Mechanisms of peripheral T cell deletion: anergized T cells are Fas resistant but undergo proliferation-associated apoptosis

The complementary receptor pair Fas ligand: Fas controls apoptosis during activation-induced cell death (AICD) of peripheral T cells sensitized for the Fas signal pathway by interleukin-2 (IL-2). In the present study, we used the bacterial superantigen staphylococcal enterotoxin B (SEB) to anergize ligand-reactive peripheral T cells in wild-type and Fas-defective lpr mice. In a second step, we investigated whether apoptosis in anergized and thus operationally IL-2-defective peripheral T cells is triggered via the Fas signal pathway. We report here that SEB-driven anergy induction and deletion of anergized peripheral Vβ8⁺ T cells is similar in wild-type and healthy C3H/lpr mice. In monitoring SEB-driven Vβ8⁺ T cell apoptosis in situ, we observe in both wild-type and lpr mice an intimate association between proliferation and apoptosis of anergized Vβ8⁺ T cells. We further show that Vβ8⁺ T cells activated in vitro from wild-type mice express a Fas-sensitive phenotype determined by Fas cross-linking which causes apoptosis. In contrast, Vβ8⁺ T cells anergized in vivo from wild-type mice are Fas resistant. As expected, T cells from lpr mice activated in vitro or anergized in vivo are Fas resistant. Taken together, these data indicate that both in wild-type and Fas-defective C3H/lpr mice, anergized T cells become deleted via a Fas-independent, proliferation-associated apoptosis signal pathway.     

超抗原诱导T细胞凋亡或增殖的体外研究

研究抗原递呈细胞在超抗原诱导人外周血特异性Ｔ细胞反应中的作用。方法金黄色葡萄球菌Ａ肠毒素刺激短期人外周血ＳＥＡ反应Ｔ细胞系的作用中,通过去除或加入Ａｐｃ观察细胞形态,ＦＣＭ检测细胞亚ＧＯ／Ｇ１峰大小及１．８％ＤＮＡ琼脂糖凝胶电泳观察凋亡特征条带。     

Immunotoxicity and pulmonary toxicity induced by paints in Egyptian painters

Associations between painting, sensitization, and respiratory disease have received little attention, despite the extensive use of paint and paint removal products. The objectives of this study were to investigate the possible immunotoxicity and pulmonary toxicity induced by paints in Egyptian painter workers. This study was carried out on 60 adult males. Subjects were designated as controls (n = 30 healthy persons) or paint-exposed workers (n = 30). The controls and workers were then divided into four equal groups (15 individuals/group): Group I, Control group—never smoked; Group II, Smoker controls; Groups III, paint-exposed non-smoking workers; and Group IV, paint-exposed smoker workers. A complete physical examination, chest radiograph, and pulmonary function test (PFT) were performed with each subject. Serum levels of immunoglobulin (Ig) E and interleukin (IL)-4, -6, and -10, WBC sub-set counts, total numbers of WBC, and leukocyte differentials were also assessed. The pulmonary toxicity due to the paint exposures appeared in the form of allergic manifestations in the respiratory tract, significant reductions in FVC, FEV₁, FEV1/FVC ratio and PEF parameters, and a reticular pattern in both lung fields. Immunotoxicity was evidenced by increases in total leukocyte levels, total lymphocytes, CD8⁺ T-lymphocytes, B (CD19⁺)-lymphocytes, NK (CD3⁺CD16⁺CD56⁺) cells, and eosinophils, as well as a significant decrease in CD4+ T-lymphocyte; there were also significant elevations in serum IgE, IL-4, and IL-6, and a significant reduction in IL-10, levels in these hosts. Based on these results, we assert that repeated paint exposure is associated with pulmonary and immune system toxicities that may lead to an augmentation of allergic diseases.     

