畜牧兽医学报  2022, Vol. 53 Issue (7): 2354-2363. DOI: 10.11843/j.issn.0366-6964.2022.07.032    PDF    
紫锥菊通过调控TLR4-NF-κB通路增强免疫抑制鸡的免疫功能
季艳菊1,2, 钟高龙1, 常晓月1, 李英1, 胡莲美1, 张辉1, 潘家强1, 唐兆新1     
1. 华南农业大学兽医学院, 广州 510642;
2. 惠州工程职业学院, 惠州 516023
摘要:紫锥菊是一种重要的免疫增强剂,常作为替抗药物用于饲料添加剂,但其作用机制有待进一步研究。本试验旨在研究紫锥菊对免疫抑制鸡免疫功能的影响及其机制。将120羽7日龄的雏鸡随机均分为:对照组、环磷酰胺组、紫锥菊组、紫锥菊+环磷酰胺组(联合组)。环磷酰胺组和联合组雏鸡连续3 d胸肌注射生理盐水配制的环磷酰胺溶液(80 mg·kg-1),同时对照组和紫锥菊组连续3 d注射等量生理盐水,除紫锥菊组和联合组每天饲喂含紫锥菊全草粉末(含量为1%)的基础日粮外,其余各组雏鸡饲喂基础日粮,每天称重并记录,连续饲喂21 d。试验结束时,分析体重及脾脏指数的变化,检测炎性因子(NF-κB、IκB、IL-2、IL-4、IL-6、TNF-α、IFN-γ)和TLR家族(TLR2、TLR4、TLR7、MyD88)基因mRNA及蛋白的表达含量。结果显示,紫锥菊处理提高了雏鸡的生长性能,环磷酰胺抑制了雏鸡的生长并显著降低了脾脏系数(P<0.05),且环磷酰胺组脾组织病理变化明显,而在联合组中上述病理变化得到缓解。与对照组相比,环磷酰胺组的NF-κBIL-2、IL-4、IL-6、IFN-γTLR2、TLR4、TLR7、MyD88的mRNA水平均显著下调(P<0.05、P<0.01或P<0.001),而联合组相比于环磷酰胺组,除TLR7外,上述基因mRNA表达量均显著上调(P<0.05、P<0.01或P<0.001)。此外,紫锥菊的添加显著提高了炎性因子和TLR家族相关蛋白的表达水平。结果表明:紫锥菊可通过调控TLR4/NF-κB通路增强免疫抑制鸡的免疫功能。
关键词紫锥菊    环磷酰胺    免疫抑制    NF-κB    TLR4    
Echinacea Enhances the Immune Function of Immunosuppressed Chicken by Regulating TLR4-NF-κB Pathway
JI Yanju1,2, ZHONG Gaolong1, CHANG Xiaoyue1, LI Ying1, HU Lianmei1, ZHANG Hui1, PAN Jiaqiang1, TANG Zhaoxin1     
1. College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China;
2. Huizhou Engineering Vocational College, Huizhou 516023, China
Abstract: Echinacea is an important immune enhancer, which is often used as a substitute for antibiotic as feed additive, however, its immune mechanism needs further study. The purpose of this study was to investigate the effects of Echinacea on enhancing immune function of immunosuppressed chicken by regulating TLR4-NF-κB pathway. A total of 120 7-day-old chicken were randomly divided into 4 groups: the control group, cyclophosphamide group, Echinacea group and Echinacea + cyclophosphamide group (combined group), respectively. The chickens of cyclophosphamide group and combined group were chest muscles injected with saline compound cyclophosphamide solution (80 mg·kg-1) for 3 consecutive days, while the control group and Echinacea group were injected with the same amount of normal saline for 3 days. The chickens of Echinacea and combined groups were fed with basal diet which containing Echinacea herb powder (1%) daily, and the rest of the chickens were fed with the basal diet. All the chikens were weighed and recorded every day. The experiment lasted for 21 days. At the end of the experiment, the changes of body weight and spleen index were analyzed, and the mRNA and protein expression levels of inflammatory factors (NF-κB, IκB, IL-2, IL-4, IL-6, TNF-α, IFN-γ) and TLR family (TLR2, TLR4, TLR7, MyD88) were detected. The results showed that Echinacea improved the growth performance of chickens, while cyclophosphamide inhibited the growth of chickens. The spleen coefficient of chickens in cyclophosphamide group was significantly lower than that in other groups (P < 0.05), while the pathological changes of spleen tissue sections in the cyclophosphamide group were obvious, and the pathological changes in the combined group were relieved. Compared with the control group, the mRNA levels of NF-κB, IL-2, IL-4, IL-6, IFN-γ, TLR2, TLR4, TLR7 and MyD88 in cyclophosphamide group were significantly decreased to varying degrees (P < 0.05, P < 0.01 or P < 0.001). Compared with the cyclophosphamide group, the above genes(except TLR7) significantly increased in the combined group(P < 0.05, P < 0.01 or P < 0.001). In addition, the supplementation of Echinacea significantly increased the expression levels of inflammatory factors and TLR family-related proteins. The results indicated that Echinacea enhanced the immune function of immunosuppressed chickens by regulating TLR4-NF-κB pathway.
Key words: Echinacea    cyclophosphamide    immunosuppression    NF-κB    TLR4    

