The alarmins IL-1 and IL-33 differentially regulate the functional specialisation of Foxp3+ regulatory T cells during mucosal inflammation

CD4(+)Foxp3(+) regulatory T (T-REG) cells are critical mediators of peripheral tolerance and modulators of immune responses. Functional adaptation of T-REG cells, through acquisition of secondary transcription factors is critical for their effector differentiation towards local inflammatory stimuli including infections. The drivers and consequences of this adaptation of T-REG cell function remain largely unknown. Using an unbiased screen, we identified receptors of the IL-1 family controlling the adaptation of T-REG cells. Through respiratory infection models, we show that the IL-33 receptor (ST2) and the IL-1 receptor (IL1R1) selectively identify stable and unstable T-REG cells at mucosal surfaces, respectively. IL-33, not IL-1, is specifically required for maintaining the suppressive function of T-REG cells. In the absence of ST2, T-REG cells are prone to lose Foxp3 expression and acquire ROR gamma T and IL1R1, while, in the absence of IL-1R1, they maintain Foxp3 expression and resist the acquisition of a Th17 phenotype. Finally, lack of IL-1 signalling enhances the accumulation of ST2(+) T-REG over pro-inflammatory T-REG cells in a Cryptococcus neoformans infection. These observations show that IL-1 and IL-33 exert opposing functions in controlling the functional adaptation of T-REG cells, ultimately dictating the dynamics of adaptive immunity to pathogens.