Fas ligand mediates activation-induced cell death in human T lymphocytes

Fas ligand enhances malignant behavior of tumor cells through interaction with Met, hepatocyte growth factor receptor, in lipid rafts

Many late-stage cancer cells express Fas ligand (FasL) and show high malignancy with metastatic potential. We report here a novel signaling mechanism for FasL that hijacks the Met signal pathway to promote tumor metastasis. FasL-expressing human tumor cells express a significant amount of phosphorylated Met. The down-regulation of FasL in these cells led to decreased Met activity and reduced cell motility. Ectopic expression of human FasL in NIH3T3 cells significantly stimulated their migration and invasion. The inhibition of Met and Stat3 activities reverted the FasL-associated phenotype. Notably, FasL variants activated the Met pathway, even though most of their intracellular domain or Fas binding sites were deleted. FasL interacted with Met through the FasL(105-130) extracellular region in lipid rafts, which consequently led to Met activation. Knocking down Met gene expression by RNAi technology reverted the FasL-associated motility to basal levels. Furthermore, treatment with synthetic peptides corresponding to FasL(117-126) significantly reduced the FasL/Met interaction, Met phosphorylation, and cell motility of FasL(+) transfectants and tumor cells. Finally, the transfectants of truncated FasL showed strong anchorage-independent growth and lung metastasis potential in null mice. Collectively, our results establish the FasL-Met-Stat3 signaling pathway and explains the metastatic phenotype of FasL-expressing tumors.

Exosomal miRNAs: Biological Properties and Therapeutic Potential

MicroRNAs (miRNAs), small non-coding regulatory RNAs that regulate gene expression at the post-transcriptional level, are master regulators of a wide array of cellular processes. Altered miRNA expression could be a determinant of disease development and/or progression and manipulation of miRNA expression represents a potential avenue of therapy. Exosomes are cell-derived extracellular vesicles that promote cell–cell communication and immunoregulatory functions. These “bioactive vesicles” shuttle various molecules, including miRNAs, to recipient cells. Inappropriate release of miRNAs from exosomes may cause significant alterations in biological pathways that affect disease development, supporting the concept that miRNA-containing exosomes could serve as targeted therapies for particular diseases. This review briefly summarizes recent advances in the biology, function, and therapeutic potential of exosomal miRNAs.

NEMO differentially regulates TCR and TNF-α induced NF-κB pathways and has an inhibitory role in TCR-induced NF-κB activation

NF-κB essential modulator (NEMO), the regulatory subunit of the IκB kinase (IKK) complex, is an essential adaptor both for inflammation stimuli and TCR-induced NF-κB activation. However, the exact mechanism of its function has not been fully understood. Here, we report that knockdown of NEMO by RNA interference in Jurkat E6.1 cells enhanced TCR-induced NF-κB report gene activity and IL-2 production by promotion of IκBα degradation and p65 nuclear translocation, whereas inhibited TNF-α and LPS-induced IκBα degradation without influencing the phosphorylation of MAPKs. In human primary T and Jurkat E6.1 cells, both CD3/CD28 and PMA/Ionomycin induced NF-κB activation showed a para-curve correlation with the dosage of small interfering RNA targeting NEMO (siNEMO): the NF-κB report gene activity was increased along with ascending doses of transfected siNEMO and reached the highest activity when knockdown about 70% of NEMO, then turned to decline and gradually be blocked once almost thoroughly knockdown of NEMO. Meanwhile, TNF-α induced NF-κB was always inhibited no matter how much NEMO was knockdown. Subcellular fractionation results suggested that upon CD3/CD28 costimulation, NEMO and IKKβ may not cotranslocate to cytoskeleton fraction as a conventional NEMO/IKK complex with a static stoichiometric ratio, instead the ratio of NEMO: IKKβ continuously shift from high to low. Depletion of NEMO accelerated TCR-induced cytoskeleton translocation of IKKβ. Altogether, this study suggests that NEMO may function as a rheostat exerting a negative action on TCR-induced NF-κB activation and differentially regulates TNF-α and TCR-induced NF-κB pathways.

Recent advances on the role of tumor exosomes in immunosuppression and disease progression

Exosomes are endosomal-derived nanovesicles released by most cells types, including tumor cells, and principally involved in intercellular communication in physiology and disease. Tumor exosomes are gaining increasing interest in medicine and oncology as efficient tools for the delivery of defined signals. Representing the acellular replicas of tumor cells, they contain a great variety of bioactive molecules, such as proteins, RNA, miRNA and DNA. Their great ability to recirculate in body fluids and their structure allow them to transport their cargo to distant targets. Major studies have shown that tumor exosomes convey information not only between tumor cells but also to other cell types, including different immune cell components. There is increasing evidence that these nanovesicles may contribute to cancer progression by influencing different immune cell types, likely blunting specific T cell immunity and skewing innate immune cells toward a pro-tumorigenic phenotype. Because of this function and the additional property to deliver molecular signals modulating neoangiogenesis and stroma remodeling, tumor exosomes are believed to play a role in tumor progression by favoring metastatic niche onset. This review outlines the recent knowledge on immune suppressive mechanisms mediated by tumor exosomes. We will discuss our view on the role of these nanovesicular structures in cancer progression and how their presence could interfere with cancer therapy.

Yeast aging and apoptosis

A concerted balance between proliferation and apoptosis is essential to the survival of multicellular organisms. Thus, apoptosis per se, although it is a destructive process leading to the death of single cells, also serves as a pro-survival mechanism pro-survival mechanism that ensures healthy organismal development and acts as a life-prolonging or anti-aging anti-aging program. The discovery that yeast also possess a functional and, in many cases, highly conserved apoptotic machinery has made it possible to study the relationships between aging and apoptosis in depth using a well-established genetic system and the powerful tools available to yeast researchers for investigating complex physiological and cytological interactions. The aging process of yeast, be it replicative replicative or chronological chronological aging, is closely related to apoptosis, although it remains unclear whether apoptosis is a causal feature of the aging process or vice versa. Nevertheless, experimental results obtained during the past several years clearly demonstrate that yeast serve as a powerful and versatile experimental system for understanding the interconnections between these two fundamentally important cellular and physiological pathways.

Age-associated alteration of γδ T-cell repertoire and different profiles of activation-induced death of Vδ1 and Vδ2 T cells

It has been suggested that γδ T cells are involved in certain autoimmune disorders. To establish reference data for clinical studies to explore the role of γδ T cells in autoimmune bone marrow failure syndrome, we examined the γδ T-cell repertoire in 120 healthy Japanese individuals by flow cytometry. The average numbers of T lymphocytes in blood were as follows: 1,084 ± 369 (SD) αβ T cells, 68 ± 44 γδ T cells, 16 ± 12 Vδ1 T cells, and 43 ± 36 Vδ2 T cells (/μl). Absolute numbers of γδ T cells decreased with aging (R = -0.378, P < 0.001). The decrease of γδ T cells was the result of reduction of Vδ2, but not of Vδ1, T cells. Numbers of Vδ2 T cells were significantly higher in male than in female donors (P = 0.007). The Vδ2 T cells but not Vδ1 T cells showed a rapid reduction in cell numbers on mitogen stimulation, which was accompanied by modest down-regulation of Bcl-2 protein expression. These results indicate that age and gender have a major impact on γδ T-cell repertoire in Japanese donors, as well as European and American donors. The age-related decrease of Vδ2 T cells may be explained by their susceptibility to activation-induced cell death.

