A novel paraprobiotic strain, <i>Lentilactobacillus hilgardii</i> H-50 enhances intestinal IgA production via TLR2-dependent IL-6 induction driven by its cell surface components

Lactic acid bacteria enhance intestinal immunoglobulin A (IgA) secretion; however, the underlying mechanisms are often strain specific. In this study, we found a novel strain, Lentilactobacillus hilgardii H-50, that enhanced intestinal IgA production among L. hilgardii strains. Heat-killed H-50 strain increased IgA secretion from mouse Peyer's patch cells and elevated faecal IgA levels in vivo. Although this strain also induced the secretion of interleukin-6 (IL-6) and IL-10, IL-6 was essential for IgA production, whereas IL-10 less contributed to it. Cell surface components, including cell wall components and S-layer protein, but not nucleic acids, enhanced IL-6 induction and IgA production. Furthermore, H-50 exhibited TLR2 ligand activity, and blockade of TLR2 signalling abolished IL-6 induction and IgA production. These results indicate that H-50 enhances intestinal IgA production via a TLR2-dependent, IL-6-mediated mechanism. This strain can potentially be used as a paraprobiotics.