In addition, there are several functionally less well characterized interferon-induced genes, such as INDO, CXCL9, CXCL10, GBP1, GBP2, GBP4, IFITM1 and CD274. CD274 is up-regulated on lymphocytes upon IFN-gamma activation and plays a role in T cell co-stimulation and apoptosis during viral infections [32]. Here, IDO1 is linked to viral infectious disease.