Particulate and solubilized β-glucan and non-β-glucan fractions of Euglena gracilis induce pro-and anti-inflammatory innate immune cell responses and exhibit antioxidant properties

PURPOSE: The purpose of this work was to determine the pro-and anti-inflammatory properties of the single-cell organism Euglena gracilis (EG) and various fractions of its whole biomass. METHODS: Heterotrophically grown EG was tested, along with its aqueous fraction (E-AQ), the intact linear β-glucan paramylon granules (PAR), and alkaline-solubilized paramylon. Peripheral blood mononuclear cell cultures were treated with the test products and analyzed for a variety of cellular responses. Immune cell activation was evaluated by flow cytometry detection of CD69 levels on CD3(−)CD56(+) NK cells, CD3(+)CD56(+) NKT cells, and monocytes, and cytokines were analyzed from the cell culture supernatants. Antioxidant capacity was measured by Folin–Ciocalteu assay and cellular antioxidant protection and MTT assays. RESULTS: EG and E-AQ were the most effective in driving immune cell responses as measured by CD69 upregulation on NK and NKT cells and proinflammatory (tumor necrosis factor, IL-6, IL-1β) cytokine production. None of the test products effectively stimulated monocyte. EG and PAR inhibited reactive oxygen species under conditions of oxidative stress. E-AQ contained antioxidants capable of providing cellular antioxidant protection from oxidative damage and protection of mitochondrial function under inflammatory conditions. CONCLUSION: The effects of EG on immune function are only partially attributable to the content of the β-glucan, paramylon. The regulation of additional cellular responses, such a reactive oxygen species production and resistance to oxidative stress, is likely mediated by currently unknown molecules found in the EG cell.