In contrast, treatment with LGG wild-type results in an up-regulation of TLR-1, -2 and -4 compared to the dltD-treated group, highlighting the impact of inactivating the dltD gene. It is known that LTA molecules of certain bacteria can induce

proinflammatory signalling in macrophages by interaction with TLR-2 [56]. The exact role of d-alanylation in interaction of LTA with specific TLRs (TLR-2, TLR-6) and co-receptors (CD14, CD36) is not yet well established. Based on the crystal structure of TLR-2, the two acyl chains of LTA are suggested to interact with the lipid binding pocket of TLR-2, while the hydrophilic Ixazomib in vitro glycerophosphate chain is thought to be exposed to solvent or to interact with TLR-6 or another co-receptor of TLR-2 [57–59]. However, as LTA is a major cell wall compound of lactobacilli, changing the structure

of LTA by removing d-alanine residues might as well effect the interactions with other surface molecules and therefore cause pleiotropic effects that can impact indirectly on the anti-inflammatory capacity of the lactobacilli. Nevertheless, our results with the dltD mutant compared to the wild-type probiotic strain are in line with those of the study by Grangette et al. [36], where a dltB mutant of L. plantarum NCIMB8826 also showed, compared to the wild-type strain, an enhanced anti-inflammatory capacity in vitro in monocytes and in a trinitrobenzene sulphonic acid (TNBS) colitis model [60]. Obeticholic Acid in vivo Although both experimental set-ups (probiotic strains and colitis models) differ significantly, the study by Grangette et al. [36] and this study both suggest a key role for LTA modification in pro-/anti-inflammatory

effects of probiotic lactobacilli. Finally, the data from our experiments with LGG in the DSS-induced murine colitis model cannot be translated easily to the clinical setting, as introducing bacterial mutants in humans is not straightforward. However, it is interesting to mention that we also performed a pilot study with LGG in patients with active pouchitis (unpublished). Lepirudin Two patients with acute pouchitis received daily 1011 CFU/ml of LGG (Valio, Helsinki, Finland) in capsules for 4 weeks in a randomized cross-over trial (4 weeks probiotics, 4 weeks placebo). In one of the patients, the symptoms of active pouchitis seemed to be exacerbated by the treatment. This study was discontinued and we decided to focus upon animal models, such as presented in this report, to understand more clearly the interaction of LGG with the intestinal mucosa. The data from our experiments, together with reports from other research groups on animal models [28,29] and Crohn’s disease patients [61], underline that caution should be taken when applying the wild-type strain of the well-known probiotic LGG in patients with active IBD.