瘦素预处理的MSC 体外调节SLE 患者淋巴细胞亚群的初步研究

目的:前期研究证实系统性红斑狼疮(SLE)患者血清异常升高的瘦素可加剧间充质干细胞(MSC)衰老,本研究旨在探讨瘦素预处理MSC 对淋巴细胞亚群免疫调节的变化情况。方法:分离脐带MSC,并收集SLE 患者外周血单个核细胞(PBMC),分为三组:PBMC 组,MSC+PBMC,瘦素(100 ng/ ml)预处理MSC 3 d+PBMC,1 .10 共培养3 d,收集悬浮细胞。流式细胞仪检测淋巴细胞亚群:CD4+ CD25+ Foxp3+调节性T(Treg)细胞、CD4+ IL-17+ Th17 细胞、CD4+ CXCR5+ PD-1+滤泡辅助T(Tfh)细胞、CD19+ B 细胞,并检测CD3+ T 细胞、CD19+ B 细胞表面CD25、CD69 平均荧光强度(MFI)。结果:与对照组相比,瘦素预处理的MSC 对Treg 细胞上调作用受损[(8.53±2.33)% vs (6.79±2.14)%,P<0.01],对Th17 细胞下调亦受影响[(1.28±0.70)%vs (1.64±0.55)%,P<0.01],Tfh 细胞比例有增加的趋势,但差异无统计学意义[(1.48±1.36) % vs (2.08±1.52)%,P =0.051]。与MSC 组比较,瘦素预处理组T 细胞活化分子CD25、CD69 表达增加。而在B 淋巴细胞活化指标,瘦素预处理后CD25 MFI 较前有升高[(19.16±3.62) vs (21.05±2.36),P<0.05],但对CD69 影响则无统计学差异。结论:瘦素体外作用于MSC,不仅使加剧其细胞衰老,亦损伤其对T、B 淋巴细胞的免疫调节能力。     

异体角膜刺激引起的人外周血T细胞及其亚群CD25分子表达

目的：观察异体角膜体外对人外周血T细胞及其亚群CD25分子表达的影响。方法： 异体角膜与外周血淋巴细胞体外共同培养后，进行单克隆抗体标记和流式细胞分析。结果： 对照组T细胞CD25表达为25.2％；受角膜或沸波醇酯（PDB）激活后T细胞CD25表达分别为56.8％和80.9％；受角膜和沸波醇酯共同激活后T细胞CD25表达为70.2％；受异体角膜激活后，CD4和CD8 T淋巴细胞CD25表达分别为67.3％和52.3％。结论： 异体角膜组织体外能够刺激人外周T细胞CD25表达和T细胞活化，CD4 T细胞比CD8 T细胞活化更明显。     

连翘提取物对小鼠T淋巴细胞体外活化与增殖的影响

目的:分析连翘(FS)提取物对小鼠淋巴结T细胞的体外活化与增殖的影响,初步探讨其免疫抑制作用机制.方法:无菌分离小鼠淋巴结细胞,加入多克隆刺激剂刀豆蛋白A(ConA)进行刺激,利用荧光标记的单克隆抗体(mAb)染色结合流式细胞术(FCM),检测小鼠T淋巴细胞的表达的活化抗原CD69、CD25、CD71的表达情况;以羧基荧光素乙酰乙酸琥珀酰亚胺酯(CFDA-SE)染色,以FCM分析FS对淋巴细胞体外增殖的影响.结果:终浓度为40、80、160 mg/L的FS均对ConA刺激诱导的T细胞CD69、CD25和CD71的表达有降低作用(P＜0.05).CFDA-SE染色分析显示,上述浓度的FS对ConA诱导的小鼠T淋巴细胞增殖具有抑制作用(P＜0.05).结论:FS对ConA诱导的T细胞早、中、后期活化和体外增殖有抑制作用.     

