The roles played by the gut microbiome in human health are increasingly recognized, and the prevalence of specific microorganisms has been correlated with different diseases. For example, blooms of the Gram-positive bacterium Ruminococcus gnavus have been correlated with inflammatory bowel disease, and recently a polysaccharide produced by this organism was shown to stimulate release of inflammatory cytokines. This stimulation was proposed to signal through toll-like receptor 4 (TLR4). We have synthesized the pentasaccharide repeating unit of this polysaccharide and showed that it stimulates TNF-α and IL-6 release from bone marrow-derived dendritic cells (BMDCs) in a TLR4-dependent manner. A related glycan does not stimulate significant cytokine release, demonstrating TLR4 selectivity in glycan recognition.
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