Lipoteichoic acid (LTA) derived from Staphylococcus aureus is reported to be a ligand of TLR2. However, we previously demonstrated that LTA fraction prepared from bacterial cells contains lipoproteins, which activate cells via TLR2. In this study, we investigated the immunobiological activity of LTA fraction obtained from S. aureus wild-type strain, lipoprotein diacylglycerol transferase deletion (Δlgt) mutant, which lacks palmitate-labeled lipoproteins, and its complemented strain and evaluated the activity of LTA molecule. LTA fraction was prepared by butanol extraction of the bacteria followed by hydrophobic interaction chromatography. Although all LTA fractions activated cells through TLR2, the LTA from Δlgt mutant was 100-fold less potent than those of wild-type and complemented strains. However, no significant structural difference in LTA was observed in NMR spectra. Further, alanylation of LTA molecule showed no effect in immunobiological activity. These results showed that not LTA molecule but lipoproteins are dominant immunobiologically active TLR2 ligand in S. aureus.

Clostridium difficile is a Gram-positive obligate anaerobic pathogen that causes pseudomembranous colitis in antibiotics-treated individuals. However, host immune protective mechanisms against C. difficile are largely unknown. In this study, we show that C. difficile possesses potent stimulatory activity for nucleotide-binding oligomerization domain 1 (Nod1), an intracellular pattern recognition molecule that senses bacterial peptidoglycan-related molecules. Nod1−/−, but not Nod2−/−, mice exhibited increased lethality in response to C. difficile intestinal infection despite comparable levels of intestinal damage and epithelial permeability in Nod1−/− and control mice. The enhanced lethality was accompanied by impaired C. difficile clearance, increased bacterial translocation, and elevated levels of endotoxin and IL-1β in the serum of Nod1−/− mice. Histological and flow cytometric analyses revealed that Nod1−/− mice had defective recruitment of neutrophils, but not macrophages, to the intestine after C. difficile infection. The reduced recruitment of neutrophils correlated with impaired production of CXCL1, but not CCL2, XCL1, and other cytokines/chemokines, in infected Nod1−/− mice. The influx of neutrophils also was reduced when C. difficile was administered i.p., suggesting that Nod1 directly recognizes C. difficile to induce the recruitment of neutrophils to the infected site. These results indicate that Nod1 regulates host susceptibility to C. difficile and suggest that Nod1-mediated neutrophil recruitment is an important immune response against the enteric pathogen.

Summary Periodontitis is a common disease that is characterized by resorption of the alveolar bone and mediated by commensal bacteria that trigger host immune responses and bone destruction through unidentified mechanisms. We report that Nod1, an innate intracellular host receptor for bacterial peptidoglycan-related molecules, is critical for commensal-induced periodontitis in a mouse model. Mice lacking Nod1 exhibit reduced bone resorption as well as impaired recruitment of neutrophils to gingival tissues and osteoclasts to the alveolar bone, which mediate tissue and bone destruction. Further analysis showed that accumulation of a Nod1-stimulating commensal bacterium, NI1060, at gingival sites was sufficient to induce neutrophil recruitment and bone resorption. Genomic sequencing revealed that NI1060 is a mouse-specific bacterium that is related to bacteria associated with the development of aggressive periodontitis in humans. These findings provide insight into commensal-host interactions contributing to periodontitis and identify a potential target for preventing this common oral disease.

Lipoteichoic acid (LTA) derived from Staphylococcus aureus is reported to be a ligand of Toll-like receptor 2 (TLR2). In this study, we demonstrated that lipoproteins obtained from S. aureus are potent activators of TLR2. A fraction obtained by Triton X-114 phase partitioning activated cells through TLR2. The fraction contained proteins and LTA. The activity was detected in compounds in a mass range of 12-40 kDa. Proteinase K digested the active compounds into lower molecular weight active materials <10 kDa. In contrast, hydrofluoric acid treatment, which decomposes LTA, did not alter the molecular mass of the active compounds. Further, most of the activity was abrogated by lipoprotein lipase digestion. These results suggested that lipoproteins are predominant TLR2 ligands in S. aureus cell wall components.