骨髓增生异常综合征患者Th1/Th2细胞平衡改变的临床意义

目的：探讨骨髓增生异常综合征（MDS）患者外周血CD4^＋、CD8^＋细胞亚群平衡的改变，以及与活化T细胞之间关系的临床意义。方法：选择14例难治性贫血患者（RA）和1例难治性贫血伴原始细胞增多患者（RAEB）的外周血，在PMA、Ionomycin、Monensin存在的条件下体外培养，进行细胞膜表面抗原和细胞内因子染色，并用流式细胞仪计数外周血表达CD3^＋ CD8^-IFN-γ^＋细胞（Th1）、CD3^＋CD8^-IL-4^＋细胞（Th2）、CD3^＋CD8^＋IF-γ^＋细胞（Tcl）、CD3^＋CD8^＋IL-4^＋细胞（Tc2）的百分率。结果与活化T细胞之间关系做相关性分析。结果：MDS组患者Th1细胞高于正常对照组（P〈0．05），体内的Th细胞向Th1细胞漂移，产生过多的造血抑制因子如IFN-γ，TNF-β等。Th2，Tc1，Tc2细胞与正常对照组相比无显著差异（P〉0．05）；CD4^＋CD45RO^＋细胞的百分率和Th1细胞的百分率呈正相关，相关系数为r=0．573（P〈0．05），CD4^＋CIN5RA^＋细胞的百分率和Th1细胞的百分率呈负相关，相关系数为r=-0．509（P=0．05），而和Th2，Tc1，Tc2的百分率无明显的相关性（P〉0．05）。结论：MDS患者存在有Th1／Th2细胞因子网络的失衡以及过多的造血抑制因子，且这些因子主要来源于T淋巴细胞。     

骨髓增生异常综合征淋巴细胞亚群及其激活状态的分析

本研究探讨骨髓增生异常综合征（MDS）患者外周血T细胞亚群，B细胞，NK细胞数量及激活状态的临床意义．采用流式细胞术对30例MDS患者外周血T细胞，B细胞，NK细胞及其表面活化分子CD28，CD45RA，CD45RO，CD69，HLA—DR的表达进行检测和分析。30例MDS患者中低危组（RA＋RAS）22例，高危组（RAEB＋RAEBT）8例。结果表明：MDS组T细胞（CD3^＋细胞）的百分率低于正常对照组，CD4^＋CD45RA^＋细胞（未致敏CD4^＋细胞）的数值低于正常对照组。MSD组早期活化T细胞（CD3^＋CD69^＋细胞）和晚期活化T细胞（CD3^＋HLA—DR^＋细胞）的数值均显著高于正常对照组。低危组（RA和RAS）主要表现为T细胞活化功能的改变：早期活化T细胞（CD3^＋CD69^＋细胞）和晚期活化T细胞（CD3^＋HLA—DR^＋细胞）比例均增高，以及B细胞数量的减少。高危组（RAEB和RAEBT）主要表现为T细胞亚群数量的改变：CD3^＋细胞，CD3^＋CD4^＋CD8^-细胞（T辅助细胞）数量的减少，CD3^＋细胞HLA—DR和CD69的表达并不增高。NK细胞数量减少。结论：MDS病人存在有T细胞数量和功能的异常，且随着病情的进展而发生改变，所以T细胞亚群及活化功能的检测对于判断疾病的进程和指导治疗具有重要的意义。     

再生障碍性贫血、骨髓增生异常综合征、急性髓系白血病患者CD8＋T细胞亚群的变化及临床意义

摘要本研究检测再生障碍性贫血（AA）、骨髓增生异常综合征（MDS）和急性髓系白血病（AML）患者细胞毒T细胞亚群平衡及其活性的改变，探讨三种疾病造血异常的细胞免疫机制，为临床治疗选择提供实验室依据。采用流式细胞术检测AA组17例、MDS组35例（其中RA19例，RAEB16例）、AML组15例和正常对照组10例的细胞毒性T细胞（Tc1、Tc2）以及部分T细胞亚群比例并进行对比分析。结果表明：与正常对照组相比，AA组、MDS-RA组Tc1、Tc1／Tc2、CD8＋HLA-DR＋、CD3＋CD8＋CD28＋、CD8＋CIM5RO＋显著升高，Tc2无明显统计学差异，CD8＋CD45RA＋显著减低；MDS-RAEB组Tc1、CD3＋CD8＋CD28＋、CD8＋HLA．DR＋比例显著减低，Tc、Tc1／Tc2无明显变化，CD8＋CD45RA＋减低但差异不明显，CD8＋CD45RO＋显著升高；AML组Tcl、CD3＋CD8＋CD28＋、CD8＋CD45RA＋、CD8＋CD45RO＋、CD8＋HLA。DR＋，Tc1／Tc2显著减低，Tc2显著上升。结论：AA、MDS不同阶段、AML患者的细胞免疫状态不同，在AA和MDS早期阶段，Tc1／Tc2的平衡向Tcl偏移，且伴有T细胞亚群活性增加；而在MDS晚期和AML阶段，则向Tc2偏移，T细胞亚群活性减低。前者可能与骨髓造血衰竭密切相关，而后者可能是恶性克隆免疫挑挽的重要机制之一．     

