Beyond autoantibodies: Biological roles of human autoreactive B cells in rheumatoid arthritis revealed by RNA-sequencing.

OBJECTIVE: To obtain the comprehensive transcriptome profile of human citrulline-specific B cells from patients diagnosed with rheumatoid arthritis (RA).

METHODS: Citrulline and hemagglutinin (HA) specific B cells were flow-sorted using peptide-streptavidin conjugates from peripheral blood of RA patients and healthy individuals respectively. Transcriptome profile of the sorted cells was obtained by RNA-sequencing, and expression of key protein molecules was evaluated by aptamer-based SOMAscan assay and flow cytometry. The ability of these proteins to effect differentiation of osteoclasts and proliferation and migration of synoviocytes was examined by in vitro functional assays.

RESULTS: Citrulline-specific B cells, in comparison to citrulline-negative B cells differentially express IL15RA, and genes related to protein citrullination and cyclic AMP signaling. By analyzing an independent cohort of CCP seropositive RA patients, we demonstrate that: (1) the expression of IL15Rα protein is enriched in citrulline-specific B cells within RA patients, and (2) surprisingly, all B cells from RA patients were capable of producing epidermal growth factor ligand, amphiregulin (AREG). AREG directly led to increased migration and proliferation of fibroblast-like synoviocytes (FLS), and in combination with anti-citrullinated protein antibodies (ACPA) led to the increased differentiation of osteoclasts.

CONCLUSION: To the best of our knowledge, this is the first study documenting the whole transcriptome profile of autoreactive B cells in any autoimmune disease. Our data identifies several genes and pathways that may be targeted by repurposing several FDA- approved drugs and can serve as the foundation for the comparative assessment of B-cell profiles in other autoimmune diseases. This article is protected by copyright. All rights reserved.