Generation of functional murine CD11c⁺ age-associated B cells in the absence of B cell T-bet expression

Age-associated B cells (ABC), a novel subset of activated B cells defined by CD11b and CD11c expression, have been linked with both protective anti-viral responses and the pathogenesis of systemic autoimmunity. Expression of the T_H 1 lineage transcription factor T-bet has been identified as a defining feature of ABC biology, with B cell-intrinsic expression of this transcription factor proposed to be required for ABC formation. In contrast to this model, we report that Tbx21 (encoding T-bet)-deficient B cells upregulate CD11b and CD11c surface expression in vitro in response to integrated TLR and cytokine signals. Moreover, B cell-intrinsic T-bet deletion in a murine lupus model exerted no impact of ABC generation in vivo, with Tbx21^-/- ABCs exhibiting an identical surface phenotype to wild-type (WT) ABCs. Importantly, WT and Tbx21^-/- ABCs sorted from autoimmune mice produced equivalent amounts of IgM and IgG ex vivo following TLR stimulation, indicating that T-bet-deficient ABCs are likely functional in vivo. In summary, our data contradict the established literature by demonstrating that T-bet expression is not uniformly required for ABC generation.