Clonal deletion as direct consequence of an in vivo T cell response to bacterial superantigen

To date clonal deletion of peripheral mature T cells is restricted to in vivo model systems characterized by prolonged exposure of mice to antigens and clonal T cell expansion preceding clonal deletion. Here we describe that upon challenge of mice with the superantigen staphylococcal enterotoxin B two immediate events become imposed on ligand-reactive Vβ8⁺ T cells in lymph node cells draining the local site of injection. First, and within hours Vβ selective clonal deletion is initiated via an apoptotic process. Second, the remaining Vβ8⁺ T cells first develop a profound state of ligand-specific unresponsiveness and subsequently initiate clonal in vivo growth. It is suggested that the dichotomy of events observed reflects a direct consequence of T cell receptor occupancy in the context of inappropriate signalling.     

饮水中二溴乙酸对小鼠免疫功能影响机制的研究

目的 探讨二溴乙酸对小鼠免疫功能影响的机制.方法 清洁级BALB/c小鼠40只,分为四组:即二溴乙酸5、20和50 mg/kg剂量组以及阴性对照.连续灌胃28 d后,检测脾和胸腺细胞因子白细胞介素(IL)-2、IL-4分泌水平,脾和胸腺内细胞凋亡率,以及凋亡相关基因(Fas,Bcl-2,TRAF-2和bax)和蛋白(Fas/FasL)的表达.结果 与阴性对照组相比,二溴乙酸染毒组脾细胞的IL-2分泌水平明显增加(P＜0.01)而胸腺细胞的IL-2分泌水平降低(50 mg/kg剂量组有统计学意义,P＜0.05),脾细胞和胸腺细胞的IL-4的分泌水平明显降低(P＜0.01).脾和胸腺细胞凋亡率明显增加.胸腺和脾内的Fas和TRAF2基因表达显著增加,Fas/FasL的蛋白表达显著增加,具有统计学意义(P均为＜0.05).结论 饮水中二溴乙酸对小鼠免疫器官的损伤是通过Fas/FasL途径诱导细胞凋亡.     

T cell stimulation in the absence of exogenous antigen: a T cell signal is induced by both MHC-dependent and -independent mechanisms

Mature T cells residing in peripheral lymphoid organs have frequent contact with antigen presenting cells (APC). Such contact may be required for T cell survival, but the degree to which signals in mature T cells are induced by TCR recognition of self peptide/MHC complexes is unclear. We have used induction of the early growth response gene 1 (Egr1) as an indicator of signal transduction in 3.L2 (I-Ek-restricted) T cells interacting with APC in the absence of exogenous antigen. The data show that Egr1 can be induced in 3.L2 T cells by TCR recognition of self peptides presented by I-Ek. However, a more transient induction of Egr1 can be induced in 3.L2 T cells interacting with dendritic cells derived from class II/beta2m double-deficient mice. Egr1 induction after T cell-APC contact was also observed in a freshly isolated polyclonal CD4 T cell population. The data suggest that self peptide/MHC recognition by the TCR induces a signal in T cells and that dendritic cells can also induce a more transient T cell signal by an MHC-independent mechanism.     

Linomide inhibits programmed cell death of peripheral T cells in vivo

Programmed cell death (PCD) is involved in the physiological regulation of lymphocyte turnover, as well in the antigen-driven selection of T and B cells. Here it is shown that the immunomodulator linomide (quinoline-3-carboxamide) inhibits the apoptotic decay of peripheral T lymphocytes in response to three different stimuli. First, linomide reduces the superantigen-mediated apoptosis and deletion of specific T lymphocytes of both the CD4⁺ and the CD8⁺ subsets without affecting other superantigen-triggered phenomena such as T cell expansion and anergy. Second, linomide abolishes the T lymphopenia and inhibits PCD of splenic CD4⁺ and CD8⁺ T cells induced by exogenous glucocorticoids. This effect is restricted to peripheral T lymphocytes and does not concern thymocytes. Finally, linomide abolishes the development of lymphopenia that follows infection with vaccinia virus, while reducing PCD of CD4⁺ and CD8⁺ peripheral T cells. The anti-apoptotic effect of linomide could account for its immunostimulatory properties and might be relevant to the treatment of immunodeficiencies associated with an increased apoptotic decay of T lymphocytes.     

