Rheumatoid Factor and Anti–Modified Protein Antibody Reactivities Converge on IgG Epitopes

Abstract

Objective. Rheumatoid arthritis (RA) patients often develop rheumatoid factors (RFs), antibodies that bind IgG Fc, and anti-modified protein antibodies (AMPAs), multireactive autoantibodies that commonly bind citrullinated, homocitrullinated, and acetylated antigens. Recently, antibodies that bind citrulline-containing IgG epitopes were discovered in RA, suggesting that additional undiscovered IgG epitopes could exist and that IgG could be a shared antigen for RFs and AMPAs. This study was undertaken to reveal new IgG epitopes in rheumatic disease and to determine if multireactive AMPAs bind IgG.Methods. Using sera from patients with RA, systemic lupus erythematosus, Sjögren's disease (SjD), or spondyloarthropathy, IgG binding to native, citrulline-containing, and homocitrulline-containing linear epitopes of the IgG constant region was evaluated by peptide array, with highly bound epitopes further evaluated by enzyme-linked immunosorbent assay (ELISA). Binding of monoclonal AMPAs to IgG-derived peptides and IgG Fc was also evaluated by ELISA.Results. Seropositive RA sera showed high IgG binding to multiple citrulline-and homocitrulline-containing IgGderived peptides, whereas anti-SSA+ sera from SjD patients showed consistent binding to a single linear native epitope of IgG in the hinge region. Monoclonal AMPAs bound citrulline-and homocitrulline-containing IgG peptides and modified IgG Fc.Conclusion. The repertoire of epitopes bound by AMPAs includes modified IgG epitopes, positioning IgG as a common antigen that connects the otherwise divergent reactivities of RFs and AMPAs.

Antibody landscape of C57BL/6 mice cured of B78 melanoma via immunotherapy

“…This same type of workflow could be applied to other types of cancer or diseases as well as to the analyses of patients that have received effective immunotherapy associated with a clear immune mediated anti-tumor response to their cancer to evaluate the equivalent antibody-recognized human tumor "immunome". Some work in this cancer realm, and in analyses of auto-immunity and anti-viral immunity has been reported and is underway (Heffron et al, 2021;Mergaert et al, 2022;Potluri et al, 2020;Zheng et al, 2021). Serum samples from mice described in Figure 1A were run on the Nimble Therapeutics mouse whole proteome peptide microarray.…”

Novel autoantibodies help diagnose anti-SSA antibody negative Sjögren disease and predict abnormal labial salivary gland pathology

“…For the human peptidome array and validation ELISAs, we used sera from eight anti-SSA antibody negative (SSA−; meaning negative for Ro52 and/or Ro60) participants with SjD meeting SjD American College of Rheumatology (ACR)/EULAR 2016 criteria9 and eight age-matched and sex-matched controls without autoimmune disease (table 1) as previously described from the University of Wisconsin (UW) Rheumatology Biorepository 10 11…”

“…The SICCA registry recorded rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) diagnosed by the treating physician but did not independently confirm these diagnoses. Additional analyses were performed comparing samples from the SICCA registry for SSA+ SjD (n=75) and from the UW Rheumatology Biorepository for rheumatologist-diagnosed SLE (n=20), and rheumatologist-diagnosed subjects with RA (n=20) 11…”

Ranking Antibody Binding Epitopes and Proteins Across Samples from Whole Proteome Tiled Linear Peptides

“…In this paper, we use the normalized log-transformed data, which is part of the suggested use of the Box-Cox transformation [45]. Other methods for analyzing high-throughput peptide binding array data perform a log-log transformation before estimating the statistics [13,15]. While studying the application of permutation calibration, we will investigate the usefulness of the Box-Cox transformations when calculating the statistics and calibration procedures.…”

“…There are many existing methods for analyzing microarray and peptide array data [2][3][4][5][6][7][8][9][10][11][12][13][14][15], including pepStat, which was designed to analyze different viral strains for a single protein, and a few methods for analyzing these ultra-dense, highdimensional array data [13,15,16], but additional methods are necessary to advance understanding of immune response as antibody binding signals from arrays represent an aggregate of complex biological and biochemical interactions. Antibodies may bind to peptides via various mechanisms of interaction based on the antibody's antigen binding site and amino acid configuration of the peptides, affecting binding affinity, and each protein may have multiple epitopes that are bound by antibodies, amplifying the immune response to the protein.…”