Toll样受体家族基因多态性与移植后相关疾病研究进展

魏巴金 周琳

·综述·

Toll样受体家族基因多态性与移植后相关疾病研究进展

魏巴金1, 2周琳1

Toll样受体(TLRs)家族是人体固有免疫系统的重要组成部分，目前共有13种蛋白家族成员。TLRs通过识别病原相关分子模式，在固有免疫应答中发挥着重要的作用，被认为是连接人体固有免疫与获得性免疫的桥梁。近年来，关于TLRs家族和移植后相关疾病的研究(如排斥反应、移植物失功及感染等)取得了较大的进展。许多研究发现，TLRs家族基因多态性不仅可以影响TLRs家族基因的表达，与器官移植术后相关疾病也密切相关。本综述系统阐述了近年来TLRs家族基因多态性与移植后相关疾病的研究进展，希望为将来临床上开展同类研究提供一定的参考。

基因多态性； Toll样受体； 移植

Toll样受体(toll-like receptors，TLRs)家族属于模式识别受体(pattern recognition receptors，PRRs)家族的一员，是人体固有免疫系统的重要组成部分。目前已经发现13种TLRs家族成员，其中TLR1～2、TLR4～6表达于细胞膜表面，其余蛋白家族成员则表达于细胞内部。通过识别病原相关分子模式，如细菌细胞壁成分，进而激活下游髓样分化因子88(myeloid differentiation factor 88，MyD88)依赖和不依赖的信号通路，最终引起诸多细胞因子的分泌，在固有免疫应答中发挥着重要的作用，被认为是连接人体固有免疫和获得性免疫的桥梁[1-2]。

移植物对于受者而言是进入身体的“异物”，受者通过自身免疫系统对移植物发动攻击，达到清除“异物”的作用。TLRs对移植相关的排斥反应、感染、移植物失功等方面有着重要的影响。部分TLRs的信使RNA(messenger RNA，mRNA)水平在发生急性排斥反应的肾移植受者中明显升高，且与炎症反应密切相关[3]。在一项小鼠肾移植实验中发现，通过OPN301抑制TLR2，对移植物的缺血再灌注损伤具有保护作用[4]。丙型肝炎患者肝移植术后肝硬化与其TLR3和TLR7/8功能缺失存在一定的联系[5]。

部分TLRs家族的单核苷酸多态性(single nucleotide polymorphism，SNP)(如位点rs4986790、rs11536889等)可以引起TLRs蛋白表达改变，继而影响TLRs及下游相关基因的激活，影响移植术后受者预后以及并发症发生情况[6-7]。本文就TLRs家族基因多态性与移植相关疾病的研究进展作一综述。

1 肝移植

TLR3位点rs3775291等位基因T是肝移植受者术后发生急性排斥反应的保护因素，携带等位基因T的受者和非携带受者相比，急性排斥反应的发生率降低近60%[8]。而且，单因素研究指出，位点rs3775291的基因多态性与丙型肝炎患者肝移植预后有关，但多因素分析未能提示阳性结果[9]。美国一项研究指出，TLR2位点rs5743708纯合子基因型与丙型肝炎患者肝移植术后发生移植物失功和死亡率存在关联[10]。同时，该位点基因多态性对肝移植术后感染性疾病也有诸多影响，虽然该位点与肝移植术后革兰阳性菌感染无关，但其变异型基因携带者具有较高的感染再发率和休克发生率[11]；此外，该位点纯合子基因型的肝移植受者术后发生CMV感染时，CMV复制和发生组织侵犯性CMV感染的风险均有所提高[12-13]。Brown等[14]研究证明，该位点SNP可以影响TLR2对HCV核心蛋白和非结构蛋白3的识别，可能会为肝移植术后移植物失功发病机制的研究提供新的思路。有研究表明，TLR4位点rs4986790和rs4986791基因多态性与肝移植术后是否发生革兰阴性菌感染无明显联系[15]。Dhillon等[16]认为，受者位点rs4986790是变异型时，丙型肝炎肝移植术后发生移植物失功的风险较高；另一项研究指出，供者位点rs11536865和rs5030717对肝移植术后发生移植物失功也有影响[17]。一个位于TLR4基因3′-UTR区的位点rs11536889 CC基因型可能会提高肝移植术后乙型肝炎复发风险，后期实验发现其还可以影响TLR4的表达和功能[7]。他克莫司的用量也受到供者TLR4位点rs1927907的影响，在移植早期，拥有该位点等位基因A的受者他克莫司浓度/剂量比值一般较低[18]。

