Avidity (ELISA)
To test IgG antibody avidity against SARS-CoV-2 full spike protein and
RBD protein, threefold serial dilutions of 1/20 diluted mice sera, were
added to ELISA plates coated over night with 1.0µg/ml RBD and spike
proteins, respectively. After incubation at RT for 1h, the plates were
washed once in PBS-0.01% Tween, and then washed 3x with 7M urea in
PBS-0.05%Tween or with PBS-0.05% Tween for 5min every time. After
washing with PBS-0.05%Tween, goat anti-mouse IgG conjugated to
Horseradish Peroxidase (HRP) (Jackson ImmunoResearch, West Grove,
Pennsylvania) was added 1/2000 and incubated for 1h at RT. Plates were
developed and read at OD450 nm.