Natural killer cell activity and lymphocyte activation: Investigating the effects of a selection of essential oils and components in vitro

A selection of essential oils and components were tested in vitro for potential immunomodulating effects on natural killer cell activity (NKCA) and lymphocyte activation through CD69 expression. Matricaria recutita, Boswellia carteri, Pelargonium graveolens, Lavandula angustifolia, Citrus limon, Melaleuca alternifolia, Melaleuca viridiflora, Santalum spicatum, Cedrus atlantica, and Thymus vulgaris ct. linalool essential oils were solubilised with ethanol and methylated β-cyclodextrin 1:5:25 (w/v) and pre-incubated at 10 μg/mL and 2 μg/mL (M. alternifolia and C. atlantica: 2 and 1 μg/mL) with human peripheral blood mononuclear cells (PBMC) for 2 h. They were then incubated for 2 h with K562 target cells before determination of NKCA. The first 6 of these oils were similarly solubilised, pre-incubated for 2 h with aliquots of whole blood, then incubated with PHA for 4 h before measurement of CD69 antigen expression. Reference components α-pinene, S-(-)-limonene, linalool, geraniol, thymol, 1,8-cineole, linalyl acetate, eugenol, (+)-terpinen-4-ol, and trans-caryophyllene were solubilised with ethanol 1:5 and similarly tested. Dose-dependent stimulation of NKCA was found for trans-caryophyllene and linalyl acetate. No other effects of essential oils or components were found in these assays. Methylated β-cyclodextrin proved to be a less than ideal agent for enhancing solubility of essential oils, due to substantial effects on assay outcomes