畜牧兽医学报  2020, Vol. 51 Issue (3): 594-601. DOI: 10.11843/j.issn.0366-6964.2020.03.019    PDF    
绵羊痒螨巨噬细胞迁移抑制因子重组蛋白对兔外周血单个核细胞Th1/Th2型和Th17/Treg型特征因子表达的影响
郑友乐, 陈宇航, 谢跃, 杨光友, 何冉, 古小彬     
四川农业大学动物医学院 动物寄生虫病研究中心, 成都 611130
摘要:为了初步探讨绵羊痒螨巨噬细胞迁移抑制因子(PoMIF)对健康新西兰兔外周血单个核细胞(PBMC)中Th1/Th2和Th17/Treg细胞平衡的变化。采用RT-PCR从绵羊痒螨总RNA中扩增得到MIF全长基因,经原核表达、纯化重组PoMIF(rPoMIF)蛋白,并分析其氧化还原酶和互变异构酶活性。筛选与健康新西兰兔PBMC孵育的最佳rPoMIF浓度,且用最佳浓度rPoMIF(0.2 μg·mL-1)与PBMC共同孵育0、1、6、12、24、36 h后收集细胞,用荧光定量PCR检测其Th1/Th2/Th17/Treg细胞相对应的特征性转录因子T-bet/GATA-3/RORc/Foxp3和特征性细胞因子IFN-γ/IL-4/IL-17A/IL-10 mRNA表达变化。结果表明:PoMIF全长363 bp,rPoMIF大小为32 ku(含pET32a标签蛋白19 ku),且具有互变异构酶活性;rPoMIF刺激后PBMC中Th1细胞的T-betIFN-γ先下降后上升,Th2细胞的GATA-3和IL-4均呈下降趋势,且T-bet/GATA-3和IFN-γ/IL-4比值在12、24和36 h均升高;Th17细胞的RORc和IL-17A在各时间点下降,而Treg细胞的Foxp3和IL-10在各时间点升高,且RORc/Foxp3和IL-17A/IL-10比值在各时间点均变低。rPoMIF可造成家兔外周血单个核细胞的Th1/Th2和Th17/Treg平衡分别向Th1和Treg偏移。
关键词绵羊痒螨        巨噬细胞迁移抑制因子    外周血单个核细胞    Th1/Th2平衡    Th17/Treg平衡    
The Effects of Recombinant Macrophage Migration Inhibitory Factor of Psoroptes ovis on the Characteristic Molecules of Th1/Th2 and Th17/Treg Type Immune Responses in Rabbits Peripheral Blood Mononuclear Cells in vitro
ZHENG Youle, CHEN Yuhang, XIE Yue, YANG Guangyou, HE Ran, GU Xiaobin*     
Department of Parasitology, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, China
Abstract: To explore the effects of macrophage migration inhibitory factor of Psoroptes ovis (PoMIF) on Th1/Th2 and Th17/Treg balance of rabbit peripheral blood mononuclear cells (PBMC) in vitro, the PoMIF gene was amplified from the extracted total RNA from P. ovis mites by the reverse transcription-polymerase chain reaction (RT-PCR), and the recombinant protein rPoMIF was expressed with prokaryotic expression system, then the oxidoreductase and tauromerase activities of rPoMIF was evaluated. PBMCs isolated from healthy New Zealand rabbits were cultured with different concentrations of rPoMIF, and the optimum concentration of rPoMIF was screened. Finally, the expression levels of Th1, Th2, Th17 and Treg-specific transcription factors of T-bet, GATA-3, RORc, Foxp3 and specific cytokines of IFN-γ, IL-4, IL-17A and IL-10 in PBMC incubated with the optimal concentration of rPoMIF for 0, 1, 6, 12, 24 and 36 h were detected by real time fluorescence quantitative PCR (qPCR). The results showed that the full-length of PoMIF was 363 bp, containing 357 bp open reading frame; rPoMIF was mainly in the supernatant of Escherichia coli (E. coli) lysate, with a molecular size of 32 kD (including an extra 19 kD for the attached His-tag fusion peptide); and it has tautomerism activity; the mRNA levels of Th1-specific T-bet and IFN-γ decreased firstly and then increased after treatment, while Th2-specific GATA-3 and IL-4 decreased at all tested time points, and the ratio of T-bet/GATA-3 and IFN-γ/IL-4 increased at 12, 24 and 36 h; the mRNA levels of Th17-specific RORc and IL-17A decreased at all tested time points, while Foxp3 and IL-10 from Treg cells increased at all tested time points, and the ratio of RORc/Foxp3 and IL-17A/IL-10 decreased at all tested time points. In conclusion, rPoMIF can cause the shifts of Th1/Th2 and Th17/Treg towards Th1 and Treg in PBMC of rabbits.
Key words: Psoroptes ovis    rabbit    macrophage migration inhibitory factor    peripheral blood mononuclear cells    Th1/Th2 cell balance    Th17/Treg cell balance    

