T-bet or not T-bet: taking the last bow on the autoimmunity stage

The search for the encephalitogenic factor driving pathogenic T cells in autoimmune diseases such as rheumatoid arthritis, multiple sclerosis (MS), and psoriasis has proven to be a long and difficult mission, which is not yet completed. In this issue of the European Journal of Immunology, the importance of the transcription factor T-bet, previously shown to be essential for the induction of autoimmune disease in mice, is challenged. Two independent groups, O'Connor et al. [Eur. J. Immunol. 2013. 43:2818-2823] report] and Grifka-Walk et al. [Eur. J. Immunol. 2013. 43:2824-2831], report that T-bet is not mandatory for T cells to cause experimental autoimmune encephalomyelitis (EAE), which serves as a paradigmatic T-cell-mediated autoimmune disease. Both groups found that T-bet KO mice were fully susceptible to develop EAE, both after immunization with self-antigen and after adoptive transfer of IL-23-polarized autoaggressive T cells. T-bet deficiency mediated the loss of IFN-γ expression but retained or even enhanced GM-CSF and IL-17 production by central nervous system (CNS)-infiltrating T cells. These findings indicate that we have lost the last transcriptional regulator previously held to be required for the generation of autoimmune pathogenic T cells.