Plasmablast-like Phenotype Among Antigen-Experienced CXCR5-CD19(low) B Cells in Systemic Lupus Erythematosus

Objective Altered composition of the B cell compartment in the pathogenesis of systemic lupus erythematosus (SLE) is characterized by expanded plasmablast and IgD-CD27- double-negative B cell populations. Previous studies showed that double-negative B cells represent a heterogeneous subset, and further characterization is needed. Methods We analyzed 2 independent cohorts of healthy donors and SLE patients, using a combined approach of flow cytometry (for 16 healthy donors and 28 SLE patients) and mass cytometry (for 18 healthy donors and 24 SLE patients) and targeted RNA-Seq analysis. To compare B cell subset formation during the acute immune response versus that during autoimmune disease, we investigated healthy donors at various time points after receipt of the BNT162b2 messenger RNA COVID-19 vaccine and patients with acute SARS-CoV-2 infection, using flow cytometry. Results We found that IgD-CD27+ switched and atypical IgD-CD27- memory B cells, the levels of which were increased in SLE patients, represented heterogeneous populations composed of 3 different subsets each. CXCR5+CD19(intermediate), CXCR5-CD19(high), and CXCR5-CD19(low) populations were found in the switched memory and double-negative compartments, suggesting the relatedness of IgD-CD27+ and IgD-CD27- B cells. We characterized a hitherto unknown and antigen-experienced CXCR5-CD19(low) subset that was enhanced in SLE patients, had a plasmablast phenotype with diminished B cell receptor responsiveness, and expressed CD38, CD95, CD71, PRDM1, XBP1, and IRF4. Levels of CXCR5-CD19(low) subsets were increased and correlated with plasmablast frequencies in SLE patients and in healthy donors who received BNT162b2, suggesting their interrelationship and contribution to plasmacytosis. The detection of CXCR5-CD19(low) B cells among both CD27+ and CD27- populations calls into question the role of CD27 as a reliable marker of B cell differentiation. Conclusion Our data suggest that CXCR5-CD19(low) B cells are precursors of plasmablasts. Thus, cotargeting this subset may have therapeutic value in SLE.