Expression of TRAIL receptors in human autoreactive and foreign antigen-specific T cells

Impact of soluble tumor necrosis factor-related apoptosis-inducing ligand released by engineered adipose mesenchymal stromal cells on white blood cells

BACKGROUND AIMS

The proapoptotic protein tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is physiologically expressed by immune cells and performs regulatory functions in infections, autoimmune diseases and cancer, where it acts as a tumor suppressor. Adipose-derived mesenchymal stromal cells (AD-MSCs) also may play immunomodulatory roles in both primary and acquired immune responses. We have previously demonstrated the efficacy of an anticancer gene therapy based on AD-MSC engineered to secrete a soluble TRAIL variant (sTRAIL) against pancreatic cancer. However, the impact of AD-MSC sTRAIL on leukocyte subsets has been not yet considered also to predict a possible immunotoxicity profile in the clinical translation of this cell-based anticancer strategy.

METHODS

Monocytes, polymorphonuclear cells and T lymphocytes were freshly isolated from the peripheral blood of healthy donors. Immunophenotype and functional (DR4 and DR5) and decoy (DcR1 and DcR2) TRAIL receptors were tested by flow cytometry. The viability of white blood cells treated with sTRAIL released by gene-modified AD-MSC or co-cultured with AD-MSC sTRAIL was then evaluated by both metabolic assays and flow cytometry. In addition, cytokine profile in co-cultures was analyzed by multiplex enzyme-linked immunosorbent assay.

RESULTS

Monocytes and polymorphonuclear cells showed high positivity for DR5 and DcR2, respectively, whereas T cells revealed negligible expression of all TRAIL receptors. Irrespective of TRAIL receptors' presence on the cell membrane, white blood cells were refractory to the proapoptotic effect displayed by sTRAIL secreted by gene-modified AD-MSC, and direct cell-to-cell contact with AD-MSC sTRAIL had negligible impact on T-cell and monocyte viability. Cytokine crosstalk involving interleukin 10, tumor necrosis factor alpha, and interferon gamma secreted by T lymphocytes and vascular endothelial growth factor A and interleukin 6 released by AD-MSC was highlighted in T-cell and AD-MSC sTRAIL co-cultures.

CONCLUSIONS

In summary, this study demonstrates the immunological safety and thus the clinical feasibility of an anticancer approach based on AD-MSC expressing the proapoptotic molecule sTRAIL.

Targeting Immune Modulators in Glioma While Avoiding Autoimmune Conditions

Communication signals and signaling pathways are often studied in different physiological systems. However, it has become abundantly clear that the immune system is not self-regulated, but functions in close association with the nervous system. The neural-immune interface is complex; its balance determines cancer progression, as well as autoimmune disorders. Immunotherapy remains a promising approach in the context of glioblastoma multiforme (GBM). The primary obstacle to finding effective therapies is the potent immunosuppression induced by GBM. Anti-inflammatory cytokines, induction of regulatory T cells, and the expression of immune checkpoint molecules are the key mediators for immunosuppression in the tumor microenvironment. Immune checkpoint molecules are ligand-receptor pairs that exert inhibitory or stimulatory effects on immune responses. In the past decade, they have been extensively studied in preclinical and clinical trials in diseases such as cancer or autoimmune diseases in which the immune system has failed to maintain homeostasis. In this review, we will discuss promising immune-modulatory targets that are in the focus of current clinical research in glioblastoma, but are also in the precarious position of potentially becoming starting points for the development of autoimmune diseases like multiple sclerosis.

Cytokine and Chemokine Signals of T-Cell Exclusion in Tumors

The success of cancer immunotherapy in solid tumors depends on a sufficient distribution of effector T cells into malignant lesions. However, immune-cold tumors utilize many T-cell exclusion mechanisms to resist immunotherapy. T cells have to go through three steps to fight against tumors: trafficking to the tumor core, surviving and expanding, and maintaining the memory phenotype for long-lasting responses. Cytokines and chemokines play critical roles in modulating the recruitment of T cells and the overall cellular compositions of the tumor microenvironment. Manipulating the cytokine or chemokine environment has brought success in preclinical models and early-stage clinical trials. However, depending on the immune context, the same cytokine or chemokine signals may exhibit either antitumor or protumor activities and induce unwanted side effects. Therefore, a comprehensive understanding of the cytokine and chemokine signals is the premise of overcoming T-cell exclusion for effective and innovative anti-cancer therapies.

Insight into the divergent role of TRAIL in non-neoplastic neurological diseases

Tumour necrosis factor–related apoptosis‐inducing ligand (TRAIL) is a member of the tumour necrosis factor (TNF) superfamily which mainly induces apoptosis of tumour cells and transformed cell lines with no systemic toxicity, whereas they share high sequence homology with TNF and CD95L. These unique effects of TRAIL have made it an important molecule in oncology research. However, the research on TRAIL‐related antineoplastic agents has lagged behind and has been limited by the extensive drug resistance in cancer cells. Given the several findings showing that TRAIL is involved in immune regulation and other pleiotropic biological effects in non‐malignant cells, TRAIL and its receptors have attracted widespread attention from researchers. In the central nervous system (CNS), TRAIL is highly correlated with malignant tumours such as glioma and other non‐neoplastic disorders such as acute brain injury, CNS infection and neurodegenerative disease. Many clinical and animal studies have revealed the dual roles of TRAIL in which it causes damage by inducing cell apoptosis, and confers protection by enhancing both pro‐ and non‐apoptosis effects in different neurological disorders and at different sites or stages. Its pro‐apoptotic effect produces a pro‐survival effect that cannot be underestimated. This review extensively covers in vitro and in vivo experiments and clinical studies investigating TRAIL. It also provides a summary of the current knowledge on the TRAIL signalling pathway and its involvement in pathogenesis, diagnosis and therapeutics of CNS disorders as a basis for future research.

The Role of TRAIL/DRs in the Modulation of Immune Cells and Responses

Expression of TRAIL (tumor necrosis factor–related apoptosis–inducing ligand) by immune cells can lead to the induction of apoptosis in tumor cells. However, it becomes increasingly clear that the interaction of TRAIL and its death receptors (DRs) can also directly impact immune cells and influence immune responses. Here, we review what is known about the role of TRAIL/DRs in immune cells and immune responses in general and in the tumor microenvironment in particular.

