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. 2024 Apr 1;12(4):377. doi: 10.3390/vaccines12040377

Figure 2.

Figure 2

Wide linear dynamic range of the FCCA. Detection of anti-RBD (A) IgG and (B) IgA antibodies over the indicated large range of serum dilutions from three SARS-CoV-2 exposed and vaccinated (N3-E1, B172-V2, B157-V2; red, green, blue line graphs, respectively) and three SARS-CoV-2 non-exposed (A008, A035, A045; diamond, circle, square shapes in grey, respectively) individuals was performed with the FCCA using HEK-293T-RBD-Wuhan-Hu-1 cells (left). The right parts of the figure show results from an ELISA performed with recombinant RBD-Wuhan-Hu-1. In both (A) and (B), log10-transformed ∆gMFI (left y-axes) values obtained by FCCA and OD(405–492) (right y-axes) acquired in ELISA are displayed. On the x-axes, sample dilutions in log10 steps are represented. The estimated linear range window of both assays is highlighted by colored underlays (IgG::red; IgA::cyan). The indicated threshold for FCCA was set at 1 SD of the mean gMFI obtained with the respective secondary antibody (APC-anti-human IgG, PE-anti-human IgA) without serum in 18 independent experiments (IgG::log10 = 3.14; IgA::log10 = 2.93; light blue color underlay), while the ELISA threshold was fixed at 1 SD of the mean OD value obtained with the dilution buffer control on the RBD-coated wells (i.e., for IgG and IgA; Log10: = −2.96; ocher color underlay).