The interaction between CD8+ cytotoxic T cells and Leishmania-infected macrophages

Leishmania is resident within the macrophages of its vertebrate host. In any intramacrophage infection, where the pathogen is present in a form capable of mediating cell to cell transmission, the contribution of a cytotoxic T cell response to protective immunity is questionable. This study presents data from an in vitro model designed to elucidate the outcome of an interaction between CD8+, cytotoxic T cells and infected macrophages. Experiments were conducted with an H-2d-restricted, cytotoxic CD8+ T cell clone and Leishmania parasites present in mixed macrophage cultures, with the parasites confined to either histocompatible BALB/c macrophages, or incompatible CBA macrophages. Initial experiments indicated that the viability of Leishmania was unaffected by the lysis of its host macrophage by cytotoxic T cells. However, extended experiments showed that the parasites were killed between 24 and 72 h. The same results were obtained regardless of whether the parasites were resident in the target, BALB/c, macrophages or the bystander, CBA, macrophages. Addition of neutralizing, anti-IFN-g antibody to the cultures ablated most of the leishmanicidal behavior, indicating that parasite death was attributable to macrophage activation, resulting from cytokine secretion from the T cells following the initial recognition event.     

转录因子t-bet在人CD8+ T细胞和γδ T细胞干扰素-γ产生中的作用

目的:探讨转录因子t-bet对人CD8 T细胞和γδT细胞干扰素-γ(IFN-γ)产生的调控作用。方法:化学合成针对人t-bet基因的小干扰RNA(siRNA),转染体外培养的人γδT细胞和αβT细胞,利用流式细胞仪分选纯化CD8 T细胞和δγT细胞,半定量RT-PCR检测CD8 T细胞和γδT细胞中t-bet mRNA的表达变化,流式细胞术检测转染前后IFN-γ产生的变化情况。结果:转染siRNA后的人CD8 T细胞和γδT细胞t-bet mRNA表达强度分别为(24.75±1.18)%和(25.28±1.04)%,较转染前明显减小(P<0.05);在t-bet表达受到抑制的同时,γδT细胞中IFN-γ 细胞为(56.57±6.67)%,与错义序列组比较差异有显著性(P<0.05)。结论:siRNA可有效降低人CD8 T细胞和γδT细胞t-bet的基因表达,转录因子t-bet在γδT细胞IFN-γ产生中所起的作用与CD8 T细胞不完全相同。     

Complementary dendritic cell-activating function of CD8+ and CD4+ T cells: helper role of CD8+ T cells in the development of T helper type 1 responses

Dendritic cells (DCs) activated by CD40L-expressing CD4+ T cells act as mediators of "T helper (Th)" signals for CD8+ T lymphocytes, inducing their cytotoxic function and supporting their long-term activity. Here, we show that the optimal activation of DCs, their ability to produce high levels of bioactive interleukin (IL)-12p70 and to induce Th1-type CD4+ T cells, is supported by the complementary DC-activating signals from both CD4+ and CD8+ T cells. Cord blood- or peripheral blood-isolated naive CD8+ T cells do not express CD40L, but, in contrast to naive CD4+ T cells, they are efficient producers of IFN-gamma at the earliest stages of the interaction with DCs. Naive CD8+ T cells cooperate with CD40L-expressing naive CD4+ T cells in the induction of IL-12p70 in DCs, promoting the development of primary Th1-type CD4+ T cell responses. Moreover, the recognition of major histocompatibility complex class I-presented epitopes by antigen-specific CD8+ T cells results in the TNF-alpha- and IFN-gamma-dependent increase in the activation level of DCs and in the induction of type-1 polarized mature DCs capable of producing high levels of IL-12p70 upon a subsequent CD40 ligation. The ability of class I-restricted CD8+ T cells to coactivate and polarize DCs may support the induction of Th1-type responses against class I-presented epitopes of intracellular pathogens and contact allergens, and may have therapeutical implications in cancer and chronic infections.     