Apoptosis of tumor-infiltrating T lymphocytes: a new immune checkpoint mechanism

Immunotherapy based on checkpoint inhibitors is providing substantial clinical benefit, but only to a minority of cancer patients. The current priority is to understand why the majority of patients fail to respond. Besides T-cell dysfunction, T-cell apoptosis was reported in several recent studies as a relevant mechanism of tumoral immune resistance. Several death receptors (Fas, DR3, DR4, DR5, TNFR1) can trigger apoptosis when activated by their respective ligands. In this review, we discuss the immunomodulatory role of the main death receptors and how these are shaping the tumor microenvironment, with a focus on Fas and its ligand. Fas-mediated apoptosis of T cells has long been known as a mechanism allowing the contraction of T-cell responses to prevent immunopathology, a phenomenon known as activation-induced cell death, which is triggered by induction of Fas ligand (FasL) expression on T cells themselves and qualifies as an immune checkpoint mechanism. Recent evidence indicates that other cells in the tumor microenvironment can express FasL and trigger apoptosis of tumor-infiltrating lymphocytes (TIL), including endothelial cells and myeloid-derived suppressor cells. The resulting disappearance of TIL prevents anti-tumor immunity and may in fact contribute to the absence of TIL that is typical of "cold" tumors that fail to respond to immunotherapy. Interfering with the Fas-FasL pathway in the tumor microenvironment has the potential to increase the efficacy of cancer immunotherapy.

Altered expression of TRAIL on mouse T cells via ERK phosphorylation by Rhodiola rosea L. and its marker compounds

Rhodiola rosea L. extracts have shown neuroprotective, anti-fatigue, anti-inflammatory and anti-tumor properties. However, the studies on their effect on T cell function are rather scarce. We examined the potential of R. rosea extract and its major constituents - salidroside, rosarin, rosavin and rosin to alter cell growth of human Jurkat T cells, apoptosis of splenic mouse CD3 T cells and expression of the surface markers and phosphorylation of extracellular signal-regulated kinase (ERK). The initial screening for cell viability in Jurkat T cells and for apoptosis of mouse T cells showed the strongest activity for rosavin and rosarin. Rosarin and rosavin did not alter significantly the dynamic of CD69 expression upon stimulation, but altered TNF-related apoptosis-inducing ligand (TRAIL) expression. Rosavin inhibited TRAIL up-regulation, while rosarin showed an opposite effect. Indeed, rosarin increased the frequencies of CD3⁺TRAIL⁺ T cells and the fold inhibition of ERK phosphorylation. Our data showed that different effects of rosarin and rosavin on TRAIL expression can involve distinct action on ERK signaling and hence highlighted their potential to manipulate TRAIL as a tool to rescue the resistance to apoptosis in autoimmune diseases and cancer.

Upregulation of TRAIL expression on human T lymphocytes by interferon b and glatiramer acetate

We measured the in vivo and in vitro effects of interferon (IFN)b and glatiramer acetate (GA) on the expression of the regulatory molecule, tumor necrosis factor related apoptosis inducing ligand (TRAIL), in patients with multiple sclerosis (MS). We confirmed the prior observation that TRAIL is enhanced on anti-CD3 activated T cells by the in vitro addition of IFNβ. T cells from IFNβ-treated patients stimulated with anti-CD3 only, had higher levels of TRAIL than untreated patients, suggesting that in vivo IFNβ exposure has an effect on TRAIL expression in association with T cell activation. In vitro IFNβ-induced TRAIL upregulation on anti-CD3 or phytohemagglutinin-activated T cells was comparable for IFNβ-treated and non-treated MS patients and controls, indicating that IFN receptors were neither saturated nor down-regulated by current IFNβ therapy. Although GAin vivo orin vitro did not induce TRAIL, the IFNβ-GA combination in vitro enhanced TRAIL expression to higher levels than IFNβ alone on CD4+ T cells obtained from MS patients, regardless of GA treatment status, and healthy donors, and on GA reactive T cell lines derived from GA-treated patients or controls. Whether any observed therapeutic effects of GA/IFNβ combination therapy will correlate with TRAIL expression and function remains to be determined.

Activation of TRAIL-DR5 pathway promotes sensorineural degeneration in the inner ear

Tumor necrosis factor (TNF) family cytokines are important mediators of inflammation. Elevated levels of serum TNF‐α are associated with human sensorineural hearing loss via poorly understood mechanisms. We demonstrate, for the first time, expression of TNF‐related apoptosis‐inducing ligand (TRAIL) and its signaling death receptor 5 (DR5) in the murine inner ear and show that exogenous TRAIL can trigger hair cell and neuronal degeneration, which can be partly prevented with DR5‐blocking antibodies.

TRAIL and TRAIL receptors splice variants during long-term interferon β treatment of patients with multiple sclerosis: evaluation as biomarkers for therapeutic response

OBJECTIVE

We aimed to assess the effects of interferon β (IFNβ) treatment on the expression of the splice variants of the Tumour necrosis factor-Related Apoptosis Inducing Ligand (TRAIL) and its receptors in different cell subpopulations (CD14+, CD4+ and CD8+) from patients with multiple sclerosis (MS), and to determine whether this expression discriminated responders from non-responders to IFNβ therapy.

METHODS

We examined mRNA expression of the TRAIL and TRAIL receptors variants in patients with MS, at baseline and after one year of IFNβ therapy, according to responsiveness to this drug.

RESULTS

Long-term therapy with IFNβ increased the expression of TRAIL-α in T cell subsets exclusively from responders and decreased the expression of the isoform 2 of TRAILR-2 in monocytes from responders as well as non-responders. Lower expression of TRAIL-α, and higher expression of TRAIL-β in monocytes and T cells, was found before the onset of IFNβ therapy in patients who will subsequently become responders. Baseline expression of TRAILR-1 was also significantly higher in monocytes and CD4+ T cells from responders.

CONCLUSIONS

The present study shows that long-term IFNβ treatment has a direct influence on TRAIL-α and TRAILR-2 isoform 2 expression. Besides, receiver operating characteristic analysis revealed that the baseline expression of TRAIL-α in monocytes and T cells, and that of TRAILR-1 in monocytes and CD4+ T cells, showed a predictive value of the clinical response to IFNβ therapy, pointing to a role of TRAIL system in the mechanism of action of IFNβ in MS that will need further investigation.

Immunotherapy with liposome-bound TRAIL overcomes partial protection to soluble TRAIL-induced apoptosis offered by down-regulation of Bim in leukemic cells

PURPOSE

Human Apo2-Ligand/TRAIL secreted by natural killer cells and cytotoxic T lymphocytes plays an important role immunosurveillance controlling tumor growth and metastasis. Moreover, the fact that Apo2L/TRAIL is capable of inducing cell death in tumor cells but not in normal cells makes this death ligand a promising anti-tumor agent. Previous data from our group demonstrated that Apo2L/TRAIL was physiologically released as transmembrane protein inserted in lipid vesicles, called exosomes. Recently, we demonstrated that artificial lipid nanoparticles coated with bioactive Apo2L/TRAIL (LUV-TRAIL) resembling the natural exosomes, greatly improved Apo2L/TRAIL activity and were able to induce apoptosis in hematological malignancies. In this study, we have deepened in the underlying mechanism of action of LUV-TRAIL in hematologic cells.