间充质干细胞对不同刺激条件下Th1/Th2细胞比值的影响

目的探讨间充质干细胞(MSC)对不同刺激作用下T淋巴细胞向Th1及Th2亚群转化的影响。方法将MSC植入24孔板中,在第3天加入经佛波脂(PMA)及离子霉素(ionomyc in)刺激的T淋巴细胞,或者按照不同比例将MSC加入双向混合淋巴细胞培养体系中,用流式细胞术分析各组T淋巴细胞亚群和内因子IL-4、IFN-γ的分泌变化情况,从而间接了解Th1及Th2亚群的改变。结果对于共刺激作用下单独培养的T细胞,MSC能轻度抑制其Th1细胞的转化;而在混合淋巴细胞培养体系(MLC)中,MSC能够明显抑制其中的CD8 T细胞亚群和Th1细胞,轻度提高Th2细胞比率。结论MSC在体外能抑制CD8 T细胞(CTL)和Th1细胞,升高Th2细胞。所以在临床上可能有减轻移植后急性移植物抗宿主病(aGVHD)的发生,而保留移植物抗白血病(GVL)的潜力。     

CD226在系统性红斑狼疮患者T淋巴细胞亚群上的表达

目的：研究CD226在SLE患者外周血T淋巴细胞亚群上的表达，以阐明CD226抗原在SLE患者体内T细胞活化中作用以及与SLE发病的关系。方法：31例SLE患者和30例健康志愿者外周血单个核细胞，在体外培养72h后，三色荧光标记的单克隆抗体染色，利用流式细胞仪测定T细胞亚群细胞表面CD226抗原的表达。结果；SLE患者组的CD3^ 、CD4^ 、CD8^ T淋巴细胞上CD226^ 表达均高于正常对照组（P＜0．01）；活动期SLE组、静止期SLE组的CD3^ 、CD4^ 、CD8^ T细胞上CD226^ 表达均显著高于对照组（P＜0．01），而活动期与静止期患者之间T细胞亚群上CD226^ 表达则无显著性差异（P＞0．05）。SLE患者CD3^ 、CD4^ 、CD8^ T细胞CD226^ 抗原表达水平与SLEDAI之间无明显相关性（P＞0．05）。结论：SLE患者体内存在T细胞亚群异常活化；活动期、静止期SLET淋巴细胞CD226^＋表达均增高，CD226^ 可能参与了SLE的免疫发病。     

霉酚酸及其衍生物对人T淋巴细胞及混合淋巴细胞免疫应答的影响

目的探讨霉酚酸及霉酚酸衍生物对人T淋巴细胞和混合淋巴细胞免疫应答的影响。方法从正常人外周血中分离单个核淋巴细胞(PBMC),在抗CD3刺激下和混合淋巴细胞反应体系中,加入或不加霉酚酸及其衍生物共培养,应用ELISA和流式细胞术检测CD4+和CD8+T细胞细胞因子的产生、细胞活化和增殖情况。结果经抗CD3刺激后,PBMC产生的细胞因子明显增加,加入霉酚酸及其衍生物后,IFN-γ及TNF-α明显降低,IL-2产生略有增加。在混和淋巴细胞反应体系中,3种细胞因子产生皆被抑制。抗CD3刺激和混和淋巴细胞反应后,T细胞表面活化分子CD25及CD69表达增加,加入霉酚酸及其衍生物共培养24、48 h后,T细胞CD25及CD69的表达并未被抑制。霉酚酸及其衍生物可抑制抗CD3刺激下和混和淋巴细胞反应后T细胞的增殖。结论霉酚酸及其衍生物对T淋巴细胞和混合淋巴细胞体系中因子的产生和细胞增殖都有抑制作用,为其在临床自身免疫疾病及移植排斥中的广泛应用提供了理论依据。     

