趙海豐 張翼鷟

綜述

CD4+CD25+調(diào)節(jié)性T細(xì)胞在免疫性血小板減少癥發(fā)病中的研究進(jìn)展*

趙海豐 張翼鷟△

免疫性血小板減少癥(ITP)是一種器官特異性的自身免疫性疾病，是由于自身抗血小板抗體導(dǎo)致血小板破壞過(guò)多和生產(chǎn)不足造成血小板減少，是臨床最常見(jiàn)的出血性疾病，其發(fā)病機(jī)制目前仍未完全明確。調(diào)節(jié)性T細(xì)胞(regulatory T cell，Treg)是體內(nèi)一類(lèi)具有免疫調(diào)節(jié)功能的特殊T細(xì)胞亞群，CD4+CD25+Treg是在Treg家族中研究最多也是最主要的一群，對(duì)維持機(jī)體免疫平衡狀態(tài)起重要作用。無(wú)論在ITP動(dòng)物模型還是在ITP患者均發(fā)現(xiàn)Treg細(xì)胞數(shù)量的降低和功能的缺陷，表明CD4+CD25+Treg與免疫性血小板減少癥的發(fā)生和進(jìn)展密切相關(guān)。本文對(duì)Treg的特征、作用及其與ITP發(fā)病機(jī)制的關(guān)系做一綜述。

T淋巴細(xì)胞,調(diào)節(jié)性；血小板減少；自身免疫疾?。痪C述；免疫性血小板減少癥；CD4+CD25+調(diào)節(jié)性T細(xì)胞

免疫性血小板減少癥（immune thrombocytopenia,ITP）是一種器官特異性的自身免疫性疾病，以外周血血小板數(shù)量減少、皮膚黏膜出血為主要臨床特征[1]。目前認(rèn)為ITP的發(fā)病是一個(gè)多步驟的過(guò)程，T細(xì)胞、B細(xì)胞和抗原遞呈細(xì)胞（APC）等在其發(fā)病過(guò)程中均發(fā)揮重要作用[2]。調(diào)節(jié)性T細(xì)胞(regulatory T cell，Treg)是體內(nèi)一類(lèi)具有免疫調(diào)節(jié)功能的特殊T細(xì)胞亞群，對(duì)維持機(jī)體免疫平衡狀態(tài)起重要作用[3]。近年Treg在ITP發(fā)病機(jī)制中的作用愈來(lái)愈受到重視。筆者就Treg與ITP發(fā)病的關(guān)系綜述如下。

1 Treg概述

Treg是一群具有免疫抑制功能的T細(xì)胞,約占外周血CD4+T細(xì)胞的5%～10%，在自身免疫疾病的發(fā)生發(fā)展中起重要作用[3-6]。根據(jù)不同的免疫表型，Treg主要包括：CD4+CD25+Treg、Tr1型CD4+Treg、Th3型CD4+Treg和CD8+Treg等亞群。目前，CD4+CD25+Treg是在Treg家族中研究最多也是最主要的一群。根據(jù)CD4+CD25+Treg的來(lái)源和作用機(jī)制的不同,可以分為獲得性Treg細(xì)胞(inducible Treg，iTreg)和自然性Treg (naturally occurring Treg，nTreg)兩大類(lèi)。iTreg和nTreg具有類(lèi)似的表型和作用，均是通過(guò)降低APC的功能來(lái)發(fā)揮免疫抑制的作用，區(qū)別在于iTreg細(xì)胞通過(guò)介導(dǎo)如轉(zhuǎn)化生長(zhǎng)因子（TGF）-β等可溶性因子的存在發(fā)揮作用，而nTreg細(xì)胞主要通過(guò)細(xì)胞與細(xì)胞直接接觸等方式發(fā)揮免疫抑制作用；iTreg細(xì)胞主要由成熟的T細(xì)胞經(jīng)誘導(dǎo)產(chǎn)生，而nTreg細(xì)胞主要由胸腺中幼稚T細(xì)胞分化得到，高表達(dá)CD25，低表達(dá)CD127，同時(shí)表達(dá)轉(zhuǎn)錄因子（Foxp）3、淋巴細(xì)胞相關(guān)抗原（CTLA）-4和膜型TGF-β等特點(diǎn)，主要通過(guò)識(shí)別自身抗原復(fù)合物獲得免疫抑制表型[7]。CD4+CD25+Treg主要指的是nTreg。CD4+CD25+Treg主要是通過(guò)降低機(jī)體對(duì)抗原的免疫應(yīng)答來(lái)保持機(jī)體的自身免疫耐受，具有免疫抑制和免疫應(yīng)答低下兩大特征[8]。免疫抑制是指Treg被激活后即可以通過(guò)細(xì)胞相互接觸和(或)分泌TGF-β、白細(xì)胞介素（IL）-10和IL-4等細(xì)胞因子發(fā)揮抑制效應(yīng)，對(duì)維持機(jī)體免疫平衡起重要作用，而免疫應(yīng)答低下是指在T細(xì)胞激活狀態(tài)下，Treg不增殖，不分泌細(xì)胞因子，呈現(xiàn)一種低應(yīng)答狀態(tài)。

