Chronic TLR7 activation promotes expansion of activated CD11c+ double-negative B cells and autoreactive humoral responses in lupus-like autoimmunity.

Age-associated B cells (ABCs) have emerged as a distinct B cell population associated with aging, chronic inflammation, and autoimmunity. Notably, the expansion of ABC-like CD11c-expressing B cells has been observed in patients with systemic lupus erythematosus and in experimental models of lupus-like disease, suggesting their potential involvement in disease pathogenesis. Although their relevance in autoimmunity is increasingly appreciated, the identity and functional contribution of CD11c+ B cell populations arising during chronic Toll-like receptor 7 (TLR7)-driven immune activation remain incompletely defined. In this study, we investigated the role of CD11c+CD21-CD23- B cells (hereafter DN CD11c+ B cells) in a lupus-like model induced by chronic activation of TLR7. Young female C57BL/6 mice were treated with the TLR7 agonist imiquimod for 10 weeks, leading to systemic immune activation characterized by splenomegaly, elevated proinflammatory cytokines, anti-nuclear autoantibodies, and early renal alterations. This was accompanied by a marked remodeling of the B cell compartment, including expansion of non-canonical subsets, particularly DN CD11c+ B cells. Phenotypic analysis revealed that DN CD11c+ B cells exhibited an activated profile, with increased expression of T-bet, TLR7, costimulatory molecules, and activation-associated markers, as well as a higher proportion of class-switched cells. Functional assays demonstrated that DN CD11c+ B cells from imiquimod-treated mice were hyperresponsive to TLR7 stimulation. Furthermore, DN CD11c+ B cells were a major ex vivo source of autoreactive antibodies, including IgG directed against nuclear antigens, whereas conventional B cell subsets showed minimal contribution. In addition, DN CD11c+ B cells were detected in renal tissue prior to the development of overt pathology, suggesting a role in early tissue infiltration. Importantly, pharmacological activation of the adenosine A2A receptor preferentially reduced the frequency of DN CD11c+ B cells, autoantibody production, and immune cell infiltration, while largely sparing conventional B cell subsets. Collectively, these findings identify expanded and activated DN CD11c+ B cells as important effectors linking chronic innate immune activation to autoreactive humoral responses and highlight A2A receptor signaling as a potential strategy to selectively modulate pathogenic B cell responses in lupus-like autoimmunity.