To investigate the immunomodulatory activities of phytocompounds for potential therapeutics, we devised an in vivo, transgenic, human cytokine gene promoter assay using defined epidermal skin cells as test tissue. Test compounds were topically applied to mouse skin before or after gene gun transfection, using a cytokine gene promoter-driven luciferase reporter. Croton oil, an inflammation inducer, induced transgenic GM-CSF and TNF-alpha promoter activities in skin epidermis 6-fold and 3.4-fold, respectively; however, it produced a less than 1.5-fold and 1.7-fold change in IL-1beta and IL-18 promoter activity, respectively. The phytocompound shikonin drastically inhibited inducible GM-CSF promoter activity. However, a fraction of Dioscorea batatas extract significantly increased the GM-CSF promoter activity in normal and inflamed skin. Shikonin suppressed the transcriptional activity of GM-CSF promoter by inhibiting the binding of TFIID protein complex (TBP) to TATA box. Our results demonstrate that this in vivo transgenic promoter activity assay system is cytokine gene-specific, and highly responsive to pro-inflammatory or anti-inflammatory stimuli. Currently it is difficult to profile the expression and cross-talk of various types of cytokines in vivo. This investigation has established a bona fide in vivo, in situ, immune tissue system for research into cytokine response to inflammation.