Human CD25+CD4+ T suppressor cell clones produce transforming growth factor beta,but not interleukin 10, and are distinct from type 1 T regulatory cells

T regulatory (Tr) cells are essential for the induction of peripheral tolerance. Several types of Tr cells exist, including CD4(+) T cells which express CD25 constitutively and suppress immune responses via direct cell-to-cell interactions, and type 1 T regulatory (Tr1) cells, which function via secretion of interleukin (IL)-10 and transforming growth factor (TGF)-beta. The relationship between CD25(+)CD4(+) T cells and Tr1 cells remains unclear. Here, we demonstrate at the clonal level that Tr1 and CD25(+)CD4(+) T cells are two distinct subsets of regulatory cells with different cytokine production profiles. Furthermore, CD25(-)CD4(+) T cells can be rendered anergic by IL-10 and differentiated into Tr1 cells in the absence of CD25(+)CD4(+) T cells. Cloned human CD25(+)CD4(+) T cell populations are heterogeneous and only a subset of clones continues to express high levels of CD25 and is suppressive. The intensity of CD25, cytotoxic T lymphocyte antigen (CTLA)-4, and glucocorticoid-induced tumor necrosis factor (TNF) receptor expression correlates with the suppressive capacity of the T cell clones. None of the CD25(+)CD4(+) T cell clones with suppressive function produce IL-10, but all produce TGF-beta. Suppression mediated by CD25(+)CD4(+) T cell clones is partially dependent on TGF-beta, but not on constitutive high expression of CD25. Together these data indicate that naturally occurring human CD25(+)CD4(+) T cells are distinct from IL-10-producing Tr1 cells.     

Production of transforming growth factor beta by human T lymphocytes and its potential role in the regulation of T cell growth

This study examines the potential role of transforming growth factor beta (TGF-beta) in the regulation of human T lymphocyte proliferation, and proposes that TGF-beta is an important autoregulatory lymphokine that limits T lymphocyte clonal expansion, and that TGF-beta production by T lymphocytes is important in T cell interactions with other cell types. TGF-beta was shown to inhibit IL-2-dependent T cell proliferation. The addition of picograms amounts of TGF-beta to cultures of IL-2-stimulated human T lymphocytes suppressed DNA synthesis by 60-80%. A potential mechanism of this inhibition was found. TGF-beta inhibited IL-2-induced upregulation of the IL-2 and transferrin receptors. Specific high-affinity receptors for TGF-beta were found both on resting and activated T cells. Cellular activation was shown to result in a five- to sixfold increase in the number of TGF-beta receptors on a per cell basis, without a change in the affinity of the receptor. Finally, the observations that activated T cells produce TGF-beta mRNA and that TGF-beta biologic activity is present in supernatants conditioned by activated T cells is strong evidence that T cells themselves are a source of TGF-beta. Resting T cells were found to have low to undetectable levels of TGF-beta mRNA, while PHA activation resulted in a rapid increase in TGF-beta mRNA levels (within 2 h). Both T4 and T8 lymphocytes were found to make mRNA for TGF-beta upon activation. Using both a soft agar assay and a competitive binding assay, TGF-beta biologic activity was found in supernatants conditioned by T cells; T cell activation resulted in a 10-50-fold increase in TGF-beta production. Thus, TGF-beta may be an important antigen-nonspecific regulator of human T cell proliferation, and important in T cell interaction with other cell types whose cellular functions are modulated by TGF-beta.     

