Euglena gracilis Enhances Innate and Adaptive Immunity through Specific Expression of Dectin-1 in CP-Induced Immunosuppressed Mice

Background: Euglena gracilis (E. gracilis), a species of unicellular algae, can accumulate large amounts of beta-1,3-glucan paramylon, a polysaccharide, in its cytoplasm and has recently attracted interest as a bioproduct due to its various health benefits. In this study, the immune-enhancing effect of E. gracilis powder (EP) was investigated in vitro and in vivo. Methods: In vitro, the production of NO and cytokines and the mechanism of the signaling pathway of beta-1,3-glucan were identified in RAW264.7 cells. In vivo, cyclophosphamide-induced (CP-induced) immunosuppressed C57BL/6 female mice were orally administered with three different concentrations (100, 300, and 600 mg/kg) of EP daily. After 14 days, the organs and whole blood were collected from each animal for further study. Results: The weight loss of CP-treated mice was reversed by treatment with EP to levels comparable to those of control mice. In addition, the frequencies of NK1.1(+), CD3(+), CD4(+), CD8(+), and B220(+) in immune cells isolated from the spleen were increased by EP treatment compared with water or RG. The secretion of TNF-alpha, IFN-gamma, and IL-12 from splenocytes was also increased by EP treatment, as was the level of IgM in the serum of the mice. Finally, EP treatment specifically upregulated the expression of dectin-1 in the liver of CP-treated mice. Conclusions: E. gracilis could be a good candidate for a natural immune stimulator in the innate and adaptive response by secreting TNF-alpha, IFN-gamma, and IL-12 through stimulating dectin-1 expression on the surface of immune cells.