J Manipulative Physiol Ther. 1999 Sep; 22(7): 447-53.

Biological activity of Melaleuca alternifola (Tea Tree) oil component, terpinen-4-ol, in human myelocytic cell line HL-60.

Budhiraja SS, Cullum ME, Sioutis SS, Evangelista L, Habanova ST.

Department of Research, National College of Chiropractic, Lombard, Ill, USA.

BACKGROUND: Tea tree oil is an aboriginal Australian traditional medicine for bruises, insect bites, and skin infections. It was rediscovered in the 1920s as a topical antiseptic that is more effective than Phenol. Previous studies 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 action through white blood cell activation. METHODS: Crude oil and the purified "active" component were studied by using a model system that responds to bioactive components by induction of differentiation in white blood cells. Methods used included white blood cell oxidative burst assay (nitroblue tetrazolium [NBT] dye reduction); cell proliferation assay (tritiated thymidine incorporation); cell surface differentiation marker assay (flow cytometric quantitation of phycoerythrin-anti-CD 11b binding); cell viability assay (trypan blue exclusion); and cellular differentiation enzyme assay (white cell esterase staining). RESULTS: Collectively, five assays that measure differentiation in white blood cells indicated monocytic differentiation after treatment with either crude oil or the purified active component. Both the crude oil and the purified active component, (+:-) terpinene-4-ol, caused a similar type and amount of differentiation. The culture of cells in medium containing serum caused more activation than in medium containing no serum. CONCLUSION: The antiseptic activity of tea tree oil appears to be due, in part, to white blood cell activation.