Symbiotic bacteria-dependent expansion of MR1-reactive T cells causes autoimmunity in the absence of Bcl11b

MHC class I-related protein 1 (MR1) is a metabolite-presenting molecule that restricts MR1-reactive T cells including mucosal-associated invariant T (MAIT) cells. In contrast to MAIT cells, the function of other MR1-restricted T cell subsets is largely unknown. Here, we report that mice in which a T cell-specific transcription factor, B-cell lymphoma/leukemia 11B (Bcl11b), was ablated in immature thymocytes (Bcl11b( increment iThy) mice) develop chronic inflammation. Bcl11b( increment iThy) mice lack conventional T cells and MAIT cells, whereas CD4(+)IL-18R(+) alpha beta T cells expressing skewed Traj33 (J alpha 33)(+) T cell receptors (TCR) accumulate in the periphery, which are necessary and sufficient for the pathogenesis. The disorders observed in Bcl11b( increment iThy) mice are ameliorated by MR1-deficiency, transfer of conventional T cells, or germ-free conditions. We further show the crystal structure of the TCR expressed by Traj33(+) T cells expanded in Bcl11b( increment iThy) mice. Overall, we establish that MR1-reactive T cells have pathogenic potential. MR1 functions as an antigen presenting protein on cells in addition to MAIT cells. Here the authors use an early T cell-specific Bcl11b-deficient mouse that develops autoimmunity through a population of nonconventional MR1-restricted T cells and characterise their function.

Automated summary

By studying a Bcl11b-deficient mouse model, the authors found that MR1-reactive T cells have pathogenic potential and that MR1 functions as an antigen presenting protein on cells other than MAIT cells.