FIGURE 2.

Stabilized, trimeric S antigen is a superior antigen to detect Ab in NHC. (a) Size‐exclusion chromatogram (SEC) for SARS‐CoV‐2 S protein fractions collected for further use and denoted by dashed grey lines. (b) Coomassie‐stained SDS‐PAGE gel for two separate expressions of SARS‐CoV‐2 (left) and silver stain of batch 1 under reducing and non‐reducing conditions (right). (c) Surface plasmon resonance (SPR) characterizing the interaction between SARS‐CoV‐2 S protein and Ace2. The plotted lines represent the averages of three analytical repeats at each concentration. (d) Serological responses from hospitalized (HS, n = 5) or pre‐2019 normal donors (Pre19, n = 6) as determined by ELISA using HRP‐labelled anti‐IgG represented as absorbance values or (e) signal:noise ratio at each serum dilution against 0·1 µg purified viral trimeric spike protein (S) or the S1 fragment (S1). (f) Mean absorbance values of 4 sera per group against 0·1 or 0·2 µg S or nucleocapsid (N). (g) Signal:noise ratio at each serum dilution against 0·1 or 0·2 µg of S or N. Error bars represent standard deviation from the mean (SD)