Autoreactive B cells in rheumatoid arthritis consist of activated CXCR3+ memory B cells and plasmablasts

Many autoimmune diseases (AIDs) are characterized by persistence of autoreactive B cell responses which is often directly implicated in disease pathogenesis. How and why these cells are generated or how they are maintained for years is largely unknown. Rheumatoid arthritis is among the most common AIDs and characterized by autoantibodies recognizing proteins with post-translational modifications (PTMs). This PTM-directed, autoreactive B cell compartment is ill defined. Here, we visualized the B cell response against the three main types of PTM antigens implicated in RA by spectral flow cytometry. Our results show extensive cross-reactivity of autoreactive B cells against all three PTM antigens (citrulline, homocitrulline and acetyllysine). Unsupervised clustering revealed several distinct memory B cell (mBC) populations. Autoreactive cells clustered with the most recently activated, class-switched mBC phenotype, expressing high CD80, low CD24 and low CD21. Notably, patients also harbored large fractions of autoreactive plasmablasts (PB). Both PTM-directed mBC and PB showed high expression of CXCR3, a receptor for chemokines abundantly present in arthritic joints. Together, our data provide novel, detailed insight into the biology of B cell autoreactivity and its remarkable, seemingly exhaustless persistence in a prominent human AID.