痒螨病是由绵羊痒螨(Psoroptes ovis)寄生于绵羊、兔、牛、鹿、骆驼等家养和野生动物皮肤表面引起的外寄生虫疾病,该病呈全球流行[1-2],引起动物以瘙痒、结痂、脱毛为主的临床特征,给家养动物养殖业带来重大经济损失和严重的动物福利问题[3]。寄生虫可以打破宿主Th1/Th2和Th17/Treg细胞间的平衡,从而影响病程的发展和转归[4-5]。痒螨感染宿主后,宿主Foxp3+ T细胞大量浸润于皮肤中,即宿主Naïve CD4+ T细胞更多偏向Treg细胞分化,打破Th17/Treg平衡,表现出Treg细胞占优势,抑制免疫的作用[6];并且随着痒螨病病变程度的增加,宿主的Th2免疫反应受到抑制(GATA-3的表达降低),而Th1免疫反应增强(IFN-γ和T-bet的表达增高),从而维持寄生部位炎症的发生[7]。这些说明Th1/Th2和Th17/Treg细胞的平衡在痒螨感染中具有重要意义。

巨噬细胞迁移抑制因子(MIF)属于寄生虫的排泄/分泌物质之一,具有促炎和调节宿主免疫反应等生物学功能,并在抗寄生虫感染中被广泛研究[8-9]。胞内寄生虫MIF可以上调宿主Th2型免疫并下调Th1型免疫,从而影响宿主患处局部或者全身免疫的平衡[10];而一些胃肠道寄生虫MIF可以抑制Th2型免疫并激活Treg型免疫,从而抑制宿主免疫功能,利于其在宿主体内长期生存[11]。目前,在绵羊痒螨的转录组数据中发现了MIF基因[12],但其蛋白的功能研究未见报道。因此本研究探究绵羊痒螨巨噬细胞迁移抑制因子重组蛋白(rPoMIF)对家兔外周血单个核细胞(PBMC)的Th1/Th2型和Th17/Treg型免疫反应的影响,以期为更好地了解痒螨入侵宿主、维持长期寄生的过程奠定基础,也为新的药物靶点和疫苗研制提供新的思路。

1 材料与方法 1.1 主要仪器和试剂

MiniBEST Universal RNA Extraction Kit(9767,TaKaRa);PrimeScriptTM RT reagent Kit with gDNA Eraser(RR047A,TaKaRa);EtEraserTM HP内毒素去除试剂盒(ER0015,厦门鲎试剂生物科技股份有限公司);定量显色基质法鲎试剂盒(EC32545S,厦门鲎试剂生物科技股份有限公司);荧光定量PCR预混液(DRR820A,TaKaRa);荧光定量PCR引物,由上海生工生物有限公司合成;兔外周血单个核细胞分离液试剂盒(P4470,Solarbio);Multiskan GO酶标仪;NanoDrop OneC核酸蛋白仪;百乐荧光定量PCR仪。人源巨噬细胞迁移抑制因子重组蛋白(BP4437,Bosterbio)。

1.2 实验动物

3只健康新西兰兔(3月龄)购于四川成都某养殖场。试验方案经四川农业大学动物保护与利用委员会批准(SYXK 2019-187)。

1.3 螨虫收集、总RNA的提取和cDNA反转录

从自然感染痒螨的新西兰兔外耳道结痂中收集痒螨,经形态学鉴定[13]后用总RNA抽提试剂盒(9767,TaKaRa)提取虫体总RNA,随后使用cDNA反转录试剂盒(RR047A,TaKaRa)进行反转录合成cDNA,保存于-70 ℃待用。