METHODS/PATIENTS

Cytotoxic ability of LUV-TRAIL was assessed on Jurkat cells either over-expressing the anti-apoptotic protein Mcl1 or down-regulating the pro-apoptotic protein Bim previously generated in our laboratory. We also tested LUV-TRAIL cytotoxic ability against primary human leukemic cells from T-cell ALL patient.

RESULTS

Silencing Bim but not Mcl-1 over-expression partially protects Jurkat cells from apoptosis induced by sTRAIL. LUV-TRAIL induced caspase-8 and caspase-3 activation and killed Jurkat-Mcl1 and Jurkat-shBim more efficiently than sTRAIL independently of the mitochondrial pathway. On the other hand, LUV-TRAIL were clearly more cytotoxic against primary leukemic cells from a T-cell ALL patient than sTRAIL.

CONCLUSION

Tethering Apo2L/TRAIL to the surface of lipid nanoparticles greatly increases its bioactivity and could be of potential use in anti-tumor therapeutics.

TRAIL-receptor costimulation inhibits proximal TCR signaling and suppresses human T cell activation and proliferation

The TRAIL-receptor/TRAIL system originally described to induce apoptosis preferentially in malignant cells is also known to be involved in T cell homeostasis and the response to viral infections and autoimmune diseases. Whereas the expression of TRAIL on activated NK and T cells increases their cytotoxicity, induction of TRAIL on APCs can turn them into apoptosis inducers but might also change their immunostimulatory capacity. Therefore, we analyzed how TRAIL-receptor (TRAIL-R) costimulation is modulating TCR-mediated activation of human T cells. T cells triggered by rTRAIL in combination with anti-CD3 and -CD28 Abs exhibited a strong decrease in the expression of activation markers and Th1 and Th2 cytokines compared with CD3/CD28-activated T cells. Most importantly, proliferation of TRAIL-R costimulated T cells was strongly impaired, but no apoptosis was induced. Addition of exogenous IL-2 could not rescue T cells silenced by TRAIL-R costimulation, and TRAIL-mediated inhibition of T cell proliferation only prevented TCR-triggered proliferation but was ineffective if T cells were activated downstream of the TCR. Inhibition of T cell proliferation was associated with abrogation of proximal TCR signaling by inhibiting recruitment of TCR-associated signaling molecules to lipid rafts, followed by abrogation of protein tyrosine phosphorylation of ZAP70, phospholipase C-γ1, and protein kinase C-θ, and impaired nuclear translocation of NFAT, AP-1, and NF-κB. Most importantly, TRAIL-R costimulation efficiently inhibited alloantigen-induced T cell proliferation and CD3/28-induced activation and proliferation of autoreactive T cells derived from patients with Omenn syndrome, indicating that coactivation of TRAIL-R and TCR represents a mechanism to downmodulate T cell immune responses.

Role of Apo2L/TRAIL in immunity: Applications to rheumatoid arthritis

Rheumatoid arthritis (RA) is the most common inflammatory disease of the musculoskeletal system primarily affecting the joints. It is characterized by massive synovial hyperplasia and subsequent destruction of articular cartilage and bone. Although various aspects in the pathogenesis of RA remain unclear, genetic, environmental and of course immunological factors have been involved. Defects in apoptosis seem to play a role in both initiation and perpetuation of RA. Apo2 ligand/ tumor necrosis factor (TNF) related apoptosis-inducing ligand (Apo2L/TRAIL) is a cytokine that belongs to the TNF superfamily capable of inducing apoptosis on tumor cells through activation of the extrinsic pathway. Besides this function, like other members of the TNF superfamily, Apo2L/TRAIL has been shown to exert important functions in the regulation of the immune system. Concerning pathological conditions, the Apo2L/TRAIL signaling pathway plays an important role in the response to infections, in immune surveillance against tumors and in autoimmune diseases such as RA. Furthermore, its implication in suppression of autoimmunity suggests that Apo2L/TRAIL has potential as therapeutic agent not only in cancer but also in autoimmune diseases. In fact, Apo2L/TRAIL-based therapies have been shown effective in various animal models of RA. This review summarizes the current knowledge on the biology of Apo2L/TRAIL and its role in RA.

Effects of IFN-B on TRAIL and Decoy Receptor Expression in Different Immune Cell Populations from MS Patients with Distinct Disease Subtypes

Using quantitative RT-PCR, we compared mRNA levels for TRAIL [tumor necrosis factor (TNF)-related apoptosis-inducing ligand] and its receptors in various immune cell subsets derived from the peripheral blood of untreated normal subjects (NS) and patients with distinct subtypes of multiple sclerosis (MS): active relapsing-remitting MS (RRA), quiescent relapsing-remitting MS (RRQ), secondary-progressive MS (SPMS) or primary-progressive MS (PPMS). Consistent with a role for TRAIL in the mechanism of action of interferon-β (IFN-β), TRAIL mRNA levels were increased in monocytes from patients clinically responsive to IFN-β (RRQ) but not those unresponsive to this therapeutic (RRA). TRAIL-R3 (decoy receptor) expression was elevated in T cells from untreated RRMS patients while IFN-β therapy reversed this increase suggesting that IFN-β may promote the apoptotic elimination of autoreactive T cells by increasing the amount of TRAIL available to activate TRAIL death receptors. Serum concentrations of soluble TRAIL were increased to a similar extent by IFN-β therapy in RRQ, RRA and SPMS patients that had not generated neutralizing antibodies against this cytokine. Although our findings suggest altered TRAIL signaling may play a role in MS pathogenesis and IFN-β therapy, they do not support use of TRAIL as a surrogate marker for clinical responsiveness to this therapeutic.

TRAIL death receptor-4, decoy receptor-1 and decoy receptor-2 expression on CD8+ T cells correlate with the disease severity in patients with rheumatoid arthritis

Background

Rheumatoid Arthritis (RA) is a chronic autoimmune inflammatory disorder. Although the pathogenesis of disease is unclear, it is well known that T cells play a major role in both development and perpetuation of RA through activating macrophages and B cells. Since the lack of TNF-Related Apoptosis Inducing Ligand (TRAIL) expression resulted in defective thymocyte apoptosis leading to an autoimmune disease, we explored evidence for alterations in TRAIL/TRAIL receptor expression on peripheral T lymphocytes in the molecular mechanism of RA development.

Methods

The expression of TRAIL/TRAIL receptors on T cells in 20 RA patients and 12 control individuals were analyzed using flow cytometry. The correlation of TRAIL and its receptor expression profile was compared with clinical RA parameters (RA activity scored as per DAS28) using Spearman Rho Analysis.