Viral superantigen-induced hyporesponsiveness of T cells and polyclonal B cell activation in HIV-1 infection

The mechanisms of CD4 depletion and hyporesponsiveness during human immunodeficiency virus (HIV) infection are still unknown. Given the ability of superantigens to stimulate a higher number of lymphocytes than conventional antigens, they may play a major role in this process. Recently, a novel superantigen, the rabies virus nucleocapsid (NC), was described in humans. In the present work, we tested the responses of peripheral blood lymphocytes from asymptomatic HIV-infected patients to this superantigen. In contrast to its effect in normal controls, NC failed to expand T cells from HIV-infected individuals expressing the Vβ8 family, and induced a strong decrease in the response to CD3 activation. This absence of response was not the consequence of programmed cell death, and was explained by an anergic state induced by the superantigen. NC superantigen was also able to induce polyclonal activation of B cells, as measured by the secretion of anti-HIV antibodies and autoantibodies. Moreover, Vβ8 depletion experiments showed that induction of autoantibody secretion was Vβ8 dependent, whereas secretion of HIV-1 antibody was not. Interleukin secretion studies showed that NC was able to induce high levels of interleukin-4 and interleukin-10. Taken together, our results suggest a role for exogenous viral superantigens such as NC in the induction of T cell hyporesponsiveness and polyclonal B cell activation during HIV infection. The induction of a T_h2 response and the role of these superantigens in the immunopathogenesis of acquired immunodeficiency syndrome are discussed.     

Involvement of the Fas (CD95) system in peripheral cell death and lymphoid organ development

Fas-mediated apoptosis is a form of cell death that operates through a Fas-Fas ligand (FasL) interaction. In this study we investigated the role of the Fas system during development of normal and Fas-mutated lymphocytes. Irradiated RAG2^–/– recipients were reconstituted with bone marrow cells from B6 and lpr mice (Fas defective) or from B6 and gld mice (FasL defective), and analyzed for long-term development. The results showed a primary role of the Fas system in peripheral cell death and thymic colonization. In the periphery, the interaction in vivo between Fas⁺ and Fas^– T cell populations indicated that cellular homeostasis was defective. Indeed, we observed a FasL-mediated cytotoxic effect on normal-derived T cells, explaining the dominance of lpr T cells in the mixed chimeras. The Fas mutation affected neither cell activation nor cell proliferation, as the effector (Fas^–) and target (Fas⁺) cells behaved similarly with regard to activation marker expression and cell cycle status. However, Fas^– T cells failed to seed the periphery and the thymus in the long term. We suggest that this could be due to the fact that FasL is involved in the structural organization of the lymphoid compartment.     

超抗原SEB体外诱导胸腺细胞凋亡的研究

目的：观察超抗原SEB能否在APC的辅助下体外诱导胸腺细胞凋亡，并研究其机制。方法：SEB作用于与APC混合培养的胸腺细胞，用DNA凝胶电泳、DNA片段测定等判定胸腺细胞凋亡并作定量分析；用间接免疫荧光法标记并以流式细胞仪检测Fas、FasL的表达。结果：SEB处理组胸腺细胞有凋亡表现且凋亡率明显高于对照组，Fas、FasL的表达明显高于对照组。结论：SEB可以于体外在APC辅助下诱导胸腺细胞凋亡，Fas、FasL的高表达可能在凋亡中起重要作用，这可能为体外研究胸腺细胞阴性选择过程提供一种方法。     

Development of T and B cell areas in peripheral lymphoid organs of the rat

In the present study the early development of peripheral lymphoid organs (spleen, popliteal lymph node, mesenteric lymph node and Peyer's patches) is described in terms of homing patterns of T and B cells, demonstrated with immunohistoperoxidatic detection of characteristic membrane antigen in normal rats and with routine histology in neonatally thymectomized rats. In the first days after birth the peripheral lymphoid organs are almost exclusively populated by T cells. After neonatal thymectomy lymphocytes appear in the dome areas of Peyer's patches from four to six days after birth, in mesenteric and popliteal lymph nodes lymphocytes are found in the outer cortex from day 6 and day 8 respectively and in the marginal zone of the spleen from eight days onwards. These lymphocytes showed no membrane staining when reacted for T antigen with immunohistoperoxidatic techniques. The morphological evidence for considering Peyer's patches of rats as central inductive sites for the generation of B cells is poor. The discrepancy in the order of appearance of T and B cell (sub)populations in spleen compartments in normal ontogenetic development and lethally irradiated, stem cell reconstituted animals is discussed.     