骨髓增生异常综合征CD3^＋CD4^＋T细胞共刺激分子表达的研究

本研究检测骨髓增生异常综合征（myelodysplastic syndromes，MDS）CD3^＋CD4^＋T细胞共刺激分子的表达，为进一步探讨MDS发病机制积累信息。以38例初治MDS患者为研究对象，依据FAB分型将他们进一步划分为RA／RARS、RAEB／RAEB-t组；以11例献血员为正常对照，应用流式细胞术检测两组外周血CD3^＋CD4^＋T细胞共刺激分子CD28、CD154、CTLA-4、PD-1、CD25的表达。结果表明：MDS组CD28表达下降，CD154升高，CTLA-4、PD-1、CD25表达明显升高。随着疾病恶性程度的增高，RAEB／RAEB-t组CTLA-4、PD-1的表达以及CTLA-4／CD28比值亦较RA／RARS组升高。结论：MDS患者CD3^＋CD4^＋T细胞共刺激分子表达存在异常改变，其表达异常可能在MDS的发病机制中起一定作用。     

CD4+CD25+调控T细胞及其在移植耐受中的作用

CD4^ CD25^ 调控T细胞是一群表型和功能特异的T细胞亚群,能抑制CD4^ CD25^-和CD8^ T细胞的活化和增殖,以及IL-2和IFN-γ的产生,在移植免疫耐受中发挥着重要的作用,其免疫调控机理仍不明确。CD4^ CD25^ 在体外能有效地被分离、活化和扩增,并能保持其免疫调控能力,其活化后的免疫抑制功能是抗原非特异性的。体外活化和扩增的CD4^ CD25^ 调控T细胞有广阔的应用前景。     

肾综合征出血热患者免疫发病机制的探讨

目的 研究肾综合征出血热患者的细胞免疫功能异常情况。方法 应用流式细胞仪检测T细胞亚群CD4^＋T淋巴细胞、CD8^＋T淋巴细胞。结果 肾综合征出血热患者早期、后期与正常人比较，均有CD4^＋淋巴细胞计数降低（P=0.000，P=0．000），CD8^＋T淋巴细胞计数明显升高（P=0．000，P=0．002），CD4^＋／CD8^＋明显降低（P=0．000，P=0．000）。CD4^＋T淋巴细胞计数病程早期与病程后期无明显差异（P=0．985），CD8^＋1淋巴细胞计数病程早期明显高于病程后期（P=0．000），CD4^＋／CD8^＋病程早期明显低于病程后期（P=0．000）。结论 肾综合征出血热患者发病早期存在明显细胞免疫功能异常．在发病后期逐渐恢复。     

胃肠道癌患者外周血CD8＋T细胞功能相关标志物的检测及意义

目的　探讨胃肠道癌患者外周血T细胞亚群和CD8 T细胞CD2 8共刺激分子等功能相关性标志物的表达及意义。方法　用三色或四色荧光标记流式细胞术检测 2 7例胃肠道癌患者及 16例正常对照的外周血淋巴细胞。结果　与正常对照组相比 ,肿瘤患者外周血T细胞标志如CD3 、CD4 、CD8 表达水平及CD4 /CD8 比值差异无显著性 ;CD8 CD2 8-T细胞显著增加 (P <0 .0 1) ,而CD8 CD2 8 T细胞显著降低 (P <0 .0 5 )。表达HLA DR的活化CD8 T细胞显著增加 (P <0 .0 1) ,分泌IFN γ的CD8 T细胞 (Tc1)明显增多 (P <0 .0 1) ,而分泌IL 4的CD8 T细胞 (Tc2 )则正常人和肿瘤患者均很低。患者CD8 T细胞CD2 8及IFN γ的表达变化与肿瘤分期无关。结论　胃肠道癌患者中CD8 T细胞存在系统性活化的表现 ,其机制可能与CD2 8/B7以外的信号传递有关。胃肠道癌患者体内Tc1细胞的增加与肿瘤的分期缺乏明确关系。     

