ABSTRACT
Ectopic lymphoid structures (ELS) are present in rheumatoid arthritis (RA) synovial tissue, but the precise pathways of B cell activation and the role of in situ synovial B cell differentiation and selection in disease are not well understood. Here, we identified a B cell population in the synovium characterized by expression of NR4A1-3, a family of orphan nuclear receptors, that is highly enriched at both early and late stages of RA. NR4A B cells are rare in healthy peripheral blood, RA blood, and SLE kidney, but share markers with blood transcriptomic signatures that peak during RA disease flare. Using combined single cell transcriptomics and B cell receptor (BCR) sequencing, we demonstrate that NR4A synovial B cells have an activated transcriptomic profile that significantly overlaps with germinal center (GC) light zone (LZ) B cells and an accrual of somatic hypermutation that correlates with loss of naïve B cell status. NR4A B cells uniquely co-express lymphotoxin β and IL6, supporting important functions in ELS promotion and pro-inflammatory cytokine production. The presence of shared clones in this activated B cell state, NR4A expressing synovial plasma cells (PC), and CCR6+ memory B cell (MBC) precursors further points to in situ differentiation. NR4A1 was expressed at the protein level in RA synovial B cells and PC, was high in tonsil GC B cells with a light zone (LZ)-dark zone (DZ) intermediate phenotype, and was rapidly induced at both the RNA and protein level upon activation through the BCR. Taken together, we identified a dynamic progression of B cell activation in RA synovial ELS, with NR4A as a read-out of likely antigen activation and local adaptive immune responses.
Competing Interest Statement
Soumya Raychauduri is a paid consultant for Gilead, Pfizer, Rheos, J&J and a founder of Mestag, Inc. Dana Orange is an inventor of two non-licensed patents US 63/031,861 entitled Markers and Cellular Antecedents of Rheumatoid Arthritis Flares and US 63/050,155 entitled Method and System for RNA Isolation from Self-Collected and Small Volume Samples. Susan Goodman receives research support from Novartis and a consultant for UCB The rest of authors have no competing interest.
Footnotes
↵* A list of members and affiliations appears at the end of the paper