Figure 5.

Lack of correlation between the gray intensity units and avidity indices of IgG towards NP of SARS‐CoV‐2 NP of four seasonal coronaviruses. (A) The gray intensity units for IgG towards NP of SARS‐CoV‐2 (as determined in Figure 1) were plotted against the gray intensity units of IgG towards NP of the seasonal coronaviruses 229 E, NL63, OC43, and HKU1 which had been determined in the same assays. With one exception, the gray intensity units obtained for IgG towards NP of seasonal coronaviruses was always much lower than the values obtained for IgG towards NP of SARS‐CoV‐2 (p < 0.001), thus excluding that the values obtained for SARS‐CoV‐2 were due to cross‐reaction with IgG directed towards NP of the seasonal coronaviruses. (B) The avidity indices corresponding to the data presented under A, determined by treatment with 7 M urea versus untreated controls, were plotted (NP SARS‐CoV‐2 vs. NP of seasonal coronaviruses). The data show that only in five cases the avidity index of one of the seasonal coronaviruses was matching the avidity index of IgG towards NP of SARS‐CoV‐2, whereas the avidity indices of IgG towards the NPs of seasonal coronaviruses were lower in 6 cases and higher in 30 cases, compared to the avidity of IgG towards NP of SARS‐CoV‐2. The data from Figure 5A,B indicate that in the vast majority of cases the IgG response towards NP of SARS‐CoV‐2 cannot be explained by crossreactive IgG directed towards NPs of the four seasonal coronaviruses tested. IgG, immunoglobulin G; NP, nucleoprotein; SARS‐CoV‐2, severe acute respiratory syndrome coronavirus 2