Biological activity of Melaleuca alternifolia (tea tree) oil component, terpinen-4-ol, in human myelocytic cell line HL-60

Background: Tea tree oil is an aboriginal Australian traditional medicine f or bruises, insect bites, and skin infections; It was rediscovered in the 1 920s as a topical antiseptic that is more effective than Phenol. Previous s tudies have demonstrated its antiseptic qualities, but its effects on human white blood cells have never been investigated. Objective: To test the hypothesis that tea tree oil exerts its antiseptic a ction through white blood cell activation. Methods: Crude oil and the purified "active" component were studied by usin g a model system that responds to bioactive components by induction of diff erentiation in white blood cells. Methods used included white blood cell ox idative burst assay (nitroblue tetrazolium [NBT] dye reduction); cell proli feration assay (tritiated thymidine incorporation); cell surface differenti ation marker assay (flow cytometric quantitation of phycoerythrin-anti-CD 1 1b binding); cell viability assay (trypan blue exclusion); and cellular dif ferentiation enzyme assay (white cell esterase staining). Results: Collectively, five assays that measure differentiation in white bl ood cells indicated monocytic differentiation after treatment with either c rude oil or the purified active component. Both the crude oil and the purif ied active component, (+:-) terpinene-4-ol, caused a similar type and amoun t of differentiation. The culture of cells in medium containing serum cause d more activation than in medium containing no serum. Conclusion: The antiseptic activity of tea tree oil appears to be due, in p art, to white blood cell activation.