FAS mRNA editing in Human Systemic Lupus Erythematosus

FAS/FASL system plays a central role in maintaining peripheral immune tolerance. Human Systematic Lupus Erythematosus (SLE) is a prototypic systemic autoimmune disease characterized by expansion of autoreactive lymphocytes. It remains unclear whether a defective FAS/FASL system is involved in the pathogenesis of SLE. In this study, we have discovered a novel nucleotide insertion in FAS mRNA. We demonstrate that this novel FAS mutation occurs at mRNA levels, likely through a site-specific mRNA editing process. The mRNA editing mutation is unique for human FAS because the similar mRNA editing event is absent in other human TNF receptor (TNFR) family genes with death domains (DR5, DR6, and TNFR1) and in murine FAS. The adenine insertion mutation in the coding region message causes the alteration of human FAS mRNA reading frame. Functionally, cells expressing the edited FAS (edFAS) were refractory to FAS-mediated apoptosis. Surprisingly, cells from SLE patients produced significantly more edFAS products compared to cells from normal healthy controls. Additionally, we demonstrated that persistent engagement of T-cell receptor increases human FAS mRNA editing in human T cells. Our data suggest that the site-specific FAS mRNA editing mutation may play a critical role in human immune responses and in the pathogenesis of human chronic inflammatory diseases.

MicroRNA regulation of molecular networks mapped by global microRNA, mRNA, and protein expression in activated T lymphocytes

MicroRNAs (miRNAs) regulate specific immune mechanisms, but their genome-wide regulation of T lymphocyte activation is largely unknown. We performed a multidimensional functional genomics analysis to integrate genome-wide differential mRNA, miRNA, and protein expression as a function of human T lymphocyte activation and time. We surveyed expression of 420 human miRNAs in parallel with genome-wide mRNA expression. We identified a unique signature of 71 differentially expressed miRNAs, 57 of which were previously not known as regulators of immune activation. The majority of miRNAs are upregulated, mRNA expression of these target genes is downregulated, and this is a function of binding multiple miRNAs (combinatorial targeting). Our data reveal that consideration of this complex signature, rather than single miRNAs, is necessary to construct a full picture of miRNA-mediated regulation. Molecular network mapping of miRNA targets revealed the regulation of activation-induced immune signaling. In contrast, pathways populated by genes that are not miRNA targets are enriched for metabolism and biosynthesis. Finally, we specifically validated miR-155 (known) and miR-221 (novel in T lymphocytes) using locked nucleic acid inhibitors. Inhibition of these two highly upregulated miRNAs in CD4(+) T cells was shown to increase proliferation by removing suppression of four target genes linked to proliferation and survival. Thus, multiple lines of evidence link top functional networks directly to T lymphocyte immunity, underlining the value of mapping global gene, protein, and miRNA expression.

Negative autoregulation by Fas stabilizes adult erythropoiesis and accelerates its stress response

Erythropoiesis maintains a stable hematocrit and tissue oxygenation in the basal state, while mounting a stress response that accelerates red cell production in anemia, blood loss or high altitude. Thus, tissue hypoxia increases secretion of the hormone erythropoietin (Epo), stimulating an increase in erythroid progenitors and erythropoietic rate. Several cell divisions must elapse, however, before Epo-responsive progenitors mature into red cells. This inherent delay is expected to reduce the stability of erythropoiesis and to slow its response to stress. Here we identify a mechanism that helps to offset these effects. We recently showed that splenic early erythroblasts, 'EryA', negatively regulate their own survival by co-expressing the death receptor Fas, and its ligand, FasL. Here we studied mice mutant for either Fas or FasL, bred onto an immune-deficient background, in order to avoid an autoimmune syndrome associated with Fas deficiency. Mutant mice had a higher hematocrit, lower serum Epo, and an increased number of splenic erythroid progenitors, suggesting that Fas negatively regulates erythropoiesis at the level of the whole animal. In addition, Fas-mediated autoregulation stabilizes the size of the splenic early erythroblast pool, since mutant mice had a significantly more variable EryA pool than matched control mice. Unexpectedly, in spite of the loss of a negative regulator, the expansion of EryA and ProE progenitors in response to high Epo in vivo, as well as the increase in erythropoietic rate in mice injected with Epo or placed in a hypoxic environment, lagged significantly in the mutant mice. This suggests that Fas-mediated autoregulation accelerates the erythropoietic response to stress. Therefore, Fas-mediated negative autoregulation within splenic erythropoietic tissue optimizes key dynamic features in the operation of the erythropoietic network as a whole, helping to maintain erythroid homeostasis in the basal state, while accelerating the stress response.

Sensitization of human bladder tumor cells to TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis with a small molecule IAP antagonist

Urothelial carcinoma of the bladder accounts for approximately 5% of all cancer deaths in humans. The large majority of bladder tumors are non-muscle invasive at diagnosis, but even after local surgical therapy there is a high rate of local tumor recurrence and progression. Current treatments extend time to recurrence but do not significantly alter disease survival. The objective of the present study was to investigate the tumoricidal potential of combining the apoptosis-inducing protein TNF-related apoptosis-inducing ligand (TRAIL) with a small molecule inhibitor of apoptosis proteins (IAP) antagonist to interfere with intracellular regulators of apoptosis in human bladder tumor cells. Our results demonstrate that the IAP antagonist Compound A exhibits high binding affinity to the XIAP BIR3 domain. When Compound A was used at nontoxic concentrations in combination with TRAIL, there was a significant increase in the sensitivity of TRAIL-sensitive and TRAIL-resistant bladder tumor lines to TRAIL-mediated apoptosis. In addition, modulation of TRAIL sensitivity in the TRAIL-resistant bladder tumor cell line T24 with Compound A was reciprocated by XIAP small interfering RNA-mediated suppression of XIAP expression, suggesting the importance of XIAP-mediated resistance to TRAIL in these cells. These results suggest the potential of combining Compound A with TRAIL as an alternative therapy for bladder cancer.

