Plasma from recovered COVID-19 subjects inhibits spike protein binding to ACE2 in a microsphere-based inhibition assay

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 (ACE2) Plasma from 22 subjects who recovered from mild Coronavirus disease 2019 (COVID-19) and expressed anti-spike-trimer IgGs inhibited ACE2-spike binding to a greater degree than controls The degree of inhibition correlated with anti-spike IgG 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 recovered COVID-19 patients or vaccine recipients in a cell-free assay system