Isolation and characterization of a high molecular mass β-glucan from Lactobacillus fermentum Lf2 and evaluation of its immunomodulatory activity.

When grown in a semi-defined medium, L. fermentum Lf2 synthesizes significant quantities (∼2 g/L) of two exopolysaccharides (EPS). The two EPS were separated by preparative size exclusion chromatography to give a high molecular mass β-glucan (1.23 × 106  Da) and a medium molecular mass heteroglycan (8.8 × 104  Da). The structure of the high molecular mass β-glucan was determined using a combination of NMR spectroscopy, monomer and linkage analysis. The EPS has the following structure: The immunomodulatory activity of the high molecular mass EPS was studied in peripheral blood mononuclear cells (PBMC). Exposure of PBMC to an aqueous solution of the EPS for 24 h led to increased cell proliferation, changes in expression of the cytokines CD14 and TLR2, and to an increase in production of TNF-α compared to controls. In contrast, when cells that had been treated with EPS for 24 h and from which the EPS had been removed, were subsequently exposed to the bacterial antigen LPS very low levels of TNF-α production were observed. This result indicates that the EPS imparts immunotolerance in PBMC. An ability to modulate the release of the proinflammatory mediators, such as TNF-α, is an important goal in the development of therapies for the treatment of diseases, such as Crohn's disease and ulcerative colitis, associated with excessive release of inflammatory mediators.