Results

While no change was detected in the ratio of CD4⁺ to CD8⁺ T cells between controls and RA patient groups, upregulation of TRAIL and its receptors (both death and decoy) was detected on both CD4⁺ and CD8⁺ T cells in RA patients compared to control individuals. Death Receptor-4 (DR4) and the decoy receptors DcR1 and DcR2 on CD8⁺ T cells, but not on CD4⁺ T cells, were positively correlated with patients' DAS scores.

Conclusions

Our data suggest that TRAIL/TRAIL receptor expression profiles on T cells might be important in revelation of RA pathogenesis.

Blocking TRAIL-DR5 signaling with soluble DR5 reduces delayed neuronal damage after transient global cerebral ischemia

Mechanisms underlying delayed selective neuronal death after global cerebral ischemia remain to be clarified. Here, we report a critical role for tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) in the pathogenesis of cerebral ischemia. C57BL/6j mice were subjected to transient global brain ischemia. RT-PCR and immunohistochemistry showed that the expression of TRAIL and DR5 was upregulated following transient ischemia-reperfusion. Dual immunofluorescence analysis indicated that TRAIL expression was significantly more pronounced in astrocytes and activated microglia/macrophages, whereas DR5 expression was more pronounced in neurons, which had a good correlation with the distribution of apoptotic cells. Treatment with soluble DR5 reduced ischemic cell death after transient global ischemia through blocking the interaction of endogenous TRAIL with DR5. These results indicate that TRAIL plays a deleterious role in the pathogenesis of delayed neuronal damage after global cerebral ischemia and inhibition of TRAIL function in the brain may represent a novel neuroprotective strategy to treat ischemic stroke.

Emerging role of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) as a key regulator of inflammatory responses

1. Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in tumour cells while leaving most non-transformed cells unharmed. Binding of TRAIL to its death receptors (DR4 and DR5) activates the extrinsic apoptotic pathway by recruiting procaspase 8 into the death-inducing silencing complex. Cleavage of the BH-3 only peptide Bid by caspase 8 links the apoptotic TRAIL signal to the mitochondrial pathway and the subsequent release of cytochrome c. 2. In addition, TRAIL binds to neutralizing decoy receptors (DcR1 and DcR2). Signalling through DcR2, DR4 and DR5 can activate pro-inflammatory intracellular molecules such as mitogen-activated protein kinase, protein kinase B and nuclear factor-kappaB. 3. Recent studies have identified an important role for TRAIL in regulating immune responses to viruses, self-antigen and allergens. Increased concentrations of TRAIL are found in virus infections of the lung and TRAIL affects the antiviral response and resolution of infection. In addition, TRAIL is upregulated in the airways of asthmatics and inhibition results in reduced inflammation, T helper 2 cytokine and CCL20 release, as well as abolishing the development of airway hyperreactivity in experimental models. 4. Characterization of the specific receptor systems activated and the pro-inflammatory factors regulated by TRAIL in vivo may lead to the development of novel therapeutic strategies for diseases as diverse as infection, autoimmunity and asthma.

Large-scale production and characterization of novel CD4+ cytotoxic T cells with broad tumor specificity for immunotherapy

Immune-cell-based approaches using cytotoxic and dendritic cells are under constant scrutiny to design novel therapies for the treatment of tumors. These strategies are hampered by the lack of efficient and economical large-scale production methods for effector cells. Here we describe the propagation of large amounts of a unique population of CD4(+) cytotoxic T cells, which we termed tumor killer T cells (TKTC), because of their potent and broad antitumor cell activity. With this cultivation strategy, TKTCs from peripheral blood mononuclear cells are generated within a short period of time using a pulse with a stimulating cell line followed by continuous growth in serum-free medium supplemented with a mixture of interleukin-2 and cyclosporin A. Expression and functional profiling did not allow a classification of TKTCs to any thus far defined subtype of T cells. Cytotoxic assays showed that TKTCs kill a panel of tumor targets of diverse tissue origin while leaving normal cells unaffected. Blocking experiments revealed that TKTC killing was, to a significant extent, mediated by tumor necrosis factor-related apoptosis-inducing ligand and was independent of MHC restriction. These results suggest that TKTCs have a high potential as a novel tool in the adoptive immunotherapy of cancer.

TRAIL limits excessive host immune responses in bacterial meningitis

Apart from potential roles in anti-tumor surveillance, the TNF-related apoptosis-inducing ligand (TRAIL) has important regulatory functions in the host immune response. We studied antiinflammatory effects of endogenous and recombinant TRAIL (rTRAIL) in experimental meningitis. Following intrathecal application of pneumococcal cell wall, a TLR2 ligand, we found prolonged inflammation, augmented clinical impairment, and increased apoptosis in the hippocampus of TRAIL(-/-) mice. Administration of rTRAIL into the subarachnoid space of TRAIL(-/-) mice or reconstitution of hematopoiesis with wild-type bone marrow cells reversed these effects, suggesting an autoregulatory role of TRAIL within the infiltrating leukocyte population. Importantly, intrathecal application of rTRAIL in wild-type mice with meningitis also decreased inflammation and apoptosis. Moreover, patients suffering from bacterial meningitis showed increased intrathecal synthesis of TRAIL. Our findings provide what we believe is the first evidence that TRAIL may act as a negative regulator of acute CNS inflammation. The ability of TRAIL to modify inflammatory responses and to reduce neuronal cell death in meningitis suggests that it may be used as a novel antiinflammatory agent in invasive infections.

The effect of TRAIL molecule on cell viability in in vitro beta cell culture

Insulin-dependent diabetes mellitus (IDDM) is an organ-specific autoimmune disorder triggered by autoreactive T cells directed to pancreas beta-cell antigens. In this disorder, more than 90% of beta cells are destroyed. Cell death may be mediated via soluble or membrane-bound cell death ligands. One of these ligands may be tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a member of the TNF-alpha superfamily. In the present study, we examined whether TRAIL had cytotoxic effects on adult rat pancreas beta cell cultures and INS1-E rat insulinoma cell line cultures or not. In this study, cell destruction models were built with TRAIL concentrations of 10, 100 and 1000 ng. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test was used for evaluating cell viability. It was detected that cell cultures with TRAIL added showed no differences statistically when compared with control cultures containing no toxic additions. These results showed that TRAIL did not have significant cytotoxic effects on pancreas beta cell culture and INS-1E rat insulinoma cell line cultures. Detection of the expression of TRAIL receptors and natural apoptosis inhibitor proteins will be favourable to investigate the resistance mechanisms to TRAIL-induced cell death in this cell culture system.

