Abstract: 【Objective】 The study was aimed to investigate the effects of Astragalus polysaccharide (APS) on the intestinal morphology and local mucosal immune in chicks, in order to clarify the mechanism of APS in reducing intestinal mucosal injury in chickens with enteritis.【Method】 Fifteen 14-day-old SPF-grade chicks were randomly divided into three groups:Control group (Con), low-dose lipopolysaccharide (LPS) model group (D_L) and high-dose LPS model group (D_H), 5 chicks in each group.Control group was gavaged with normal saline, D_L and D_H groups were gavaged with 1 and 2 mg/kg BW LPS, respectively.After 3 days of continuous treatment, the small intestine were taken.HE staining method was used to observe the pathological changes of small intestine, and Real-time quantitative PCR was used to detect the changes in the expression of interleutin 1β (IL-1β) and tumor necrosis factor α (TNF-α), and screen the best LPS dose for constructing LPS-induced enteritis model.In the protection test of APS against intestinal mucosal injury, twenty 7-day-old chicks were divided into four groups:Control group (C), LPS inflammation group (L), APS group (A) and APS inhibited inflammation group (A+L), 5 chicks in each group.A and A+L groups were treated with APS (1.0 g/L) from 7-day-old to the end of this experiment, C group was fed water during this period.Chicks in L and A+L groups were given the selected optimal dose of LPS, after 3 consecutive days, the thymus, spleen, bursa of Fabricius and small intestine tissues were collected, the immune organ indexes of chicks were calculated in each group.HE staining was used to detect the pathological changes of chick small intestine, PAS staining was used to observe the number changes of goblet cells, Real-time quantitative PCR was used to detect the mRNA expression of tight junction proteins Occludin-1, Claudin-1 and ZO-1.【Result】 In the experiment of constructing LPS-induced enteritis model, the small intestinal mucosa lamina propria of chicks in D_Land D_H groups were congested and intestinal villi were injured, and the expressions of IL-1β and TNF-α mRNA were significantly higher than that of control group (P<0.05), which indicated that the intestinal tissues in D_L group had obvious pathological changes.Therefore, it was determined to feed 1 mg/kg BW LPS to establish enteritis model.In the protective test of APS against intestinal mucosal injury, compared with control group, for the chicks in L group, the villus of small intestine were broken, the lamina propria was congested, and the immune organ indexes were significantly decreased (P<0.05), the crypt depth of small intestine was significantly increased (P<0.05), the V/C was significantly decreased (P<0.05), and the goblet cells of small intestine were significantly decreased (P<0.05), the mRNA expression of tight junction protein Occludin-1, Claudin-1 and ZO-1 were all significantly decreased (P<0.05).Compared with L group, the immune organ indexes of chicks in A+L group were significantly increased (P<0.05), the intestinal mucosal damage was decreased, the intestinal villus height and V/C were significantly increased (P<0.05), the crypt depth was significantly decreased (P<0.05), the goblet cells were increased significantly (P<0.05), and the expression of tight junction proteins mRNA in jejunum and ileum were significantly increased (P<0.05).Compared with other groups, the number of goblet cells and the expression of tight junction protein in jejunum and ileum of chicks in A group were significantly increased (P<0.05).【Conclusion】 The enteritis model could be successfully established by feeding 1 mg/kg BW LPS to chicks.1.0 g/L APS could optimize the intestinal morphology, promote the development of local mucosal immune system of chicks, protect the intestinal tissue and intestinal mucosa of chicks with enteritis from damage, and finally achieve the effect of preventing bacterial enteritis in chicks.

Key words: Astragalus polysaccharide(APS); enteritis; mucosal immunity; goblet cells; tight junction protein