Background: Medicinal plants have been broadly used in treatment of various diseases. Mints are a group of plants belonging to labiatae family have anti-bacterial, anti-tumoral and anti-inflammatory effects. Peppermint is a mint specious extensively used in therapy of several disorders such as common cold and bronchitis. The anti-bronchospasmodic and anti-allergic effects of peppermint have also been shown. Elevation of interleukin-13 (IL-13) (a Th2- type cytokine) level is a well known indicator of allergy. In the present study the effect of aqueous extract of peppermint on IL-13 production in human peripheral blood mononuclear cells (hPBMCs) has been assessed in vitro. Methods: The hPBMCs were isolated from the venous blood of healthy volunteers by ficoll-hypaque-gradiant centrifugation. Then the PBMCs were cultured in complete RPMI medium. The cells at logarithmic growth phase, were incubated with different concentrations of aqueous extract of peppermint leaves (0.01-10 mg/ml) in triplicate for 24 hours. Afterward the cell culture supernates were collected and the IL-13 concentration was measured using a standard ELISA kit. Results: Peppermint aqueous extract significantly decreased the IL-13 production in hPBMCs dose-dependently. Conclusions: The results of this study indicate that peppermint aqueous extract down-regulates the production of IL-13 in hPBMCs. Regarding the important role of IL-13 in atopic allergy, the anti-allergic activity of peppermint and also its inhibitory effect on bronchospasm (a symptom of respiratory allergy), may be partly due to its inhibitory effects on IL-13 production.