1.4 PoMIF基因的克隆、表达与纯化

参照绵羊痒螨转录组数据(GenBank accession No. PRJNA317241)[12]MIF基因序列设计特异性引物(上游引物5′-CGCGGATCCATGCCAACTTTACTCATACGA-3′,BamHⅠ酶切位点为下划线序列;下游引物5′-CCGCTCGAGTTA-AATTAAATCATCAAAAGTTGT-3′,XhoⅠ酶切位点为下划线序列)。以cDNA为模板进行PCR扩增,反应条件:预变性94 ℃ 5 min,变性94 ℃ 30 s,退火60 ℃ 30 s,延伸72 ℃ 30 s,35个循环,72 ℃延伸5 min。PCR产物经琼脂糖凝胶电泳后用试剂盒(DP214-03,天根)回收纯化,并克隆导入pMD19-T载体,转化入DH5α感受态细胞,经酶切鉴定正确的质粒pMD19-T-PoMIF送上海生物工程有限公司测序。对测序正确的重组质粒pMD19-T-PoMIF经BamHⅠ、XhoⅠ双酶切回收后,亚克隆入pET-32a(+)载体,并转化DH5α感受态细胞,用试剂盒(DP103-03,天根)提取pET-32a(+)-PoMIF质粒后转入表达菌BL21(DE3)中,于0.5 mmol·L-1 IPTG 16 ℃条件下诱导12 h。诱导后的菌液经离心,菌体超声裂解,收集上清液,沉淀用8 mol·L-1尿素溶解,经SDS-PAGE验证蛋白大小后,用Ni2+亲和层析柱(780-0811,Bio-Rad)纯化表达上清产物,经超滤管(UFC901096,Millipore)超滤浓缩,再经SDS-PAGE验证蛋白纯化效果,使用NanoDrop OneC测定其浓度,置于-70 ℃待用。

1.5 PoMIF内毒素去除及酶活测定

参照EtEraserTM HP内毒素去除试剂盒和试管定量显色基质法鲎试剂盒说明书对PoMIF进行内毒素的去除和检测,内毒素标准品的测定结果用线性回归建立标准方程y=ax+b,其中y为标准品在545 nm处吸光度值,x为标准品内毒素的浓度,并计算线性回归决定系数R2

氧化还原酶活性测定参考Kleemann等[14]的方法,将5 μL的200 mmol·L-1还原型谷胱甘肽加到195 μL含有2 mmol·L-1的EDTA和1 mg·mL-1胰岛素的100 mmol·L-1预冷PBS缓冲液(pH=7.2)中,将200 μL该底物加入到96孔板中,然后加入rPoMIF至终浓度0.06 mg·mL-1,同行设置阳性对照组(终浓度为0.06 mg·mL-1的人源MIF,huMIF)和阴性对照组(100 mmol·L-1 PBS溶液)。采用Multiskan GO酶标仪在650 nm波长下进行间隔1 min长达12 min吸光度测试。

互变异构酶活性测定参考Alam等[15]的方法,室温下(25 ℃)将12 μL的10 mmol·L-1盐酸左旋多巴甲酯和8 μL的20 mmol·L-1高碘酸钠加入到180 μL含1 mmol·L-1 EDTA和100 mmol·L-1PBS(pH=6.2)中,反应后生成L-多巴色素甲醇,将200 μL该底物加入到96孔板中,然后分别加入rPoMIF至终浓度0.06或0.15 mg·mL-1。同行设置阳性对照(终浓度为0.06 mg·mL-1的人MIF (huMIF)和阴性对照(100 mmol·L-1的PBS溶液)。另设置互变异构酶抑制剂组(0.06 mg·mL-1 rPoMIF + 20 μmol·L-1 Z590)。采用Multiskan GO酶标仪统一在475 nm波长下进行间隔2 min长达30 min吸光度测试。

