E) and negative correlation between neutralization and Angiotensin II, which binds ACE2 and might compete for the binding of viral particles. (F) A regularized linear fit that takes into account both ACE2 and Angiotensin II explains little more than one third of the variance of the neutralization (p=0.005).

Figure 3

Serum ACE2 and anti-S IgG levels in infected seropositive patients according with the type of symptoms. (A) ACE2 serum levels determined by ELISA in the indicated patient groups ***p<0.001. (B) Detection of anti-S protein antibodies in human patient sera by flow cytometry of Jurkat cells stably expressing the full-length native S protein of SARS-CoV-2.

Figure 4

Serum ACE2 levels and severity. (A) ACE2 serum levels determined by ELISA in the indicated patients groups (B) The fraction of samples with low ACE2 (ACE2<7.3, lowest 25% of all samples), ***p<0.0001. (C) The fraction of samples with high ACE2 (ACE2>12.3, highest 25% of all samples).