THBS1 and cytomegalovirus infection: To characterize the mechanism by which HCMV infection might induce active TGF-β1 production, we added known inhibitors of TGF-β1 activation - aprotinin (serine protease inhibitor against plasmin), GM6001 (matrix metalloprotease inhibitor), anti-thrombospondin-1, anti-αvβ6 integrin - to HCMV infected HK-2 cells prior to raTGF-β1 stimulation and again after washing, and the TGF-β1 luciferase bioassay was performed (Figure 5A).