Computational identification of transcriptional regulators in human endotoxemia

One of the great challenges in the post-genomic era is to decipher the underlying principles governing the dynamics of biological responses. As modulating gene expression levels is among the key regulatory responses of an organism to changes in its environment, identifying biologically relevant transcriptional regulators and their putative regulatory interactions with target genes is an essential step towards studying the complex dynamics of transcriptional regulation. We present an analysis that integrates various computational and biological aspects to explore the transcriptional regulation of systemic inflammatory responses through a human endotoxemia model. Given a high-dimensional transcriptional profiling dataset from human blood leukocytes, an elementary set of temporal dynamic responses which capture the essence of a pro-inflammatory phase, a counter-regulatory response and a dysregulation in leukocyte bioenergetics has been extracted. Upon identification of these expression patterns, fourteen inflammation-specific gene batteries that represent groups of hypothetically ‘coregulated’ genes are proposed. Subsequently, statistically significant cis-regulatory modules (CRMs) are identified and decomposed into a list of critical transcription factors (34) that are validated largely on primary literature. Finally, our analysis further allows for the construction of a dynamic representation of the temporal transcriptional regulatory program across the host, deciphering possible combinatorial interactions among factors under which they might be active. Although much remains to be explored, this study has computationally identified key transcription factors and proposed a putative time-dependent transcriptional regulatory program associated with critical transcriptional inflammatory responses. These results provide a solid foundation for future investigations to elucidate the underlying transcriptional regulatory mechanisms under the host inflammatory response. Also, the assumption that coexpressed genes that are functionally relevant are more likely to share some common transcriptional regulatory mechanism seems to be promising, making the proposed framework become essential in unravelling context-specific transcriptional regulatory interactions underlying diverse mammalian biological processes.

Inflammatory cytokines determine the susceptibility of human CD8 T cells to Fas-mediated activation-induced cell death through modulation of FasL and c-FLIP(S) expression

The nature of inflammatory signals determines the outcome of T cell responses. However, little is known about how inflammatory cytokines provided to human CD8 T cells during activation affects their susceptibility to post-activation cell death. We have examined and compared the effects of the inflammatory cytokine IL-12, as well as the combination of IL-1, IL-6, and IL-23 (IL-1/6/23) on the susceptibility of primary human CD8 T cells to post-activation cell death. Human CD8 T cells activated in the presence of IL-1/6/23 underwent significantly less cell death after activation as compared with those activated in IL-12. This was due to reduced susceptibility to Fas-mediated activation-induced cell death (AICD). Mechanistically, the reduced level of cell death in CD8 T cells activated in IL-1/6/23 was a result of a low level of FasL expression and high level of c-FLIP(S) expression. When the effect of IL-1, IL-6, and IL-23 individually was examined, IL-1 or IL-6 alone was sufficient to inhibit CD8 T cell death that occurs after activation in IL-12. IL-1, but not IL-6, inhibited expression of FasL, whereas IL-6, but not IL-1, increased c-FLIP(S) expression. Our findings show that the presence of IL-1 and/or IL-6 during activation of human CD8 T cells attenuates Fas-mediated AICD, whereas IL-12 increases the susceptibility of activated CD8 T cells to this form of cell death.

Auto-antibody production and glomerulonephritis in congenic Slamf1-/- and Slamf2-/- [B6.129] but not in Slamf1-/- and Slamf2-/- [BALB/c.129] mice

Several genes in an interval of human and mouse chromosome 1 are associated with a predisposition for systemic lupus erythematosus. Congenic mouse strains that contain a 129-derived genomic segment, which is embedded in the B6 genome, develop lupus because of epistatic interactions between the 129-derived and B6 genes, e.g. in B6.129chr1b mice. If a gene that is located on chromosome 1 is altered through homologous recombination in 129-derived embryonic stem cells (ES cells) and if the resultant knockout mouse is backcrossed with B6, interpretation of the phenotype of the mutant mouse may be affected by epistatic interactions between the 129 and B6 genomes. Here, we report that knockout mice of two adjacent chromosome 1 genes, Slamf1(-/-) and Slamf2(-/-), which were generated with the same 129-derived ES cell line, develop features of lupus, if backcrossed on to the B6 genetic background. By contrast, Slamf1(-/-) [BALB/c.129] and Slamf2(-/-) [BALB/c.129] do not develop disease. Surprisingly, Slamf1(-/-) [B6.129] mice develop both auto-antibodies and glomerulonephritis between 3 and 6 months of age, while disease fully develops in Slamf1(-/-) [B6.129] mice after 9-14 months. Functional analyses of CD4(+) T cells reveals that Slamf2(-/-) T cells are resistant to tolerance induction in vivo. We conclude that the Slamf2(-/-) mutation may have a unique influence on T-cell tolerance and lupus.

Fas expression in conjunctival epithelial cells of patients with cystic fibrosis

Cystic fibrosis (CF) is a genetic disease caused by mutations in the cystic fibrosis transmembrane regulator (CFTR) gene resulting in absent or deficient expression and function of CFTR protein. It has recently been reported that CFTR may also be involved in the apoptotic process of epithelial cells. In this study we examined the expression of Fas on conjunctival epithelial cells and the serum and tear fluid concentrations of soluble Fas (sFas) in patients with cystic fibrosis. This article studied 25 patients with CF and 25 normal subjects. Conjunctival epithelial cells were obtained by impression cytology, and processed and analyzed for flow cytometry. The amount of sFas in serum and tear fluid was measured by enzyme-linked immunosorbent assay (ELISA). The analysis of Fas expression showed significant increases in the CF patients compared with the control group (P = 0.000012). There was no difference in the concentration of serum and tear fluid sFas between CF patients and controls (P = 0.0515 and P < 0.05, respectively). Fas expression in cystic fibrosis conjunctival epithelium could play an important role in controlling local inflammatory cell apoptosis and may confirm the role of Fas in maintaining ocular immune privilege.

The power and the promise of restimulation-induced cell death in human immune diseases

Controlled expansion and contraction of lymphocytes both during and after an adaptive immune response are imperative to sustain a healthy immune system. Both extrinsic and intrinsic pathways of lymphocyte apoptosis are programmed to eliminate cells at the proper time to ensure immune homeostasis. Genetic disorders of apoptosis described in mice and humans have established Fas and Bim as critical pro-apoptotic molecules responsible for T-cell death in response to T-cell receptor restimulation and cytokine withdrawal, respectively. Emerging evidence prompts revision of this classic paradigm, especially for our understanding of restimulation-induced cell death (RICD) and its physiological purpose. Recent work indicates that RICD employs both Fas and Bim for T-cell deletion, dispelling the notion that these molecules are assigned to mutually exclusive apoptotic pathways. Furthermore, new mouse model data combined with our discovery of defective RICD in X-linked lymphoproliferative disease (XLP) patient T cells suggest that RICD is essential for precluding excess T-cell accumulation and associated immunopathology during the course of certain infections. Here, we review how these advances offer a refreshing new perspective on the phenomenon of T-cell apoptosis induced through antigen restimulation, including its relevance to immune homeostasis and potential for therapeutic interventions.

Apoptosis regulators Fas and Bim synergistically control T-lymphocyte homeostatic proliferation

The size of the peripheral T-lymphocyte compartment is governed by complex homeostatic mechanisms that balance T-cell proliferation and death. Proliferation and survival signals are mediated in part by recurrent self-peptide/MHC-TCR interactions and signaling by the common γ chain-containing cytokine receptors, including those for IL-7 and IL-15. We have previously shown that the death receptor Fas (CD95/APO-1) regulates apoptosis in response to repeated TCR stimulation, whereas the Bcl-2 homology domain 3-only protein Bim mediates cytokine withdrawal-induced apoptosis. We therefore reasoned that these two molecules might cooperate in the regulation of homeostatic proliferation. In this study, we observe that the combined loss of Fas and Bim synergistically enhances the accumulation of T cells in lymphopenic host mice, and this is particularly pronounced for the unusual CD4(-) CD8(-) TCRαβ(+) T cells that are characteristic of Fas-deficient (Fas(lpr/lpr) ) mice. Our findings demonstrate that these CD4(-) CD8(-) TCRαβ(+) T cells arise from homeostatic proliferation of CD8(+) T cells. These studies also underscore the profound rate of baseline T-cell proliferation that likely occurs in wild-type mice even in the absence of foreign antigen, and the consequent need for its coordinated regulation by multiple death-signaling pathways.

