黄芪皂甙对斑点叉尾鮰非特异性免疫和抗病力的影响

分别向基础饲料中添加黄芪皂甙Astragalus membranaceus0（对照组）、300（低剂量组）、500（中剂量组）、800 mg/kg（高剂量组）制备4种试验饲料,饲喂同一家系的1龄斑点叉尾鮰Ictalures punctatus,饲喂期为60 d。以斑点叉尾鮰血清溶菌酶（LSZ）、碱性磷酸酶（AKP）、超氧化物歧化酶（SOD）活性以及肝脏、脾、头肾组织中Toll样受体——TLR2、TLR3表达水平为指标,结合嗜水气单胞菌攻毒试验,探讨了不同剂量的黄芪皂甙对斑点叉尾鮰免疫抗病力的影响。结果表明：中、高剂量组斑点叉尾鮰血清中LSZ、AKP活力均显著高于对照组和低剂量组（P〈0.05）,其中高剂量组血清LSZ活力显著高于其它各组（P〈0.05）,具有明显的剂量效应;与对照组相比,各试验组斑点叉尾鮰血清中SOD活力有所提高,但无显著性差异（P〉0.05）;黄芪皂甙可以显著提高TLR3基因在肝脏中的表达量,低、中、高剂量组斑点叉尾鮰肝脏中TLR3基因的表达量均显著高于对照组（P〈0.05）;高剂量黄芪皂甙可以显著提高TLR3基因在脾、头肾组织中的表达量（P〈0.05）,呈现较为明显的剂量效应;与对照组相比,黄芪皂甙中、高剂量组斑点叉尾鮰脾中TLR5表达量均有显著性提高（P〈0.05）;黄芪皂甙对TLR5基因在肝脏、头肾组织中的表达具有剂量效应,中、高剂量黄芪皂甙可以显著提高TLR5基因的表达水平（P〈0.05）,低剂量组与对照组相比无显著性差异（P〉0.05）。攻毒后试验鱼累积死亡率表明,摄食含有不同剂量的黄芪皂甙饲料以后,斑点叉尾鮰抵抗嗜水气单胞菌感染的能力显著增强,对照组斑点叉尾鮰的最终累积死亡率（61.11%±6.94%）显著高于中、高剂量组（31.11%±3.75%、30.01%±5.34%）（P〈0.05）。上述结果说明：特定剂量的黄芪皂甙可以显著提高斑点叉尾鮰机体的非特异性免疫力,黄芪皂甙可以作为一种安全高效的口服免疫增强剂应用于斑点叉尾鮰健康养殖及病害防治。

Effects of total saponins from Astragalus membranaceus on non-specific immunity in channel catfish

A feeding experiment was conducted to evaluate the effects of total saponins from Astragalus membranaceus on non-specific immunity of channel catfish Ictalurus punctatus by serum activities of lysozyme（LSZ）,alkaline phosphatase（AKP） and superoxide dismutase（SOD）.The fish were fed the diets containing 0（control）,300,500 or 800 mg/kg saponins twice daily for 60 days.Furthermore,the expression levels of TLR3 and TLR5 gene were detected using real time quantitative PCR.Results showed that the non-specific immunity and the survival were significantly affected by the dietary saponins.The activities of LSZ and AKP were found to be significantly higher in the fish fed 500 and 800 mg/kg saponins than those in the fish fed 300 mg/kg saponins and in the control group（P0.05）.There was higher SOD activity in the treatment groups than that in the control group without significant difference（P0.05）.The saponins showed effect on the TLR3 gene expression in a dose-dependent manner in spleen and the head kidney,and significantly increased the expression level of TLR3 in liver in all treatment groups（P0.05）.There was significant increase in TLR3 gene expression in the fish fed 500 and 800 mg/kg saponins（P0.05）.Compared with control group,the expression level of TLR5 was unregulated in spleen tissues in the fish fed 500 and 800 mg/kg saponins（P0.05）.The effect of saponins on the TLR5 gene expression was found to be dose-dependent in liver and the head kidney.The fish fed 800 mg/kg showed a significantly enhanced TLR5 expression in comparison with the control group in the liver and head kidney.The Aeromonas hydrophila challenge showed that the fish fed diets containing mid-（30.01%±5.34%） and high（31.11%±3.75%） dose of saponins had significantly lower cumulative mortality than the fish the control group（61.11%±6.94%） did（P0.05）,indicating that the saponins as an efficacious immunostimulant significantly improved the non-specific immunity and disease resistance of channel catfish.