骨髓增生异常综合征患者CD4^＋ CD25^＋调节性T细胞、调控基因FOXP3的表达及意义

目的探讨骨髓增生异常综合征（MDS）患者CD4^＋ CD25^＋调节性T细胞（CD4^＋ CD25^＋ Treg细胞）和调控基因FOXP3的表达及意义。方法分离22例MDS患者[MDS组,根据MDS分型标准分为：难治性贫血组（RA组）6例、难治性血细胞减少伴有多系发育异常组（RCMD组）11例、难治性贫血伴原始细胞增多组（RAEB组）5例]和8例正常健康者骨髓单个核细胞,采用免疫荧光标记和流式细胞仪检测CD4^＋ CD25^＋ Treg细胞占CD4^＋ T细胞比例;提取骨髓单个核细胞RNA,采用RT-PCR检测FOXP3基因的表达水平。结果MDS组CD4^＋ CD25^＋ Treg细胞比例、FOXP3基因表达水平与正常对照组比较,差异均无统计学意义（均P〉0.05）;RA组、RAEB组CD4^＋ CD25^＋ Treg细胞比例、FOXP3基因表达水平与正常对照组比较,差异均有统计学意义（均P〈0.01）;RCMD组CD4^＋ CD25^＋ Treg细胞比例、FOXP3基因表达水平与正常对照组比较,差异均无统计学意义（均P〉0.05）;RCMD组、RAEB组CD4^＋ CD25^＋ Treg细胞比例、FOXP3基因表达水平与RA组比较,差异均有统计学意义（均P〈0.01）;RA组、RCMD组CD4^＋ CD25^＋ Treg比例、FOXP3基因表达水平与RAEB组比较,差异均有统计学意义（均P〈0.01）。结论MDS患者CD4^＋ CD25^＋ Treg占CD4^＋ T细胞比例及FOXP3基因表达水平随预后危险级别的升高而升高,提示免疫异常是MDS疾病的发生、发展的一个促进因素。     

2例异体手移植术后受者T细胞亚群与CD3^＋HLA—DR^＋细胞水平的动态观察

目的 研究异体复合组织移植－手移植术后病人外周血T淋巴细胞亚群及CD3^ HLA-DR^ T细水平的动态变化。方法 用流式细胞术测定了2例异体手移植术后不同时间外周血CD3^ 、CD3^ 、CD4^ 、CD3^ 、CD8^ 、CD3^ HLA-DR^ (活化T细胞）细胞百分率，及CD4／CD8比值，以病人 术前一周结果作对照。结果 使用免疫抑制剂后，于术后第1日CD3^ 、CD3^ 、CD4^ 、CD3^ 、CD8^ 、CD3^ HLA-DR^ 细胞水平，CD4／CD8比值都开始降低，以3－5日为最低水平。术后8日，上术指标逐渐回升，至15日后基本趋于平稳，但CD3^ 、CD3^ 、CD4^ 及CD4／CD8比值仍明显低于术前，而CD3^ 、CD8^ 、CD3^ HLA-DR^ 细胞水平则高于术前。结论 异体复合组织－手移植术后病人外周血T淋巴细胞亚群及CD^3 HLA-DR^ 细胞水平的变化与单一组织器官移植（肾移植）术后稳定期的变化一致，也与病人术后的稳定病情相吻合。     

炎症性肠病患者外周血CD4^＋CD25^＋Treg细胞的表达及意义

[目的]探讨CD4^＋CD25^＋Treg细胞在炎症性肠病（IBD）发病中的作用及其与疾病活动性的关系。[方法]采用三色流式细胞术检测40例IBD患者，其它肠病患者30例和健康对照者30例。IBD患者中活动期患者25例，缓解期患者15例，使用和未使用激素和／或免疫抑制剂活动期IBD患者分别为16例和9例。对以上各组外周血中CD4^＋CD25^＋T细胞亚群的百分率进行测定。[结果]疾病活动期IBD患者外周血CD4^＋CD25^＋Treg细胞比例明显低于其他肠病和正常对照组（P〈0．01），疾病活动期IBD患者外周血CD4^＋CD25^＋Treg细胞比例明显低于疾病稳定期患者（P〈0．01）。活动期IBD患者中使用激素和／或免疫抑制剂与未使用激素和／或免疫抑制剂结果差异有统计学意义。IBD患者外周血CD4^＋CD25^＋Treg细胞表达率与疾病活动指数评分呈负相关性。[结论]IBD患者外周血CD4^＋CD25^＋Treg细胞异常表达，可能参与疾病的发生发展，与疾病的活动性密切相关。     