1.6 兔PBMC的分离、培养和分组处理

用含有肝素钠的无菌真空采血管从健康新西兰兔耳缘静脉采集全血,参照兔外周血单个核细胞分离液试剂盒(P4470,Solarbio)分离获得单个核细胞,加入含有10%胎牛血清的RPMI1640培养基中重悬计数,调整细胞数为1×106个·mL-1;每孔3 mL细胞悬液接种于6孔细胞培养板,放入37 ℃、5% CO2浓度的培养箱中培养至细胞铺满培养孔的70%时,进行如下两组试验:①将PBMC分别与0、0.02、0.2、2、20 μg·mL-1的rPoMIF共同于37 ℃、5% CO2浓度的培养箱中孵育12 h,收集细胞,通过“1.7”荧光定量PCR检测IL-8 mRNA表达量,判定最佳上样浓度;②选用上述得出最佳上样浓度的rPoMIF与PBMC共同在37 ℃、5% CO2浓度的培养箱中孵育,分别于0、1、6、12、24、36 h收集细胞,通过荧光定量PCR(详见“1.7”)检测目标因子(T-betGATA-3、RORc、Foxp3、IFN-γ、IL-4、IL-17A、IL-10)mRNA表达变化。其中,以0 h组为对照组(control group,CG),其他时间点为试验组(experimental group,EG)。

1.7 PBMC的实时荧光定量PCR检测

按照总RNA抽提试剂盒(9767,TaKaRa)操作要求提取“1.6”中收集细胞的总RNA,随后使用cDNA反转录试剂盒(RR047A,TaKaRa)进行反转录合成cDNA。根据GenBank中相应的基因序列设计IL-8、T-betGATA-3、RORc、Foxp3、IFN-γIL-4、IL-17A、IL-10的引物(表 1),以兔β-actin为内参基因,通过荧光实时定量PCR检测上述基因的mRNA相对表达水平。Real-time反应体系(25 μL):SYBR premix Ex TaqⅡ(Tli RNaseH Plus)(2 ×)12.5 μL,上游引物1.0 μL,下游引物1.0 μL,cDNA 2 μL,灭菌水8.5 μL。反应设定条件:①预变性:95 ℃ 5 min;②扩增反应:95 ℃预变性5 s,60 ℃退火与延伸31 s,40个循环;③熔解曲线形成:95 ℃ 15 s,60 ℃ 1 min,95 ℃ 15 s。反应后根据熔解曲线分析产物的特异性,导出目的基因和内参基因的Ct值(Ct_targetCt_control)。

表 1 实时荧光定量PCR引物信息 Table 1 Primer information of RT-qPCR
1.8 统计学分析

所有试验均设置三个独立的生物学重复。采用Livak相对定量分析法[16]计算目标基因的mRNA相对表达量。计算公式为2-ΔΔCt=2(Ct_target-Ct_control) sample CG - (Ct_target-Ct_control)sample EG。所有数据均采用t检验进行统计分析,数据用“x±s”表示,0.01<P<0.05表示差异具有显著学意义,用“*”表示;P<0.01表示差异极显著,用“**”表示。

2 结果 2.1 PoMIF的扩增、原核表达和纯化

PoMIF基因全长363 bp,含357 bp的开放阅读框,编码118个氨基酸,预测相对分子质量为13.00 ku。rPoMIF主要以上清形式存在,Ni2+柱纯化后SDS-PAGE显示为单一条带,大小为32 ku,符合预期大小(含pET32a标签蛋白19 ku)(图 1)。

M.蛋白质相对分子质量标准;1. IPTG诱导BL21重组表达rPoMIF上清;2. IPTG诱导BL21重组表达rPoMIF沉淀;3. pET32a空载蛋白;4.纯化重组表达rPoMIF上清 M. Protein marker; 1. Soluble fraction of extracts from IPTG induced E. coli cultures; 2. Insoluble fraction of extracts from IPTG induced E. coli cultures; 3. Protein of the empty pET32a vector; 4. Purified rPoMIF from soluble extracts 图 1 绵羊痒螨巨噬细胞迁移抑制因子的原核表达及纯化 Fig. 1 Prokaryotic expression and purification of macrophage migration inhibitory factor of Psoroptes ovis
2.2 rPoMIF内毒素去除及酶活测定

为避免内毒素对后续细胞试验的影响,去除rPoMIF中的内毒素,经测定标准品内毒素标准曲线y=1.513x+0.035,R2=0.981,经计算纯化后rPoMIF样品的内毒素含量为0.029 EU·mL-1,符合要求。

