We present a microsphere-based flow cytometry assay that quantifies the ability of plasma to inhibit the binding of spike protein to angiotensin-converting enzyme 2. Plasma from 22 patients who had recovered from mild coronavirus disease 2019 (COVID-19) and expressed anti-spike protein trimer immunoglobulin G inhibited angiotensin-converting enzyme 2-spike protein binding to a greater degree than controls. The degree of inhibition was correlated with anti-spike protein immunoglobulin G levels, neutralizing titers in a pseudotyped lentiviral assay, and the presence of fever during illness. This inhibition assay may be broadly useful to quantify the functional antibody response of patients recovered from COVID-19 or vaccine recipients in a cell-free assay system.
Keywords: ACE2; COVID-19; SARS-COV-2; Spike protein; binding inhibition; neutralization; serology.
© The Author(s) 2020. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: email@example.com.