Background/Purpose: The cellular and molecular mechanisms underlying the progression from anti-citrullinated protein antibody (ACPA) positivity to clinical rheumatoid arthritis (RA) remain poorly understood. Defining these early immunologic events is essential for identifying predictive biomarkers and developing preventive strategies.

Methods: We conducted longitudinal single-cell profiling of peripheral blood mononuclear cells (PBMCs) collected at two timepoints: a preclinical baseline and a follow-up approximately one year later. Participants were classified into three groups: (1) ACPA⁺ converters who were ACPA-positive at baseline and developed clinical RA at follow-up; (2) ACPA⁺ non-converters who did not develop clinical RA; and (3) healthy controls who were ACPA-negative and RA-free at both timepoints. B cells were isolated and analyzed using an integrated multi-modal single-cell approach, including 5′ scRNA-seq, VDJ-seq, and CITE-seq.

Results: Single-cell analysis revealed a marked preclinical expansion of IGHM⁺ IGHD⁺ CXCR5⁺ CD69⁺ activated naïve (aNAV) B cells in ACPA⁺ converters. These aNAV cells exhibited a distinct pro-inflammatory transcriptional profile, characterized by upregulation of genes involved in immune activation, antigen presentation, impaired tolerance, and cellular stress, compared to non-converters and healthy controls. VDJ repertoire analysis revealed that within converters, IgM-expressing aNAV cells dominated the BCR landscape and exhibited elevated clonal diversity along with distinct V–J gene rearrangements across both heavy and light chains. Recombinant monoclonal antibodies derived from these IgM⁺ aNAV cells demonstrated broad autoreactivity to multiple RA-associated autoantigens, including both native and citrullinated epitopes. In contrast, aNAV cells from non-converters more closely resembled those of healthy controls in their transcriptional profiles, BCR repertoires, and autoreactivity patterns.

Conclusion: These findings identify a preclinical expansion of IGHM⁺ IGHD⁺ CXCR5⁺ CD69⁺ naïve B cells in ACPA⁺individuals who progress to RA. These cells are transcriptionally stressed, pro-inflammatory, and resistant to immune tolerance. Their BCR repertoire is enriched for diverse, autoreactive IgM antibodies with distinct V–J rearrangements. This autoreactive IgM pool may contribute to early immunologic activation and the eventual onset of rheumatoid arthritis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/preclinical-expansion-of-autoreactive-naive-b-cells-drives-ra-onset-in-acpa-individuals/