Palmitoylation of human FasL modulates its cell death-inducing function

Fas ligand (FasL) is a transmembrane protein that regulates cell death in Fas-bearing cells. FasL-mediated cell death is essential for immune system homeostasis and the elimination of viral or transformed cells. Because of its potent cytotoxic activity, FasL expression at the cell surface is tightly regulated, for example, via processing by ADAM10 and SPPL2a generating soluble FasL and the intracellular fragments APL (ADAM10-processed FasL form) and SPA (SPPL2a-processed APL). In this study, we report that FasL processing by ADAM10 counteracts Fas-mediated cell death and is strictly regulated by membrane localization, interactions and modifications of FasL. According to our observations, FasL processing occurs preferentially within cholesterol and sphingolipid-rich nanodomains (rafts) where efficient Fas–FasL contact occurs, Fas receptor and FasL interaction is also required for efficient FasL processing, and FasL palmitoylation, which occurs within its transmembrane domain, is critical for efficient FasL-mediated killing and FasL processing.

Mechanisms of IFNγ regulation of autoimmune myocarditis

A protective effect of interferon-gamma (IFNγ) has been described in a number of models of autoimmune disease, including experimental autoimmune myocarditis (EAM). Some reports have suggested that regulation of apoptosis in autoreactive lymphocytes mediate these protective functions. We examined the potential of IFNγ to regulate apoptotic mechanisms in detail, both in vitro and in vivo in EAM. We observed multiple apoptotic defects in caspase activity, and the expression of TNF superfamily members on CD4(+) T cells. In addition, we observed selective defects in CD4(+) T cell activation in response to antigenic stimulation. These activation and apoptotic defects were CD4(+) cell autonomous, independent of the genotype of APCs. Inhibition of nitric oxide production in vivo did not reproduce the severe form of EAM of IFNγ-deficient mice, indicating that this pathway does not mediate the protective effect of IFNγ. Crosswise adoptive transfer of wild type, IFNγ(-/-), and IFNγR(-/-)EAM demonstrated that IFNγ signaling was critical in CD4(+) cells, but that non-CD4(+) sources of IFNγ production were also involved in the control of disease. Together, these data indicate multiple mechanisms of autonomous and non-autonomous CD4(+) T cell regulation mediated by IFNγ in the control of autoimmune heart disease.

T-cell receptor complex is essential for Fas signal transduction

The Fas receptor (also known as CD95 and APO-1) is a member of the tumor necrosis factor alpha-family of death receptors that mediate T-cell responses. Here, we show that Fas receptor signaling requires a functional T-cell receptor (TCR) complex. Fas receptor directly binds to and activates TCR components in a stimulus-dependent manner. Fas receptor stimulation does not activate canonical downstream TCR pathways, but instead the TCR complex is required specifically for Fas-mediated calcium release. Importantly, null mutations in Lck, ZAP70, and the TCR alpha- and beta-chains abrogate Fas signaling. Our results reveal a direct role for the TCR complex in mediating Fas-specific signaling events critical for T-cell homeostasis.

Resistance of CD45RA- T cells to apoptosis and functional impairment, and activation of tumor-antigen specific T cells during radiation therapy of prostate cancer

The effect of radiation therapy (RT) to the pelvis on circulating T cells was studied in prostate cancer (PCa) patients to provide a baseline for a more informed design of combination radioimmunotherapy. Peripheral blood samples taken from 12 PCa patients with locally advanced tumor before, during, and after hypofractionated RT were analyzed for T cell phenotype and function. There was significantly more loss of naive and early memory compared with more differentiated T cells during RT. The proportions of annexin-V(+) and Fas-expressing T cells were elevated in patients during RT and in PBMC irradiated in vitro (< or = 5.0 Gy), with preferential increases in CD45RA(+) T cells. The baseline level of apoptosis of CD45RA(-) T cells increased > 2-fold in the presence of an IkappaB-kinase inhibitor, indicating a protective effect via this pathway. T cell proliferation was impaired during RT with IL-2-dependent recovery post-RT. Recall T cell responses to common viral Ags, measured by IFN-gamma production, were little affected by RT. In vitro irradiation of healthy donor PBMCs resulted in a significantly increased frequency of responding T cells, due at least partly to the preferential elimination of CD45RA(+) T cells. Most importantly, antitumor CD4(+) and CD8(+) T cell responses were detectable after, but not before or during RT. The results indicate that generating tumor-specific T cell responses before RT and boosting their activity post-RT are ways likely to amplify the frequency and function of antitumor T cells, with implications for scheduling immunotherapy in PCa.

A schizont-derived protein, TpSCOP, is involved in the activation of NF-kappaB in Theileria parva-infected lymphocytes

Theileria parva is a tick-transmitted intracellular protozoan parasite that causes East Coast fever, a fatal bovine lymphoproliferative disease. The molecular mechanisms that underlie host cell transformation by T. parva schizonts have been studied extensively, and it is known that the nuclear factor-kappa B (NF-kappaB) is activated in schizont-infected cells, making T. parva-transformed cells resistant to apoptosis. However, the mechanism by which the parasite triggers the activation of NF-kappaB remains enigmatic. In the present study, we biochemically characterized a novel protein, which we termed TpSCOP (T. parvaschizont-derived cytoskeleton-binding protein), which is expressed in the schizont stage of T. parva. TpSCOP was shown to interact with F-actin in vitro. Expression of TpSCOP in a murine lymphocytic cell line resulted in the activation of NF-kappaB signaling pathways, leading to apoptosis resistance. The activation of mitogen-activated protein kinase (MAPK), including extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), was also detected. Furthermore, the introduction of TpSCOP into T. parva-infected cells also enhanced the activation of NF-kappaB. This is the first report to demonstrate that a parasite-derived molecule has the ability to activate the host NF-kappaB pathway. Based on these results, TpSCOP likely plays an important role in apoptosis inhibition during Theileria infection.

Melatonin protects CD4+ T cells from activation-induced cell death by blocking NFAT-mediated CD95 ligand upregulation

Over the past 20 y, the hormone melatonin was found to be produced in extrapineal sites, including cells of the immune system. Despite the increasing data regarding the biological effects of melatonin on the regulation of the immune system, the effect of this molecule on T cell survival remains largely unknown. Activation-induced cell death plays a critical role in the maintenance of the homeostasis of the immune system by eliminating self-reactive or chronically stimulated T cells. Because activated T cells not only synthesize melatonin but also respond to it, we investigated whether melatonin could modulate activation-induced cell death. We found that melatonin protects human and murine CD4(+) T cells from apoptosis by inhibiting CD95 ligand mRNA and protein upregulation in response to TCR/CD3 stimulation. This inhibition is a result of the interference with calmodulin/calcineurin activation of NFAT that prevents the translocation of NFAT to the nucleus. Accordingly, melatonin has no effect on T cells transfected with a constitutively active form of NFAT capable of migrating to the nucleus and transactivating target genes in the absence of calcineurin activity. Our results revealed a novel biochemical pathway that regulates the expression of CD95 ligand and potentially other downstream targets of NFAT activation.