银杏内酯B对小鼠T淋巴细胞体外活化、增殖与凋亡的影响

目的银杏内酯B(GB)是已知的天然而强效的血小板激活因子(PAF)受体(PAFR)拮抗剂,本文研究GB对小鼠T淋巴细胞活化、增殖及凋亡3大体外行为的影响,初步探讨其潜在的免疫调节作用与机制,从而为临床应用提供可靠的实验依据。方法分离小鼠淋巴细胞,培养前以不同浓度的GB预孵;以刀豆蛋白A(Con A)诱导细胞的活化与增殖,以荧光抗体双色标记(anti-CD3 mAb-PE/anti-CD69 mAb-FITC、anti-CD3 mAb-PE/anti-CD25 mAb-FITC)结合流式细胞术分别检测T淋巴细胞早、中期活化标志--表面抗原CD69与CD25的表达,以活体荧光染料CFDA-SE标记结合流式细胞术检测细胞增殖并用MTT法佐证;以地塞米松(Dex)诱导细胞的凋亡,以荧光染料双色标记[DiOC6(3)/PI]结合流式细胞术区别凋亡、死亡与活细胞群。结果 Con A刺激后6 h和24 h,T细胞早期活化标志CD69和中期活化标志CD25分别大量表达,Con A刺激后48 h活化的T细胞增殖至第4代,而经终浓度为5、10、20μmol/L GB在Con A刺激前对细胞进行4 h预孵处理可以显著下调T细胞表面抗原CD69、CD25的表达并能有效抑制细胞增殖。Dex诱导后12 h细胞凋亡和死亡群显著增大,而经同样的GB预孵处理可以在一定程度上抑制细胞的凋亡进程,对细胞凋亡显示出一定的保护作用。结论 GB能有效抑制小鼠T淋巴细胞的活化与增殖,并且对细胞凋亡起到一定的保护作用,凭借GB对T细胞此3大行为出色的调节作用,理应将其作为天然的免疫抑制剂候选者进行更深入的研究。     

人骨髓MSC对PHA活化T细胞周期以及表型和细胞因子分泌的影响

目的研究人骨髓间充质干细胞(MSC)对T细胞周期和活化的影响,探讨MSC对T细胞增殖抑制的作用机制。方法Ficoll密度梯度离心法分离纯化人骨髓MSC,体外扩增培养3代后用于实验。应用流式细胞术分析MSC对PHA作用下T细胞周期和早期表型CD25、CD69表达的影响,ELISA法检测细胞因子水平。结果人骨髓MSC体外可使PHA刺激下的T细胞滞留于细胞周期的G0/G1期,下调活化T细胞早期表型CD25、CD69的表达,抑制IL-2、IFN-r的分泌。结论人骨髓MSC体外可通过对T细胞周期的影响抑制其活化和增殖。     

手足口病患者外周血淋巴细胞亚群激活与CD95表达的检测与意义

目的 研究手足口病（HFMD）患者外周血淋巴细胞CD95、HLA-DR活化分子表达的变化及其意义.方法 以健康儿童作为对照,采用流式细胞术,检测58例手足口病患者外周血淋巴细胞CD95标志、T细胞亚群及其HLA-DR抗原表达.结果 HFMD患者外周血CD3^＋T细胞的百分率（63.82±7.74）%与健康对照组比较差异有统计学意义（P〈0.001）,CIM^＋T细胞的百分率（34.29±7.33）%明显低于正常对照组（P〈0.005）;HLA-DR^＋淋巴细胞（28.30±7.61）%比正常对照组显著增高（P〈0.005）;CD8^＋T细胞表达HLA-DR水平（1.34±1.12）%明显高于对照组（P〈0.005）;淋巴细胞CD95表达差异无统计学意义（P〉0.05）.结论 HFMD患者存在细胞免疫功能紊乱和淋巴细胞异常激活现象,T淋巴细胞的激活以CD8^＋T细胞为主,其在抗病毒感染中起着重要作用.     

PHA对人扁桃体T淋巴细胞亚群变化及活化抗原表达的效应

应用FITC和PE双色荧光试剂并经流式细胞计分析了人扁桃腺T淋巴细胞亚群组成,以及用PHA刺激后T淋巴细胞亚群的变化和活化抗原的表达情况。结果表明:1)人扁桃体T淋巴细胞以CD4~+细胞占优势,CD4~+与CD8~+细胞比值约为5.32±0.55;2),经PHA刺激培养72小时,CD4~+CD8~+细胞明显增加;3)经PHA刺激培养后,IL-2受体(CD25)和HLA-DR抗原表达增加。本实验结果为深入研究人扁桃体T淋巴细胞的表型变化提供了客观指标,对进一步探讨其在免疫系统中的作用具有一定的意义。     

Mesenchymal stem cells inhibit the expression of CD25 (interleukin-2 receptor) and CD38 on phytohaemagglutinin-activated lymphocytes

