A High Through-put Assay for Circulating Antibodies Directed against the S Protein of Severe Acute Respiratory Syndrome Corona virus 2

Svenja Weiss; Jeromine Klingler; Catarina Hioe; Fatima Amanat; Ian Baine; Erna Milunka Kojic; Jonathan Stoever; Sean Liu; Denise Jurczyszak; Maria Bermudez-Gonzalez; Viviana Simon; Florian Krammer; Susan Zolla-Pazner

To determine the dynamic range of the assay and determine the titer of Abs present in COVID-19positive sera, titrations were performed with all 11 specimens using the mSpike antigen, and with seven of these specimens using the mRBD antigen; the three specimens from the uninfected subjects were titrated against both antigens. The titration curves are shown in Figure 2 . A prozone effect (the phenomenon in which a value below the peak is observed at low dilutions of sera) is suggested by the curves generated by six of the 11 sera tested against the mSpike. The prozone phenomenon was less apparent when using the mRBD antigen. Generally the maximum MFI values were achieved with serum dilutions of 1:100 or 1:200. Levels of Abs varied greatly between the specimens tested. For example, MFI values at a serum dilution of 1:200 from infected patients ranged from 25,000 to >200,000 (Figure 1) . Of interest, titration curves show that the specimens with the highest Ab levels (P#1c and P#2b) were from two different patients (P#1 and P#2), and these two subject were the two patients with severe disease at the time of the blood draw. (Table I) . Further study is needed to ascertain how and whether disease severity affects the level and type of Abs induced. However, it is notable that the level of Abs increased over a period of a few days in each of the two patients from whom we had longitudinal specimens (P#1 and P#2, Table I ). The factors that affect the variation in Ab responses (severity of disease, length of infection, gender, genetics, etc) are yet to be determined and will require a large panel of specimens from patients with adequate clinical and demographic data.