Figure 3. Mapping the immunodominant epitopes of the SARS-CoV-2 RBD protein by Pepscan analysis against antisera from COVID-19 patients and identification of the immunodominant peptide. (A) Sera of COVID-19 patients (n = 66) and healthy blood donors (n=23) were subjected to 5 pools (A to E) of overlapping peptides. Each pool containing three 20-mer adjacent peptides that covers the entire RBD domain of S protein. The reactivity of sera with the overlapping peptide pools from RBD protein was determined by ELISA. (B)Identification of the immunodominant epitope among ”pool E” peptides from RBD protein. Individual peptides (P181-200, P196-215, and P204-223) of the positive peptide pool of RBD (pool E) were screened with plasma samples from 25 COVID-19 patients having the highest reactivity with this pool to determine the most reactive peptide. The solid lines represent mean values ± SD, P<0.001 (***),P<0.0001 (****). RBD: Receptor binding domain; P: Patients; NI: Normal individuals.