Role of B cell activation through Toll-like receptors in Systemic Lupus Erythematosus.

Introduction/Rationale: Systemic Lupus Erythematosus (SLE) is an autoimmune disease and a leading cause of death in young women. Its high clinical heterogeneity makes therapy development challenging. SLE is marked by autoantibodies targeting DNA and associated proteins, patients often display interferon and plasmablast transcriptomic signatures. One notable B cell subset in SLE is the double negative 2 (DN2; CD27⁻ IgD⁻ CD11c⁺ CD21⁻) population, expanded in patients with active disease and are poised to differentiate into autoreactive antibody-secreting cells, contributing to disease progression.

Methods: We used novel activation and culture protocols based on TLR7/9 stimulation and CD40L co-stimulation of naïve B cells (nBCs) from healthy donors and SLE patients, and the generation of a human tonsil organoid model aimed to mimic the heterogeneity observed in late B cell developmental stages in SLE, including likely pathogenic DN2 B cells, plasmablasts (PBs) and plasma cells (PCs), as well as the B cell receptor (BCR) repertoire encoded by VDJ recombination commonly associated with autoreactive B cells in SLE.

Results: Data showed that TLR7 and CD40L co-stimulation of peripheral nBCs enhanced B cell survival and differentiation into late developmental stages, such as PBs and PCs after 7 and 14 days of stimulation. DN2 expansion was also showed as previously reported. Nevertheless, differentiation of nBCs was controlled when stimulated through TLR9 or the mixed activation cocktail containing ligands for both TLR7 and TLR9 and co-stimulation. Single Cell RNA sequencing (sc-RNAseq) data of VDJ rearrangements after TLR stimulation showed the presence of at least one BCR rearrangement, denominated VH4-34, previously reported as autoreactive. Similar behavior was observed on tonsil organoids consisting of nBCs from tonsil samples of healthy individuals.

Conclusion: B cell differentiation and fate is controlled by the kind of TLR used to activate these cells, enhancing autoreactivity when TLR7 is stimulated.