B cells in Takayasu’s arteritis upregulate genes involved in RNA splicing, protein synthesis, and BCR signaling compared to healthy individuals 2258135

Introduction Aortic specimens from patients with large vessel vasculitis (LVV) have shown prominent B cells organizing into arterial tertiary lymphoid structures with germinal centers. We hypothesized that B cells in LVV patients would show transcriptional changes associated with enhanced B cell activation and function. Methods To test this hypothesis, CD19+ cells were flow cytometry purified from peripheral blood mononuclear cells (PBMCs) of patients with Takayasu arteritis (TAK) (n = 7), giant cell arteritis (GCA) (n = 1), or healthy controls (n = 4) and single-cell RNA-seq/BCR-seq profiling was performed using the 10X Genomics platform. Pathway analysis was performed using g:Profiler. Results Seurat analysis identified n = 12 transcriptionally defined clusters, with no major differences in cluster distribution noted between TAK or HC individuals. TAK patients showed upregulated genes relative to healthy donors (FC > 1.5, padj < 0.05) in naïve (n = 119 genes), transitional (n = 21 genes), activated (n = 19 genes), and memory (n = 192 genes) B cell subsets. In Memory B cells, upregulated genes were involved in RNA alternative splicing (RBFOX2), mitochondrial function (MT-ND3 and MT-ATP8), protein synthesis (RPS18 and RPL3), T cell co-stimulation (CD86), actin cytoskeleton rearrangement (TAGLN2 and ACTG1), and cell proliferation (DHFR and GAREM1). Pathway analysis on memory B cells identified upregulation of B cell receptor signaling (THEMIS2 and GCSAM). In activated B cells, upregulated genes were involved in endocytosis (RABGAP1L and BMP2K), cell migration (ARHGEF18), and cell proliferation (DLEU2 and IKZF3). Conclusion In conclusion, TAK patient B cells exhibit a distinct transcriptional program that might support interactions with autoreactive T cells and contribute to autoimmune disease liability. Future studies will be required to evaluate the functional consequences of these changes with respect to tissue damage in vasculitis. Funding Source NIH Grants R01 DK131070 (R.H.B.), T32 AR059039 (G.J.R.), and a VICTR Pilot & Feasibility Award (R.H.B. and J.M.S.) supported this work.