Background/Purpose: Rheumatoid arthritis (RA) is an autoimmune disease characterized by joint inflammation and bone destruction. RA is preceded by a subclinical phase defined by elevated levels of RA-associated autoantibodies, most preeminently anti-citrullinated protein antibodies (ACPA). Nonetheless, we have an incomplete understanding of the changes in the B cell compartment that contribute to the breaking of tolerance that underlies risk of RA development. Here, we performed a multi-omics study of peripheral B cells from ACPA+ at-risk individuals (ARI) and longitudinally studied those ARI that progressed to clinical RA, referred to as disease ‘converters’.

Methods: We applied single-cell RNA sequencing (scRNA-seq) and flow cytometry to peripheral blood from 45 ACPA+ ARI. For converters, we profiled blood samples over a period of 2 years prior to the onset of clinical RA (n=13). The productive immunoglobulin heavy chain (IgH) isotype of B cell subsets was determined from scRNA-seq data. We applied spectral flow cytometry to characterize cytokine profiles of activated peripheral B cells from age-matched ACPA- control and ACPA+ ARI after TLR9 ligand and CD40 stimulation.

Results: Upon productive IgH isotype labeling, IGHG3 sterile IgH expression by unswitched naive B cells was significantly increased among ARI (FDR=0.1). This suggests a greater likelihood that naïve B cells of ARI will class-switch to the IgG3+ isotype upon activation. A subset of naïve B cells also expanded in RA converters (FDR=0.02), a feature previously reported to correlate with activation in ACPA+ individuals (Inamo et al. 2023, JCI). Pathway analysis showed increased activation and antigen presentation activity compared to controls. Upon in vitro stimulation, naive B cells from ARI had higher frequencies of IL-6+ and RANKL+ cells compared to controls (FDR< 0.05) and trended toward elevated TNFα+ cells (FDR=0.19), suggesting they are primed for proinflammatory cytokine and RANKL secretion. Further, we identified a subset of CD27- ITGAX/CD11c+ effector memory B cells that increase in abundance during progression to clinical RA (FDR=0.11). This population has transcriptional features of chronic BCR engagement, including elevated class-switched cells as compared to the non-expanding effector memory subset, and a gene program associated with long-lived humoral immunity. Together these data show broad activation across naive and memory ARI B cell populations with evidence of a naive B cell primed state in ACPA+ ARI.

Conclusion: Our results indicate proinflammatory-skewed naive and memory B cell subsets among ARI, coinciding with systemic inflammation. An increased activation signature and IGHG3 GLT suggest that naive B cells from ARI may be in a functionally “primed” state. Further, a subset of CD27- atypical or effector memory B cells with an activated transcriptional profile are found in converters as clinical RA approaches. Collectively, these data suggest that in addition to ACPA production, ongoing B cell activation is a feature of progression to clinical RA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-b-cell-compartment-exhibits-a-pro-inflammatory-skewing-during-progression-to-rheumatoid-arthritis/