Autoreactive B Cell Differentiation in Diffuse Ectopic Lymphoid-Like Structures of Inflamed Pemphigus Lesions

Pemphigus is an organ-specific autoimmune disease that targets skin and/or mucous membranes. Our previous study showed that infiltrating lymphocytes in pemphigus vulgaris (PV) lesions produce anti-desmoglein (Dsg) 1/3 antibodies after in vitro culture. In this study, we found diffuse ectopic lymphoid-like structures (ELSs) commonly present in the lesions of both PV and pemphigus foliaceus. Notably, pemphigus lesions contained centroblasts, plasmablasts, and plasma cells, which recapitulated the different stages of B cell differentiation. Elevated mRNA expression levels of the differentiation-related transcription factors BLIMP-1, IRF4, and BCL-6 were observed in pemphigus lesions. Moreover, B cell receptor repertoire analysis revealed the clonal expansion of the lesional B cells. Lesional B cells might recirculate among lesions, lymph nodes, and peripheral blood. Increased mRNA expression levels of multiple chemokines in pemphigus lesions and elevated expression levels of chemokine receptors on lesional B cells were also observed. Collectively, these results show that the ELSs in pemphigus lesions might act as a niche, supporting in situ B cell differentiation and clonal expansion.