For an optimized and more focused application of LGG – and other probiotics – in IBD, more knowledge about the molecular mechanisms of action is needed. Bacterial cell surface molecules are expected to be key players in determining strain-specific probiotic–host interactions [49]. check details As LTA is presumed to be a major proinflammatory molecule in Gram-positive

bacteria [31], we studied the importance of LGG’s LTA structure for its probiotic effects in a murine colitis model by using a mutant that shows a drastic LTA modification. Instead of complete removal of LTA a modification of LTA was introduced, as LTA is an essential part of the cell wall and mutants lacking LTA are not viable [50]. This LGG dltD mutant contains LTA molecules that are completely devoid of D-Ala ester substituents, resulting in an altered cell surface charge and altered cell morphology (for details see [37]). In this work, the performance of LGG wild-type and dltD mutant was compared in two experimental set-ups of DSS-induced colitis after confirming that the mutation had no significant effect on survival. In both set-ups, the dltD mutant performed SAR245409 better than LGG wild-type, i.e. this mutant appeared to relieve the severity of colitic parameters. LGG wild-type exacerbated the colitic parameters in the moderate to severe model, but this detrimental effect was not seen

in the mild chronic model. We hypothesize that these results could be due to severe disruption of the epithelial barrier by DSS in the moderate to severe colitis model, which was much less pronounced in the mild chronic model. One of the suggested results of this disruption is the increased

passage of bacteria (including probiotic LGG) across the epithelial barrier, and subsequent increased internalization Quinapyramine and processing by macrophages and dendritic cells in the lamina propria [51]. LTA and other proinflammatory bacterial cell wall components will then become increasingly able to induce a proinflammatory response in these cells. Dysregulation of TLR expression in IBD could contribute to the proinflammatory response [51]. In the present work, we observed that application of the dltD mutant of LGG correlated with a significant down-regulation of TLR-2 expression in the mild chronic 1% DSS-induced colitis model compared to the PBS-treated group. This specific down-regulation of TLR-2 by treatment with the dltD mutant could explain the lower expression of the proinflammatory cytokines IL-12 and IFN-γ (as reviewed in [52]). The lower expression of IL-12 suggests that the dltD mutant induces fewer proinflammatory cytokines in macrophages and dendritic cells, as IL-12 is a proinflammatory cytokine that is produced mainly by these cell types [53]. DSS-induced colitis also involves the adaptive immune system, especially in more chronic experimental set-ups [54].