Effects of astragalus polysaccharide on intestinal immune function of rats with severe scald injury

Objective To observe the effects of astragalus polysaccharide (AP) on the intestinal mucosal morphology, level of secretory IgA (s–IgA) in intestinal mucus, and distribution of T lymphocyte subsets in Peyer′s patch in rats with severe scald injury. Methods One hundred and thirty SD rats were divided into sham injury group (SI, sham injured, n=10), scald group (S, n=30), low dosage group (LD, n=30), moderate dosage group (MD, n=30), and high dosage group (HD, n=30) according to the random number table. Rats in the latter 4 groups were inflicted with 30% TBSA full–thickness scald on the back. From post injury hour 2, rats in groups LD, MD, and HD were intraperitoneally injected with 0.5 mL AP solution with the dosage of 100, 200, and 300 mg/kg each day respectively, and rats in group S were injected with 0.5 mL normal saline instead. Ten rats from group SI immediately after injury and 10 rats from each of the latter 4 groups on post injury day (PID) 3, 7, 14 were sacrificed, and their intestines were harvested. The morphology of ileal mucosa was examined after HE staining; the level of s–IgA in ileal mucus was determined with double–antibody sandwich ELISA method; the proportions of CD3⁺, CD4⁺, CD8⁺ T lymphocytes in Peyer′s patches of intestine were determined with flow cytometer, and the proportion of CD4⁺ to CD8⁺ was calculated. Data were processed with one–way analysis of variance, analysis of variance of factorial design, and SNK test. Results (1) Villi in normal form and intact villus epithelial cells were observed in rats of group SI immediately after injury, while edema of villi and necrosis and desquamation of an enormous amount of villi were observed in groups with scalded rats on PID 3, with significant infiltration of inflammatory cells. On PID 7, no obvious improvement in intestinal mucosal lesion was observed in groups with scalded rats. On PID 14, the pathology in intestinal mucosa of rats remained nearly the same in group S, and it was alleviated obviously in groups LD and MD, and the morphology of intestinal mucosa of rats in group HD was recovered to that of group SI. (2) On PID 3, 7, and 14, the level of s–IgA in intestinal mucus significantly decreased in groups S, LD, MD, and HD [(43±5), (45±5), (46±5) μg/mL; (47±5), (48±5), (49±6) μg/mL; (50±6), (51±5), (52±5) μg/mL; (53±6), (54±5), (55±5) μg/mL] as compared with that of rats in group SI immediately after injury [(69±4) μg/mL, with P values below 0.05]. The level of s–IgA in intestinal mucus of rats in group MD was significantly higher than that in group S at each time point (with P values below 0.05), and that of group HD was significantly higher than that in groups S and LD at each time point (with P values below 0.05). (3) Compared with those of rats in group SI immediately after injury, the proportions of CD3⁺ T lymphocytes and CD4⁺ T lymphocytes significantly decreased in groups with scalded rats at each time point (with P values below 0.05), except for those in group HD on PID 14. The proportion of CD4⁺ T lymphocytes of rats in group LD was significantly higher than that in group S on PID 3 (P<0.05). The proportions of CD3⁺ T lymphocytes and CD4⁺ T lymphocytes were significantly higher in groups MD and HD than in groups S and LD (except for the proportion of CD4⁺ T lymphocytes in group MD on PID 3 and 14) at each time point (with P values below 0.05). The proportion of CD3⁺ T lymphocytes on PID 7 and 14 and that of CD4⁺ T lymphocytes on PID 3 were significantly higher in group HD than in group MD (with P values below 0.05). Compared with that of rats in group SI immediately after injury, the proportion of CD8⁺ T lymphocytes significantly increased in the other 4 groups at each time point (with P values below 0.05). The proportion of CD8⁺ T lymphocytes was significantly lower in rats of group LD on PID 7 and 14 and groups MD and HD at each time point than in group S (with P values below 0.05). The proportion of CD8⁺ T lymphocytes was significantly lower in rats of group MD on PID 7 and 14 and group HD at each time point than in group LD (with P values below 0.05). The proportion of CD8⁺ T lymphocytes was significantly lower in rats of group HD on PID 7 and 14 than in group MD (with P values below 0.05). On PID 3, 7, and 14, the proportion of CD4⁺ to CD8⁺ was significantly lower in groups S, LD, MD, and HD (0.65±0.11, 0.68±0.13, 0.73±0.22; 0.76±0.15, 0.78±0.14, 0.90±0.10; 0.85±0.21, 0.89±0.18, 1.08±0.19; 0.99±0.20, 1.05±0.21, 1.25±0.23) as compared with that of rats in group SI immediately after injury (1.74±0.20, with P values below 0.05). The proportion of CD4⁺ to CD8⁺ was significantly higher in rats of group HD than in group MD on PID 7 (P<0.05), and the proportion was significantly higher in these two groups than in group S at each time point (with P values below 0.05). The proportion of CD4⁺ to CD8⁺ was significantly higher in rats of group MD on PID 14 and group HD at each time point than in group LD (with P values below 0.05). Compared within each group, the proportions of CD3⁺, CD4⁺, CD8⁺ T lymphocytes and the proportion of CD4⁺ to CD8⁺ of rats in groups LD, MD, and HD showed a trend of gradual elevation along with passage of time. Conclusions AP can improve the injury to intestinal mucosa and modulate the balance of T lymphocyte subsets in Peyer′s patch in a time– and dose–dependent manner, and it can promote s–IgA secretion of intestinal mucosa in a dose–dependent manner.