A 3D Surface Plot for the Effective Visualization of Specific Serum Antibody Binding Properties

When an antigen molecule is exposed to serum, many different kinds of antibodies bind to it. The complexity of these binding events is only poorly characterized by assays that generate a single variable as readout. We have previously devised an assay that delivers the essential biochemical variables as output. Here we propose a visualization method for the practical and informative display of those variables. Using total antigen concentration, free and bound antibody concentration as coordinates in a three-dimensional space, a surface plot can depict the behavior of serum antibodies in the measurement range and identify key variables of binding activity. This surface display (antibody binding in 3-concentration display, Ab3cD) was used for the characterization of antibody binding to SARS-CoV-2 spike protein in seronegative and seropositive sera. We demonstrate that this visualization scheme is suitable for presenting both individual and group differences and that epitope density changes, commonly not measured by immunoassays, are also revealed by the method. We recommend the use of 3D visualization whenever detailed, informative and characteristic differences in serum antibody reactivity are studied.