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

Mechanisms of apoptosis of T-cells in human tuberculosis

The role of TGF-beta TNF-alpha FasL and Bcl-2 in apoptosis of CD4 T-cells during active TB was studied. Coculture of PBMC from TB patients with neutralizing antibodies to TGF-beta or TNF-alpha decreased spontaneous (P < or = 0.05) and MTB-induced (P < or = 0.02) T-cell apoptosis by 50-90%, but effects were not additive. Interestingly, only levels of TGF-beta in supernatants correlated with rates of spontaneous and MTB-induced apoptosis. FasL surface and mRNA expression were higher in unstimulated and MTB-stimulated PBMC from patients than controls, and neutralization of FasL abrogated apoptosis of T-cells from patients only. Intracellular Bcl-2 protein was lower among unstimulated CD4 T-cells from patients than those from controls (P < or = 0.02), and MTB stimulation reduced intracellular Bcl-2 content in CD4 T-cells from patients only (P < or = 0.001). These findings may indicate that, during TB, predisposition of CD4 T-cells to apoptosis may involve both low expression of Bcl-2, and excessive expression of TGF-beta TNF-alpha and FasL.

Immune Modulation after Total Hip Surgery

BACKGROUND

Major trauma affects the immune system, and immunosuppression may render the patients susceptible to septic complications. The purpose of this study was to investigate lipopolysaccharide (LPS)-induced releases of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) in whole blood in patients undergoing total hip replacement.

METHODS

Seven patients (6 females) who underwent elective total hip replacement were included. Ex vivo LPS-induced releases of TNF-alpha and IL-6 were measured in a whole blood assay at days 1, 6, 9 and 12 postoperatively, using low- and high-dose LPS incubation. At the same time, white blood cell counts were analyzed.

RESULTS

The amount of TNF-alpha release was significantly reduced at days 6 and 12. Compared to monocyte counts, TNF-alpha release was significantly decreased also at day 9 in low- and high-dose LPS stimulation. IL-6 in plasma was significantly increased at day 1 and normalized thereafter. There were no differences in LPS-induced IL-6 levels compared to the levels before surgery.

CONCLUSION

This in vivo/ex vivo study shows a reduced capacity of whole blood to release LPS-induced TNF-alpha at day 6 through to day 12 after major orthopedic surgery. Attenuated TNF-alpha release may contribute to an increased postoperative susceptibility to gram-negative sepsis.

The critical role of protein kinase C-theta in Fas/Fas ligand-mediated apoptosis

A functional immune system not only requires rapid expansion of antigenic specific T cells, but also requires efficient deletion of clonally expanded T cells to avoid accumulation of T cells. Fas/Fas ligand (FasL)-mediated apoptosis plays a critical role in the deletion of activated peripheral T cells, which is clearly demonstrated by superantigen-induced expansion and subsequent deletion of T cells. In this study, we show that in the absence of protein kinase C-theta (PKC-theta), superantigen (staphylococcal enterotoxin B)-induced deletion of Vbeta8(+) CD4(+) T cells was defective in PKC-theta(-/-) mice. In response to staphylococcal enterotoxin B challenge, up-regulation of FasL, but not Fas, was significantly reduced in PKC-theta(-/-) mice. PKC-theta is thus required for maximum up-regulation of FasL in vivo. We further show that stimulation of FasL expression depends on PKC-theta-mediated activation of NF-AT pathway. In addition, PKC-theta(-/-) T cells displayed resistance to Fas-mediated apoptosis as well as activation-induced cell death (AICD). In the absence of PKC-theta, Fas-induced activation of apoptotic molecules such as caspase-8, caspase-3, and Bid was not efficient. However, AICD as well as Fas-mediated apoptosis of PKC-theta(-/-) T cells were restored in the presence of high concentration of IL-2, a critical factor required for potentiating T cells for AICD. PKC-theta is thus required for promoting FasL expression and for potentiating Fas-mediated apoptosis.