NOD鼠体内CD_4~+NKG2D~+T细胞与CD_8~+T细胞间关系

目的探讨NOD鼠体内CD_4~+NKG2D~+T细胞与CD_8~+T细胞间关系。方法动态监测NOD鼠外周血中CD_4~+NKG2D~+T及CD8+NKG2D~+T细胞在不同周龄频率。利用IGRP206-214特异性CTL清除的NOD鼠,对其外周血中CD_4~+NKG2D+/CD_4~+T及CD8+NKG2D+/CD_8~+T细胞频率进行分析。将磁珠分选所得CD_4~+NKG2D~+T细胞分别与经CFSE标记的纯CD_4~+NKG2D-T细胞、CD_8~+T细胞共培养4 d,检测体系中CD_4~+NKG2D-T细胞、CD_8~+T细胞CFSE的荧光强度变化。结果 NOD鼠外周血CD_4~+NKG2D+/CD_4~+T及CD8+NKG2D+/CD_8~+T细胞频率均随其1型糖尿病疾病进程发展逐渐升高,且二者之间呈正相关。IGRP206-214特异性CTL清除的NOD鼠,外周血中CD_4~+NKG2D+/CD_4~+T细胞频率随CD8+NKG2D+/CD_8~+T细胞频率降低显著下降。与单独培养的CD_4~+NKG2D-T细胞相比,加入CD_4~+NKG2D~+T细胞的培养体系中,CD_4~+NKG2D-T细胞增殖加快。但CD_4~+NKG2D~+T细胞对CD_8~+T增殖作用不明显。结论 NOD鼠体内存在着一群与1型糖尿病疾病进程正相关的CD_4~+NKG2D~+T细胞,且该群细胞极有可能是通过直接作用于CD_4~+NKG2D-T细胞而间接对CD_8~+T细胞产生作用。     

CD4(+)CD25(+) regulatory T cells can mediate suppressor function in the absence of transforming growth factor beta1 production and responsiveness

CD4(+)CD25(+) regulatory T cells inhibit organ-specific autoimmune diseases induced by CD4(+)CD25(-) T cells and are potent suppressors of T cell activation in vitro. Their mechanism of suppression remains unknown, but most in vitro studies suggest that it is cell contact-dependent and cytokine independent. The role of TGF-beta1 in CD4(+)CD25(+) suppressor function remains unclear. While most studies have failed to reverse suppression with anti-transforming growth factor (TGF)-beta1 in vitro, one recent study has reported that CD4(+)CD25(+) T cells express cell surface TGF-beta1 and that suppression can be completely abrogated by high concentrations of anti-TGF-beta suggesting that cell-associated TGF-beta1 was the primary effector of CD4(+)CD25(+)-mediated suppression. Here, we have reevaluated the role of TGF-beta1 in CD4(+)CD25(+)-mediated suppression. Neutralization of TGF-beta1 with either monoclonal antibody (mAb) or soluble TGF-betaRII-Fc did not reverse in vitro suppression mediated by resting or activated CD4(+)CD25(+) T cells. Responder T cells from Smad3(-/-) or dominant-negative TGF-beta type RII transgenic (DNRIITg) mice, that are both unresponsive to TGF-beta1-induced growth arrest, were as susceptible to CD4(+)CD25(+)-mediated suppression as T cells from wild-type mice. Furthermore, CD4(+)CD25(+) T cells from neonatal TGF-beta1(-/-) mice were as suppressive as CD4(+)CD25(+) from TGF-beta1(+/+) mice. Collectively, these results demonstrate that CD4(+)CD25(+) suppressor function can occur independently of TGF-beta1.     

A critical role for transforming growth factor-beta but not interleukin 4 in the suppression of T helper type 1-mediated colitis by CD45RB(low) CD4+ T cells

A T helper type 1 (Th1)-mediated colitis with similarities to inflammatory bowel disease in humans developed in severe combined immunodeficiency mice reconstituted with CD45RB(high) CD4+ splenic T cells and could be prevented by cotransfer of CD45RB(low) CD4+ T cells. Inhibition of this Th1 response by the CD45RB(low) T cell population could be reversed in vivo by an anti-transforming growth factor (TGF) beta antibody. Interleukin (IL) 4 was not required for either the differentiation of function of protective cells as CD45RB(low) CD4+ cells from IL-4-deficient mice were fully effective. These results identify a subpopulation of peripheral CD4+ cells and TGF-beta as critical components of the natural immune regulatory mechanism, which prevents the development of pathogenic Th1 responses in the gut, and suggests that this immunoregulatory population is distinct from Th2 cells.     