免疫抑制作用是由病毒、霉菌毒素、农用化学物质等多种因素引起的免疫系统紊乱或对机体免疫系统产生抑制功能[1]。近些年来,一些免疫抑制性疾病在肉鸡养殖中频发,如马立克氏病、传染性法氏囊病和禽白血病[2-3],其能够抑制免疫应答,降低宿主对疫苗的敏感性,从而增加鸡群的发病率和死亡率,给家禽养殖业造成严重的经济损失。现阶段应对这些免疫抑制疾病的策略主要是通过长期的疫苗接种和适当的药物治疗。但是灭活疫苗产生的抗体不持久,而药物的过度使用也会产生诸多的食品安全问题。因此,寻找一种预防和治疗免疫抑制疾病的新方法是亟待解决的问题,其中使用中草药来增强动物的免疫力被认为是最有前景的方法。

中药具有毒性低、副作用小的优势,已然成为一种新颖的药物治疗手段。紫锥菊是一种传统的药用植物,具有免疫调节、抗氧化、抗炎、抗癌、抗病毒等作用[4-6]。免疫调节是紫锥菊重要的生物活性作用,能够增加宿主的免疫和抗感染能力。研究发现,紫锥菊乙醇提取物对流感病毒H1N1、H5N1、H7N7有良好的抑制作用[7-8]。同时,饲料中添加紫锥菊能显著促进注射蓝耳病弱病毒仔猪的生长及弱病毒的免疫效果[9]。可见紫锥菊具有一定免疫调节作用,可作为一种潜在的免疫诱导剂。环磷酰胺是一种免疫抑制剂,也是一种抗肿瘤药物,在杀灭肿瘤细胞的同时也会造成机体免疫力降低,诱发多个系统的慢性疾病[10-11]。已有研究表明,紫锥菊可以提高肉鸡的生长性能和免疫器官指数(脾、胸腺、法氏囊),并对免疫抑制鸡的免疫系统具有调节功能[12-13]。脾是机体内最大的外周淋巴器官,也是免疫反应的重要部位,但目前关于紫锥菊对免疫抑制鸡脾组织保护作用的潜在机制尚不清楚。因此,本研究利用环磷酰胺诱导的免疫抑制动物模型探讨紫锥菊对免疫抑制鸡的免疫调节功能的影响。

1 材料与方法 1.1 试验动物及处理

120羽1日龄雏鸡适应性饲养7 d后,随机分为4组:对照组、环磷酰胺组、紫锥菊组、环磷酰胺+紫锥菊组(联合组),每组6个重复,每个重复30羽。对照组和紫锥菊组雏鸡连续3 d胸肌注射等量的生理盐水,环磷酰胺组和联合组雏鸡连续3 d按80 mg·kg-1体重注射生理盐水配制的环磷酰胺诱导免疫抑制模型,紫锥菊组和联合组每天饲喂含有紫锥菊全草粉末的基础日粮(含量为1%),其余各组饲喂基础日粮。试验期间雏鸡自由饮水,给予光照每天12 h,第1周室温控制在31~33 ℃,每过1周温度降1~2 ℃。每天称重并记录每只鸡的重量,连续饲喂21 d,并观察雏鸡的生长情况。试验结束时,每重复组随机选取6只鸡,称取体重,迅速采集脾并称重,并计算脾脏指数。取一部分脾用预冷PBS(磷酸盐缓冲液)清洗后放入4%的多聚甲醛中,用于形态学病理检测。其余的放入冻存管于液氮之中暂存,用于分子检测。

1.2 试验试剂和仪器

TRIzol购自TaKaRa公司;Prime Script RT Master Mix、2×ChamQ SYBR qPCR Master Mix和BCA蛋白检测试剂盒购自南京诺唯赞生物科技有限公司;RIRA裂解液购自Beyotime公司;PAGE凝胶快速制备试剂盒(12.5%)购自上海雅酶生物科技有限公司;炎症抗体均购自武汉三鹰生物技术有限公司;紫锥菊全草购自安国市宏宇中药材公司,产地河北。其他试剂均为国产分析纯。

