Complementary immunoregulatory effects of Bifidobacterium longum 1714TM 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 <i>Bifidobacterium longum</i> 1714™ on innate inflammatory responses and to identify the strain-associated features that mediate its immunomodulatory effects. <i>B. longum</i> 1714 induced peripheral blood mononuclear cell (PBMC) and monocyte derived dendritic cell (MDDC) cytokine secretion and costimulatory molecule expression in a strain specific manner. <i>B. longum</i> 1714 consumption reduced excessive cytokine responses in LPS-induced, stress-induced and obesity-induced inflammation in murine models. <i>B. longum</i> 1714 produced a branched hexasaccharide repeating unit exopolysaccharide (EPS), which selectively induced PBMC secretion of IL-10. Furthermore, <i>B. longum</i> 1714 produced tryptophan and indole lactic acid (ILA) <i>in vitro</i>, 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 <i>B. longum</i> 1714 consumption. <i>B. longum</i> 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.