Exopolysaccharide -(2,6)-levan-type fructans have a molecular-weight-dependent modulatory effect on Toll-like receptor signalling

Scope: Fructans are a group of dietary fibers which are known to have many beneficial effects including immune-modulating effects. A family of fructans are beta-(2,6)-linked levan-type fructans that are known to serve as exopolysaccharides in the cell wall of many species of bacteria including commensal bacteria and probiotics. It is still largely unknown whether and how they can serve as immunomodulating molecules. Results: Microbial beta-(2,6)-fructans were found to induce TLR-dependent activation of THP-1 cells, in a dose-dependent fashion. Low molecular weight (Mw), medium Mw and high Mw beta-(2,6)-fructans activated both TLR2 and 4 in a dose- and molecular weight-dependent fashion. In addition, it was found that beta-(2,6)-fructans were able to inhibit signalling of various TLRs with the strongest effect on TLR5 and 8, which were inhibited by all the beta-(2,6)-fructans in a dose- and molecular weight-dependent fashion. The final effect of this activation and inhibition of TLRs on cytokine responses in human dendritic cells (DCs) was minor which may be explained by the counter-activating effects of the different beta-(2,6)-linked levan-type fructans on inhibition of TLR signalling in the DCs. Conclusion: A mechanism by which exopolysaccharide levan beta-(2,6)-fructans can be immune-modulating is by impacting TLR signalling. This knowledge could lead to food in which exopolysaccharide levan beta-(2,6)-fructans are added for preventing disorders where TLR-signalling is modulated. Fructans are a group of dietary fibers which are known to have many beneficial effects including immune-modulating effects.