TDZ5-WS型冷冻离心机,购自湖南湘仪实验室仪器开发有限公司;5200型凝胶成像系统,购自上海医科大学仪器厂;LightCycler480型荧光定量PCR仪,购自美国Bio-Rad公司;Unique-R10型超纯水仪,购自厦门锐思捷科学仪器有限公司;DM1000型光学显微镜,购自广州德真科学仪器有限公司。

1.3 脾组织重量分析

分离的脾组织用滤纸吸干表面血液,称重并记录。并计算脾脏指数:脾脏指数=脾重量(g)×100%/体重(g)。

1.4 病理切片的制备

分离的脾组织在4%的多聚甲醛中固定24 h后,在梯度酒精中脱水,二甲苯透明,放入蜡机中制成石蜡块。切片机将组织蜡块切成5 μm厚的切片,经烤片、二甲苯Ⅰ、二甲苯Ⅱ、100%、90%、80%、70%、60%的梯度酒精复水(各3 min),苏木精染色,1%的盐酸酒精分色,自来水反蓝15 min,60%、70%、80%、90%的梯度酒精脱水(各3 min),伊红染色,100%酒精(2次)、二甲苯Ⅲ(5 min)、二甲苯Ⅳ(10 min),封片,光学显微镜先观察并拍照。

1.5 实时荧光定量PCR

称取脾组织50 mg,提取总RNA,其方法按照TaKaRa试剂盒说明书进行。简而言之,RNA浓度用NanaDrop-2000微量核算测定仪检测。GAPDH作为看家基因。引物由Prime Express 5设计,由生工生物工程股份有限公司合成,引物序列见表 1。将RNA反转录成cDNA,按照试剂盒说明书进行。随后进行RT-qPCR反应。反应总体系为10 μL:其中cDNA 1 μL, 2× Cham Q SYBR qPCR Master Mix 5 μL,上、下游引物均为0.4 μL。反应条件:预变性95 ℃ 5 min,95 ℃ 30 s,60 ℃ 30 s;进行40次循环;检测NF-κBIκBIL-2、IL-4、IL-6、TNF-αIFN-γTLR2、TLR4、TLR7、MyD88的mRNA水平。

表 1 引物序列 Table 1 Primer sequences
1.6 蛋白免疫印迹

用蛋白免疫印迹法检测鸡脾组织NF-κB、p-NF-κB、IκB、p-IκB、IL-2、IL-4、IL-6、TNF-α、IFN-γ和TLR4的蛋白表达量,以β-tubulin和GAPDH作为内参。称取鸡脾组织30 mg,加500 μL RIPA裂解液冰上匀浆、离心(12 000×g,4 ℃,15 min)取上清获得总蛋白,测定蛋白浓度后稀释至同一浓度,煮沸10 min后-80 ℃保存。采用12.5% SDS-聚丙酰胺凝胶电泳分离目的蛋白,通过转膜将目的蛋白转移到PVDF膜上,TBST洗涤3次,每次5 min,5%的脱脂牛奶封闭1 h,目的蛋白相应的一抗4 ℃摇床孵育过夜。TBST洗涤3次,然后与相应二抗摇床室温孵育1 h,后用TBST充分洗涤。ECL发光液显影,拍照并分析。

1.7 数据处理

试验数据先用Excel 2019初步处理,数据均以“平均值±标准差(Mean ± SD)”表示,用SPSS统计分析软件进行差异显著性检验,使用GraphPad Prism 9.0软件进行做图。P<0.05被认为有统计学意义。

2 结果 2.1 紫锥菊对环磷酰胺致免疫功能降低肉鸡一般状况的影响

图 1A所示,注射环磷酰胺后,在14 d时,环磷酰胺组雏鸡体重和对照组相比显著降低(P<0.05),而其他组无明显差异。在21日龄时,紫锥菊组雏鸡体重和对照组相比极显著增加(P<0.001),而环磷酰胺组雏鸡生长迟缓(P<0.05),联合组雏鸡体重显著高于环磷酰胺组雏鸡(P<0.05)。在28日龄时,体重差异更为明显,紫锥菊组雏鸡体重是4个组中最高的(P<0.001),而环磷酰胺组雏鸡最低(P<0.001),联合组雏鸡体重较环磷酰胺组显著增加(P<0.001)。脾脏指数结果如图 1B所示,环磷酰胺组鸡的脾脏指数显著低于对照组和联合组(P<0.05)。这些试验结果表明,实验动物模型造模成功。

