In vitro inhibitory effects of thymol and carvacrol on dendritic cell activation and function

Context: Thyme has been used in traditional medicine for medicinal purposes since ancient times.Objective: The objective of this study was to investigate the effects of thymol and carvacrol as two major constituents of thyme on dendritic cells (DCs) maturation and T cell activation.Materials and methods: Splenic DCs were treated with non-cytotoxic concentrations of the components and then analyzed for MHC II, CD86, and CD40 expression by flow cytometry. The effects of compounds on mitogenic, as well as allogenic T cell responses in mixed lymphocyte culture (MLR) and the release of cytokines were investigated.Results: At 0.1 mu g/ml, reduced mean fluorescent intensity (MFI) of CD86 for thymol (80.30.2% of untreated control) and CD40 for carvacrol (79.5 +/- 0.14%) was observed (p<0.001). Decreased mitogenic T cell proliferation by thymol [proliferation index (PI) from 0.93 +/- 0.11 at 1 mu g/ml to 0.42 +/- 0.16 at 100 mu g/ml (p<0.01)] and carvacrol [PI from 1.08 +/- 0.3 at 1 mu g/ml to 0.28 +/- 0.1 at 100 mu g/ml (p<0.001)] was seen. Ten micrograms/ml thymol (PI, 0.85 +/- 0.04) and carvacrol (PI, 0.89 +/- 0.03) inhibited allogenic T cell response (p<0.05). Decreased IFN- level in MLR supernatant from 1441 +/- 27.7pg/ml in untreated cells to 944 +/- 32.1 at 10 mu g/ml of thymol and of carvacrol (886 +/- 31.7pg/ml) (p<0.01) was found. IL-4 levels were decreased in the presence of both compounds (p<0.01).Conclusion: These data showed the suppressive effects of thymol and carvacrol on DCs maturation and function, as well as T cell responses.