The proportions of B and T lymphocytes in lymphomas, peripheral nerves and lymphoid organs in Marek's disease

The proportions of cells bearing B cell, T cell and immunoglobulin (Ig), cell membrane markers have been studied in chickens with Marek's disease (MD). The proportions of B, T and Ig-bearing cells were similar in lymphomas arising in various organs and in infiltrated nerves, irrespective of type of nerve lesion. T cells provided the major component, and B and Ig cells the minor components, of the lymphoid cell populations. Compared with the corresponding organ from uninfected control chickens, bursa and spleen from MD-affected birds showed increases in the proportions of T cells and decreases of B and Ig cells. In the bursa, and probably in the spleen, the increase in the proportion of T cells was caused by lymphomatous infiltration. In the thymus of MD-affected chickens the proportion of T cells was decreased, and of B cells increased.     

Ligand-dependent regulation of T cell development and activation

Mature CD4⁺ and CD8⁺T lymphocytes develop in the thymus from precursors with diverse clonally distributed receptors, possessing binding sites with negligible, intermediate, or high affinity for self-peptide: major histocompatibility complex (MHC) ligands. Positive-and negative-selection processes acting on this precursor pool yield a peripheral T cell population comprised of cells with receptors (TCR) capable of self-peptide: MHC ligand recognition, but largely depleted of those able to mediate overt self-responsiveness. The Lymphocyte Biology Section of the Laboratory of Immunology studies how self-ligand recognition guides T cell development in the thymus and influences the functionality of naive and activated T cells in the periphery. It also seeks to define the molecular basis for the discrimination between self-ligands and foreign antigens that controls T cell activation to effector function. Finally, it uses a combination of conventional cellular immunological methods, biochemical and biophysical studies, and advanced imaging techniques to visualize, quantitate, and model the various steps in the development of primary and memory T cell immune responses.     

雷公藤内酯醇诱导人淋巴细胞凋亡的作用与细胞周期的关系

目的：通过观察雷公藤仙酯醇诱导淋巴细胞发生凋亡与细胞周期的关系。探讨该化合物导致细胞凋亡作用的机制。方法;以人外周血Ｔ细胞为研究对象,选择流式细胞分析术,ＤＮＡ凝胶电泳及ＤＮＡ片段测定等作为检测细胞凋亡的方法。结果;雷公藤内酯醇只能造成活化的Ｔ细胞发生细胞凋亡,且与雷公藤内酯醇的浓度正相关;雷公藤内酯醇诱导活化Ｔ细胞发生细胞凋亡的作用与细胞活化的程度密切相关;     

Fas可能是雷公藤红素诱导HMC—1细胞凋亡的途径之一

目的：探讨雷公藤红素对ＨＭＣ－１细胞表达Ｆａｓ、Ｆａｓ－Ｌ的影响及凋亡的关系。方法：以式细胞仪检测细胞凋亡和Ｆａｓ、Ｆａｓ－Ｌ的表达。结果：ＨＭＣ－１细胞能自发表达Ｆａｓ,不表达Ｆａｓ－Ｌ。经雷公藤红素作用,Ｆａｓ呈先升后降的变化,Ｆａｓ－Ｌ水平表达。Ｆａｓ阳性率下降与凋亡率增加相关。结论：Ｆａｓ可能是雷公藤红素诱导ＨＭＣ－１细胞凋亡的途径之一。     

Development of T and B cell areas in peripheral lymphoid organs of the rat.