2 有關(guān)Treg的ITP動(dòng)物實(shí)驗(yàn)研究

Nishimoto等[9]為研究Treg在ITP發(fā)病中的作用機(jī)制，將去除Treg的CD4+CD25-的BALB/c鼠的脾細(xì)胞輸注到裸鼠中制成ITP動(dòng)物模型，監(jiān)測(cè)3周后，發(fā)現(xiàn)部分裸鼠皮膚出現(xiàn)淤點(diǎn)淤斑，且其外周血的血小板呈進(jìn)行性減少狀態(tài)。繼續(xù)觀(guān)察，約1/3的裸鼠會(huì)出現(xiàn)血小板減少癥，檢測(cè)IgG抗體，提示明顯增加，表明Treg缺陷鼠出現(xiàn)的血小板減少癥是通過(guò)IgG自身抗體破壞血小板導(dǎo)致的。為進(jìn)一步研究CD4+CD25+Treg的作用，將CD4+CD25+Treg和CD4+CD25-Treg同時(shí)輸注入裸鼠中，能阻止血小板減少癥的發(fā)生，而將CD4+CD25+Treg輸注入血小板減少的裸鼠后，卻未觀(guān)察到血小板的恢復(fù)，表明Treg的免疫抑制作用主要是在血小板減少癥發(fā)生的初始誘發(fā)階段，而不是在血小板減少癥的形成后。Chow等[10]以野生型血小板致敏的GPⅢa敲除鼠的脾細(xì)胞輸注入免疫缺陷鼠形成的ITP動(dòng)物模型為研究對(duì)象，發(fā)現(xiàn)Treg數(shù)量在胸腺中明顯增加，而在脾臟中明顯減少；在使用丙種球蛋白治療后，Treg數(shù)量在胸腺和脾臟均恢復(fù)正常，表明外周Treg的減少是由于Treg在胸腺中滯留過(guò)多導(dǎo)致的[11]。

3 有關(guān)Treg的ITP臨床研究

至今，已有較多關(guān)于ITP患者Treg數(shù)量和功能異常的研究，見(jiàn)表1。大多數(shù)研究表明，與正常對(duì)照相比，ITP患者尤其是活動(dòng)性ITP患者和（或）血小板特別低的患者，外周Treg數(shù)量明顯減少；當(dāng)ITP患者處于緩解期時(shí)，Treg數(shù)量會(huì)增高[12-18]。有研究表明兒童ITP患者Treg數(shù)量的減少程度與血小板減少的時(shí)間呈顯著相關(guān)性，Treg還可以作為ITP的一個(gè)預(yù)后因素指導(dǎo)臨床治療與評(píng)估[12]。但也有研究指出ITP患者Treg數(shù)量與健康對(duì)照無(wú)明顯差異，如以CD4+CD25highFoxp3+定義的Treg在ITP外周血中的數(shù)量與正常對(duì)照無(wú)差異[19-21]。

