The gut microbiota guide the development of the host immune system by setting a systemic threshold for immune activation. Lipopolysaccharides (LPSs) from gut bacteria are able to trigger systemic and local proinflammatory and immunomodulatory responses, and this capability strongly relies on their fine structures. Up to now, only a few LPS structures from gut commensals have been elucidated; therefore, the molecular motifs that may be important for LPS–mammalian cell interactions at the gut level are still obscure. Here, we report on the full structure of the LPS isolated from one of the prominent species of the genus Bacteroides , Bacteroides vulgatus . The LPS turned out to consist of a particular chemical structure based on hypoacylated and mono -phosphorylated lipid A and with a galactofuranose-containing core oligosaccharide and an O-antigen built up of mannose and rhamnose. The evaluation of the immunological properties of this LPS on human in vitro models revealed a very interesting capability to produce anti-inflammatory cytokines and to induce a synergistic action of MD-2/TLR4- and TLR2-mediated signaling pathways.

Alcaligenes faecalis is the predominant Gramnegative bacterium inhabiting gut-associated lymphoid tissues, Peyersp atches.W ep reviously reported that an A. faecalis lipopolysaccharide (LPS) acted as aweak agonist for Toll-like receptor 4( TLR4)/myeloid differentiation factor-2 (MD-2) receptor as well as ap otent inducer of IgA without excessive inflammation, thus suggesting that A. faecalis LPS might be used as as afe adjuvant. In this study,w ec haracterized the structure of both the lipooligosaccharide (LOS) and LPS from A. faecalis.W esynthesized three lipid Amolecules with different degrees of acylation by an efficient route involving the simultaneous introduction of 1-and 4'-phosphates.H exaacylated A. faecalis lipid As howed moderate agonistic activity towards TLR4-mediated signaling and the ability to elicit adiscrete interleukin-6 release in human cell lines and mice.It was thus found to be the active principle of the LOS/LPS and apromising vaccine adjuvant candidate.

No abstract

Alcaligenes faecalis is the predominant Gramnegative bacterium inhabiting gut-associated lymphoid tissues, Peyersp atches.W ep reviously reported that an A. faecalis lipopolysaccharide (LPS) acted as aweak agonist for Toll-like receptor 4( TLR4)/myeloid differentiation factor-2 (MD-2) receptor as well as ap otent inducer of IgA without excessive inflammation, thus suggesting that A. faecalis LPS might be used as as afe adjuvant. In this study,w ec haracterized the structure of both the lipooligosaccharide (LOS) and LPS from A. faecalis.W esynthesized three lipid Amolecules with different degrees of acylation by an efficient route involving the simultaneous introduction of 1-and 4'-phosphates.H exaacylated A. faecalis lipid As howed moderate agonistic activity towards TLR4-mediated signaling and the ability to elicit adiscrete interleukin-6 release in human cell lines and mice.It was thus found to be the active principle of the LOS/LPS and apromising vaccine adjuvant candidate.

No abstract