TNF-related apoptosis-inducing ligand (TRAIL): a new path to anti-cancer therapies

Since its discovery in 1995, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a member of the tumor necrosis factor super family, has been under intense focus because of its remarkable ability to induce apoptosis in malignant human cells while leaving normal cells unscathed. Consequently, activation of the apoptotic signaling pathway from the death-inducing TRAIL receptors provides an attractive, biologically-targeted approach to cancer therapy. A great deal of research has focused on deciphering the TRAIL receptor signaling cascade and intracellular regulation of this pathway, as many human tumor cells possess mechanisms of resistance to TRAIL-induced apoptosis. This review focuses on the current state of knowledge regarding TRAIL signaling and resistance, the preclinical development of therapies targeted at TRAIL receptors and modulators of the pathway, and the results of clinical trials for cancer treatment that have emerged from this base of knowledge. TRAIL-based approaches to cancer therapy vary from systemic administration of recombinant, soluble TRAIL protein with or without the combination of traditional chemotherapy, radiation or novel anti-cancer agents to agonistic monoclonal antibodies directed against functional TRAIL receptors to TRAIL gene transfer therapy. A better understanding of TRAIL resistance mechanisms may allow for the development of more effective therapies that exploit this cell-mediated pathway to apoptosis.

Role of the Fas/FasL pathway in HIV or SIV disease

Human immunodeficiency virus disease involves progressive destruction of host immunity leading to opportunistic infections and increased rates for malignancies. Both depletion in immune cell numbers as well as defects in their effector functions are responsible for this immunodeficiency The broad impact of HIV reflects a similarly broad pattern of cell depletion including subsets that do not express viral receptors or support viral replication. Indirect cell killing, the destruction of uninfected cells, is due partly to activation of the Fas/FasL system for cell death. This death-signaling pathway is induced during HIV disease and contributes significantly to viral pathogenesis and disease.

Generation of NO by bystander human CD8 T cells augments allogeneic responses by inhibiting cytokine deprivation-induced cell death

Nitric oxide (NO), generated by inducible NO synthase (iNOS) in bystander human CD8 T cells, augments the accumulation of allogeneically activated human CD8 T cells in vitro and in vivo. Here, we report that iNOS-derived NO does not affect T-cell proliferation but rather inhibits cell death of activated human CD8 T cells after activation by allogeneic endothelial cells in culture. Exogenous NO did not affect activation-induced cell death of human CD8 T cells but specifically reduced death of activated T cells due to cytokine deprivation. NO-mediated inhibition of T-cell death did not involve cGMP signaling, and NO did not affect the expression of Bcl-2-related proteins known to regulate cytokine deprivation-induced cell death. However, NO inhibited the activity of caspases activated as a consequence of cytokine deprivation in activated T cells. This protective effect correlated with S-nitrosylation of caspases and was phenocopied by z-VAD.fmk and z-LEHD.fmk, pharmacological inhibitors of caspases. In summary, our findings indicate that NO augments the accumulation of activated human T cells principally by inhibiting cytokine deprivation-induced cell death through S-nitrosylation of caspases.

Tubular cell HIV-1 gp120 expression induces caspase 8 activation and apoptosis

Renal biopsy data indicate that tubular epithelial cells serve as a reservoir for HIV-1 infection. We studied the effect of HIV-1 gp120 envelope gene expression on tubular cell apoptosis. HIV-1 gp120 was expressed in a lentiviral vector pHR-CMV-IRES2-EGFP-DeltaB. This plasmid construct was used to produce pseudotyped virus using VSV-G envelope to enhance the tropism for efficient viral transduction. Human proximal tubular (HK-2) cells were transduced and assayed for cellular injury by trypan blue exclusion, Hoechst and PI staining, TUNEL, and cell cycle staging. HIV-1 gp120-transduced HK-2 cells showed cellular injury in a time-dependent manner. Gp120-transduced cells showed 2.5-fold greater apoptosis when compared with vector-transduced cells. Cell cycle analysis did not reveal any alteration between gp120-transduced cells and vector-transduced cells. Gp120-transduced cells showed higher expression of both Fas and FasL, whereas pretreatment with anti-FasL antibody partially inhibited gp120-induced tubular cell apoptosis. Similarly, pretreatment with caspase-8 inhibitor attenuated gp120-induced HK2 cell apoptosis. Moreover, gp120-transduced cells showed activation of caspase 8. These results suggest that HIV-1 gp120 expression induces tubular cell apoptosis through the extrinsic pathway by enhancing Fas and FasL expression and activation of caspase-8.

CD95, BIM and T cell homeostasis

The relative importance of the intrinsic and extrinsic apoptotic pathways in the control of haematopoietic cell homeostasis has been a matter of debate for many years. Cell death is omnipresent in this cellular compartment and ensures the removal of cells that are not properly equipped to assume their function as well as those that have assumed function but are no longer required. In this Review we focus on the roles of CD95 (also known as FAS) and BCL-2-interacting mediator of cell death (BIM), two major regulators of apoptosis in T cell homeostasis, with a particular emphasis on their cooperation in the shutdown of T cell responses.

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.

Malignant catarrhal fever of cattle is associated with low abundance of IL-2 transcript and a predominantly latent profile of ovine herpesvirus 2 gene expression

Background

Malignant catarrhal fever (MCF) is a lethal disease of cattle, characterized by vasculitis, necrosis, and accumulation of activated, dysregulated cytotoxic lymphocytes in various tissues. Ovine gamma herpesvirus 2 (OvHV-2) is a causative agent of MCF, which may trigger the disease through immunopathogenic pathways. Lymphocytes are the main target of the virus. However, the pathogenic basis of the disease is still mysterious.

Methods/Findings

We hypothesized that the gene expression patterns of OvHV-2 and the relative abundances of host cell transcripts in lymphnodes may be used to identify pathways that help to explain the pathogenesis of MCF. Therefore, viral and host cell gene expression patterns in lymph nodes of animals with MCF and healthy controls were analyzed by microarray. Two regions on the viral genome were transcriptionally active, one encoding an orthologue to the latency-associated nuclear antigen (ORF73) of other gamma herpesviruses, the other with no predicted open reading frame. A vast number of transcripts related to inflammatory processes, lymphocyte activation, cell proliferation and apoptosis were detected at different abundances. However, the IL-2 transcript was eminent among the transcripts, which were, compared to healthy controls, less abundant in animals with MCF. The ratio between CD4- and CD8-positive T-lymphocytes was decreased in the lymphnodes of animals with MCF compared to healthy controls. In contrast, the same ratio was stable, when peripheral blood lymphocytes were analyzed.

