Self-reactive B cells are increased in all major stages of peripheral development in Sjögren's disease

Sjögren's disease (SjD) is a chronic autoimmune disorder characterized by increased circulating self-reactive B cells. While many of these self-reactive B cells emerge from the bone marrow, it is not known whether they are excluded from or enriched in specific developmental stages in the periphery. The aim of this study was to determine the immunophenotype of circulating self-reactive B cells in SjD to inform more precise therapeutic targeting. Five major B cell populations: transitional, mature naïve, switched memory, double negative and plasmablasts were single-cell sorted and cultured to produce IgG. Self-reactive IgG was identified by ELISA, flow cytometry of permeabilized HEK293 cells and HEp-2 indirect immunofluorescence. Immunoglobulin heavy chains were sequenced by Sanger and next-generation sequencing. Compared with healthy donor controls (HCs), SjD patients had higher frequencies of naïve and CD21^low atypical memory B cell subsets, while antigen-experienced B cells expressed more Ki67 and CD86. B cells recognizing intracellular self-antigens were identified in all stages of peripheral B cell development for SjD and HCs, but frequencies of autoreactive B cells were up to 10-fold higher in SjD. Self-reactive transitional B cells expressed higher surface CD38 and lower surface IgM. An increase in self-reactive B cells throughout peripheral development in SjD compared with HCs suggests that counterselection of autoantibody-bearing B cells during central and peripheral tolerance checkpoints are reduced in SjD. Therapeutic strategies focused on depleting B cells based on B cell receptor specificity rather than the developmental stage would be more efficient to target self-reactive B cells in SjD.