IFN-γ⁺ cytotoxic CD4⁺ T lymphocytes are involved in the pathogenesis of colitis induced by IL-23 and the food colorant Red 40

The food colorant Red 40 is an environmental risk factor for colitis development in mice with increased expression of interleukin (IL)-23. This immune response is mediated by CD4⁺ T cells, but mechanistic insights into how these CD4⁺ T cells trigger and perpetuate colitis have remained elusive. Here, using single-cell transcriptomic analysis, we found that several CD4⁺ T-cell subsets are present in the intestines of colitic mice, including an interferon (IFN)-γ-producing subset. In vivo challenge of primed mice with Red 40 promoted rapid activation of CD4⁺ T cells and caused marked intestinal epithelial cell (IEC) apoptosis that was attenuated by depletion of CD4⁺ cells and blockade of IFN-γ. Ex vivo experiments showed that intestinal CD4⁺ T cells from colitic mice directly promoted apoptosis of IECs and intestinal enteroids. CD4⁺ T cell-mediated cytotoxicity was contact-dependent and required FasL, which promoted caspase-dependent cell death in target IECs. Genetic ablation of IFN-γ constrained IL-23- and Red 40-induced colitis development, and blockade of IFN-γ inhibited epithelial cell death in vivo. These results advance the understanding of the mechanisms regulating colitis development caused by IL-23 and food colorants and identify IFN-γ⁺ cytotoxic CD4⁺ T cells as a new potential therapeutic target for colitis.