Lactiplantibacillus plantarum OLL2712 is a lactic acid bacterium originally selected for its strong induction of IL-10 in innate immune cells. We recently discovered that IL-10 induction is mediated by the C-type lectin receptor, macrophage-inducible C-type lectin receptor (Mincle), and Toll-like receptor 2 (TLR2) co-stimulation in dendritic cells. In this study, we aimed to identify the Mincle stimulatory ligand(s) in OLL2712. Lipid components were extracted from bacterial cells, fractionated by HPLC, and analyzed by liquid-chromatography tandem mass spectrometry (LC-MS/MS). We identified monoglucosyldiacylglycerol (MGDG) as a compound that activates Mincle in bacterial cells cultured in de Man, Rogosa, and Sharpe (MRS) medium. Co-stimulation with TLR2 markedly enhanced IL-10 production. Analysis of the bacterial cells cultured in a milk-based medium, which exhibited a stronger IL-10 induction, compared with those cultured in an MRS medium, revealed the presence of glucosylceramide (GlcCer) as an additional Mincle ligands. It was likely derived from the milk-based medium and adsorbed onto the cell surface of OLL2712 during cultivation; GlcCer also functioned as a Mincle agonist and synergized with TLR2 signaling to further augment IL-10 production. These results indicate that MGDG and GlcCer contribute to the OLL2712-induced IL-10 production by dendritic cells.
Shimazu et al. (Mon,) studied this question.