急性髓系白血病患者T淋巴细胞内细胞因子表达特性

T淋巴细胞在抗肿瘤的免疫反应中起着重要作用，而大部分肿瘤患者往往存在免疫功能低下。本研究通过对急性髓系白血病（AML）患者T淋巴细胞胞内细胞因子特性的研究，以了解AML患者在不同状态下T淋巴细胞的功能。18例不同状态下初诊AML患者和10例健康成人外周血中的T淋巴细胞在莫能霉素存在的情况下，体外经PMA和离子霉素（ionomycin）刺激后，分别进行CD4-FITC、CD8-FITC荧光单克隆抗体染色和IFNγ-PE、IL4-PE荧光单克隆体胞内染色，最后进行流式细胞仪分析。结果表明：初诊AML患者中CD4^＋和CD8^＋T淋巴细胞胞内IFNγ分泌水平均明显低于健康成人外周血T淋巴细胞，CD4^＋和CD8^＋T细胞胞内IL-4分泌水平与成人外周血细胞无显著差异。处于临床缓解状态的AML患者，CD8^＋T淋巴细胞刺激后胞内产生IFNγ的量明显高于初诊AML患者（P〈0、05）．但与健康成人无显著差异（P〉0、05）。复发的AML患者外周血中CD4^＋T细胞和CD8^＋T细胞刺激后胞内产生IFNγ量明显低于健康成人外周血T淋巴细胞以及处于完全缓解状态的AML患者CD8^＋T淋巴细胞（P〈0、05）．而IL-4的量明显高于健康成人和初诊AML患者CD4^＋T细胞和CD8^＋T细胞（p〈0．05）。结论：处于不同状态下的AML患者T细胞亚群分泌的细胞因子发生了改变，与之相应的是，初次诊断的AML患者外周血中CD4‘和CD8’T淋巴细胞刺激后Th1／Tcl细胞反应低下，Th2／Tc2细胞反应与健康成人T淋巴细胞无差异；完全缓解状态的AML患者T细胞Thl反应虽然仍低下，但Tcl反应明显增强，与健康成人无差异；复发的AML患者CD4^＋和CD8^＋T细胞Th2／Tc2样反应较Thl／Tcl样反应明显增强。     

Analysis of IGG and IGG4 in HIV-1 seropositive patients and correlation with biological and genetic markers.

We have compared the levels of immunoglobulins G (IgG) and G4 (IgG4) in extreme seropositive patients from the GRIV cohort consisting of 168 patients with slow progression (SP) and 60 with rapid progression (RP) as well as in 173 healthy controls. IgG levels were significantly higher in SP patients than in RP patients (P = 0.008), both higher than in seronegative individuals. IgG4 levels were significantly lower in SP patients than in RP patients (P = 0.001), both lower than in seronegative individuals. We tried to correlate these levels with biological parameters (CD4(+) and CD8(+) cells, total lymphocytes, white blood cell counts, percentage of CD4(+) cells, and viral load) as well as with genetic markers from Th1/Th2 cytokines (IL2, IL4, IL6, IL10, IL13, and IFNgamma). IgG levels were correlated with the percentage of CD4(+) cells in SP while IgG4 levels were correlated with CD8(+) cell count in SP and with percentage of CD4(+) cells in RP patients. Among the parameters measured in SP patients at the time of inclusion in the study, the best predictor of progression towards AIDS was the viral load, the best predictor for stability was CD4(+) cell count, but overall, the best predictor for SP evolution (stability vs. progression) appeared to be the percentage of CD4(+) cells. Interestingly, correlations between the levels of IgG or IgG4 and the cytokine gene polymorphisms were found, notably in the IL10 gene.     

CD8+ T cells in asthma: friend or foe?

