In addition, aminoguanidine treatment inhibited NO production (Figure S2) and prevented IDO1 protein level reductions in all IFN-γ- and IL-1β-costimulated A172 glioblastoma, IMR-32 neuroblastoma, and T98G glioblastoma human brain cell lines (Figure 2D). Here, IDO1 is linked to glioblastoma.