出現(xiàn)上述不同的研究結(jié)果，可能與研究樣本量的大小、檢測(cè)Treg細(xì)胞的標(biāo)志物不同、種族差異性、疾病活動(dòng)程度等因素有關(guān)。值得強(qiáng)調(diào)的是，Treg細(xì)胞的標(biāo)志物不同不容忽視，目前為止，有 CD4+CD25+,CD4+Foxp3+，CD4+CD25highFoxp3+,CD4+CD25bright和CD4+CD25+CD127low等不同表型。Treg數(shù)量不僅在外周血中是減少的，在其他組織如骨髓和脾臟中也是減少的[21-22]。有關(guān)Treg免疫抑制功能方面的研究大多數(shù)采用Treg與效應(yīng)CD4+T細(xì)胞的共培養(yǎng)體系，在ITP患者中Treg的抑制作用較健康對(duì)照明顯減弱[13-14,19-20]。上述研究表明，Treg的數(shù)量和功能的異常在ITP發(fā)病中起到了一定的作用。

有研究觀(guān)察了Treg數(shù)量和功能在藥物治療前后的變化情況。促血小板生成素受體激動(dòng)劑治療不能增加Treg的數(shù)量，但能改善Treg的抑制功能，同時(shí)明顯增加[20]。有研究發(fā)現(xiàn)地塞米松和美羅華治療后，Treg的比例明顯上調(diào)[14-16]，推測(cè)地塞米松和美羅華治療ITP的部分機(jī)制有可能是通過(guò)上調(diào)Treg的數(shù)量，增加其免疫抑制功能發(fā)揮作用。但也有報(bào)道在用美羅華治療前后Treg數(shù)量未見(jiàn)變化[21]。上述研究表明，可通過(guò)增加Treg數(shù)量和加強(qiáng)Treg功能的方法來(lái)治療ITP。

綜上所述，T細(xì)胞功能紊亂在ITP發(fā)病過(guò)程中起了關(guān)鍵性作用，CD4+CD25+Treg參與了ITP的發(fā)生和發(fā)展，可作為治療ITP的一個(gè)新靶點(diǎn)。

[1] Hallam S,Provan D,Newland AC.Immune thrombocytopenia--what are the new treatment options[J]?Expert Opin Biol Ther,2013,13(8):1173-1185.

[2]McKenzie CG,Guo L,Freedman J,et al.Cellular immune dysfunction in immune thrombocytopenia(ITP)[J].Br J Haematol,2013,163 (1):10-23.

[3]Dasgupta A,Saxena R.Regulatory T cells:a review[J].Natl Med J India，2012,25(6):341-351.

[4]Ulivieri C,Baldari CT.T-cell-based immunotherapy of autoimmune diseases[J].Expert Rev Vaccines，2013,12(3):297-310.

[5] Rangachari M,Kuchroo VK.Using EAE to better understand principles of immune function and autoimmune pathology[J].J Autoimmun,2013,45:31-39.

[6] Mengya Z,Hanyou M,Dong L,et al.Th17/Treg imbalance induced by increased incidence of atherosclerosis in patients with systemic lupus erythematosus(SLE)[J].Clin Rheumatol,2013,32(7):1045-1052.

[7] Sela U,Olds P,Park A,et al.Dendritic cells induce antigen-specific regulatory T cells that prevent graft versus host disease and persist in mice[J].J Exp Med,2011,208(12):2489-2496.

[8]Okamoto A,Fujio K,Okamura T,et al.Regulatory T-cell-associated cytokines in systemic lupus erythematosus[J].J Biomed Biotechnol,2011,2011:463412.

[9] Nishimoto T,Satoh T,Takeuchi T,et al.Critical role of CD4(+)CD25(+)regulatory T cells in preventing murine autoantibody-mediated thrombocytopenia[J].Exp Hematol,2012,40(4):279-289.

[10]Chow L,Aslam R,Speck ER,et al.A murine model of severe immune thrombocytopenia is induced by antibody-and CD8+T cellmediated responses that are differentially sensitive to therapy[J]. Blood,2010,115(6):1247-1253.

[11]Aslam R,Hu Y,Gebremeskel S,et al.Thymic retention of CD4+CD25+FoxP3+T regulatory cells is associated with their peripheral deficiency and thrombocytopenia in a murine model of immune thrombocytopenia[J].Blood,2012,120(10):2127-2132.

[12]Zahran AM,Elsayh KI.CD4+CD25+High FoxP3+regulatory T cells, B lymphocytes,and T lymphocytes in patients with acute ITP in Assiut Children Hospital[J].Clin Appl Thromb Hemost,2014,20(1): 61-67.