与对照组相比,*表示P<0.05,**表示P<0.01,***表示P<0.001。联合组与环磷酰胺组比,#表示P<0.05,##表示P<0.01,###表示P<0.001,n=6。下同 Compared with control group, * indicates P < 0.05, ** indicates P < 0.01, *** indicates P < 0.001. The combined group vs. the cyclophosphamide group, # represents P < 0.05, ## means P < 0.01, ### indicates P < 0.001, n=6. The same as below 图 1 鸡的体重(A)及脾脏指数(B)变化 Fig. 1 The changes in body weight(A) and spleen coefficient(B) of chickens
2.2 紫锥菊对环磷酰胺致免疫功能降低肉鸡脾组织病理学的影响

图 2所示,对照组鸡脾结构正常,白髓与红髓分界线清晰,形态良好。环磷酰胺组鸡脾出现大量空泡(红色箭头表示),淋巴细胞稀疏紊乱,白髓与红髓分界线逐渐模糊,动脉周围淋巴鞘增生,淋巴细胞生成减少。紫锥菊组鸡脾结构清晰,无明显病变。联合组鸡脾淋巴细胞生成增多,间质纤维增生减轻,空泡减少。

A~D分别为对照组、环磷酰胺组、紫锥菊组、联合组。红箭头指空泡 A-D are the control group, the cyclophosphamide treated group, the Echinacea treated group and the combined group, respectively. Red arrows point to the vacuoles degeneration 图 2 脾组织病理切片图(200×) Fig. 2 Histopathological sections of the spleen tissues (200×)
2.3 紫锥菊对环磷酰胺致免疫功能降低肉鸡脾NF-κB及TLR4信号通路相关基因mRNA表达的影响

紫锥菊对环磷酰胺致免疫功能降低肉鸡脾炎性相关基因mRNA表达的影响如图 3所示。与对照组相比,环磷酰胺处理组的NF-κBIL-2、IL-4、IL-6、IFN-γ基因的mRNA表达量均显著降低(P<0.05、P<0.01或P<0.001),而IκBTNF-α的mRNA表达量显著升高(P<0.01或P<0.001)。而紫锥菊组NF-κBIL-2、IL-4、IL-6、IFN-γ的mRNA表达量均显著高于对照组(P<0.05、P<0.01或P<0.001),IκB的mRNA表达量显著低于对照组(P<0.01),TNF-α无显著变化。联合组和环磷酰胺组相比,基因NF-κBIL-2、IL-4、IL-6、IFN-γ的表达量均显著升高(P<0.05、P<0.01或P<0.001),而IκBTNF-α显著下降(P<0.05)。与对照组相比,环磷酰胺组TLR2、TLR4、TLR7、MyD88的mRNA水平均显著下降(P<0.05、P<0.01或P<0.001),而紫锥菊组的MyD88 mRNA的表达量显著高于对照组(P<0.001),其余基因mRNA表达量无显著差异。此外,联合组相比环磷酰胺组,TLR2、TLR4、MyD88的mRNA的表达水平显著上升(P<0.05,P<0.001),TLR7的mRNA表达量无显著差异。

图 3 紫锥菊对环磷酰胺致免疫功能降低肉鸡的脾组织中炎性和免疫相关基因mRNA表达的影响 Fig. 3 Effects of Echinacea on the mRNA expression of inflammatory- and immune-related genes in spleen of immunosupressed chickens induced by cyclophosphamide
2.4 紫锥菊对环磷酰胺致免疫功能降低肉鸡脾组织NF-κB、TLR4通路相关蛋白的表达影响

结果如图 4,相比于对照组,p-NF-κB/NF-κB在环磷酰胺组显著降低(P<0.001),而在紫锥菊组显著升高(P<0.01),且联合组较环磷酰胺组显著增加(P<0.001)。与p-NF-κB/NF-κB相反,环磷酰胺组p-IκB /IκB显著高于对照组(P<0.01),而其他组则无显著差异。与对照组相比,环磷酰胺组炎性因子IL-2、IL-4、IL-6、TNF-α、IFN-γ的蛋白表达水平均显著降低(P<0.05或P<0.001),而上述蛋白表达量在紫锥菊组则显著增加(P<0.05或P<0.01),且联合组IL-2、IL-4、IL-6、TNF-α、IFN-γ的蛋白表达水平显著高于环磷酰胺组(P<0.05或P<0.001)。环磷酰胺组TLR4蛋白表达水平显著低于对照组,而联合组的TLR4蛋白表达水平则显著高于对照组和环磷酰胺组(P<0.01或P<0.001)。

