Background: Disease pathogenesis in rheumatoid arthritis (RA) involves complex interactions between immune cells and mesenchymal cells, resulting in persistent joint inflammation, cartilage destruction, and bone erosion. B cells comprise a diverse set of functionally distinct subsets and are key contributors to RA pathogenesis, as evidenced by the presence of autoantibodies and the clinical efficacy of B-cell–targeted therapies. In addition to antibody production, B cells drive disease through antigen presentation and cytokine secretion. Despite growing evidence that disinct memory B cell (MBC) subsets contribute to different pathological processes in RA, MBCs remain incompletely characterized. We have previously linked a CD21 ⁻ CD11c ⁺ T-bet ⁺ MBC subset to bone erosion in early RA, but not to inflammatory disease activity, highlighting the need to better define additional pathogenic MBC subsets.

Objectives: To identify and characterize MBC subsets associated with inflammatory disease activity in early RA

Methods: Peripheral blood mononuclear cells from newly diagnosed, untreated RA patients (n=49) and healthy controls (n=11) were analyzed by flow cytometry to identify MBC subsets. Common B-cell markers but also CD21, CD11c, and T-bet were used. Frequencies of identified MBC subsets were correlated with clinical parameters, including markers of systemic inflammation and the number of tender and swollen joints. Selected MBC populations from n=4 patients were further analyzed using single-cell RNA sequencing combined with V(D)J sequencing to define transcriptional profiles, B-cell receptor repertoires, clonal expansion, and lineage relationships. Gene set enrichment analyses were used to infer functional properties of identified subsets.

Results: In addition to the previously described CD21 ⁻ CD11c ⁺ T-bet ⁺ MBCs (McGrath et al), a distinct MBC subset lacking CD21, CD11c, and T-bet was identified. The frequency of this CD21 ⁻ CD11c ⁻ T-bet ⁻ MBC subset correlated with markers of systemic inflammation and joint inflammation. Analysis of existing single-cell RNA-sequencing data showed that these cells correspond to a distinct transcriptional cluster with a unique gene expression profile, supporting functional heterogeneity within the CD21 ⁻ MBC compartment.

Conclusions: Specific MBC subsets in early RA seem to be associated with different disease features. Whereas CD21 ⁻ CD11c ⁺ T-bet ⁺ MBCs are linked to structural joint damage (McGrath et al), a novel CD21 ⁻ CD11c ⁻ T-bet ⁻ MBC subset is associated with inflammatory disease activity. Therefore, elucidating the phenotypes and functional properties of poorly characterised MBC subsets will improve our understanding of RA pathogenesis.

REFERENCES: [1] McGrath S. et al. Correlation of Professional Antigen-Presenting Tbet+CD11c+ B Cells With Bone Destruction in Untreated Rheumatoid Arthritis. Arthritis & Rheumatology Vol. 76, No. 8, August 2024, pp 1263–1277 DOI 10.1002/art.42857

Acknowledgments: NIL.

Disclosure of Interests: Inger Gjertsson: None declared, Paul Haase: None declared, Kristoffer Grimstad: None declared, Sarah McGrath: None declared, Monica Leu Agelii: None declared, Charlotte Jonsson: None declared, Anna-Karin H Ekwall AbbVie, advisory board fees from Pfizer and AbbVie, speaker honorar from Boehringer Ingelheim, Aqilion, Inga-Lill Mårtensson: None declared.