In this study, we first determined that E. granulosus infection decreased the symptoms and signs of IBD in a murine model, thereby supporting the conception that helminth infection likely reduces the severity or consequence of autoimmune diseases.
Several studies have shown the ability of helminth parasites, including Heligmosomoides polygyrus bakeri , Trichuris suis  and Schistosoma japonicum, to attenuate intestinal inflammation in different animal models of colitis. However, the underlying mechanisms involved are poorly understood. We previously showed that E. granulosus infection impacted allergic asthma inflammatory responses through decreased eosinophil numbers in the airway and blood . E. granulosus has been shown to regulate host immunity by biasing a Th1/Th2 response towards a chronic Th2 response  as the infection induced a remarkable increase in the transcriptional levels of IFN-γ, IL-2, IL-4, IL-5 and IL-10 . Mice infected with E. granulosus had significant levels of Th2-type immunoglobulins (IgG1, IgG2b and IgE) against HCF antigens in their sera . Similarly, a secondary infection of mice with larval E. multilocularis infection reduced DSS-induced colitis in mice, which likely occurred through attenuation of the Th1/Th17 balance . Moreover, in another study, passive transfusion of M2 cells from mice infected with Taenia crassiceps into DSS-challenged mice significantly reduced IBD symptoms and signs . These studies indicate that E. granulosus and other helminth parasites may share similar mechanisms by inducing M2 macrophages, which upregulate Th2 responses and reduce characteristic indicators of IBD. In fact, Th2 responses play a crucial role in the chronic phases of parasite infection . Th2-type cytokines, including IL-4, IL-10, and IL-13, may play a role in the reduction of IBD symptoms and signs.
Secreted antigens likely play an important role in the regulation of immune responses by parasitic helminths. Given that HCF is a major source of secreted Echinococcus antigens, we inoculated mice to determine whether this complex of native mixed antigens produced as E. granulosus infection had protective effects similar to the protective effects of E. granulosus infection on DSS-induced IBD, but we showed that this was not the case.
In addition, a crude extract of the laminated cystic layer from E. granulosus has been shown to attenuate mucosal intestinal damage and inflammatory responses induced by DSS in mice , indicating that cyst wall antigens may contain antigens that stimulate immune responses against IBD. Another study showed that the laminated layer of the E. granulosus cyst is composed of AgB.
E. granulosus larval cysts can survive in human organs for a long time, up to 53 years , and release a large number of circulating antigens in serum, up to 680 ng protein per ml . As AgB is the most immunogenic and abundant secreted echinococcal protein present in Echinococcus HCF , we purified this protein from HCF and undertook a similar series of experiments. We pretreated mice with AgB and then challenged these animals with DSS. The results showed a significant reduction in clinical symptoms induced by DSS. We thus consider that AgB may affect the polarization of macrophages and bias the host immune response to a Th2 predominant profile, thereby reducing IBD symptoms.
We showed that AgB decreased the number of type 1 macrophages (F4/80 + CD11c+) in the peritoneal cavity of mice and increased F4/80+ and CD206+ M2 macrophage numbers in intestinal lamina propria cells. AgB preintervention decreased iNOS levels (p < 0.05) and increased Fizzl levels (p < 0.05) (Fig. 7) in the IBD mouse model. Peritoneal macrophages play an important role in the control of inflammation and defence against abdominal infection [22, 29, 30].
AgB likely affects/regulates the host intestinal flora or microbiome, which may explain why E. granulosus reduces the inflammatory response in IBD and why AgB may be a good reagent for prevention and protection against IBD, asthma and other autoimmune diseases. The normal balance of the intestinal flora protects the intestinal mucosal barrier, so the disturbance of the microecological balance of the intestinal microflora is a key factor in the formation of IBD. Gut microbiota analysis indicated that AgB altered the numbers of Prevotellaceae and Ruminococcaceae in the gut of mice induced by DSS. Notably, this variation correlated strongly with disease status, i.e., inflammation had a significant impact on the microbiota composition . The loss of beneficial microbiota in the gut potentially contributes to chronic inflammatory diseases . Additionally, helminths and the gut microbiota have coevolved within their mammalian hosts , but the mechanisms of these interactions and the consequence of decreased exposure to intestinal helminths remain unclear. Helminths can reduce intestinal inflammatory responses by promoting the expansion of protective bacterial communities that inhibit proinflammatory bacterial taxa .
The intestinal bacteria of IBD patients are different from the intestinal bacteria of normal people, but the relationship between the characteristics of the flora and immunity in the intestine is unclear. IBD has been shown to be associated with parabacteroides (vc23) . We found a significant negative association between the numbers of paracharacteroids and the percentage of CD206 + cells in the colon, which were increased, likely through increased numbers of Lachnospiraceae (vc39) and Parabacteroides (R = 0.6). AgB increased CD206 + cells via parabacteroides and reduced IBD symptoms and signs.
Mucispirillum schaedleri has been shown to protect mice from Salmonella enterica serotype typhoid, and this protective effect may be associated with the consumption of nitrate . We confirmed that mucispirillum was negatively correlated with the expression of iNOS in colon tissue, while it was positively correlated with the proportion of CD206+ cells in the colon, indicating that Mucispirillum may be a protective factor for IBD, although it is unknown whether Mucispirillum schaedleri has other harmful effects on gut and human health.
We showed that AgB inhibited the differentiation of macrophages to M1 macrophages. When cultured M0 cells were blocked with AgB and then stimulated with LPS, we found that far fewer M0 cells were differentiated into M1 cells, but we identified more M2 cells. Meanwhile, the concentration of NO in the culture supernatant was lower than the concentration of NO in the culture supernatant of control cells stimulated by LPS only. We showed that AgB inhibited the secretion of NO by macrophages cultured with LPS, indicating that this protein may regulate macrophage differentiation to M2, which may be beneficial for treating and preventing autoimmune diseases.