While it is well established that CD4(+) T lymphocytes play a crucial role in the initiation, progression and persistence of asthma, the role of CD8(+) T cells is less understood. CD8(+) T cells form functionally similar subsets which exhibit similar cytokine profiles as Th1 and Th2 cells, known as Tc1 and Tc2. Evidence from animal studies suggest that CD8(+) T cells are capable of regulating IgE production through the induction of IL-12 and IL-18 production in dendritic cells, and that CD8(+) T cells may act to moderate Th2 polarisation within the localised lymph nodes during allergic sensitisation. Such findings have led to the suggestion that Th1 polarising, CD8(+) T cell-inducing vaccines would inhibit the development of airway hyperresponsiveness (AHR) and Th2 cell infiltration. Despite these positive findings, the role of CD8(+) T cells within the lung remains poorly understood. While CD8(+) T cells, particularly those expressing the Tc1 phenotype, are capable of moderating inflammation and suppressing AHR, it has been postulated that Tc2 CD8(+) T cells predominate within established asthma and may act to amplify the inappropriate immune response which defines the condition. Within the clinic, the association between CD8(+) T cells and asthma is almost universally defined as injurious, further suggesting a prejudicial role for these cells within the established disease. CD8(+) T cells may be a valuable potential target for therapeutic intervention, either by potentiating their regulatory effects prior to the development of sensitisation, or through suppressing their pro-inflammatory properties within established atopy.     

Disease-associated bias in T helper type 1 (Th1)/Th2 CD4(+) T cell responses against MAGE-6 in HLA-DRB10401(+) patients with renal cell carcinoma or melanoma

T helper type 1 (Th1)-type CD4(+) antitumor T cell help appears critical to the induction and maintenance of antitumor cytotoxic T lymphocyte (CTL) responses in vivo. In contrast, Th2- or Th3/Tr-type CD4(+) T cell responses may subvert Th1-type cell-mediated immunity, providing a microenvironment conducive to disease progression. We have recently identified helper T cell epitopes derived from the MAGE-6 gene product; a tumor-associated antigen expressed by most melanomas and renal cell carcinomas. In this study, we have assessed whether peripheral blood CD4(+) T cells from human histocompatibility leukocyte antigens (HLA)-DRbeta1*0401(+) patients are Th1- or Th2-biased to MAGE-6 epitopes using interferon (IFN)-gamma and interleukin (IL)-5 enzyme-linked immunospot assays, respectively. Strikingly, the vast majority of patients with active disease were highly-skewed toward Th2-type responses against MAGE-6-derived epitopes, regardless of their stage (stage I versus IV) of disease, but retained Th1-type responses against Epstein-Barr virus- or influenza-derived epitopes. In marked contrast, normal donors and cancer patients with no current evidence of disease tended to exhibit either mixed Th1/Th2 or strongly Th1-polarized responses to MAGE-6 peptides, respectively. CD4(+) T cell secretion of IL-10 and transforming growth factor (TGF)-beta1 against MAGE-6 peptides was not observed, suggesting that specific Th3/Tr-type CD4(+) subsets were not common events in these patients. Our data suggest that immunotherapeutic approaches will likely have to overcome or complement systemic Th2-dominated, tumor-reactive CD4(+) T cell responses to provide optimal clinical benefit.     

Rules of chemokine receptor association with T cell polarization in vivo

Current concepts of chemokine receptor (CKR) association with Th1 and Th2 cell polarization and effector function have largely ignored the diverse nature of effector and memory T cells in vivo. Here, we systematically investigated the association of 11 CKRs, singly or in combination, with CD4 T cell polarization. We show that Th1, Th2, Th0, and nonpolarized T cells in blood and tissue can express any of the CKRs studied but that each CKR defines a characteristic pool of polarized and nonpolarized CD4 T cells. Certain combinations of CKRs define populations that are markedly enriched in major subsets of Th1 versus Th2 cells. For example, although Th0, Th1, and Th2 cells are each found among blood CD4 T cells coordinately expressing CXCR3 and CCR4, Th1 but not Th2 cells can be CXCR3(+)CCR4(-), and Th2 but only rare Th1 cells are CCR4(+)CXCR3(-). Contrary to recent reports, although CCR7(-) cells contain a higher frequency of polarized CD4 T cells, most Th1 and Th2 effector cells are CCR7(+) and thus may be capable of lymphoid organ homing. Interestingly, Th1-associated CKRs show little or no preference for Th1 cells except when they are coexpressed with CXCR3. We conclude that the combinatorial expression of CKRs, which allow tissue- and subset-dependent targeting of effector cells during chemotactic navigation, defines physiologically significant subsets of polarized and nonpolarized T cells.     

