Plasma Antibody Profiling for SARS-CoV-2

Optimization experiments declared the optimal concentration of the plasma for studying the humoral response following SARS-CoV-2 infection to be 10.000-fold dilution. As previously described^{10 (link),31} , 50 µL of a bead mixture containing all different S-proteins in a concentration of 20 beads per µL were added to 50 µL of diluted plasma and incubated overnight on a rotator at 4 °C. The next day, plates were washed with TBS containing 0.05% Tween-20 (TBST) and resuspended in 50 µL of Goat-anti-human IgG-PE (Southern Biotech) with a concentration of 1.3 µg/mL. After 2 h of incubation on a rotator at room temperature, the beads were washed with TBST and resuspended in 70 µL Magpix drive fluid (Luminex). Read-out of the plates was performed on a Magpix (Luminex). The binding of antibodies is expressed as the Median Fluorescence Intensity (MFI) of approximately 50 to 100 beads per well. MFI values are corrected for background signals by subtracting the MFI of wells containing only buffer and beads.