Department of Life Science and Biotechnology, Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita, Osaka, Japan.
Laboratory of Vaccine Materials and Laboratory of Gut Environmental System, Microbial Research Center for Health and Medicine, National Institutes of Biomedical Innovation, Health, and Nutrition, Ibaraki, Osaka, Japan.
Appl Environ Microbiol. 2024 Oct 23;90(10):e0119724. doi: 10.1128/aem.01197-24. Epub 2024 Sep 6.
Some strains of lactic acid bacteria can regulate the host's intestinal immune system. Bacterial cells and membrane vesicles (MVs) of JCM 15950 promote immunoglobulin A (IgA) production in murine Peyer's patch cells via toll-like receptor (TLR) 2. This study aimed to investigate the role of lipoteichoic acid (LTA), a ligand of TLR2, in the immunostimulatory activity of these bacterial cells and their MVs. LTA extracted from bacterial cells was purified through hydrophobic interaction chromatography and then divided into fractions LTA1 and LTA2 through anion-exchange chromatography. LTA1 induced greater interleukin (IL)-6 production from macrophage-like RAW264 cells than LTA2, and the induced IL-6 production was suppressed by TLR2 neutralization using an anti-TLR2 antibody. The LTAs in both fractions contained two hexose residues in the glycolipid anchor; however, LTA1 was particularly rich in triacyl LTA. The free hydroxy groups in the glycerol phosphate (GroP) repeating units were substituted by d-alanine (d-Ala) and α-glucose in LTA1, but only by α-glucose in LTA2. The dealanylation of LTA1 slightly suppressed IL-6 production in RAW264 cells, whereas deacylation almost completely suppressed IL-6 production. Furthermore, IL-6 production induced by dealanylated LTA1 was markedly higher than that induced by dealanylated LTA2. These results indicated that the critical moieties for the immunostimulatory activity of -derived LTA were the three fatty acid residues rather than the substitution with d-Ala in GroP. LTA was also detected in MVs, suggesting that the triacyl LTA, but not the diacyl LTA, translocated to the MVs and conferred immunostimulatory activity.
Some lactic acid bacteria activate the host intestinal immune system via toll-like receptor (TLR) 2. Lipoteichoic acid (LTA) is a TLR2 ligand; however, the moieties of LTA that determine its immunostimulatory activity remain unclear because of the wide diversity of LTA partial structures. We found that JCM 15950 has three types of LTAs (triacyl, diacyl, and monoacyl LTAs). Specifically, structural analysis of the LTAs revealed that triacyl LTA plays a crucial role in immunostimulation and that the fatty acid residues are essential for the activity. The three acyl residues are characteristic of LTAs from many lactic acid bacteria, and our findings can explain the immunostimulatory mechanisms widely exhibited by lactic acid bacteria. Furthermore, the immunostimulatory activity of membrane vesicles released by JCM 15950 is due to the transferred LTA, demonstrating a novel mechanism of membrane vesicle-mediated immunostimulation.
某些乳酸菌通过 Toll 样受体（TLR）2 激活宿主肠道免疫系统。脂磷壁酸（LTA）是 TLR2 的配体；然而，由于 LTA 部分结构的多样性，决定其免疫刺激活性的 LTA 部分仍不清楚。我们发现 JCM 15950 有三种类型的 LTA（三酰基、二酰基和单酰基 LTA）。具体来说，LTA 的结构分析表明，三酰基 LTA 在免疫刺激中起关键作用，脂肪酸残基是活性所必需的。这三个酰基残基是许多乳酸菌 LTA 的特征，我们的发现可以解释乳酸菌广泛表现出的免疫刺激机制。此外，JCM 15950 释放的膜泡的免疫刺激活性归因于转移的 LTA，这证明了膜泡介导的免疫刺激的一种新机制。
