Fig. 1. Analysis of antibody responses against 244,000 bacterial and viral peptide antigens indicates aberrant Igs against flagellins as the key difference between patients with severe ME/CFS and healthy controls.

(A) PhIP-Seq (46) methodology to analyze serum antibody epitope repertoires against a diverse library (47) of peptide antigens. (B) Blood samples for antibody profiling were obtained from 40 patients with severe ME/CFS and an equal number of age- and sex-matched healthy controls. (C) The absolute number of antibody-bound peptides per patient and the diversity of Ig repertoires were not significantly different between patients with severe ME/CFS and healthy controls. See Methods for details on the statistics applied. (D) Antibody responses against bacterial flagellins are significantly [t₍₇₈₎ = 11.0, P = 4 × 10⁻²⁸] overrepresented in patients with severe ME/CFS compared to healthy controls. Each dot represents a peptide, with its prevalence in the respective cohort plotted on the x and y axes. Bacterial flagellins as previously annotated (47) are marked. See table S1 for a detailed list. When applying Fisher’s exact test to test for the differences between patients with severe ME/CFS and healthy controls, no peptides were significantly enriched (after false discovery rate for the 20,694 peptides bound in at least one person of the cohort). (E and F) Bacterial flagellins represent the main antigen subgroup within the library that exhibits differential binding in patients with severe ME/CFS and healthy controls (see Methods for details). ns, not significant. *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001, ****P ≤ 1.00 × 10⁻⁰⁴. n.a., not applicable.