Cell contact-dependent immunosuppression by CD4(+)CD25(+) regulatory T cells is mediated by cell surface-bound transforming growth factor beta

CD4(+)CD25(+) T cells have been identified as a population of immunoregulatory T cells, which mediate suppression of CD4(+)CD25(-) T cells by cell-cell contact and not secretion of suppressor cytokines. In this study, we demonstrated that CD4(+)CD25(+) T cells do produce high levels of transforming growth factor (TGF)-beta1 and interleukin (IL)-10 compared with CD4(+)CD25(-) T cells when stimulated by plate-bound anti-CD3 and soluble anti-CD28 and/or IL-2, and secretion of TGF-beta1 (but not other cytokines), is further enhanced by costimulation via cytotoxic T lymphocyte-associated antigen (CTLA)-4. As in prior studies, we found that CD4(+)CD25(+) T cells suppress proliferation of CD4(+)CD25(-) T cells; however, we observed here that such suppression is abolished by the presence of anti-TGF-beta. In addition, we found that CD4(+)CD25(+) T cells suppress B cell immunoglobulin production and that anti-TGF-beta again abolishes such suppression. Finally, we found that stimulated CD4(+)CD25(+) T cells but not CD4(+)CD25(-) T cells express high and persistent levels of TGF-beta1 on the cell surface. This, plus the fact that we could find no evidence that a soluble factor mediates suppression, strongly suggests that CD4(+)CD25(+) T cells exert immunosuppression by a cell-cell interaction involving cell surface TGF-beta1.     

Blockade of transforming growth factor-{beta} signaling in tumor-reactive CD8(+) T cells activates the antitumor immune response cycle

Transforming growth factor-beta (TGF-beta) is a potent immunosuppressant. Overproduction of TGF-beta by tumor cells leads to evasion of host immune surveillance and tumor progression. Results of our early studies showed that adoptive transfer of tumor-reactive, TGF-beta-insensitive CD8(+) T cells into immunocompetent mice was able to eradicate lung metastasis of mouse prostate cancer. The present study was conducted with three objectives. (a) We tested if this technology could be applied to the treatment of solid xenograft tumors in allogeneic immunodeficient hosts. (b) We determined relevant variables in the tumor microenvironment with the treatment. (c) We tested if immune cells other than CD8(+) T cells were required for the antitumor effect. Mouse prostate cancer cells, TRAMP-C2 of the C57BL/6 strain, grown in immunodeficient allogeneic hosts of BALB/c strain, were used as a xenograft model. Tumor-reactive CD8(+) T cells from C57BL/6 mice were isolated, expanded ex vivo, and rendered insensitive to TGF-beta by introducing a dominant-negative TGF-beta type II receptor vector. Seven days following s.c. injection of TRAMP-C2 cells (5 x 10(5)) into the flank of male BALB/c-Rag1(-/-) mice, tumor-reactive, TGF-beta-insensitive CD8(+) T cells (1.5 x 10(7)) were transferred with and without the cotransfer of an equal number of CD8-depleted splenocytes from C57BL/6 donors. Naive CD8(+) T cells or green fluorescent protein-empty vector-transfected tumor-reactive CD8(+) T cells were transferred as controls. Forty days following the transfer, the average tumor weight in animals that received cotransfer of tumor-reactive, TGF-beta-insensitive CD8(+) T cells and CD8-depleted splenocytes was at least 50% less than that in animals of all other groups (P < 0.05). Tumors in animals of the former group showed a massive infiltration of CD8(+) T cells. This was associated with secretion of relevant cytokines, decreased tumor proliferation, reduced angiogenesis, and increased tumor apoptosis. Based on these results, we postulated a concept of antitumor immune response cycle in tumor immunology.     

