Reciprocal differentiation and tissue-specific pathogenesis of Th1, Th2, and Th17 cells in graft-versus-host disease

In acute graft-versus-host disease (GVHD), naive donor CD4⁺ T cells recognize alloantigens on host antigen-presenting cells and differentiate into T helper (Th) subsets (Th1, Th2, and Th17 cells), but the role of Th subsets in GVHD pathogenesis is incompletely characterized. Here we report that, in an MHC-mismatched model of C57BL/6 donor to BALB/c recipient, WT donor CD4⁺ T cells predominantly differentiated into Th1 cells and preferentially mediated GVHD tissue damage in gut and liver. However, absence of interferon-γ (IFN-γ) in CD4⁺ T cells resulted in augmented Th2 and Th17 differentiation and exacerbated tissue damage in lung and skin; absence of both IL-4 and IFN-γ resulted in augmented Th17 differentiation and preferential, although not exclusive, tissue damage in skin; and absence of both IFN-γ and IL-17 led to further augmentation of Th2 differentiation and idiopathic pneumonia. The tissue-specific GVHD mediated by Th1, Th2, and Th17 cells was in part associated with their tissue-specific migration mediated by differential expression of chemokine receptors. Furthermore, lack of tissue expression of the IFN-γ-inducible B7-H1 played a critical role in augmenting the Th2-mediated idiopathic pneumonia. These results indicate donor CD4⁺ T cells can reciprocally differentiate into Th1, Th2, and Th17 cells that mediate organ-specific GVHD.