Mesenchymal stem cells (MSC) are immunomodulatory and inhibit lymphocyte proliferation. We studied surface expression of lymphocyte activation markers and secreted cytokines, when lymphocytes were activated in the presence of MSC. MSC suppressed the proliferation of phytohaemagglutinin (PHA)-stimulated CD3+, CD4+ and CD8+ lymphocytes. MSC significantly reduced the expression of activation markers CD25, CD38 and CD69 on PHA-stimulated lymphocytes. Mixed lymphocyte culture (MLC) supernatants containing MSC suppressed proliferation of MLC and PHA-stimulated lymphocytes dose-dependently. MSC secrete osteoprotegerin (OPG), but not hepatocyte growth factor (HGF) or transforming growth factor-beta (TGF-beta). Stromal-cell-derived factor-1 (SDF-1) is not expressed on the cell surface. A recent report suggested that T-cell suppression by MSC is mediated by HGF and TGF-beta. MSC suppression was not restored by the addition of neutralizing antibodies against SDF-1, OPG, HGF or TGF-beta, alone or in combination. Addition of guanosine to PHA-stimulated lymphocyte cultures containing MSC did not affect lymphocyte proliferation. The immunosuppressive effects of cyclosporine and MSC did not interfere, when present in the cultures of PHA-activated lymphocytes. In summary, human MSC suppress proliferation of both CD4+ and CD8+ lymphocyte and decrease the expression of activation markers.     

Murine Mesenchymal Stem Cells Suppress T Lymphocyte Activation Through IL-2 Receptor α (CD25) Cleavage by Producing Matrix Metalloproteinases

Mesenchymal stem cells (MSCs) are multipotent, non-hematopoietic stem cells that exhibit the capacity to inhibit the proliferation of a variety of immune cells. However, the underlying mechanisms of the immunosuppressive effects of MSCs are still obscure. Therefore, we attempted to identify the mechanisms underlying immunosuppression toward the activated T lymphocytes by MSCs in a murine model. In particular, we aimed to find possible factors derived from MSCs that drive this phenomenon. We found that T lymphocytes incubated with conditioned media of MSCs (MSC CM) entered into apoptosis and were subjected to cell cycle arrest during the course of activation, and these phenomena were accompanied by the reduction of IL-2 production. Specifically, matrix metalloproteinases (MMPs) derived from MSCs caused cleavage of IL-2 receptor α (CD25) from the surface of activated T cells, and as a consequence, IL-2 signaling in response to engagement of the IL-2 receptor (IL-2R) was downregulated. The inhibition of MMP activity in the MSC CM by GM6001 abrogated CD25 cleavage and restored IL-2 production from the activated splenocytes. However, the blockade of MMP activity could not fully restore the proliferative response and apoptosis of T cells altered by MSC CM. In conclusion, MSC-derived MMPs have a significant role in the suppression of IL-2 production through induction of CD25 cleavage and have a partial role in the suppression of T cell proliferation.     

Mesenchymal stem cells alter migratory property of T and dendritic cells to delay the development of murine lethal acute graft-versus-host disease

Due to the potent immunoregulatory capacity, mesenchymal stem cells (MSCs) have been used in clinical trials to treat acute graft-versus-host disease (aGvHD), although the detailed in vivo mechanisms remain elusive. In a murine lethal aGvHD model, MSCs delayed the development of the disease. Interestingly, we found that MSC infusion increased the number of T lymphocytes in the secondary lymphoid organs (SLOs). Since the expression of CD62L and CCR7 is prerequisite for lymphocyte migration into SLOs, the in vitro experiments revealed that in the presence of MSCs, T lymphocytes (including CD4(+)CD25(+) regulatory T cells) preferred to take the naive-like phenotype (CD62L(+)/CCR7(+)) in mixed lymphocyte reaction and maintained the migratory activity elicited by secondary lymphoid tissue chemokine (SLC). Dendritic cells (DCs) are the initiator of immune response. CCR7 expression is pivotal for their maturation and migration into SLOs. However, CCR7 expression and SLC-driven migratory activity of DCs were remarkably suppressed by MSC coculture. The processes above were realized mainly through secretory mechanism. Consistently, MSC infusion maintained T lymphocytes to take CD62L(+)/CCR7(+) phenotype and decreased the CCR7 expression and proportion of DCs in SLOs of aGvHD mice. In conclusion, the altered migratory properties of T cells and DCs might contribute to the immunosuppressive activity of transplanted MSCs in the setting of aGvHD. Disclosure of potential conflicts of interest is found at the end of this article.     

