They used the T cell transfer colitis model, an invaluable model to dissect pathogenic and protective mechanisms of CD4+ T cells (11) and scRNA-seq to identify a new population of IFNγ-secreting CD4+ cytotoxic T lymphocytes that were induced by IL-23 and the food dye Red 40 to promote colitis pathogenesis (27). Here, CD4 is linked to colitis.