2 肾移植

肾移植研究中，关于急性排斥反应、感染、移植物失功等与TLRs基因多态性的相关性研究愈来愈深入。Nogueira等[19]发现，在肾移植受者中，TLR2和TLR4的表达均较低，且TLR4位点rs4986790和rs4986791的基因多态性不仅影响TLR4的基因表达，还可以影响TLR2的基因表达，提示可能存在不同基因间的连锁不平衡。Ducloux等[20]将拥有TLR4位点rs4986790和rs4986791的任意变异型受者定义为变异型携带者，与野生型携带者相比，变异型携带者肾移植术后急性排斥反应发生率较低而感染发生率较高。TLR4位点rs4986790和rs4986791基因多态性与肾移植术后受者是否发生急性排斥反应无关，但接受携带变异型基因型供器官的受者移植术后急性排斥反应发生率较低[21]。也有研究指出，TLR4位点rs4986790和rs4986791的基因型变化对受者肾移植术后急性肾小管坏死、排斥反应和感染等并发症的发生没有影响[22]。同样，在关于TLR4和白细胞分化抗原14的一项联合研究中，研究人员发现，TLR4位点rs4986790的基因多态性未影响受者肾移植术后急性排斥反应、慢性移植物肾病等并发症发生情况[23]。无论是受者还是供者携带TLR4位点rs10759932的等位基因C时，肾移植术后急性排斥反应发生率降低，且相比未携带等位基因C的受者，携带等位基因C的受者术后急性排斥反应发生风险降低了近75%[24]。此外，TLR4位点rs4986790和rs4986791的基因多态性不但与CMV感染相关，而且还是CMV病的影响因素[25]。

在一项德国的研究中，研究人员检测了TLR2、TLR3、TLR4、TLR5、TLR9内11个SNP位点，发现携带TLR3位点rs3775291非等位基因C的受者具有较高的急性排斥反应发生率，TLR9位点rs5743836的基因多态性可能提示移植后严重心脏不良事件(心肌梗死、恶性心律失常、急性心力衰竭和心脏介入手术等)，但未发现TLRs上述位点基因多态性与移植物生存、移植肾功能和各类术后感染相关[26]。受者在没有接受移植术前预防性用药的情况下，TLR9位点rs5743836的等位基因TT对于术后CMV感染的发生具有明显的保护作用[27]。在一项关于肾移植受者术后急性排斥反应发生情况的研究中，研究人员发现TLR9位点rs352140等位基因AA与GG相比，具有较好的保护作用，急性排斥风险可以降低约70%[28]。TLR9位点rs187084的等位基因C和rs352140等位基因A紧密连锁(I2=0.93)，均对肾移植受者术后急性排斥反应发生和肾小球滤过率有保护作用[29]。

3 造血干细胞移植

芬兰一项关于异基因造血干细胞的研究发现，TLR1位点rs4833079、TLR4位点rs4837656和rs17582214、TLR5位点rs10737416、TLR6位点rs6531656以及TLR10位点rs337629均与移植术后发生急性移植物抗宿主病(graft versus host disease，GVHD)相关，而且TLR5的两个位点rs2800237和rs2800230还与慢性GVHD有关[30]。与其他基因型相比，受者具有TLR4位点rs2770150等位基因TT，其发生严重GVHD的风险提高11倍[31]。供者TLR9位点rs352139和rs352140的基因多态性被认为可以影响受者移植术后急性GVHD和CMV感染的发生情况，二者的单倍体基因型甚至可以作为预测受者5年生存率的影响因子[32]。但西班牙一项研究发现，TLR9位点rs352140与CMV感染不存在联系[33]。Mensah等[34]将TLR4位点rs4986790和rs4986791同时存在变异型定义为“危险等位基因”，其对受者术后是否发生革兰阴性菌感染存在边缘预测意义(P=0.06)。一项涉及TLR2、TLR3、TLR4、TLR9的基因多态性与移植后曲霉感染的相关性研究中，非亲属间移植，供者TLR4位点rs4986790和rs4986791组成的单倍体基因型可以预测移植术后进展性曲霉病发生情况[35]。