[13]Liu B,Zhao H,Poon MC,et al.Abnormality of CD4(+)CD25(+)regulatory T cells in idiopathic thrombocytopenic purpura[J].Eur J Haematol,2007,78(2):139-143.

[14]Stasi R,Cooper N,Del Poeta G,et al.Analysis of regulatory T-cell changes in patients with idiopathic thrombocytopenic purpura receiving B celldepleting therapy with rituximab[J].Blood,2008,112 (4):1147-1150.

[15]Ling Y,Cao X,Yu Z,et al.Circulating dendritic cells subsets and CD4+Foxp3+regulatory T cells in adult patients with chronic ITP before and after treatment with high-dose dexamethasome[J].Eur J Haematol,2007,79(4):310-316.

[16]Li Z,Mou W,Lu G,et al.Low-dose rituximab combined with shortterm glucocorticoids upregulates Treg cell levels in patients with immune thrombocytopenia[J].Int J Hematol,2011,93(1):91-98.

[17]Sakakura M,Wada H,Tawara I,et al.Reduced CD4+CD25+T cells in patients with idiopathic thrombocytopenic purpura[J].Thromb Res,2007,120(2):187-193.

[18]Aboul-Fotoh Lel-M MM,El-Deen MA,Osman AM.Role of CD4+CD25+T cells in children with idiopathic thrombocytopenic purpura [J].J Pediatr Hematol Oncol,2011,33(2):81-85.

[19]Yu J,Heck S,Patel V,et al.Defective circulating CD25 regulatory T cells in patients with chronic immune thrombocytopenic purpura [J].Blood,2008,112(4):1325-1328.

[20]Bao W,Bussel JB,Heck S,et al.Improved regulatory T-cell activity in patients with chronic immune thrombocytopenia treated with thrombopoietic agents[J].Blood,2010,116(22):4639-4645.

[21]Audia S,Samson M,Guy J,et al.Immunologic effects of rituximab on the human spleen in immune thrombocytopenia[J].Blood,2011, 118(16):4394-4400.

[22]Olsson B,Ridell B,Carlsson L,et al.Recruitment of T cells into bone marrow of ITP patients possibly due to elevated expression of VLA-4 and CX3CR1[J].Blood,2008,112(4):1078-1084.

（2013-10-08收稿 2013-10-30修回）

（本文編輯 陳麗潔）

Recent Research in Role of CD4+CD25+Regulatory T Cell in Pathogenesis of Immune Thrombocytopenia

ZHAO Haifeng，ZHANG Yizhuo
Tianjin Medical University Cancer Institute and Hospital,National Clinical Research Center for Cancer,Key Laboratory of Cancer Prevention and Therapy,Tianjin 300060,China

Immune thrombocytopenia(ITP),the most common hemorrhagic disease,is an organ-specific autoimmune disease characterized by decreased platelets count due to auto-antibodies mediating platelets destruction and insufficient platelets production.The etiology of ITP is still not completely known.Regulatory T cells,also called Tregs,are characterized by CD4+CD25+,and positive of transcription factor forkhead box P3.They belong to a subpopulation of T cells specialized for immune regulation and play an important role in maintaining the immune balance.Decreased production and defected function of CD4+CD25+Treg was found not only in the ITP animal model but also in the ITP patients.It indicates that the Treg was involved in the pathology of ITP.This review focus on the characteristic and function of Tregs and their relationship with pathogenesis of ITP.

T-lymphocytes,regulatory;thrombocytopenia;autoimmune diseases;review;immune thrombocytopenia; CD4+CD25+Treg

R558+.2

A

10.3969/j.issn.0253-9896.2014.04.030

*國(guó)家青年自然科學(xué)基金項(xiàng)目（項(xiàng)目編號(hào)：81100337）

天津醫(yī)科大學(xué)腫瘤醫(yī)院，國(guó)家腫瘤臨床醫(yī)學(xué)研究中心，天津市“腫瘤防治”重點(diǎn)實(shí)驗(yàn)室（郵編300060）

△通訊作者 E-mail:yizhuozhang111@163.com