Background
Crohn's disease (CD) is a chronic inflammatory disorder characterized by intestinal immune dysfunction. Multiple factors, including gut dysbiosis, are involved in the pathogenesis of CD. However, the effect of commensal bacteria on controlling the inflammatory response in individuals with CD remains unclear.
Methods
We detected Toll-like receptor 2 (TLR2), TLR4, and TLR5 expression in Roseburia intestinalis (R. intestinalis)-treated mice with 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis. Then, we quantified the signs of colonic inflammation, the proportion of regulatory T cells (Tregs) and the expression of thymic stromal lymphopoietin (TSLP) and transforming growth factor (TGF)-β in TLR-5-deficient (Tlr5-/-) mice, bone marrow chimera mice (generated using wild-type (WT) and Tlr5-/- mice), and anti-TSLP/anti-TGFβ-treated C57BL/6 mice with colitis induced by TNBS. In vitro, we used the lipopolysaccharide (LPS)-stimulated human intestinal epithelial cell line Caco-2 as an inflammatory colon cell model treated with or without the TLR5-siRNA intervention in the presence of R. intestinalis and incubated human monocyte-derived dendritic cells (DCs) with the supernatant of Caco-2 cells. Then, we cocultured human CD4+ T cells with the aforementioned DCs to determine the differentiation of Tregs. Additionally, samples from patients with CD were collected to analyse the correlation between TLR5/TSLP/TGFβ expression and the percentage of R. intestinalis. Findings: Here, we show that R. intestinalis inhibits the development of CD by increasing the differentiation of anti-inflammatory Tregs. Mechanistically, R. intestinalis stimulates TSLP production in intestinal epithelial cells (IECs) through TLR5 but not TLR2 or TLR4. TSLP produced by IECs specifically induces the secretion of interleukin-10 (IL-10) and TGFβ from DCs, which is necessary for subsequent Treg differentiation. Consequently, the depletion of TLR5 (using Tlr5-/- mice) or inhibition of TSLP (using anti-TSLP neutralizing antibodies) attenuates the protective effect of R. intestinalis on experimental colitis in mice. Importantly, the expression of TSLP in patients with CD is positively correlated with the level of R. intestinalis. Interpretation: These findings reveal the previously unknown mechanism of R. intestinalis-mediated intestinal immune regulation, which may provide the basis for new therapeutic strategies for CD. Funding: This work was funded by the National Natural Science Foundation of China (81670504 and 81970494), the Key Project of Research and Development Plan of Hunan Province (2019SK2041) and the Changsha Municipal Natural Science Foundation (kq2014258).