a–c, Mice of the indicated genotypes were irradiated with 8 Gy and analysed 8 h later. a, Immunofluorescence for cCaspase-3 (red) and EpCam (blue). Scale bars, 50 µm. Quantification of cCaspase-3+ cells by histology (b; Il22+/+, n = 3; Il22−/−, n = 6; Il22ra1fl/fl;Vil1-cre, n = 3; Ahrfl/fl;Rorc(γt)-cre, n = 4, mean ± s.e.m.) or by flow cytometry (c; n = 3; mean ± s.e.m.; P = 0.003). d, IL-22 neutralizing antibody or control IgG was injected intraperitoneally 36 h and 12 h before, and 12 h after AOM application. Representative immunofluorescence images of the colon 24 h after AOM treatment, stained for LGR5 (blue) and cCaspase-3 (red; arrows indicate apoptotic stem cells). Right, quantification of cCaspase-3+ crypts (n = 3; mean ± s.e.m.; P = 0.0039). e, IL-22-responsive IEC6 cells were cultured with or without recombinant IL-22. Cells were irradiated with 2 Gy or left untreated and cultured in the presence of cytochalasin B. DNA was visualized with DAPI 48 h after irradiation and number of cells containing one or more micronuclei was counted (n = 4, mean ± s.e.m.). Representative images of untreated (ctrl) or irradiated (2 Gy) IEC6 cells. Arrow indicates a micronucleus. f, Mice of the indicated genotypes were irradiated with 8 Gy. Quantification of BrdU+ cells in colonic crypts (n = 3; mean ± s.e.m.). Data are representative of two biologically independent experiments.