酶活测定结果显示rPoMIF不具有氧化还原酶活性(图 2A),但具有互变异构酶活性,且活性随浓度增加而增加(图 2B);在相同浓度下,rPoMIF明显低于rhuMIF的互变异构酶活性,但rPoMIF的互变异构酶活性不被抑制剂Z590[17]所抑制(图 2B)。

A. rPoMIF的氧化还原酶活性;B. rPoMIF的互变异构酶活性。rPoMIF.绵羊痒螨巨噬细胞迁移抑制因子重组蛋白;rhuMIF.人巨噬细胞迁移抑制因子重组蛋白;Z590.互变异构酶抑制剂。下同 A.Oxidoreductase activity of rPoMIF; B. Tautomerase activity of rPoMIF. rPoMIF. Recombinant macrophage migration inhibitory factor of Psoroptes ovis; rhuMIF. Recombinant macrophage migration inhibitory factor of human; Z590. Inhibitor of tautomerase activity. The same as below 图 2 绵羊痒螨巨噬细胞迁移抑制因子重组蛋白(rPoMIF)的酶活测定 Fig. 2 Enzymatic activity of recombination macrophage migration inhibitory factor of Psoroptes ovis
2.3 实时荧光定量PCR检测兔PBMC中免疫相关因子的mRNA水平 2.3.1 最佳rPoMIF浓度的筛选

健康新西兰兔PBMC经rPoMIF刺激12 h后,IL-8的mRNA表达量在四个上样蛋白浓度梯度中大体遵循钟形剂量反应曲线,即表达量随浓度的增加先升后降,且与空白对照组相比差异极显著(P<0.01,图 3),可见0.2 μg·mL-1 rPoMIF为最佳浓度。

与空白对照相比, **. P<0.01 Compared with the blank control, **. P < 0.01 图 3 rPoMIF对兔外周血单个核细胞(PBMC)中IL-8 mRNA相对表达量的影响 Fig. 3 Effects of different concentrations of rPoMIF on the mRNA expression of IL-8 in rabbits peripheral blood mononuclear cells
2.3.2 兔PBMC中转录因子与细胞因子变化

经0.2 μg·mL-1 rPoMIF刺激后,PBMC中转录因子与细胞因子的变化结果显示(图 4):与0 h组相比,Th1细胞特征因子T-betIFN-γ在1、6和12 h呈显著下降(P < 0.05或P < 0.01),36 h呈显著上升(P < 0.05或P < 0.01),Th2细胞特征因子GATA-3和IL-4在各时间点均呈显著性下降(P < 0.05或P < 0.01),且T-bet/GATA-3和IFN-γ/IL-4比值在12、24和36 h均升高;而Th17细胞特征因子RORc和IL-17A在1、6、24和36 h均呈显著性下降(P < 0.05或P < 0.01),Treg细胞特征因子Foxp3和IL-10在各时间点均呈显著性升高(P < 0.05或P < 0.01),且RORc/Foxp3和IL-17A/IL-10比值均变低。

3 讨论 3.1 MIF的催化活性

MIF的氧化还原酶活性[18]对细胞内的氧化还原稳态、细胞凋亡的抑制等有重要作用[19-20],而MIF的互变异构酶[21]活性对促炎有显著影响[17]。本研究发现绵羊痒螨的MIF(rPoMIF)仅具有互变异构酶活性,且酶活性随蛋白浓度升高而增强,但其酶活性明显低于同浓度的人源MIF(huMIF),这提示哺乳类MIF和寄生虫MIF在促炎方面可能存在明显差异,Liu等[22]也证实了这个观点,他们发现约氏疟原虫(Plasmodium yoelii)MIF(PyMIF)的互变异构酶活性要明显低于鼠科MIF,该虫分泌PyMIF可能是通过竞争性结合宿主受体的方式降低宿主的炎症反应,调节宿主的免疫反应,维持慢性感染,从而延迟感染动物的死亡。Cho等[23]发现重组锡兰钩口线虫(Ancylostoma ceylonicum)MIF蛋白(AcMIF)与huMIF的三维晶体结构虽然高度相似,但AcMIF蛋白的活性并不能被huMIF互变异构酶催化位点抑制剂ISO-1抑制,本试验也支持这个结论,使用最新验证比ISO-1还要高效的huMIF互变异构抑制剂Z590[17]不能明显抑制rPoMIF的活性。由此可见,宿主和寄生虫互变异构酶活性位点存在差异,因此阻断寄生虫源MIF的互变异构酶活性可能作为一种潜在的新型防控寄生虫手段[15, 17]

