To determine whether the number of HCMV infected cells could influence the amount of active TGF-β1 produced, HK-2 cells were infected with HCMV strain TR at increasing multiplicity of infection (MOI) ranging from 2 to 10, stimulated with raTGF-β1 at 15 ng/ml (0.6 nM), and supernatants assayed for TGF-β1 production by luciferase bioassay. Here, TGFB1 is linked to infection.