TNF-related apoptosis-inducing ligand as a therapeutic agent in autoimmunity and cancer

Recombinant, soluble TNF-related apoptosis-inducing ligand (TRAIL) is currently being developed as a promising natural immune molecule for trial in cancer patients because it selectively induces apoptosis in transformed or stressed cells but not in most normal cells. In cancer patients, phase 1 and 2 clinical trials using agonistic mAbs that engage the human TRAIL receptors DR4 and DR5 have also provided encouraging results. It is now evident that TRAIL suppresses autoimmune disease in various experimental animal models, suggesting that the therapeutic value of recombinant TRAIL and agonistic DR4 and DR5 mAbs might also extend to the suppression of autoimmune disease. This review provides an insight into our current understanding of the role(s) of TRAIL in disease, with a specific focus on cancer and autoimmunity. We also emphasize biological agents and drugs that sensitize tumour cells to TRAIL-mediated apoptosis and discuss the potential molecular basis for their sensitization.

Biological markers of interferon-beta therapy: comparison among interferon-stimulated genes MxA, TRAIL and XAF-1

Biological activity of interferon-beta (IFNbeta) can be assessed by measuring IFN-stimulated genes (ISGs). Among them, myxovirus resistance protein A (MxA) appears to have the highest specificity, but it has no role in the pathogenesis of multiple sclerosis (MS). To investigate the reliability of MxA as a biomarker, we compared its expression to that of two other ISGs: TNF-related apoptosis-inducing ligand (TRAIL) and X-linked inhibitor of apoptosis factor-1 (XAF-1). Both were shown to be involved in immunoregulatory mechanisms and might play a role in MS. Quantitative-PCR measurements were performed in peripheral blood mononuclear cells from 73 MS patients after short-term and long-term treatment with IFNbeta. A time-dependent response for multiple ISGs was observed in all patients after short-term treatment. In contrast, long-term treatment induced concurrent inhibition of ISGs in 12.3% (9/73) of patients, in whom neutralizing antibodies (NAbs) were detectable. Besides, 22% (16/73) of chronically treated patients showed a non-NAbs-related abrogation of TRAIL expression. In summary, 1) MxA expression was significantly higher than both TRAIL and XAF-1, and 2) MxA was the most sensitive gene to detect decreased bioavailability due to NAbs. These findings identify MxA as an appropriate biomarker for IFNbeta, although there is no evidence for a functional role of it in MS.

Tumor-necrosis-factor-related apoptosis-inducing-ligand (TRAIL)-mediated death of neurons in living human brain tissue is inhibited by flupirtine-maleate

Neuronal damage mediated by the TRAIL-system might be involved in the pathogenesis of neuroinflammatory diseases of the central nervous system. Here we used an investigator-independent approach to quantify TRAIL-mediated death of total CNS cells and neurons in a living human brain slice culture system, a model which is much closer to the in vivo situation than dissociated cell culture. We observed dose-dependent TRAIL-mediated death of both total human CNS cells and neurons, which was prevented by flupirtine-maleate, a centrally acting analgesic drug with proposed neuroprotective properties. Our data suggest flupirtine-maleate as an orally available neuroprotective approach in the course of neuroinflammation.

Programmed cell death of myelin basic protein-specific T lymphocytes is reduced in patients with acute multiple sclerosis

We investigated the apoptosis of myelin basic protein (MBP)-specific T lymphocytes in multiple sclerosis (MS) patients with acute (AMS) or stable (SMS) MS by evaluating the expression of apoptosis markers on peripheral cells. Cells of healthy controls (HC) were evaluated as well. Results showed that mitogen-stimulated apoptosis was comparable among patients and controls, whereas MBP-stimulated CD4+ and CD8+ 7-AAD+ and 7-AAD+ Fas+ cell (apoptotic cells) were significantly reduced in AMS patients. A reduction of the apoptotic rate of myelin-specific CD4+ and CD8+ T lymphocytes could be involved in the immune-mediated destruction of the myelin sheath seen in AMS patients.

Neuronal damage in autoimmune neuroinflammation mediated by the death ligand TRAIL

Here, we provide evidence for a detrimental role of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in neural death in T cell-induced experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Clinical severity and neuronal apoptosis in brainstem motor areas were substantially reduced upon brain-specific blockade of TRAIL after induction of EAE through adoptive transfer of encephalitogenic T cells. Furthermore, TRAIL-deficient myelin-specific lymphocytes showed reduced encephalitogenicity when transferred to wild-type mice. Conversely, intracerebral delivery of TRAIL to animals with EAE increased clinical deficits, while naive mice were not susceptible to TRAIL. Using organotypic slice cultures as a model for living brain tissue, we found that neurons were susceptible to TRAIL-mediated injury induced by encephalitogenic T cells. Thus, in addition to its known immunoregulatory effects, the death ligand TRAIL contributes to neural damage in the inflamed brain.

HIV-1 Tat protein concomitantly down-regulates apical caspase-10 and up-regulates c-FLIP in lymphoid T cells: a potential molecular mechanism to escape TRAIL cytotoxicity

In this study, we showed the existence of a positive correlation between the amount of human immunodeficiency virus-type 1 (HIV-1) RNA in HIV-1 seropositive subjects and the plasma levels of TRAIL. Since it has been previously demonstrated that HIV-1 Tat protein up-regulates the expression of TRAIL in monocytic cells whereas tat-expressing lymphoid cells are more resistant to TRAIL cytotoxicity, we next investigated the effect of Tat on the expression/activity of both apical caspase-8 and -10, which play a key role in mediating the initial phases of apoptosis by TRAIL, and c-FLIP. Jurkat lymphoblastoid human T cell lines stably transfected with a plasmid expressing wild-type (HIV-1) tat gene showed normal levels of caspase-8 but significantly decreased levels of caspase-10 at both mRNA and protein levels with respect to Jurkat transfected with the control plasmid or with a mutated (cys22) non-functional tat cDNA. A significant decrease of caspase-10 expression/activity was also observed in transient transfection experiments with plasmid carrying tat cDNA. Moreover, c-FLIP(L) and c-FLIP(S) isoforms were up-regulated in tat-expressing cells at both mRNA and protein level in comparison with control cells. Taken together, these results provide a molecular basis to explain the resistance of tat-expressing Jurkat cells to apoptosis induced by TRAIL and, possibly, to other death-inducing ligands.

TRAIL-R as a negative regulator of innate immune cell responses

TRAIL receptor (TRAIL-R) signaling has been implicated in inducing apoptosis in tumor cells, but little is understood about its physiological function. Here, we report the generation and characterization of TRAIL-R(-/-) mice, which develop normal lymphocyte populations but possess enhanced innate immune responses. TRAIL-R(-/-) mice exhibited increased clearance of murine cytomegalovirus that correlated with increased levels of IL-12, IFN-alpha, and IFN-gamma. Stimulation of macrophages with Mycobacterium and Toll-like receptor (TLR)-2, -3, and -4, but not TLR9, ligands resulted in high levels of TRAIL upregulation and enhanced cytokine production in TRAIL-R(-/-) cells. The immediate-early TLR signaling events in TRAIL-R(-/-) macrophages and dendritic cells are normal, but I kappa B-alpha homeostatic regulation and NF-kappa B activity at later time points is perturbed. These data suggest that TRAIL-R negatively regulates innate immune responses.