Role for interferon-gamma in the immunomodulatory activity of human bone marrow mesenchymal stem cells

Mesenchymal stem cells (MSCs) inhibit the proliferation of HLA-unrelated T lymphocytes to allogeneic stimulation, but the mechanisms responsible for this activity are not fully understood. We show here that MSCs suppress the proliferation of both CD4+ and CD8+ T lymphocytes, as well as of natural killer (NK) cells, whereas they do not have an effect on the proliferation of B lymphocytes. The antiproliferative effect of MSCs was not associated with any effect on the expression of cell-activation markers, induction of cell apoptosis, or mimicry/enhancement of T regulatory cell activity. The suppressive activity of MSCs was not contact-dependent and required the presence of interferon (IFN)-gamma produced by activated T cells and NK cells. Accordingly, even activated B cells became susceptible to the suppressive activity of MSCs in the presence of exogenously added IFN-gamma. The suppressive effect of IFN-gamma was related to its ability to stimulate the production by MSCs of indoleamine 2,3-dioxygenase activity, which in turn inhibited the proliferation of activated T or NK cells. These findings suggest that the beneficial effect on graft-versus-host disease induced by in vivo coinfusion with the graft of MSCs may be due to the activation of the immunomodulatory properties of MSCs by T cell- derived IFN-gamma.     

Human CD8(+) T cells expressing HLA-DR and CD28 show telomerase activity and are distinct from cytolytic effector T cells

Cycling lymphocytes may express the enzyme telomerase which is involved in maintenance of telomere length and cell proliferation potential. In CD8(+) T cells freshly isolated from peripheral blood, we found that in vivo cycling cells expressed HLA-DR. Furthermore, CD28-positive cells are known to have longer telomeres than CD28-negative T cells. Therefore we used HLA-DR- and CD28-specific antibodies to sort CD8(+) T cells and measure telomerase activity ex vivo. Relatively high levels of telomerase activity were found in HLA-DR/CD28 double-positive cells. In contrast, HLA-DR-negative and CD28-negative cells had almost no telomerase activity. In summary, HLA-DR expression correlates with proliferation, and CD28 expression with proliferative potential. We have previously identified that ex vivo cytolytic CD8(+) T cells are CD56 (NCAM) positive. Here we show that HLA-DR(+) cells were rarely CD56(+) and vice versa. This demonstrates that telomerase-expressing and cytolytic CD8(+) T cells can be separated on the basis of the cell surface markers HLA-DR and CD56. Thus, activated CD8(+) T cells specialize and exert distinct functions correlating with surface molecule expression.     

Age-related changes in the occurrence and characteristics of thymic CD4(+) CD25(+) T cells in mice

Natural regulatory CD4(+) CD25(+) T cells play an important role in preventing autoimmunity by maintaining self-tolerance. They express CD25 constitutively and are produced in the thymus as a functionally mature T-cell population. Changes in the potential of these cells to regulate the activity of conventional effector lymphocytes may contribute to an increased susceptibility to infection, cancer and age-associated autoimmune diseases. In this study we demonstrated that the thymi of aged mice are populated by a higher percentage of CD4(+) CD25(+) thymocytes than in young animals. The expression of several surface markers (CD69, CD5, CD28, CTLA-4, CD122, FOXP3), usually used to characterize the phenotype of CD4(+) CD25(+) T regulatory cells, was compared between young and aged mice. We also examined the ability of sorted thymus-deriving regulatory T cells of young and aged BALB/c mice to inhibit the proliferation of lymph node lymphocytes activated in vitro. Natural regulatory T cells isolated from the thymi of young mice suppress the proliferation of responder lymph node cells. We demonstrated that thymus-deriving CD4(+) CD25(+) T cells of old mice maintain their potential to suppress the proliferation of activated responder lymphocytes of young mice. However, their potential to inhibit the proliferation of old responder T cells is abrogated. Differences in the occurrence and activity of CD4(+) CD25(+) thymocytes between young and old animals are discussed in relation to the expression of these surface markers.     

