Immune Modulation by Different Types of β2→1-Fructans Is Toll-Like Receptor Dependent

Introduction: beta 2 -> 1-fructans are dietary fibers. Main objectives of this study were 1) to demonstrate direct signalling of beta 2 -> 1-fructans on immune cells, 2) to study whether this is mediated by the pattern recognition receptors Toll-like receptors (TLRs) and nucleotide-binding oligomerisation domain-containing proteins (NODs), and 3) to relate the observed effects to the chain length differences in beta 2 -> 1-fructans. Methods: Four different beta 2 -> 1-fructan formulations were characterised for their chain length profile. Human peripheral blood mononuclear cells (PBMCs) were stimulated in vitro with beta 2 -> 1-fructans, and production of IL-1Ra, IL-1 beta, IL-6, IL-10, IL-12p70, and TNF-alpha was analysed. Reporter cells for TLRs and NODs were incubated with beta 2 -> 1-fructans and analysed for NF-kappa B/AP-1 activation. Results: Cytokine production in human PBMCs was dose-and chain length-dependent. Strikingly, short chain enriched beta 2 -> 1-fructans induced a regulatory cytokine balance compared to long chain enriched beta 2 -> 1-fructans as measured by IL10/ IL-12 ratios. Activation of reporter cells showed that signalling was highly dependent on TLRs and their adapter, myeloid differentiation primary response protein 88 (MyD88). In human embryonic kidney reporter cells, TLR2 was prominently activated, while TLR4, 5, 7, 8, and NOD2 were mildly activated. Conclusions: beta 2 -> 1-fructans possess direct signalling capacity on human immune cells. By activating primarily TLR2, and to a lesser extent TLR4, 5, 7, 8, and NOD2, beta 2 -> 1-fructan stimulation results in NF-kappa B/AP-1 activation. Chain length of beta 2 -> 1fructans is important for the induced activation pattern and IL-10/IL-12 ratios.