Different Hierarchies of Anti-Modified Protein Autoantibody Reactivities in Rheumatoid Arthritis

Area of Science:

• Immunology
• Rheumatology
• Biochemistry

Background:

• Anti-citrullinated protein antibodies (ACPAs) are key biomarkers for seropositive rheumatoid arthritis (RA).
• The exact spectrum of autoantigens targeted by ACPAs in RA remains incompletely understood.
• Understanding ACPA fine specificity is crucial for elucidating RA pathogenesis.

Purpose of the Study:

• To characterize the multireactivity of patient-derived monoclonal ACPAs against various protein modifications.
• To identify distinct subsets of ACPAs based on their binding specificities.
• To explore the range of autoantigens targeted by ACPAs in rheumatoid arthritis.

Main Methods:

• Generation of 12 human monoclonal ACPAs from 6 RA patients.
• Utilized extensive peptide-screening platforms (>207,000 peptides) and a cDNA-based protein array.
• Assessed reactivity against citrullinated, carbamylated, and acetylated peptides, including histone modifications.

Main Results:

• All monoclonal ACPAs demonstrated broad multireactivity to numerous citrullinated peptides/proteins.
• Distinct ACPA subsets were identified by clone-specific binding motifs (e.g., Gly-Cit).
• ACPAs showed preference for citrullinated RNA-binding proteins and cross-reactivity with acetylated lysine (KAc) and homocitrulline motifs.

Conclusions:

• ACPAs and other anti-modified protein autoantibodies represent overlapping autoimmune responses in RA.
• ACPA binding extends to a wider array of modified proteins than previously recognized.
• Future RA research should consider the multireactivity and consensus motifs (Cit/Carb/KAc) of these autoantibodies.