Mesenchymal stem cells inhibit and stimulate mixed lymphocyte cultures and mitogenic responses independently of the major histocompatibility complex

We aimed to study the effects of mesenchymal stem cells (MSCs) on alloreactivity and effects of T-cell activation on human peripheral blood lymphocytes (PBLs) in vitro. MSCs were expanded from the bone marrow of healthy subjects. MSCs isolated from second to third passage were positive for CD166, CD105, CD44, CD29, SH-3 and SH-4, but negative for CD34 and CD45. MSCs cultured in osteogenic, adipogenic or chondrogenic media differentiated, respectively, into osteocytes, adipocytes or chondrocytes. MSC added to PBL cultures had various effects, ranging from slight inhibition to stimulation of DNA synthesis. The stimulation index (SI = (PBL + MSC)/PBL) varied between 0.2 and 7.3. The SI was not affected by the MSC dose or by the addition of allogeneic or autologous MSCs to the lymphocytes. Suppression of proliferative activity was observed in all experiments after the addition of 10,000-40,000 MSCs to mixed lymphocyte cultures (MLCs). Lymphocyte proliferation was 10-90%, compared with a control MLC run in parallel without MSCs. In contrast, the addition of fewer MSCs (10-1000 cells) led to a less consistent suppression or a marked lymphocyte proliferation in several experiments, ranging from 40 to 190% of the maximal lymphocyte proliferation in control MLCs. The ability to inhibit or stimulate T-cell alloresponses appeared to be independent of the major histocompatibility complex, as results were similar using 'third party' MSCs or MSCs that were autologous to the responder or stimulating PBLs. The strongest inhibitory effect was seen if MSCs were added at the beginning of the 6 day culture, and the effect declined if MSCs were added on day 3 or 5. Marked inhibitory effects of allogeneic and autologous MSCs (15,000) were also noted after mitogenic lymphocyte stimulation by phytohaemagglutinin (median lymphocyte proliferation of 30% of controls), Concanavalin A (56%) and protein A (65%). Little, if any, inhibition occurred after stimulation with pokeweed mitogen. Low numbers of MSCs (150 cells) were unable to inhibit mitogen-induced T-cell responses. MSCs have significant immune modulatory effects on MLCs and after mitogenic stimulation of PBL. High numbers of MSCs suppress alloreactive T cells, whereas very low numbers clearly stimulated lymphocyte proliferation in some experiments. The effect of a larger number of MSCs on MLCs seems more dependent on cell dose than histocompatibility and could result from an 'overload' of a stimulatory mechanism.     

Study of the NKT cell subsets with superantigen SEB-activated tolerance

AIM: To study the NKT cell subsets and their differentiation. METHODS: Splenic lymphocytes from C57BL/J mice that had received SEB treatment were collected as effector cells on the 10(th) day. The cells were cultured in medium containing ConA, LPS and IL-2 for 3 days and measured their response to mitogens and cytokine. The inhibitory action of the effector cells was examined. The effector cells were cultured with normal lymphocytes and above mitogens or cytokine for 3 day. The cells proliferation was assessed with MTT method.The NKT cell subsets among these effector cells with the tolerance function were analyzed and their differentiation sources and correlation of functions were detected by flow cytometry. RESULTS: The response of SEB-activated effector cells to ConA, LPS and IL-2 was significantly decreased compared with that of normal lymphocytes. The A values of cell proliferation were decreased from 0.80+/-0.04, 0.60+/-0.03 and 0.55+/-0.07 in control groups to 0.60+/-0.05, 0.30+/-0.05 and 0.27+/-0.04 in effector groups, respectively (P<0.01, n=3).The inhibitory ability of effectors cells against the response of normal lymphocytes to ConA, LPS and IL-2 were clearly observed. They inhibited the response of normal lymphocytes to several mitogens and cytokine. And the A values of cell proliferation were decreased to 0.26+/-0.02, 0.48+/-0.04 and 0.34+/-0.02, respectively (P<0.01, n=3). The CD4(+)NK1.1(+), CD8(+)NK1.1(+), TcRV8(+)NK1.1(+) NKT cell subsets among SEB-activated effector cells with tolerance function were significantly increased and shown that they come from T cell population. And the CD4(-)CD8(-)/NK1.1(+)CD3(+)NKT cells by ConA or SEB-activated were shown coming from NK cell population. CONCLUSION: The effector cells with tolerance function activated by superantigen SEB relate to CD4(+)NK1.1(+), CD8(+)NK1.1(+), TcRVbeta8(+)NK1.1(+) NKT cell subsets. The NKT cell subsets come from T cells. The CD4(-)CD8(-)/NK1.1(+)CD3(+)NKT cells differentiating from NK cells are not involved in the regulation of tolerance.