IFNG and glioblastoma: Therefore IDO expression in human glioblastoma cells (86HG39), HeLa cells and human foreskin fibroblasts (HFF) was induced by treatment with IFN-γ (500 U/mL) and cells were incubated for 72 h under normoxic conditions (20% O2), intermediate oxygen conditions (10% O2) or under hypoxic conditions (1% O2), respectively.