3.2 MIF的细胞因子功能和其浓度有关

除了生物催化活性,MIF还具有细胞因子功能,可引起下游IL-8[24]、IFN-γ[7]等炎性因子的升高,从而调节宿主的患处局部或全身免疫。IL-8是痒螨疾病发展的重要炎性因子,且已被作为重要免疫指标进行检测[25-26],因此本试验以IL-8为检测指标,来筛选rPoMIF对兔PBMC的最佳刺激浓度,发现四个不同浓度的rPoMIF刺激后,PBMC中IL-8 mRNA表达量随rPoMIF浓度的增加先升后降,这和Simons等[27]研究huMIF的试验结果类似,可能原因是低浓度MIF多表现为促炎作用,而高浓度则具抗炎作用[28-29]。Kleemann等[29]进一步阐述了高浓度MIF可以通过阻断AP-1通路的促炎基因表达,引起MIF介导的炎症抑制。De Dios Rosado和Rodriguez-Sosa[30]发现MIF蛋白在大多数寄生虫感染的宿主体内都是过度表达的,因此推测寄生虫可能是通过在感染部位分泌MIF,诱导内源性宿主MIF进一步分泌,从而产生局部或全身抗炎的宿主环境,进而影响宿主的免疫进程。但是痒螨作为一种体表寄生虫是如何根据自身生存需要调整MIF浓度,以及PoMIF调节宿主免疫的机制是什么,这些问题有待进一步探究。

与0 h进行比较,**. P<0.01; *. 0.01<P<0.05 Compared with 0 h, **. P < 0.01; *. 0.01 < P < 0.05 图 4 rPoMIF对兔外周血单个核细胞(PBMC)中免疫因子mRNA相对表达量的影响 Fig. 4 Effects of rPoMIF on the mRNA expression level of the factors related to the immune response
3.3 rPoMIF对兔PBMC Th1/Th2和Th17/Treg细胞平衡的影响

初始Naïve CD4+T细胞在抗原、共刺激分子等作用下活化分为Th1、Th2、Th17、Treg等细胞亚群,从而调节宿主的免疫平衡[31-32]。正常机体内Th1/Th2细胞间、Th17/Treg间处于平衡状态,当宿主感染病原时这种平衡状态被打破,并影响病程的发展和转归[4-5]。Th1、Th2、Th17和Treg细胞具有特征性的转录因子和细胞因子,分别为T-bet、GATA-3、RORc、Foxp3[33-34]和IFN-γ、IL-4、IL-17A、IL-10[35]。T-bet/GATA-3和IFN-γ/IL-4的比值可初步反映Th1/Th2细胞间的平衡情况,而RORc/Foxp3和IL-17A/IL-10可初步反映Th17/Treg细胞间的平衡情况[36]。本研究结果揭示rPoMIF刺激PBMC后RORc/Foxp3和IL-17A/IL-10比值降低,Th17/Treg平衡被打破,Naïve CD4+ T细胞更多地向Treg细胞分化,呈现Treg细胞占优势,有助于为痒螨感染提供一个较为稳定的免疫抑制的寄生环境[6]T-bet/GATA-3和IFN-γ/IL-4比值在rPoMIF刺激PBMC 12、24和36 h升高,Th1/Th2平衡被打破,Naïve CD4+T细胞更多地向Th1细胞分化,呈现Th1细胞占优势,而Th1属于促炎为主的免疫细胞,可以维持、扩大寄生部位的皮损和炎症,可为痒螨寄生提供充足的炎性渗出物,利于后期痒螨的大量繁殖[32]

4 结论

绵羊痒螨MIF重组蛋白具有互变异构酶催化活性,可引起家兔PBMC Th1/Th2和Th17/Treg平衡分别向Th1和Treg偏移。

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