Extended Data Fig. 4: Specificity of multiplex assays to measure anti-M IgG.

(a) Specificity of the 14-plex assay to measure IgG to M/emm cluster representative M peptides. (b) Specificity of 6-plex assay to measure IgG to E3 M/emm cluster M peptides. Positive material consisting of intravenous immunoglobulin supplemented with pooled human serum was incubated with M-peptide inhibitors at a concentration of 2 µg/mL, prior to proceeding with a standard 14-plex, or 6-plex, assay to measure IgG to M/emm cluster representative M peptides. Percentage MFI inhibition in relation to the MFI of uninhibited material was calculated as ((MFI Control − MFI Inhibited sample)/MFI control) × 100. Yellow circles represent the magnitude of the MFI of the inhibited signal for each antigen (as a surrogate marker of overall concentration of each antibody in immunoglobulin supplemented with pooled human serum). MFI = Median fluorescent intensity. Numbers in each cell is the percentage inhibition. Red boxes indicate homologous inhibition.