骨髓增生异常综合征患者细胞及体液免疫功能分析

目的 探讨骨髓增生异常综合征( myelodysplastic syndrome,MDS)患者细胞免疫和体液免疫水平的变化及意义.方法 采用流式细胞术(FCM)检测30例健康志愿者(健康对照组)及31例确诊但未治疗的MDS患者(低危、中危和高危)外周血淋巴细胞亚群,包括CD3+T淋巴细胞及其亚群、CD3 CD19+B淋巴细胞和CD3(CDI6CD56)+自然杀伤(NK)细胞比例.结果 与健康对照组比较,MDS患者的T淋巴细胞、B淋巴细胞和NK细胞总数均明显减低.另外,在T淋巴细胞亚群中,CD3+ CD4+的辅助性T细胞(Th)表达降低,CD3+ CD8+的抑制性T细胞(Ts)表达增高,Th/Ts比值倒置,比例失衡;且随着MDS疾病的进展,Ts细胞的表达逐渐增加,但低危、中危和高危3组间的差异无统计学意义,NK细胞的表达逐渐降低,但差异无统计学意义(P＞0.05),MDS 3组间T淋巴细胞和Th/Ts比值差异无统计学意义.结论 MDS患者的细胞和体液免疫功能均降低,淋巴细胞亚群检测可用来评估MDS患者免疫功能状态.     

Distinct functional lineages of human V(alpha)24 natural killer T cells

CD1d-restricted autoreactive natural killer (NK)T cells have been reported to regulate a range of disease conditions, including type I diabetes and immune rejection of cancer, through the secretion of either T helper (Th)2 or Th1 cytokines. However, mechanisms underlying Th2 versus Th1 cytokine secretion by these cells are not well understood. Since most healthy subjects express <1 NKT cell per 1,000 peripheral blood lymphocytes (PBLs), we devised a new method based on the combined used of T cell receptor (TCR)-specific reagents alpha-galactosylceramide (alphaGalCer) loaded CD1d-tetramers and anti-V(alpha)24 monoclonal antibody, to specifically identify and characterize these rare cells in fresh PBLs. We report here that CD4(+) and CD4(-)CD8(-) (double negative [DN]) NKT cell subsets represent functionally distinct lineages with marked differences in their profile of cytokine secretion and pattern of expression of chemokine receptors, integrins, and NK receptors. CD4(+) NKT cells were the exclusive producers of interleukin (IL)-4 and IL-13 upon primary stimulation, whereas DN NKT cells had a strict Th1 profile and prominently expressed several NK lineage receptors. These findings may explain how NKT cells could promote Th2 responses in some conditions and Th1 in others, and should be taken into consideration for intervention in relevant diseases.     

Chemokine receptor expression identifies Pre-T helper (Th)1, Pre-Th2, and nonpolarized cells among human CD4+ central memory T cells

We previously reported that central-memory T cells (T(CM) cells), which express lymph node homing receptors CCR7 and CD62L, are largely devoid of effector functions but acquire characteristics of effector-memory T cells (T(EM) cells) (i.e., CCR7(-) T helper [Th]1 or Th2 cells) after stimulation with T cell receptor agonists or homeostatic cytokines. Here we show that three chemokine receptors identify functional subsets within the human CD4(+) T(CM) cell pool. T(CM) cells expressing CXCR3 secreted low amounts of interferon gamma, whereas CCR4(+) T(CM) cells produced some interleukin (IL)-4, but not IL-5. In response to IL-7 and IL-15, CXCR3(+) T(CM) and CCR4(+) T(CM) cells invariably generated fully differentiated CCR7(-) Th1 and Th2 cells, respectively, suggesting that they represent pre-Th1 and pre-Th2 cells. Conversely, CXCR5(+) T(CM) cells lacking CXCR3 and CCR4 remained nonpolarized and retained CCR7 and CD62L expression upon cytokine-driven expansion. Unlike naive cells, all memory subsets had a low T cell receptor rearrangement excision circle content, spontaneously incorporated bromodeoxyuridine ex vivo, and contained cells specific for tetanus toxoid. Conversely, recall responses to cytomegalovirus and vaccinia virus were largely restricted to CXCR3(+) T(CM) and T(EM) cells. We conclude that antigen-specific memory T cells are distributed between T(EM) cells and different subsets of T(CM) cells. Our results also explain how the quality of primary T cell responses could be maintained by T(CM) cells in the absence of antigen.