Intestinal epithelium-derived galectin-9 is involved in the immunomodulating effects of nondigestible oligosaccharides.

Dietary intervention using nondigestible oligosaccharides, short-chain galacto-oligosaccharides (scGOS)/long-chain fructo-oligosaccharides (lcFOS), in combination with Bifidobacterium breve M-16V prevents allergic disease involving galectin-9. In addition, apical TLR9 signaling contributes to intestinal homeostasis. We studied the contribution of galectin-9 secreted by intestinal epithelial cells (IEC; HT-29 and T84) in Th1 and regulatory T-cell (Treg) polarization in vitro. IEC were grown in transwell filters, cocultured with CD3/CD28-activated human peripheral blood mononuclear cells (PBMC) and apically exposed to genomic DNA derived from B. breve M-16V or synthetic TLR9 ligand in the absence or presence of scGOS/lcFOS. Cytokine production and T-cell phenotype were determined and galectin expression by IEC was assessed. Galectin-9 was neutralized using lactose or a TIM-3-Fc fusion protein. IEC exposed to DNA from B. breve M-16V or TLR9 ligand in the presence of scGOS/lcFOS enhanced IFN-γ secretion by PBMC and increased the percentage of Th1 and Treg cells. Expression and secretion of galectin-9 by IEC was increased and neutralization of galectin-9 prevented the induction of IFN-γ secretion and also suppressed the production of IL-10 by PBMC. Furthermore, we show that galectin-9 induces Treg and Th1 polarization through interaction with antigen-presenting cells. Our findings show that galectin-9 secreted by IEC apically exposed to TLR9 ligand in the presence of scGOS/lcFOS is involved in Th1 and Treg polarization and may be a promising target to prevent or treat allergic disease.