The aim of the present study was to investigate the in vitro activity of 15 essential oils, 4 essential oil fractions, and 3 pure compounds (thymol, carvacrol, and eugenol) on phagocytosis by human neutrophils and on complement system. Samples were characterized by GC and GC-MS. Most of the oils (nutmeg, clove, niaouli, tea tree, bay laurel, lemon, red thyme, ginger), nutmeg terpenes, eugenol, and carvacrol showed mild to moderate inhibition of phagocytosis (25-40% inhibition at doses ranging from 40 to 60 μg/mL); highest inhibitory activity was found for thymol (72% at 56 μg/mL), whereas the mixture of bornyl and isobornyl acetates showed a mild stimulating activity (21% at 56 μg/mL). All samples were inactive in the alternative pathway of complement system, whereas on classical pathway, clove oil, eugenol, palmarosa oil, red thyme oil, tarragon oil, and carvacrol showed the highest activity, with IC50 values ranging from 65 to 78 μg/mL.
Keywords: anticomplement effects; complement system; essential oils; immune modulation; phagocytosis.