β-1,4-mannobiose stimulates innate immune responses and induces TLR4-dependent activation of mouse macrophages but reduces severity of inflammation during endotoxemia in mice.

β-1,4-Mannobiose (MNB) has been shown to exert prebiotic activity and modulate mucosal gene expression. In this study, the immune-modulating effect of MNB in healthy and endotoxemic mice and its role in Toll-like receptor (TLR) 2/4-mediated macrophage activation were investigated. Mice were supplemented daily with MNB (0, 5, 10, or 25 mg/kg) for 14 d. To examine the effect of MNB during endotoxemia, mice were supplemented with or without MNB (25 mg/kg) for 14 d, followed by challenge with intraperitoneal LPS or saline. MNB induced expression of both T helper (Th) 1- and Th2-type cytokines in the ileum (P < 0.05) and increased fecal IgA production and splenic NK cell activity (P < 0.05) in healthy mice. In endotoxemic mice, MNB reduced the expression of Tnfa, Il-6, iNos (P < 0.05), and Il-10 (P < 0.05), and reduced LPS-induced weight loss but increased Ifng, Il-12p40, Il-5, and Ifna expression (P < 0.05) and NK cell activity relative to positive control (LPS) mice. Treatment of RAW 264.7 macrophages with MNB induced TNF-α and IL-6 secretion (P < 0.05), and this effect was abrogated by inhibiting TLR4, but not TLR2, signaling. Pretreatment of RAW 264.7 cells with MNB induced tolerance to TLR2 and TLR4 agonists, reducing TNF-α production (P < 0.05) upon secondary stimulation with LPS or lipoteichoic acid. These results indicate that MNB can modulate intestinal and systemic immune responses in healthy and endotoxemic mice and prevent LPS-induced immune suppression, as well as directly stimulating innate immune mechanisms in vitro as a TLR4 agonist.