Ultimately, a study examining the combined deficiency of IL-4, IL-5, IL-9, and IL-13 within T cells using a mature mouse model indicated that this collective absence of Th2 cytokines led to enhanced T cell proliferation as well as elevated serum concentrations of TNF-α, IL-2, IFN-γ, and IL17a—culminating in exacerbated manifestations of GVHD [115]. This evidence concerns the gene IL9 and graft versus host disease.