Conclusions/Significance

The phenotype of mice with a deficient IL-2-system almost perfectly matches the clinical signs observed in cattle with MCF, which feature a significantly decreased IL-2 transcript abundance, compared to healthy cattle. This supports the hypothesis that immunopathogenic events are linked to the pathogenesis of MCF. IL-2-deficiency may play an important role in the process. Therefore, this work opens new avenues for research on MCF.

Oxidized LDL modulates apoptosis of regulatory T cells in patients with ESRD

Increased levels of oxidized low-density lipoproteins (oxLDL) contribute to the increased risk for atherosclerosis, which persists even after adjusting for traditional risk factors, among patients with ESRD. Regulatory T cells (CD4+/CD25+ Tregs), which down-regulate T cell responses to foreign and self-antigens, are protective in murine atherogenesis, but whether similar immunoregulation occurs in humans with ESRD is unknown. Because cellular defense systems against oxLDL involve proteolytic degradation, the authors investigated the role of oxLDL on proteasome activity of CD4+/CD25+ Tregs in patients with ESRD. CD4+/CD25+ Tregs isolated from uremic patients' peripheral blood, especially that of chronically hemodialyzed patients, failed to suppress cell proliferation, exhibited cell-cycle arrest, and entered apoptosis by altering proteasome activity. Treating CD4+/CD25+ Tregs with oxLDL or uremic serum ex vivo decreased the number and suppressive capacity of CD4+/CD25+ Tregs. In vitro, oxLDL promoted the accumulation of p27Kip1, the cyclin-dependent kinase inhibitor responsible for G1 cell cycle arrest, and increased apoptosis in a time- and concentration-dependent manner. In summary, proteasome inhibition by oxLDL leads to cell cycle arrest and apoptosis, dramatically affecting the number and suppressive capacity of CD4+/CD25+ Tregs in chronically hemodialyzed patients. This response may contribute to the immune dysfunction, microinflammation, and atherogenesis observed in patients with ESRD.

FasL cross-linking inhibits activation of human peripheral T cells

Activation of resting T cells in vitro is triggered by combined TCR and CD28 engagement and can be modulated by simultaneous ligation of various other surface receptors. Although the Fas ligand (FasL) is best known for its capacity to initiate cell death in Fas-bearing cells, it has recently been implicated in the regulation of T cell activation. Thus, a cross-talk between the TCR and FasL is likely, but far from being biochemically elucidated. We now report that FasL engagement by immobilized but not soluble FasFc fusion protein and anti-FasL polyclonal antibody blocks the activation of human peripheral T cells even in the presence of CD28 co-stimulation. The data presented here stress the importance of the Fas/FasL system for signal initiation via the TCR-CD3 complex and provide further arguments for a retrograde signaling capacity of FasL or a crucial role of Fas as a co-stimulatory molecule.

The many roles of FAS receptor signaling in the immune system

FAS belongs to the subgroup of the tumor necrosis factor receptor (TNF-R) family that contains an intracellular "death domain" and triggers apoptosis. Its physiological ligand FASL is a member of the TNF cytokine family. Studies with mutant mice and cells from human patients have shown that FAS plays critical roles in the immune system, including the killing of pathogen-infected cells and the death of obsolete and potentially dangerous lymphocytes. Fas thereby functions as a guardian against autoimmunity and tumor development. FAS triggers apoptosis through FADD-mediated recruitment and activation of caspase-8. In certain cells such as hepatocytes, albeit not lymphocytes, FAS-induced apoptosis requires amplification through proteolytic activation of the proapoptotic BCL-2 family member BID. Curiously, several components of the FAS signaling machinery have been implicated in nonapoptotic processes, including cellular activation, differentiation, and proliferation. This review describes current understanding of Fas-induced apoptosis signaling and proposes experimental strategies for future advances.

Immunology of mercury

The heavy metal mercury is ubiquitously distributed in the environment resulting in permanent low-level exposure in human populations. Mercury can be encountered in three main chemical forms (elemental, inorganic, and organic) which can affect the immune system in different ways. In this review, we describe the effects of these various forms of mercury exposure on immune cells in humans and animals. In genetically susceptible mice or rats, subtoxic doses of mercury induce the production of highly specific autoantibodies as well as a generalized activation of the immune system. We review studies performed in this model and discuss their implications for the role of environmental chemicals in human autoimmunity.

NF-kappa B modulates sensitivity to apoptosis, proinflammatory and migratory potential in short- versus long-term cultured human gamma delta lymphocytes

Vgamma9 Vdelta2 T lymphocytes are involved in the immune response against hematological malignancies and certain pathogens through the recognition of nonpeptidic Ags expressed by tumors and infected cells. Being equipped with proinflammatory chemokine receptors, they participate to the early phases of inflammation acting as both effector and connector cells between innate and adaptive immunity. We show in this study that after initial TCR triggering short- and long-term cultured gammadelta lymphocytes differ in their susceptibility to activation-induced apoptosis and proinflammatory phenotype. Activation-induced apoptosis was triggered by anti-CD95 mAbs or by the gammadeltaTCR stimuli isopentenyl pyrophosphate and pamidronate, the latter in the presence of monocytes. In particular, short-term cultured cells are resistant to apoptosis and characterized by expression of anti-apoptotic cellular FLIP molecules and partial spontaneous caspase-8 activation. Linked to this behavior, short-term gammadelta cells display constitutive activation of the transcription factor NF-kappaB, which is functionally related to their apoptosis-resistant phenotype. Finally, they spontaneously secreted elevated amounts of the NF-kappaB-regulated chemokines CCL3, CCL4, and CCL5, which likely contributed to down-modulation of the inflammatory CCR5 receptor. Conversely, long-term cultured apoptosis-sensitive gammadelta cells displayed uncleaved caspase-8 and no constitutive NF-kappaB activation; moreover, they secreted CC chemokines only upon TCR triggering coupled to the re-expression of CCR5. The expression of members of the TNF receptor family, including CD30 and TNFRII, also varied according to the time in culture. Altogether our data support a link between resistance to apoptosis and a proinflammatory phenotype in gammadelta T lymphocytes, unraveling the crucial role of NF-kappaB in regulating the switch from resistance to apoptosis susceptibility.

Umbilical cord blood T cells express multiple natural cytotoxicity receptors after IL-15 stimulation, but only NKp30 is functional

The natural cytotoxicity receptors (NCRs) NKp30, NKp44, and NKp46 are thought to be NK lineage restricted. Herein we show that IL-15 induces NCR expression on umbilical cord blood (UCB) T cells. NCRs were mainly on CD8(+) and CD56(+) UCB T cells. Only NKp30 was functional as demonstrated by degranulation, IFN-gamma release, redirected killing, and apoptosis. Since NCRs require adaptor proteins for function, the expressions of these adaptors were determined. The adaptors used by NKp30 and NKp46, FcepsilonR1gamma and CD3zeta, were detected in UCB T cells. There was a near absence of DAP12, the adaptor for NKp44, consistent with a hypofunctional state. NKp46 was on significantly fewer UCB T cells, possibly accounting for its lack of function. Adult peripheral blood (PB) T cells showed minimal NCR acquisition after culture with IL-15. Since UCB contains a high frequency of naive T cells, purified naive T cells from adult PB were tested. Although NKp30 was expressed on a small fraction of naive PB T cells, it was nonfunctional. In contrast to UCB, PB T cells lacked FcepsilonR1gamma expression. These results demonstrate differences between UCB and PB T cells regarding NCR expression and function. Such findings challenge the concept that NCRs are NK cell specific.

