Elevated Soluble ACE2 Activity in Children and Adults After SARS-CoV-2 Exposure Irrespective of Laboratory-Confirmed Infection

Abstract

The pivotal role of the cell entry receptor ACE2 for SARS-CoV-2 infection is well-established. When ACE2 is shed from cell surface into plasma as soluble ACE2 (sACE2), it can effectively neutralize SARS-CoV-2. This longitudinal prospective cohort study analyzed sACE2 activity in 1192 participants, aged 4 months to 81 years, 3 and 12 months after SARS-CoV-2 household exposure. Following SARS-CoV-2 exposure, participants exhibited significantly elevated sACE2 activity, irrespective of confirmed infection, with the highest levels observed in exposed children. Longitudinal analysis revealed a decline in sACE2 levels over time, reaching levels comparable to age- and sex-matched pre-pandemic controls. An increase in sACE2 activity was also confirmed in vitro in Calu-3 (human lung) cells within hours of SARS-CoV-2 exposure, providing a direct link between SARS-CoV-2 exposure and elevated sACE2. This study, therefore, challenges the dichotomy of categorizing SARS-CoV-2 exposed participants as infected or not infected solely on currently established diagnostic assays. It demonstrates lasting host responses independent of B- and T-cell memory and may help to keep SARS-CoV-2 infections in balance and contribute to successful virus clearance in children and adults lacking humoral and cellular immune responses following SARS-CoV-2 exposure. Trial Registration: German Registry for Clinical Studies; Identifier: D 00021521.

Keywords: ACE2; SARS‐CoV‐2; children; exposure; persistence.

Figure 1

Study flow diagram.

Figure 2

Soluble ACE2 (sACE2) activity in sera from unexposed pre‐pandemic controls (n = 154) and (A) participants 3 months (n = 1192) and 1 year (n = 345) after SARS‐CoV‐2 exposure, (B) categorized by participants with (n = 594) and without (n = 598) evidence of infection 3 months after exposure, and (D) categorized by participants with (n = 236) and without (n = 109) evidence of infection 12 months after exposure. (C) Longitudinal sACE2 activity from 345 participants 3−12 months after SARS‐CoV‐2 exposure. Individual data for each participant are depicted in gray. (A, B, D) Mean and 1 ± times standard deviation and (C) longitudinal mean are shown in black. p values were calculated using (A, B, D) one‐way ANOVA (A: F[2, 1688] = 184.4, p < 0.0001; B: F[2, 1343] = 61.9, p < 0.0001; D: F(2, 496) = 0.33, p = 0.72) with Tukey correction for multiple comparisons and (C) paired t‐test.

Figure 3

Soluble ACE2 (sACE2) in sera of (A) 1192 participants 3 months and (B) 345 participants 1 year after SARS‐CoV‐2 exposure stratified by sex. Mean and 1 ± times standard deviation are shown in black and individual data for each participant are depicted in gray. p values were calculated using unpaired t‐tests.

Figure 4

Soluble ACE2 (sACE2) activity stratified by age group in sera of (A) 1192 participants 3 months and (B) 345 participants 1 year after SARS‐CoV‐2 exposure and participants (C) without and (D) with evidence of infection 3 months after SARS‐CoV‐2 exposure. Mean and 1 ± times standard deviation are shown in black and individual data for each participant are depicted in gray. p values were calculated using unpaired t‐tests.

Figure 5

(A) Soluble ACE2 (sACE2) activity in sera of 67 exposed participants without prior evidence of SARS‐CoV‐2 infection (seronegative and no positive PCR) 3 months after SARS‐CoV‐2 exposure stratified by SARS‐CoV‐2 specific T‐cell response. (B) Longitudinal sACE2 activity from 22 T‐cell negative participants 3−12 months after SARS‐CoV‐2 exposure. Individual data for each participant are shown in gray. (A) Mean and 1 ± times standard deviation and (B) longitudinal mean are shown in black. p value was calculated using (A) unpaired and (B) paired t‐test.

Figure 6

(A) Schematic illustration of in vitro experiments to determine shedding of soluble ACE2 (sACE2) upon exposure to pseudovirus particles bearing a SARS‐CoV‐2 spike protein (SCoV‐2 spike) (created with BioRender.com). (B) Absolute soluble ACE2 (sACE2) activity and the change in sACE2 (∆sACE2) activity in the supernatant of Calu‐3 (human lung) cells after 16 h of exposure to pseudovirus with (yes) versus without (no) SARS‐CoV‐2 spike. Individual data points for each biologically independent experiment are depicted with black dots connected by lines. For ∆sACE2 activity, the mean and confidence intervals between the experiments are shown. The p‐value was calculated using a paired t‐test.