Absence of IL-4 and IFN-γ led to augmented Th17 differentiation and exacerbated damage in skin but not in lung. BALB/c recipients given IFN-γ^−/− donor cells were treated with rat-IgG or anti–IL-4. (A) Intracellular cytokine profiles of splenic CD4⁺ T cells 13 days after HCT. Gated CD4⁺ T cells are shown in CD4 versus cytokines. Representative of 4 replicate experiments is shown. (B-C) H&E staining of lung- and skin-tissue sections of recipients 15 days after HCT and mean ± SE of histopathology scores (n = 8).