The integration of conventional and unconventional T cells that characterizes cell-mediated responses

This review builds on evidence that cell-mediated immune responses to bacteria, viruses, parasites, and tumors are an integration of conventional and unconventional T-cell activities. Whereas conventional T cells provide clonal antigen-specific responses, unconventional T cells profoundly regulate conventional T cells, often suppressing their activities such that immunopathology is limited. By extrapolation, immunopathologies and inflammatory diseases may reflect defects in regulation by unconventional T cells. To explore the function of unconventional T cells, several extensive gene expression analyses have been undertaken. These studies are reviewed in some detail, with emphasis on the mechanisms by which unconventional T cells may exert their regulatory functions. Highlighting the fundamental nature of T-cell integration, we also review emerging data that the development of conventional and unconventional T cells is also highly integrated.

Regulation of soluble and surface-bound TRAIL in human T cells, B cells, and monocytes

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF/nerve growth factor superfamily that, apart from inducing cell death in susceptible cells, displays immunoregulatory functions influencing, for instance, T cell proliferation. It can be found in two forms: membrane-bound and soluble protein. The regulation of these is still not fully understood. In this study, we have analyzed the regulation of TRAIL surface expression and secretion in human T cells, B cells, and monocytes in response to specific stimuli. T cells, B cells, and monocytes were cultured in the presence of phytohemagglutinin (PHA)+interleukin (IL-2), anti-CD40+IL-4, and lipopolysaccharide (LPS), respectively. In particular, not only PHA+IL-2 but also LPS were able to induce secretion of soluble TRAIL, but did not enhance the expression of surface-bound TRAIL. Simultaneously, we investigated the effect of the pleiotropic stimulus interferon (IFN)-beta, known to target all leukocyte subsets, on TRAIL. Predominantly, monocytes were affected by IFN-beta, causing both release of soluble TRAIL and upregulation of the surface-bound form. IFN-beta, however, did not cause any upregulation of TRAIL in T cells. Our data serve as a basis to better understand the complex regulation of TRAIL in human peripheral immune cells and might help to clarify the role of the TRAIL system in immunopathology.

TRAIL and Malignant Glioma

Encouragingly, some types of cancer can now be considered treatable, with patients reasonably expecting their disease to be cured. Chemotherapy and radiation therapy are effective against these cancers because they activate the so-called intrinsic apoptosis pathways within the cancer cells. Unfortunately currently available treatments are only effective against a subset of tumor types. In contrast, other cancers, such as malignant glioma, typically do not respond to currently available therapies. Some of this resistance can be attributed to these tumor cells failing to undergo apoptosis upon anticancer treatment. Recently, considerable research attention has focused on triggering apoptosis in chemotherapy- and radiation-therapy-resistant cancer cells via an alternative route-the "extrinsic" pathway, as a means of bypassing this block in apoptosis. Binding of members of the tumor necrosis factor-alpha (TNF-alpha) family of death ligands to their receptors on the cell surface triggers this pathway. Death ligands can kill some cancer cells that are resistant to the apoptotic pathway triggered by conventional anticancer treatments. Some death ligands, such as TNF-alpha and FasL, cause unacceptable toxicity to normal cells and are therefore not suitable anticancer agents. However another death ligand, TNF-related apoptosis-inducing ligand (TRAIL)/Apo-2L, and antibodies that emulate its actions, show greater promise as candidate anticancer drugs because they have negligible effects on normal cells. This review will discuss the ability of TRAIL to induce apoptosis in malignant glioma cells and the potential clinical applications of TRAIL-based agents for glioma treatment.

Occurrence of an activated, profibrotic pattern of gene expression in lung CD8+ T cells from scleroderma patients

OBJECTIVE

Pulmonary fibrosis is a major cause of death in scleroderma patients. Previous studies have shown an increase in CD8+ T cells in the lungs of scleroderma patients. In the present study, we sought to determine whether activated CD8+ T cells contribute to pulmonary fibrosis in scleroderma patients through the production and activation of profibrotic mediators.

METHODS

CD8+ cells were isolated from bronchoalveolar lavage fluid obtained from 19 scleroderma patients and 7 healthy subjects. The phenotype of these cells was determined using DNA array technology. Expression of selected genes was confirmed in real-time polymerase chain reaction and enzyme-linked immunosorbent assay experiments.

RESULTS

Hierarchical clustering of gene expression profiles revealed 2 groups of subjects. Group 1 consisted of 11 patients (8 with and 3 without lung inflammation). Group 2 consisted of 15 subjects (7 healthy controls and 2 patients with and 6 without lung inflammation). Gene expression in group 1 indicated T cell activation, a type 2 phenotype, production of profibrotic factors and matrix metalloproteinases, and reduced activation-induced cell death. Increased expression of beta6 integrin messenger RNA by CD8+ T cells in group 1 suggested the possibility that these T cells might induce cell-contact-dependent activation of latent transforming growth factor beta (TGFbeta).

CONCLUSION

A subset of scleroderma patients at higher risk of progressive lung disease have activated, long-lived CD8+ T cells in their lungs that could promote fibrosis directly, through production of profibrotic factors such as interleukin-4 and oncostatin M, as well as indirectly, through activation of TGFbeta.

Cellular FLICE-inhibitory protein: an attractive therapeutic target?

Cellular FLIP (c-FLIP), also known as FLICE-inhibitory protein, has been identified as an inhibitor of apoptosis triggered by engagement of death receptors (DRs) such as Fas or TRAIL (TNF-related apoptosis-inducing ligand). cFLIP is recruited to DR signalling complexes, where it prevents caspase activation. Animal models have indicated that c-FLIP plays an important role in T cell proliferation and heart development. Abnormal c-FLIP expression has been identified in various diseases such as multiple sclerosis (MS), Alzheimer's disease (AD), diabetes mellitus, rheumatoid arthritis (RA) and various cancers. This review focuses on recent insights into c-FLIP dysregulation associated with human diseases and addresses the possibilities of using c-FLIP as a therapeutic target.

