Abstract
Specific antibody reactivities are routinely used as biomarkers but the use of antibody repertoire profiles is still awaiting recognition. Here we suggest to expedite the adoption of this class of system level biomarkers by rationally designing a peptide array as an efficient probe for an appropriately chosen repertoire compartment. Most IgM antibodies are characterized by few somatic mutations, polyspecificity and physiological autoreactivity with housekeeping function. Previously, probing this repertoire with a set of immunodominant self-proteins provided only coarse information on repertoire profiles. In contrast, here we describe the rational selection of a peptide mimotope set, appropriately sized as a potential diagnostic, that also represents optimally the diversity of the human public IgM reactivities. a 7-mer random peptide phage display library was panned on pooled human IgM. Next generation sequencing of the selected phage yielded a non-exhaustive set of 224087 mimotopes which clustered in 790 sequence clusters. A set of 594 mimotopes, representative of the most significant clusters, was used to demonstrate that this approach samples symmetrically the space of IgM reactivities. When probed with diverse patients’ sera in an oriented peptide array, this set produced a higher and more dynamic signal as compared to 1) random peptides, 2) random peptides purged of mimotope-like sequences and 3) mimotopes from a small subset of clusters. In this respect, the representative library is an optimized probe of the human IgM diversity. Proof of principle predictors for randomly selected diagnoses based on the optimized library demonstrated that it contains more than 1070 different profiles with the capacity to correlate with diverse pathologies producing well separable data. Thus, an optimized small library of IgM mimotopes is found to address very efficiently the dynamic diversity of the human IgM repertoire, providing informationally dense, structurally interpretable, IgM reactivity profiles.