Umbilical cord blood T cells express multiple natural cytotoxicity receptors after IL-15 stimulation, but only NKp30 is functional

The natural cytotoxicity receptors (NCRs) NKp30, NKp44, and NKp46 are thought to be NK lineage restricted. Herein we show that IL-15 induces NCR expression on umbilical cord blood (UCB) T cells. NCRs were mainly on CD8(+) and CD56(+) UCB T cells. Only NKp30 was functional as demonstrated by degranulation, IFN-gamma release, redirected killing, and apoptosis. Since NCRs require adaptor proteins for function, the expressions of these adaptors were determined. The adaptors used by NKp30 and NKp46, FcepsilonR1gamma and CD3zeta, were detected in UCB T cells. There was a near absence of DAP12, the adaptor for NKp44, consistent with a hypofunctional state. NKp46 was on significantly fewer UCB T cells, possibly accounting for its lack of function. Adult peripheral blood (PB) T cells showed minimal NCR acquisition after culture with IL-15. Since UCB contains a high frequency of naive T cells, purified naive T cells from adult PB were tested. Although NKp30 was expressed on a small fraction of naive PB T cells, it was nonfunctional. In contrast to UCB, PB T cells lacked FcepsilonR1gamma expression. These results demonstrate differences between UCB and PB T cells regarding NCR expression and function. Such findings challenge the concept that NCRs are NK cell specific.

c-FLIP protects mature T lymphocytes from TCR-mediated killing

Although c-FLIP has been identified as an important player in the extrinsic (death receptor-induced) apoptosis pathway, its endogenous function in mature T lymphocytes remains undefined. c-FLIP may inhibit or promote T cell death as previous data demonstrate that the c-FLIP(L) isoform can promote or inhibit caspase 8 activation while the c-FLIP(S) isoform promotes or inhibits T cell death when overexpressed. Although the c-FLIP(R) isoform inhibits cell death in cell lines, its function in T cells remains unknown. To investigate the function of c-FLIP in mature T cells, we have generated several genetic mouse models with c-FLIP or its individual isoforms deleted in mature T cells. Surprisingly, we found that c-FLIP protects mature T cells not only from apoptosis induced by the death receptors Fas and TNFR but also from TCR-mediated and spontaneous apoptosis. Thus, c-FLIP plays an essential role in protecting mature T cells from a death signal induced through the TCR itself and is required for naive T cell survival. Our results demonstrate that c-FLIP functions beyond the extrinsic death pathway.

Critical role for BIM in T cell receptor restimulation-induced death

BACKGROUND

Upon repeated or chronic antigen stimulation, activated T cells undergo a T cell receptor (TCR)-triggered propriocidal cell death important for governing the intensity of immune responses. This is thought to be chiefly mediated by an extrinsic signal through the Fas-FasL pathway. However, we observed that TCR restimulation still potently induced apoptosis when this interaction was blocked, or genetically impaired in T cells derived from autoimmune lymphoproliferative syndrome (ALPS) patients, prompting us to examine Fas-independent, intrinsic signals.

RESULTS

Upon TCR restimulation, we specifically noted a marked increase in the expression of BIM, a pro-apoptotic Bcl-2 family protein known to mediate lymphocyte apoptosis induced by cytokine withdrawal. In fact, T cells from an ALPS type IV patient in which BIM expression is suppressed were more resistant to restimulation-induced death. Strikingly, knockdown of BIM expression rescued normal T cells from TCR-induced death to as great an extent as Fas disruption.

CONCLUSION

Our data implicates BIM as a critical mediator of apoptosis induced by restimulation as well as growth cytokine withdrawal. These findings suggest an important role for BIM in eliminating activated T cells even when IL-2 is abundant, working in conjunction with Fas to eliminate chronically stimulated T cells and maintain immune homeostasis.

REVIEWERS

This article was reviewed by Dr. Wendy Davidson (nominated by Dr. David Scott), Dr. Mark Williams (nominated by Dr. Neil Greenspan), and Dr. Laurence C. Eisenlohr.

Mechanism of nuclear factor of activated T-cells mediated FasL expression in corticosterone -treated mouse Leydig tumor cells

BACKGROUND

Fas and FasL is important mediators of apoptosis. We have previously reported that the stress levels of corticosterone (CORT, glucocorticoid in rat) increase expression of Fas/FasL and activate Fas/FasL signal pathway in rat Leydig cells, which consequently leads to apoptosis. Moreover, our another study showed that nuclear factor of activated T-cells (NFAT) may play a potential role in up-regulation of FasL during CORT-treated rat Leydig cell. It is not clear yet how NFAT is involved in CORT-induced up-regulation of FasL. The aim of the present study is to investigate the molecular mechanisms of NFAT-mediated FasL expression in CORT-treated Leydig cells.

RESULTS

Western blot analysis showed that NFAT2 expression is present in mouse Leydig tumor cell (mLTC-1). CORT-induced increase in FasL expression in mLTC-1 was ascertained by Western Blot analysis and CORT-induced increase in apoptotic frequency of mLTC-1 cells was detected by FACS with annexin-V labeling. Confocal imaging of NFAT2-GFP in mLTC-1 showed that high level of CORT stimulated NFAT translocation from the cytoplasm to the nucleus. RNA interference-mediated knockdown of NFAT2 significantly attenuated CORT-induced up-regulation of FasL expression in mLTC. These results corroborated our previous finding that NFAT2 is involved in CORT-induced FasL expression in rat Leydig cells and showed that mLTC-1 is a suitable model for investigating the mechanism of CORT-induced FasL expression. The analysis of reporter constructs revealed that the sequence between -201 and +71 of mouse FasL gene is essential for CORT-induced FasL expression. The mutation analysis demonstrated that CORT-induced FasL expression is mediated via an NFAT binding element located in the -201 to +71 region. Co-transfection studies with an NFAT2 expression vector and reporter construct containing -201 to +71 region of FasL gene showed that NFAT2 confer a strong inducible activity to the FasL promoter at its regulatory region. In addition, chromatin immunoprecipitation assay further confirmed the results of reporter gene studies by showing the specific binding of NFAT2 to the -201 to +71 region.

CONCLUSION

In the present study, we demonstrated that NFAT2 directly stimulates transcription of FasL in high level CORT-treated mLTC-1. In conclusion, the present study provides further evidence for our finding that CORT-induced FasL expression in Leydig cells is mediated by NFAT.