Treatment of relapsing paralysis in experimental encephalomyelitis by targeting Th1 cells through atorvastatin

Statins, known as inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, exhibit numerous functions related to inflammation, such as MHC class II down-regulation, interference with T cell adhesion, and induction of apoptosis. Here we demonstrate that both subcutaneous and oral administration of atorvastatin inhibit the development of actively induced chronic experimental autoimmune encephalomyelitis in SJL/J mice and significantly reduce the inflammatory infiltration into the central nervous system (CNS). When treatment was started after disease onset, atorvastatin reduced the incidence of relapses and protected from the development of further disability. Both the reduced autoreactive T cell response measured by proliferation toward the encephalitogenic peptide PLP139-151 and the cytokine profile indicate a potent blockade of T helper cell type 1 immune response. In in vitro assays atorvastatin not only inhibited antigen-specific responses, but also decreased T cell proliferation mediated by direct TCR engagement independently of MHC class II and LFA-1. Inhibition of proliferation was not due to apoptosis induction, but linked to a negative regulation on cell cycle progression. However, early T cell activation was unaffected, as reflected by unaltered calcium fluxes. Thus, our results provide evidence for a beneficial role of statins in the treatment of autoimmune attack on the CNS.

Investigation of bax, bcl-2, bcl-x and p53 gene polymorphisms in multiple sclerosis

Clinical course, outcome, radiological features, severity, and histopathology are heterogenous in multiple sclerosis (MS). Since MS is considered to be a polygenic disease, the genetic background may at least partly be responsible for this variability. Some MS cases are histopathologically characterized by a dramatic oligodendrocyte loss that is in part caused by apoptosis. A dysregulated apoptotic elimination of self-reactive T cells may also contribute to disease susceptibility. To analyze genetic differences in the apoptosis regulating factors bcl-2, bax, bcl-x and p53 we investigated polymorphisms of these genes in 105 patients with a relapsing remitting disease course and 99 controls by PCR-SSCP and direct sequencing. We identified so far unpublished sequence alterations in the promotor region of the bxl-x gene, in exon 7 of the p53 gene, and in exon 1 of the bax gene. No differences were observed between MS patients and controls. Additional known polymorphisms were found in intron 3 of the bax gene and in exon 6 of the p53 gene. No significant differences in the frequency of gene sequence variations were found between MS patients and controls. The apoptosis genes studied here therefore appear less likely to be important effector genes in MS.

Death ligand TRAIL induces no apoptosis but inhibits activation of human (auto)antigen-specific T cells

TNF-related apoptosis-inducing ligand (TRAIL), a member of the TNF superfamily, induces apoptosis in susceptible cells, which can be both malignant and nontransformed. Despite homologies among the death ligands, there are great differences between the TRAIL system on the one hand and the TNF and CD95 systems on the other hand. In particular, TRAIL-induced apoptosis differs between rodents and man. Studies on animal models of autoimmune diseases suggested an influence of TRAIL on T cell growth and effector functions. Because we previously demonstrated that TRAIL does not induce apoptosis in human (auto)antigen-specific T cells, we now asked whether TRAIL exhibits other immunoregulatory properties in these cells. Active TRAIL inhibited calcium influx through store-operated calcium release-activated calcium channels, IFN-gamma/IL-4 production, and proliferation. These effects were independent of APC, Ag specificity, and Th differentiation, and no differences were detected between healthy donors and multiple sclerosis patients. TRAIL affected neither the expression of the cell cycling inhibitor p27(Kip1) nor the capacity of T cells to produce IL-2 upon Ag rechallenge, indicating that signaling via TRAIL receptor does not induce T cell anergy. Instead, the TRAIL-induced hypoproliferation could be attributed to the down-regulation of the cyclin-dependent kinase 4, indicating a G(1) arrest of the cell cycle. Thus, although it does not contribute to mechanisms of peripheral T cell tolerance such as clonal anergy or deletion by apoptosis, TRAIL can directly inhibit activation of human T cells via blockade of calcium influx.

Elevated Bcl-X(L) levels correlate with T cell survival in multiple sclerosis

T cell resistance towards apoptotic elimination by activation-induced cell death (AICD) might be a crucial pathogenic feature of multiple sclerosis (MS). Since the Bcl-2 family is critically involved in the regulation of apoptosis, we investigated the protein expression of Bcl-2, Bcl-X(L), and Bax in peripheral blood mononuclear cells (PBMC) of 23 MS patients and 29 control subjects. An in vitro model of AICD, which exemplifies the elimination of antigen-reactive T cells in vivo, was used as an indication of T cell susceptibility or resistance towards apoptosis. Increased expression of the survival factor Bcl-X(L), which directly correlated with a resistance towards AICD, was observed in peripheral immune cells of MS patients. In contrast to Bcl-X(L), no differences were found in the protein expression of Bcl-2 and Bax between patients and controls. Our data indicate that the anti-apoptotic factor Bcl-X(L), responsible for T cell resistance towards apoptosis, might be an important factor in the MS pathogenesis and a potential target for therapeutic intervention.

Potentiation of Fas-mediated apoptosis by an engineered glycosylphosphatidylinositol-linked Fas

FasL and TRAIL are apoptotic ligands of the TNF-like cytokines family, acting via activation of the transmembrane death domain containing receptors Fas for FasL, and DR4 or DR5 for TRAIL. A glycosylphosphatidylinositol-linked TRAIL receptor called DcR1 behaves as a decoy receptor inhibiting TRAIL-mediated cell death in several cellular systems. We engineered and stably expressed a chimeric GPI-linked Fas receptor (Fas-GPI) in T-lymphocyte cell lines constitutively expressing functional transmembrane Fas. Surprisingly, despite lacking the death domain region of functional Fas, Fas-GPI was able to significantly increase Fas-mediated cell death triggered by membrane bound or soluble FasL, whereas engagement of Fas-GPI alone did not trigger apoptosis. This potentiating effect, but not transmembrane Fas activation, was selectively inhibited by protein kinase C activation with phorbol esters, demonstrating that Fas-GPI activated a specific synergistic signal transduction pathway. Fas-GPI and transmembrane Fas were localized in distinct membrane compartments, since Fas-GPI, but not transmembrane Fas, was found in the glycolipid-rich membrane microdomains. These results suggest that apoptosis induced by members of this ligand/receptors family may be differentially modulated through other and parallel signalling pathways.

Expression of cytokine- and chemokine-related genes in peripheral blood mononuclear cells from lupus patients by cDNA array

Systemic lupus erythematosus (SLE) is characterized by diverse and complex immune abnormalities. In an effort to begin to characterize the full complexity of immune abnormalities, the expression pattern of 375 potentially relevant genes was analyzed using peripheral blood mononuclear cells (PBMC) from 21 SLE patients and 12 controls by cDNA arrays. When mean gene expression for patients was compared to controls, 50 genes were identified that exhibited more than 2.5-fold difference in expression level. By the Mann-Whitney U test, 20 genes were significantly different (P < 0.05) between patients and controls. Most of these genes have not been previously associated with SLE and belong to a variety of families such as TNF/death receptor, IL-1 cytokine family, and IL-8 and its receptors. Hierarchical clustering of samples and differentially expressed genes revealed that with few exceptions, patients clustered separately from controls. These results highlight the potential use of the microarray data in identifying genes associated with SLE, which could become candidate molecular markers or future therapeutic targets.

