Figure 2. Reactivity of patients’ sera with native and reduced SARS-CoV-2 RBD protein. Native and reduced SARS-CoV-2 RBD proteins were used for coating ELISA plates, and the sera from 48 COVID-19 patients were tested. Reactivity with native RBD was significantly stronger than the reduced protein, p<0.001 (***). RBD: Receptor-binding domain.