Echinococcus granulosus sensu stricto and antigen B may decrease inflammatory bowel disease through regulation of M1/2 polarization

Background Inflammatory bowel disease (IBD) is a chronic idiopathic disease characterized by inflammation-related epithelial barrier damage in the intestinal tract. Helminth infection reduces autoimmune disease symptoms through regulation of inflammatory responses based on hygiene theory. However, the underlying mechanisms remain unclear. Methods BALB/c mice were infected with microcysts of E. granulosus sensu stricto and drank water containing 3.5% dextran sodium sulfate (DSS) at the 100th day post-infection. After 7 days of drinking DSS, the mouse body weight change and disease activity index (DAI) were recorded every day, and colon length and histological score were evaluated after sacrifice. After injection with antigen B (AgB), inducible nitric oxide synthase (iNOS) and Fizz1 expression and F4/80 + CD11c + M1 and F4/80 + CD206 + M2 in the peritoneal cells and colon tissues were analysed by qPCR and flow cytometry, respectively. Gut microbiota were profiled by 16S rRNA sequencing of the mouse faecal samples. For in vitro assay, RAW264.7 macrophages were cultured in medium containing AgB before induction by lipopolysaccharide (LPS). Then, NO in the supernatant was measured, and the expression of cytokine genes associated with macrophages were determined by qRT-PCR. Results Echinococcus granulosus s.s. infection and AgB significantly reduced the symptoms and histological scores of IBD induced by DSS ( P < 0.05). Flow cytometry showed that AgB inoculation increased F4/80 + and CD206 + in peritoneal cells. The results of qPCR showed that AgB significantly decreased iNOS and increased Fizz1 expression in the colon of mice inoculated by DSS ( P < 0.05). Furthermore, AgB injection led to significant changes in the profiles of five genera ( Paraprevotella , Odoribacter , Clostridium cluster XlVa, Oscillibacter , and Flavonifractor ) in faecal samples. In vitro analysis showed that AgB reduced NO levels ( P < 0.01), with a significant decrease in iNOS expression ( P < 0.05) in RAW264.7 cells induced by LPS. Conclusions Echinococcus granulosus infection and AgB may improve IBD conditions by inducing an M2-predominant cellular (F4/80 + CD206 + ) profile and decreasing type 1 macrophages (F4/80 + CD11c + ) in the intestinal lamina propria. In addition, AgB intervention induced changes in the microbiota condition of the gastrointestinal duct and reversed NO expression. Thus, AgB may be a drug candidate for IBD treatment. Graphical Abstract