Stimulation of mouse dendritic cells by Gum Arabic

Gum Arabic (GA), a nonabsorbable nutrient manufactured from the exudate of Acacia senegal, is composed of a complex polysaccharide. GA is used by the pharmaceutical and food industry as an emulsifier but may, at an appropriate dosage, modify intestinal transport. Dendritic cells (DCs) can protrude between epithelial cells and sense the composition of the lumen. As DCs are stimulated by bacterial polysaccharides, we hypothesized that GA may similarly stimulate DCs. To test that hypothesis, mouse DCs were treated with either LPS or GA and expression of maturation markers, phagocytotic activity, cytokine production and ability to stimulate CD4(+) T cells in allogenic mixed leukocyte reaction (allo-MLR) was analyzed. As a result both LPS and GA increased the percentage of CD11c(+)CD86(+), CD11c(+)MHCII(+), CD11c(+)CD40(+), CD54-expressing DCs and decreased their phagocytic activity. Both LPS and GA stimulated the production of IL-6, IL-10, IL12p70 and TNFalpha in a p38- and/or ERK-dependent manner. GA treatment led to an enhanced IL-10 secretion, whereas LPS was more effective on IL-6 and IL-12p70 production. Both LPS- and GA-stimulated DCs enhanced CD4(+) T cell proliferation but the profile of cytokines produced in allo-MLR was different. High levels of IL-10 and IL-6 were observed in the presence of GA-treated DCs, whereas IFN-gamma and IL-12p70 production was similar with LPS- or GA-treated DCs. LPS upregulated p38 and transiently ERK1/2, while GA led to more sustained activation of ERK1/2, only. In conclusion, the observations reveal a powerful immunomodulatory effect of GA.