Complementary immunoregulatory effects of Bifidobacterium longum 1714^TM associated exopolysaccharide and tryptophan metabolism

Specific bifidobacterial strains can reduce aberrant inflammatory responses, but the strain-specific factors that promote regulatory immune responses are not well elucidated. The aims of this study were to assess the effects of Bifidobacterium longum 1714™ on innate inflammatory responses and to identify the strain-associated features that mediate its immunomodulatory effects. B. longum 1714 induced peripheral blood mononuclear cell (PBMC) and monocyte derived dendritic cell (MDDC) cytokine secretion and costimulatory molecule expression in a strain specific manner. B. longum 1714 consumption reduced excessive cytokine responses in LPS-induced, stress-induced and obesity-induced inflammation in murine models. B. longum 1714 produced a branched hexasaccharide repeating unit exopolysaccharide (EPS), which selectively induced PBMC secretion of IL-10. Furthermore, B. longum 1714 produced tryptophan and indole lactic acid (ILA) in vitro, and ILA directly reduced TLR-induced proinflammatory cytokine secretion and NF-κB activation. Finally, increased plasma levels of tryptophan and kynurenic acid were identified in humans following B. longum 1714 consumption. B. longum 1714 influences the immune system through intrinsic features associated with strain specific surface EPS and via secreted metabolic products, which demonstrates the potential for multiple mechanisms through which a specific probiotic may modulate immune responses and potential neuroprotective pathways.