FAS, also known as tumor necrosis factor receptor superfamily member 6, belongs to the death receptor subfamily of the TNF receptor superfamily and is designated TNFRSF6. This protein plays a major role in controlling viral infections. While FAS is expressed on most cell types, its cognate ligand (FasL) is restricted to activated T, NK and dendritic cells. The upregulation of FasL and TRAIL on HCMV-infected dendritic cells promotes direct killing of activated T lymphocytes, an action that may preferentially delete HCMV-specific T cells. Moreover, the activation of FasL on HCMVinfected retinal pigment epithelial cells may subvertneutrophil function in HCMV retinitis. Recombinant human FAS, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.