动脉粥样硬化患者单个核细胞Siglec-1在促进CD4+和CD8+T淋巴细胞增殖和分泌细胞因子中的作用

目的 探讨动脉粥样硬化(AS)患者单个核细胞(PBMC)唾液酸黏附素(Siglec-1)在刺激白细胞分化抗原(CD)4+和CD8+T淋巴细胞活化增殖中的作用.方法 实验研究.用磁珠分离长征医院18例急性冠状动脉综合征(ACS)和41例稳定型心绞痛(SA)患者及32名健康对照者CD14阳性PBMC后,用不同浓度α-干扰素(IFN-α,0、2、5、10 ng/ml)刺激Siglec-1高表达,或用小干扰RNA或抗Siglec-1单抗靶向抑制Siglec-1表达,再与1名第三方健康献血者CD4 +/CD8+T淋巴细胞共培养5d.然后,将实验分为11组:健康人CD14(1组),健康人CD14+ IFN-α5 ng/ml(2组),健康人CD14+ IFN-Ω 5 ng/ml+ anti-Siglec-1 2 μg/ml(3组),ACS CD14(4组),ACS CD14+ siRNA干扰对照组(Mock,5组),ACS CD14+ siRNA 679 40 nmol/L(6组),ACS CD14+ anti-Siglec-1 2μg/ml(7组),SACD14(8组),SA CD14+ Mock(9组),SA CD14+ siRNA 679 40 nmol/L(10组),SA CD14+ anti-Siglec-12 μg/ml(11组);每组测定10份标本.用CCK-8活细胞计数试剂盒检测共培养T淋巴细胞增殖,用ELISA检测共培养T淋巴细胞分泌白细胞介素(IL)-2、IL-10、IL-12、γ干扰素(IFN-γ).测定各组PBMC刺激T淋巴细胞分泌细胞因子的计量数据用中位数(四分位数)表示,采用非参数秩和检验.结果 靶向阻断Siglec-1后(6组),PBMC刺激CD4+T淋巴细胞及CD8+T淋巴细胞的增殖能力减弱,PBMC刺激CD4+T淋巴细胞分泌IL-2、IL-12、IFN-γ分别为67.00(62.50～ 87.30)、0.86(0 ～1.63)、47.82(37.60 ～ 56.67) pg/ml,且分泌能力减弱;IL-10为56.00(46.25 ～67.40) pg/ml,且分泌能力增强;未处理组(4组)上述细胞因子分别为213.70(187.50 ～ 275.30)、6.87 (4.90 ～8.93)、114.90(89.50～167.40)、21.08(15.70～33.20) pg/ml,二者差异有统计学意义(U值分别为8.50、17.00、8.50、87.50,P均＜0.05).当健康对照组单核细胞经IFN-α刺激上调Siglec-1表达后(2组),刺激CD4+T淋巴细胞分泌IL-2、IL-12、IFN-γ分别为220.44(174.30 ～ 312.30)、7.90 (6.540 ～10.40)、143.75(78.20～210.00) pg/ml,且能力增强;IL-10为21.95(16.30 ～25.00) pg/ml,而能力减弱,与1组比较,差异有统计学意义(U值分别为89.50、98.00、100.00、0,P均＜0.05).抑制或增强Siglec-1对CD8+T淋巴细胞分泌的上述细胞因子无影响(P均＞0.05).结论 IFN-α可刺激Siglec-1表达增加,Siglec-1可通过促进CD4+/CD8+T淋巴细胞增殖或CD4+T淋巴细胞分泌Th1型细胞因子参与AS发病过程.     

