Lipopolysaccharide associated with β-2,6 fructan mediates TLR4-dependent immunomodulatory activity in vitro
Ian D. Young, Sergey A. Nepogodiev, Ian Black, Gwénaëlle Le Gall, Alexandra Wittmann, Dimitrios Latousakis, Triinu Visnapuu, Parastoo Azadi, Robert A. Field, Nathalie Juge, Norihito Kawasaki
Abstract
Levan, a β-2,6 fructofuranose polymer produced by microbial species, has been reported for its immunomodulatory properties via interaction with toll-like receptor 4 (TLR4) which recognises lipopolysaccharide (LPS). However, the molecular mechanisms underlying these interactions remain elusive. Here, we investigated the immunomodulatory properties of levan using thoroughly-purified and characterised samples from Erwinia herbicola and other sources. E. herbicola levan was purified by gel-permeation chromatography and LPS was removed from the levan following a novel alkali treatment developed in this study. E. herbicola levan was then characterised by gas chromatography-mass spectrometry and NMR. We found that levan containing LPS, but not LPS-depleted levan, induced TLR4-mediated cytokine production by bone marrow-derived dendritic cells and/or activated TLR4 reporter cells. These data indicated that the immunomodulatory properties of the levan toward TLR4-expressing immune cells were mediated by the LPS. This work also demonstrates the importance of LPS removal when assessing the immunomodulatory activity of polysaccharides.