Inflammatory cytokine regulation of TRAIL-mediated apoptosis in thyroid epithelial cells

Death receptor-mediated apoptosis has been implicated in target organ destruction in chronic autoimmune thyroiditis. Depending on the circumstances, inflammatory cytokines such as IL-1, TNF and IFNgamma have been shown to contribute to either the induction, progression or inhibition of this disease. Here we demonstrate that the death ligand TRAIL can induce apoptosis in primary, normal, thyroid epithelial cells under physiologically relevant conditions, specifically, treatment with the combination of inflammatory cytokines IL-1beta and TNFalpha. In contrast, IFNgamma is capable of blocking TRAIL-induced apoptosis in these cells. This regulation of TRAIL-mediated apoptosis by inflammatory cytokines appears to be due to alterations of cell surface expression of TRAIL receptor DR5 and not DR4. We also show the in vivo presence of TRAIL and TRAIL receptors DR5 and DcR1 in both normal and inflamed thyroids. Our data suggests TRAIL-mediated apoptosis may contribute to target organ destruction in chronic autoimmune thyroiditis.

Death receptor ligands in tumors

Activation of apoptosis via death receptors is a tightly regulated event, and the death pathway itself is open to interference on the part of soluble or membrane-bound decoy receptors. The aggregation state of the death-inducing ligand is a crucial factor, particularly when these molecules are used as recombinant drugs against tumors. Whether tumors are sensitive to such ligands is determined by both the net abundance of death receptors versus decoy receptors and the balance between intracellular apoptotic and antiapoptotic mechanisms. This means that in vivo elimination of tumor cells by effector arms such as T lymphocytes, natural killer cells, macrophages, and dendritic cells is dependent on both the function of activated lymphoid cells and the genetic properties of tumor cells. Death receptor ligands, however, may be a double-edged sword. When expressed on cytotoxic T lymphocytes, natural killer cells, monocytes, and dendritic cells, they induce the apoptosis of many tumor cells, whereas their expression on tumor cells induces the apoptosis of killer cells. The in vivo result is influenced by the number of infiltrating cells, their state of activation, the cytokine repertoire in the tumor microenvironment, and the ability of the tumor to produce soluble factors inhibiting their cytolytic functions.

Induction of TRAIL-mediated glioma cell death by human T cells

Among the death ligands of the tumor necrosis factor/nerve growth factor (TNF/NGF) superfamily, TNF-related apoptosis-inducing ligand (TRAIL) is considered to play a unique role due to its binding to both apoptosis-inducing and -blocking membranous receptors, apoptosis-independent effects and distinct species differences. Here, we demonstrate that human antigen-specific T helper cells upon activation are capable of directly lysing glioma cell lines via TRAIL receptor/TRAIL interactions. Out of 17 T cell lines, nine showed predominantly TRAIL-mediated killing of glioma cell lines compared to CD95 ligand- or TNF-induced cell death. The cytotoxic potential of the T cell lines was independent of T helper differentiation, antigen specificity and donor source. Thus, TRAIL-mediated signaling is involved in T cell cytotoxicity towards glioma cell lines, which might play an important role in tumor regression.

Heightened expression of survivin in activated T lymphocytes from patients with multiple sclerosis

The perpetuation of the inflammatory process in multiple sclerosis (MS) may arise from the failure to eliminate potentially pathogenic autoreactive lymphocytes by programmed cell death (apoptosis). Such impairment may be caused by multiple abnormalities of apoptosis regulatory proteins. In this study, we investigated the expression of survivin, a recently described cell cycle-regulated antiapoptosis protein, in lymphocytes from patients with active relapsing-remitting MS and appropriate controls. Survivin reactivity was detected in intrathecal lymphocytes from some MS patients, but not in resting peripheral lymphocytes. However, mitogen stimulation of resting lymphocytes induced survivin expression, which was significantly higher in stimulated intrathecal and peripheral T lymphocytes from MS patients when compared to controls. In contrast, cellular expression of the antiapoptosis protein Bcl-2 was relatively similar between MS patients and the control groups. Moreover, heightened survivin expression in MS patients correlated with T lymphocyte resistance to apoptosis, and was independent of cellular expression of the death receptor Fas. These findings suggest that upregulation of the antiapoptotic protein survivin in mitogen-stimulated T lymphocytes is a feature of multiple sclerosis.

Differential regulation of the expression of CD95 ligand, receptor activator of nuclear factor-kappa B ligand (RANKL), TNF-related apoptosis-inducing ligand (TRAIL), and TNF-alpha during T cell activation

Members of TNF superfamily are characterized by their ability to inflict apoptosis upon binding to their cognate receptors in a homotrimeric manner. These proteins are expressed on different cell types under various conditions. However, the mechanisms governing the expression of these molecules remain elusive. We have found that the TCR signal can elicit the expression of receptor activator of NF-kappaB ligand (RANKL), TNF-alpha, CD95L, and TNF-related apoptosis inducing ligand (TRAIL) in T cell hybridoma A1.1 cells, thus allowing us to examine the expression pattern of these molecules under precisely the same conditions. We have previously reported that CD95L expression requires both protein kinase C (PKC) translocation and Ca2+ mobilization and is inhibited by cyclosporin A, and dexamethasone. We demonstrate now that activation-induced expression of RANKL is mediated by Ca2+ mobilization. PKC activation does not induce RANKL expression nor does it synergize with the Ca2+ signal. Activation-induced RANKL expression is blocked by cyclosporin A, but not by dexamethasone. The expression of TNF, in contrast, is mediated by PKC, but not by Ca2+. TNF-alpha expression is not inhibited by cyclosporin A, but is sensitive to dexamethasone. A1.1 cells constitutively express TRAIL at low levels. Stimulation with anti-CD3 leads to an initial reduction and subsequent increase in TRAIL expression. TRAIL induction is not inhibited by cyclosporin A, but highly sensitive to dexamethasone. Therefore, expression of the TNF superfamily genes is regulated by distinct signals. Detailed understanding of the regulatory mechanisms could provide crucial information concerning the role of these molecules in the modulation of the immune system.

Human brain-cell death induced by tumour-necrosis-factor-related apoptosis-inducing ligand (TRAIL)

Cell death induced by tumour-necrosis-factor-related apoptosis-inducing ligand (TRAIL) was believed to occur exclusively in tumour cells, suggesting that this drug is safe to use as an antitumour therapy. Concerns were raised, however, when cultured normal human hepatocytes were shown to be susceptible to TRAIL. Here we report that TRAIL induces apoptosis in the human brain. Our finding therefore argues against the use of TRAIL for therapy of human brain tumours. However, neuroinflammatory T cells that express TRAIL might induce apoptosis of brain tissue, indicating a potential target for treatment of multiple sclerosis.