图 4 紫锥菊对环磷酰胺致免疫功能降低肉鸡的脾组织NF-κB/TLR4通路相关蛋白的表达影响 Fig. 4 Effects of Echinacea on expression levels of NF-κB and TLR4 pathway-related proteins in spleen of immunosuppressed chickens induced by cyclophosphamide
3 讨论

环磷酰胺是一种广泛用于诱导免疫抑制动物模型的烷基化制剂,它可以抑制体液免疫和细胞免疫,导致淋巴细胞发生不可逆损伤[14-15]。因此,本研究利用环磷酰胺建立鸡免疫抑制模型,验证紫锥菊在促进雏鸡生长和免疫调节中的作用。动物的生产性能反映了饲料对机体生长发育的影响。研究表明,在猪饲料中添加紫锥菊粉末可以显著提高育肥猪的饲料转化率,且生长性能明显提高[16]。本试验结果显示,从21 ~28日龄紫锥菊组鸡的体重急剧增加且显著高于其他组,说明紫锥菊能够提高鸡的生长性能,此结果与罗俊峰等[17]的研究结果一致。体重变化可以直观地反映动物的生长状态;脾是禽类最重要的免疫器官,是各种免疫活性细胞发育、增殖分化的主要场所,免疫器官发育情况直接影响机体的免疫系统。免疫系统具有免疫监视、防御、调控的作用,当其受损时往往伴随着免疫器官的损害[18-19]。在本研究中,环磷酰胺组的脾脏指数显著低于其他组,而HE染色显示,对照组脾细胞超微结构致密,排列整齐;环磷酰胺组的脾细胞排列不规则,细胞间隙明显扩张,红、白髓结构不清晰;而联合组脾细胞的结构损伤得到缓解,病理变化减轻;紫锥菊组与对照组接近。本研究显示,紫锥菊能有效缓解环磷酰胺所致脾损伤,并通过影响免疫器官发挥其免疫调节功能。有研究显示,80 mg·kg-1的环磷酰胺作用的肉鸡脾脏指数和法氏囊指数显著低于对照组[20]。宋红卫等[21]发现,紫锥菊的添加能够显著促进免疫器官的发育,提高免疫器官指数。这与本研究结果相一致。

有研究发现,TLR家族蛋白在先天免疫中发挥重要作用[22-23]。其中TLR4在启动适应性免疫、活化抗原提呈细胞和病原体识别中起着关键作用[24-25]。TLR4的激活直接诱导核因子κB(nuclear factor kappa-B,NF-κB)进入细胞核形成磷酸化的NF-κB(p-NF-κB),进而激活免疫调节通路的级联以及下游关键转录因子[26-27]。而IκB(inhibitor of NF-κB),是NF-κB的抑制蛋白,p-IκB是其磷酸化形式,主要调节NF-κB转录[28-29]。IL-2、IL-4、IL-6、TNF-α、IFN-γ是受NF-κB调控的重要炎性因子,其对维持机体免疫功能具有重要的作用[30-31]。有研究表明,刺参糖胺聚糖、刺五加多糖、玉竹多糖和板蓝根多糖均具有较好的免疫调节功能[32-34]。紫锥菊多糖在LPS致大鼠肺损伤模型中,显著降低了白细胞、嗜酸性粒细胞、中性粒细胞、淋巴细胞和巨噬细胞的数量,减少TNF-α、IL-6和IL-1β释放,显示出较强的抗炎效果[35]。环磷酰胺作用于小鼠后,血清蛋白IgG、IgM和IgA,抗炎性因子IL-4和IL-10显著低于对照组[36]。为了阐明紫锥菊的免疫调节活性是否受TLR4/NF-κB通路的调控,本研究检测了TLR4/NF-κB通路相关的基因mRNA和蛋白的表达情况,实时荧光定量结果显示,环磷酰胺组的TLR4/NF-κB通路相关因子(除IκB外)mRNA表达水平显著低于其他各组,而联合组相关基因变化趋势与环磷酰胺组结果相反。蛋白免疫印迹结果显示,在环磷酰胺组NF-κB和IκB的磷酸化明显受阻,而添加紫锥菊后得到明显缓解,由此可见紫锥菊可激活TLR4/NF-κB信号通路,具有较强的免疫调节活性。

4 结论

紫锥菊依赖于TLR4/NF-κB通路进行免疫调节,并通过该通路上调细胞因子IL-2、IL-4、IL-6、TNF-α和IFN-γ的表达来调节机体的免疫机能。本研究结果为紫锥菊在兽医临床上的应用提供理论依据和试验基础。

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