Attenuated disease in SIV-infected macaques treated with a monoclonal antibody against FasL

Acute SIVmac infection in macaques is accompanied by high levels of plasma viremia that decline with the appearance of viral immunity and is a model for acute HIV disease in man. Despite specific immune responses, the virus establishes a chronic, persistent infection. The destruction of CD4+ and CD4- lymphocyte subsets in macaques contributes to viral persistence and suggests the importance of mechanisms for depleting both infected and uninfected (bystander) cells. Bystander cell killing can occur when FasL binds the Fas receptor on activated lymphocytes, which include T and B cell subpopulations that are responding to the infection. Destruction of specific immune cells could be an important mechanism for blunting viral immunity and establishing persistent infection with chronic disease. We inhibited the Fas pathway in vivo with a monoclonal antibody against FasL (RNOK203). Here we show that treatment with anti-FasL reduced cell death in circulating T and B cells, increased CTL and antibody responses to viral proteins, and lowered the setpoint viremia. By blocking FasL during only the first few weeks after infection, we attenuated SIVmac disease and increased the life span for infected and treated macaques.

BH3-only protein Puma contributes to death of antigen-specific T cells during shutdown of an immune response to acute viral infection

During acute T cell immune responses to viral infection, antigen-specific T cells first proliferate and differentiate into effector cells, but after pathogen clearance most are deleted by apoptosis. The developmentally programmed death of antigen-specific T cells during shutdown of a T cell response is mediated by the Bcl-2-regulated apoptotic pathway and partly depends on the proapoptotic BH3-only protein Bim. However, loss of Bim enhanced survival of antigen-activated T cells to a lesser extent than Bcl-2 overexpression, indicating that other proapoptotic factors must contribute to T cell killing. In this study, we investigated the contributions of several BH3-only proteins to the shutdown of an acute T cell immune response in vivo. After infection with human herpes simplex virus (HSV-1), mice lacking Noxa, Bid, or Bad had a normal increase and subsequent decline in the numbers of antigen-specific CD8(+) T cells. In contrast, Puma-deficient mice showed an abnormally prolonged persistence of antigen-specific CD8(+) T cells in the spleen, associated with enhanced in vitro survival of these cells in the absence of cytokines. Puma was dispensable for viral clearance and also did not play a role in proliferation or activation of HSV-1-specific CD8(+) T cells in vivo. Collectively, these findings show that Puma contributes to the death of antigen-specific T cells during shutdown of an immune response.

Fas ligand expression in glioblastoma cell lines and primary astrocytic brain tumors

Fas/APO-1 (CD95) is a cell surface receptor that mediates apoptosis when it reacts with Fas ligand (FasL) or Fas antibody. We previously reported that Fas expression is predominantly induced in perinecrotic glioma cells, suggesting that Fas induction is associated with apoptosis and necrosis formation, a histological hallmark of glioblastomas. In this study, we assessed the expression of FasL in 10 glioblastoma cell lines and in 14 astrocytic brain tumors (three low-grade astrocytomas and 11 glioblastomas). Reverse transcriptase (RT)-PCR revealed that all glioblastoma cell lines and primary astrocytic brain tumors express FasL. Immunohistochemically, FasL was predominantly expressed on the plasma membrane of glioma cells. These results suggest that FasL expression is common in human astrocytic brain tumors and may cause apoptosis of glioma cells if Fas expression is induced.

Cytokine-induced killer cells targeted by the novel bispecific antibody CD19xCD5 (HD37xT5.16) efficiently lyse B-lymphoma cells

Due to their dual binding capacity, bispecific antibodies (bsAb) can be used to cross-link cytotoxic effector cells with malignant targets and may thereby improve adoptive immunotherapy. In this study, the development and preclinical testing of the quadroma-derived bsAb HD37xT5.16 of the specificity CD19xCD5 is reported. Effector cells used were a population of ex vivo expanded and activated T cells called cytokine-induced killer (CIK) cells expressing CD5. When combined with CIK cells, the cytolytic potency of HD37xT5.16 against CD19 positive B cell lymphoma lines was comparable to that observed with a previously described CD19xCD3 bsAb. Further on, we could demonstrate that bsAb CD19xCD5, in contrast to its CD3-binding counterpart, does not induce proliferation of resting T cells and causes only little activation-induced cell death. Therefore, this novel bsAb binding effector T cells via CD5 may be particularly useful in combination with adoptive transfer of ex vivo activated T cells, e.g., in the setting of adoptive immunotherapy after allogeneic stem cell transplantation. The in vitro studies outlined here support the experimental use of bsAb HD37xT5.16 in preclinical in vivo models for evaluation of its safety and efficacy profile.

What do we know about the mechanisms of elimination of autoreactive T and B cells and what challenges remain

Tolerance to self-antigens within the adaptive immune system is safeguarded, at least in part, through deletion of autoreactive T and B lymphocytes. This deletion can occur during the development of these cells in primary lymphoid organs, the thymus or bone marrow, respectively, or at the mature stage in peripheral lymphoid tissues. Deletion of autoreactive lymphocytes is achieved to a large extent through apoptotic cell death. This review describes current understanding of the mechanisms that mediate apoptosis of autoreactive lymphocytes during their development in primary lymphoid organs and during their activation in the periphery. In particular, we discuss the roles of the proapoptotic Bcl-2 family member Bim and the small family of Nur77-related transcriptional regulators in lymphocyte negative selection. Finally, we speculate on the processes that may lead to the activation of Bim when antigen receptors are activated on autoreactive T or B cells.

Treating autoimmune demyelination by augmenting lymphocyte apoptosis in the central nervous system

The elimination of autoreactive T cells from the central nervous system (CNS) by apoptosis plays an important role in switching off autoimmune attack. B-cell apoptosis in the CNS probably also has a key role in downregulating autoimmunity. Augmenting lymphocyte apoptosis in the CNS is a potential strategy for treating autoimmune CNS diseases such as multiple sclerosis. These strategies involve modulation of the physiological pro-apoptotic and anti-apoptotic pathways that control lymphocyte fate in the CNS. In the case of T cells, apoptosis can be augmented by enhancing activation-induced T-cell apoptosis through the CD95 (Fas) pathway and by inhibiting costimulation-induced anti-apoptotic pathways mediated through BCL-2 and BCL-X L.

Fas/Fas-L expression, apoptosis and low proliferative response are associated with heart failure in patients with chronic Chagas' disease

Chagas' disease affects 16-18 million patients in South America and heart involvement is the major cause of morbidity and mortality. Heart failure is the most severe clinical manifestation of the chronic phase of infection with Trypanosoma cruzi. The intensity and nature of the immune response is associated with the clinical outcome of the disease. In murine models, a low proliferative response and T-cell apoptosis have been observed during acute infection. In the present study the immune response of patients in the chronic phase of infection was analyzed. Patients were divided into: (a) asymptomatic, i.e., without involvement of the heart or digestive system; and (b) with heart failure. Patients with heart failure presented a significantly lower peripheral blood mononuclear cell (PBMC) proliferative response to T. cruzi antigens compared to asymptomatic patients. This low response was associated with antigen-induced apoptosis. Apoptosis of PBMC and a low proliferative response were also associated with double Fas/Fas-L expression and high production of TNF-alpha, a cytokine known to induce programmed cell death. These results suggest that apoptosis of PBMC, probably triggered by double expression of Fas/Fas-L and TNF-alpha, is implicated in the immune regulatory mechanism during the chronic phase of Chagas' disease.