TLR9位点rs5743836对于受者移植术后病毒性肺炎具有保护作用，TLR4位点rs4986790和rs4986791与移植术后真菌感染的关系存在不一致现象，即上述2个位点变异型基因型的存在有助于真菌定殖，但却与真菌感染、真菌肺炎呈负相关[36]。同时，有研究表明，只要TLR4位点rs4986790和rs4986791二者存在任一变异型，受者术后发生进展性曲霉病的风险增加，但不影响受者术后生存时间[37]。荷兰的一项研究中，研究人员发现TLR4位点rs4986790的基因多态性与进展性曲霉病发生有关[38]。进展性曲霉病发生不受供者TLR1、TLR4、TLR6基因多态性的影响，而与受者TLR1位点rs5743611的基因多态性和由其构成的单倍体基因型密切相关[39]。同样，在对TLR5终止密码子位点rs5744168的研究中，研究人员发现受者携带等位基因T时，发生进展性曲霉病风险较高[40]。携带TLR4位点rs4986790的变异型受者，发生造血干细胞移植术后缺血性膀胱炎的风险降低，这一结果为研究出血性膀胱炎的发生机制提供了一些帮助[41]。Kornblit等[42]通过对10个TLRs家族基因的29个SNP位点进行检测，发现供者TLR8位点rs3764879基因多态性与造血干细胞移植预后存在相关性；携带TLR9位点rs187084等位基因CC与等位基因CT、TT相比，受者5年生存率提高了约25%[43]。

4 肺移植

位点rs4986790与rs4986790是TLR4基因中功能性SNP，研究表明，携带上述位点突变基因型受者肺移植术后急性排斥反应发生率较低[44]。在一项涉及TLR1～10基因的64个标签SNP位点的研究中，TLR2位点rs1898830和rs7656411、TLR4位点rs1927911以及TLR9位点rs352162和rs187084的基因多态性与肺移植术后发生闭塞性细支气管炎密切相关，多数发生闭塞性细支气管炎的受者携带3～4 个危险等位基因[45]。

5 总 结

虽然目前有关TLRs家族基因多态性与移植术后相关疾病的研究结果大多是初步的，而且缺乏大样本、多中心的临床试验验证，多数研究还处于探索阶段，仅提供了二者的相关性，可能存在较多的假阳性，而且对于基因多态性如何影响移植后相关疾病的发生机制目前研究较少，特别是位于非编码区的基因多态性功能研究较为缺乏，期待在未来的研究中会有更多的发现。虽然目前的实验存在许多缺陷，但是为未来个体化诊治提供了一种可能的途径，相信关于TLRs家庭基因多态性与移植术后相关疾病的研究将会受到越来越多的重视。随着测序技术的不断提高和应用成本的不断下降，期待其可以广泛应用于临床工作。

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(本文编辑：徐小明)

魏巴金, 周琳. Toll样受体家族基因多态性与移植后相关疾病研究进展[J/CD]. 中华移植杂志: 电子版, 2016,10(2):92-96.

Progress on the association between polymorphisms of toll-like receptors and correlated disease after transplantation

WeiBajin1, 2,ZhouLin1.

1KeyLaboratoryofOrganTransplantation,2DiagnosisandTreatmentofBreastDiseasesCenter,theFirstAffiliatedHospital,SchoolofMedicine,ZhejiangUniversity,Hangzhou310003,China

ZhouLin,Email：linzhou19@163.com

Toll-like receptors (TLRs) were a family receptor belonged to the pattern recognition receptors, which played a key role in innate immunity. There were 13 family members at present. TLRs activated the innate immune by recognizing pathogen-associated molecular patterns and they were considered as the bridge which could connect natural immunity and adaptive immunity. Great achievements had been obtained on the relationship between TLRs and correlated diseases after transplantation (rejection, graft dysfunction, infection and so on) in recent years. Polymorphisms in TLRs were also found to not only influence expression of itsself but also correlated diseases after transplantation. This review tried to review progress on the association between polymorphisms of TLRs family and correlated disease after transplantation, hoping to provide reference for carrying forward similar research in the furture.

Gene polymorphism; Toll-like receptors; Transplantation

10.3877/cma.j.issn.1674-3903.2016.02.010

310003 杭州，浙江大学医学院附属第一医院器官移植重点实验室1，乳腺疾病诊治中心2

周琳，Email: linzhou19@163.com

2016-02-17)