Figure 2.
Representative antibody-RBD binding titration curve (single blood draw). Using the protocol described in Figure 1 and the maximum intensity from the zero RBD concentration control, we calculate the fraction of unbound patient antibody, blocked from binding to the microparticles due to antibody-RBD complex formation. Plotting the percent inhibition as a function of added RBD protein generates a binding curve. A heuristic, standard four-parameter logistic fit is used to obtain the 50%-inhibition concentration, the inverse of which is a measure of the apparent affinity of this patient's anti-spike antibody, 0·91 × 109 M−1. error bars: ±.