Fig. 4: Analysis of antibody binding to the XBB.1.5 spike protein.
A Analysis of monoclonal antibody binding to the WT, BA.2, and XBB.1.5 spike proteins via ELISA. EC50 ratios over the WT spike protein binding EC50 are shown for each antibody assayed (N.B. no binding). B Analysis of serum IgG binding to the WT, BA.2, and XBB.1.5 spike proteins via ELISA (left) and serum neutralization of pseudoviruses harbouring the WT, BA.2, and XBB.1.5 spike proteins (right) from n = 10 vaccinated adults. Fold dilution EC50 values are plotted for each spike protein. A pairwise statistical significance test was performed using the Friedmans and Dunn’s post-test for multiple comparisons (*P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.0001, ns: not significant). Calculated P values are as follows – spike protein binding: WT vs BA.2 (P = 0.001), WT vs XBB.1.5 (P = 0.0417), BA.2 vs XBB.1.5 (P = 0.7907), pseudovirus neutralization: WT vs BA.2 (P = 0.0001), WT vs XBB.1.5 (P = 0.0304), BA.2 vs XBB.1.5 (P = 0.3526). C Negative stain electron microscopy studies of WT and XBB.1.5 spike proteins using polyclonal Fab fragments (pFabs). Top: Superposition of all Fab-spike protein reconstructions obtained using polyclonal Fabs and the WT spike protein. Maps were superposed in chimeraX and Fab densities are colourized and annotated by general location of the epitope recognized. Bottom: Representative 3D reconstruction of the XBB.1.5 spike trimer showing no additional density corresponding to Fab fragments. D ELISA analysis of polyclonal Fabs and IgGs binding to WT and XBB.1.5 spike proteins. Experiments were done in technical quadruplicate (n = 4) and are shown as points. EC50 values along with 95% confidence intervals are shown. E Negative stain electron microscopy studies of polyclonal IgG (pIgG) binding the XBB.1.5 spike protein. 2D class averages along with both side and top views of the resulting 3D reconstruction are shown. Additional density corresponding to Fab regions are coloured in pink. F Fit of a SARS-CoV-2 Spike protein model with all RBDs in the up position (PDB 7X7N with ligands removed) into the obtained 3D reconstruction of an IgG-XBB.1.5 spike protein complex.
