Anemoside B4 from Pulsatilla chinensis Ameliorates Ulcerative Colitis by Inhibiting Inflammatory Responses via the Modulation of the Gut Microbiota-Immune Interplay.

We previously demonstrated that anemoside B4 (AB4) exerts a beneficial effect in a dextran sulfate sodium (DSS)-induced murine model of ulcerative colitis (UC). In this study, we further explored the mechanism of AB4 against UC from the perspective of gut microbiota-immune interplay. The gut microbiota was depleted in two DSS-induced colitis models to investigate the modulatory effects of the gut microbiome on immune responses and the activity of AB4. In parallel, adoptive transfer of CD4[Formula: see text]CD62L[Formula: see text] T cells into Rag1-deficient (Rag1-/-) mice was used to elucidate the alterations in the gut microbiota associated with immune-mediated colitis as well as the modulation by AB4. qPCR, ELISA and western blotting were used to determine the inflammatory responses of mice with colitis, while immunohistochemistry and flow cytometry were employed to determine the CD4[Formula: see text] T cell function and the underlying mechanism. Metagenomic sequencing analysis was used to detect changes in the intestinal microbiota. The depletion of the gut microbiota attenuated disease severity and immune responses in mice with DSS-induced acute and chronic colitis. Notably, the inhibitory effects of orally administered AB4 on colitis progression and immune responses were abrogated. In addition, colitis induced by adoptive transfer of CD4[Formula: see text]CD62L[Formula: see text] T cells into Rag1-/- mice was accompanied by CD4[Formula: see text] T cell engraftment and alterations in gut microbiota. Remarkably, all these pathological changes were significantly attenuated by AB4. Crucially, we found that AB4 suppresses the proliferation, migration, and differentiation of CD4[Formula: see text] T cells, which provides a mechanistic basis for its immunosuppressive effects. Collectively, these findings indicate that the gut microbiota and the immune system, particularly CD4[Formula: see text] T cells, interact with each other in the initiation of colitis. We show that, by targeting this gut microbiota-immune interplay, AB4 is a promising therapeutic strategy for UC.