4–9 According to observations made in murine models of autoimmunity, in addition to the production of autoreactive IgG, ABCs are also implicated in the enhanced antigen presentation to T cells and the formation of spontaneous germinal centres.4,12–14 T-bet, a transcription factor which is highly expressed in ABCs, is considered to be a master regulator of all these processes,12 although recently published data indicate that functional murine ABCs can be generated, both in vivo and in vitro, in the absence of T-bet expression in B cells.15 This evidence concerns the gene TBX21 and Autoimmunity.