In the present study the early development of peripheral lymphoid organs (spleen, popliteal lymph node, mesenteric lymph node and Peyer's patches) is described in terms of homing patterns of T and B cells, demonstrated with immunohistoperoxidatic detection of characteristic membrane antigen in normal rats and with routine histology in neonatally thymectomized rats. In the first days after birth the peripheral lymphoid organs are almost exclusively populated by T cells. After neonatal thymectomy lymphocytes appear in the dome areas of Peyer's patches from four to six days after birth, in mesenteric and popliteal lymph nodes lymphocytes are found in the outer cortex from day 6 and day 8 respectively and in the marginal zone of the spleen from eight days onwards. These lymphocytes showed no membrane staining when reacted for T antigen with immunohistoperoxidatic techniques. The morphological evidence for considering Peyer's patches of rats as central inductive sites for the generation of B cells is poor. The discrepancy in the order of appearance of T and B cell (sub)populations in spleen compartments in normal ontogenetic development and lethally irradiated, stem cell reconstituted animals is discussed.     

Activation of T cells by superantigen: cytokine production but not apoptosis depends on MEK-1 activity

Engagement of the TCR may result in proliferation and cytokine release or programmed cell death. These two outcomes may be the consequence of distinct T cell receptor-coupled signal transduction pathways or may reflect quantitative differences in signaling strength via a single pathway. Here we show that genetic inhibition of MAP kinase kinase (MEK) by a dominant negative mutant or through chemical inhibition by PD98059 inhibits IL-2 secretion but not programmed cell death after TCR ligation by superantigen. This supports the hypothesis that T cell cytokine release and apoptosis result from signaling through distinct pathways and implies that the molecular signaling mechanisms regulating apoptosis of mature T cells and negative selection of thymocytes may be similar.     

Pathogenesis of the toxic shock syndrome: T cell mediated lethal shock caused by the superantigen TSST-1

The pathogenesis of the toxic shock syndrome (TSS) is only incompletely understood. We now present evidence that TSS toxin-1 (TSST-1), one of the superantigens produced by Staphylococcus aureus, induces lethal shock in D-galactosamine sensitized mice. In this model TSS is dependent on T cells, since cyclosporin A (CsA) completely blocked development of shock, and since T cell-deficient SCID mice did not show signs of disease upon injection with TSST-1. However, SCID mice repopulated with T cells succumbed to lethal shock. The disease is characterized by a burst of lymphokines like interleukin-2 (IL-2) and tumor necrosis factor (TNF) released into the sera of TSST-1-treated animals. Already 1–2 h after TSST-1 application TNF serum levels peaked and IL-2 levels peaked around 4 h after treatment. TNF appears as key mediator of TSS, because anti-TNF monoclonal antibodies protected TSST-1-challenged mice. Interestingly, the burst of TNF in serum was noted well in advance of detectable markers of T cell activation. Thus, about 5 % of all peripheral T cells started to express the IL-2 receptors as late as 4 h after treatment. Comparing TSST-1- and endotoxin-induced shock we conclude that TNF effects shock in both diseases. However, the type of cells involved appears distinct in that T cells cause TSS triggered by the exotosin TSST-1 while macrophages mediate the shock induced by endotoxins.     

Preneoplastic liver cell foci expansion induced by thioacetamide toxicity in drug-primed mice

Mice primed by feeding griseofulvin or diethyl 1,4-dihydro 1,4,6-trimethyl 3,5-pyridine decarboxylate for 5 months followed by drug withdrawal for 1 month (drug-primed mice) were given thioacetamide intraperitoneally, and the livers were subsequently studied at intervals up to 7 days. The hepatocellular proliferative response was measured by immunostaining for proliferative cell nuclear antigen. Necrosis was followed by measuring ALT. Mallory bodies were identified by immunoperoxidase stains for ubiquitin and cytokeratin. Preneoplastic foci were localized using immunofluorescence stain for glutathione S-transferase (GST mu) and histochemical stain for gamma glutamyl transpeptidase (GGT). The results showed that the preneoplastic foci selectively proliferated and expanded and formed nodules as indicated by quantitation of nuclei stained positive for proliferating cell nuclear antigen after thioacetamide treatment. Data support the hypothesis that the preneoplastic foci consisted of clones of hepatocytes which preferentially express GST mu, GGT and Mallory bodies. These preneoplastic cells selectively proliferate in response to the promoter effects of necrosis-induced liver cell regeneration ("chemical partial hepatectomy").