Complementary role of CD4+ T cells and secondary lymphoid tissues for cross-presentation of tumor antigen to CD8+ T cells

MHC class I-restricted tumor antigens can be presented to CD8+ T cells by two distinct pathways: via direct and indirect presentation. The relative contribution of these two pathways toward the initial activation of tumor antigen-specific CD8+ T cells and their subsequent tumor rejection is still vigorously debated. Using a tumor model able to dissect the relative contributions of direct and indirect presentation, we show unequivocally the inefficiency of direct presentation and the essential requirement of indirect presentation for the priming of naive tumor antigen-specific T cells leading to tumor rejection. Moreover, we characterize the essential environment under which indirect presentation occurs, and find efficient cross-priming of tumor-specific CD8+ T cells in the complete absence of secondary lymphoid tissues. The independence of this process from local lymph nodes is compromised, however, in the absence of CD4+ T cell help. Therefore, our paper demonstrates that effective immune protection against tumors requires the cross-priming of CD8+ T cells under conditions that require either CD4+ T cell help, or draining lymph nodes.     

CD4+CD25+ regulatory T cells inhibit natural killer cell functions in a transforming growth factor-beta-dependent manner

Tumor growth promotes the expansion of CD4+CD25+ regulatory T (T reg) cells that counteract T cell-mediated immune responses. An inverse correlation between natural killer (NK) cell activation and T reg cell expansion in tumor-bearing patients, shown here, prompted us to address the role of T reg cells in controlling innate antitumor immunity. Our experiments indicate that human T reg cells expressed membrane-bound transforming growth factor (TGF)-beta, which directly inhibited NK cell effector functions and down-regulated NKG2D receptors on the NK cell surface. Adoptive transfer of wild-type T reg cells but not TGF-beta-/- T reg cells into nude mice suppressed NK cell-mediated cytotoxicity, reduced NKG2D receptor expression, and accelerated the growth of tumors that are normally controlled by NK cells. Conversely, the depletion of mouse T reg cells exacerbated NK cell proliferation and cytotoxicity in vivo. Human NK cell-mediated tumor recognition could also be restored by depletion of T reg cells from tumor-infiltrating lymphocytes. These findings support a role for T reg cells in blunting the NK cell arm of the innate immune system.     

Requirement for transforming growth factor beta1 in controlling T cell apoptosis

Transforming growth factor (TGF)-beta1, a potent immunoregulatory molecule, was found to control the life and death decisions of T lymphocytes. Both thymic and peripheral T cell apoptosis was increased in mice lacking TGF-beta1 (TGF-beta1(-/-)) compared with wild-type littermates. Engagement of the T cell receptor enhanced this aberrant T cell apoptosis, as did signaling through either the death receptor Fas or the tumor necrosis factor alpha receptor in peripheral T cells. Strikingly, TGF-beta was localized within the mitochondria of normal T cells, and the absence of TGF-beta1 resulted in disruption of mitochondrial membrane potential (Deltapsi(m)), which marks the point of no return in a cell condemned to die. This TGF-beta-dependent regulation of viability appears dissociable from the TGF-beta1 membrane receptor-Smad3 signaling pathway, but associated with a mitochondrial antiapoptotic protein Bcl-XL. Thus, TGF-beta1 may protect T cells at multiple sites in the death pathway, particularly by maintaining the essential integrity of mitochondria. These findings may have broad implications not only for T cell selection and death in immune responses and in the generation of tolerance, but also for defining the mechanisms of programmed cell death in general.     

Intrapulmonary growth and dissemination of an avirulent strain of Cryptococcus neoformans in mice depleted of CD4+ or CD8+ T cells

The contribution of T lymphocyte subpopulations to intrapulmonary and systemic resistance against an opportunistic strain of Cryptococcus neoformans was examined. It was found that C. neoformans was destroyed when introduced into the lungs of normal mice, but disseminated to the brains of mice treated with an antibody that depleted them of CD4+ T cells. Depletion of either CD8+ or CD4+ T cells impaired the ability of the host to clear the yeast from the lung. These results, together with the observation that CD8+ T cells accumulate in the lungs of CD4+ T cell-deficient mice, suggest that CD8+ T cells play an important role in resistance to C. neoformans infection acquired via the respiratory tract.