Activation-induced cell death of human melanoma specific cytotoxic T lymphocytes is mediated by apoptosis-inducing factor

Activation-induced cell death (AICD) of T cells can be an impediment towards achieving a robust and long-lived cytolytic T lymphocyte (CTL) response from active specific immunization or after adoptive cell transfer in cancer immunotherapy. The mechanism of AICD in primary CTL, however, remains poorly understood. It is widely believed that AICD is driven by signals from death receptors (DR) and that the cell death takes place in a caspase-dependent manner, although it has been shown that AICD of T cells can be induced by internal triggers and that death takes place in a caspase-independent manner. We show here that AICD in human melanoma epitope-specific primary CTL involves selective mitochondrio-nuclear translocation of the apoptosis inducing factor (AIF) without cytochrome c release, caspase-3 and caspase-8 activation, and results from large-scale DNA fragmentation. The c-jun-N terminal kinase (JNK) inhibitor, SP600125, blocks the mitochondrio-nuclear translocation of AIF and prevents AICD in these CTL. These findings suggest that the AICD in human melanoma epitope specific primary CTL is mediated by mitochondrial AIF release and JNK is involved in regulation of this death process.

Cyclosporin A abolishes CD28-mediated resistance to CD95-induced apoptosis via superinduction of caspase-3

Costimulation of T cells via CD28 promotes both proliferation and resistance to apoptosis. In this study, we show that the immunosuppressive drug cyclosporin A (CsA) fully reverses resistance to CD95-mediated cell death after TCR/CD28 costimulation or superagonistic anti-CD28 mAb stimulation of primary rat lymph node T cells. This effect correlated with a pronounced superinduction of caspase-3 on both mRNA and protein levels, whereas its main antagonist, X chromosome-linked inhibitor of apoptosis, was unaffected by inclusion of CsA. Apoptosis triggered by CD95 cross-linking was characterized by robust caspase-3 activation. Furthermore, CsA sensitization to CD95-mediated apoptosis of CD28-activated T cells did not alter mRNA stability of superinduced caspase-3 mRNA, suggesting a transcriptional regulation of the caspase-3 gene. Addition of Ca(2+) ionophores to TCR/CD28 or superagonistic CD28-stimulated cells reduced caspase-3 levels, further supporting a role for Ca(2+)-dependent signaling pathways in negatively regulating caspase-3. Taken together, these findings suggest that CsA promotes sensitivity to CD95-mediated apoptosis in CD28-stimulated T cells by superinduction of the caspase-3 gene via a mechanism involving suppression of the calcineurin pathway.

Oxidized Low-Density Lipoproteins Activate CD4+T Cell Apoptosis in Patients with End-Stage Renal Disease through Fas Engagement

Oxidized LDL (oxLDL) are cytotoxic to vascular cells, but their possible toxic action on T cells from patients with ESRD has not been evaluated. oxLDL concentrations were measured and compared in patients who were on long-term hemodialysis (HD), in patients who had ESRD and were on continuous ambulatory peritoneal dialysis, in nondialyzed patients with chronic kidney disease, and in age- and gender-matched control subjects. In parallel, the proliferative capacity of CD69+/CD4+ T cells and their rate of apoptosis, IL-2 expression, and intracellular expression of Bcl-2 and Bax were determined in vitro. The oxLDL concentrations were significantly higher in HD patients (all P = 0.001). Upon phytohemagglutinin stimulation, CD69+/CD4+ T cells from HD patients proliferated significantly less than those from the other patients' group (both P < 0.001). oxLDL but not the native LDL were led to CD69+/CD4+ T cells' program cell death in a dosage- and time-dependent manner through Fas pathway (P = 0.001). Cell surface Fas expression was followed by DNA fragmentation when CD69+/CD4+ T cells from HD patients or control subjects were cultured with oxLDL (200 microg/ml; 31 +/- 3 versus 25 +/- 3%; P = 0.001). In the presence of oxLDL, CD69+/CD4+ T cells from HD patients expressed significantly lower IL-2 levels, which strongly correlated with a decrease in the antiapoptotic Bcl-2 and conversely with an increase in the proapoptotic Bax expression. In conclusion, these data suggest that, in HD patients, exposure of activated CD4+ T cells to oxLDL leads to Fas-mediated apoptosis in association with inhibition of IL-2 expression. Subsequently, this may favor activation of mitochondria-dependent apoptotic pathways, leading to activated CD4+ T cell dysfunction.

Requirement for Daxx in mature T-cell proliferation and activation

The protein Daxx promotes Fas-mediated cell death through activation of apoptosis signal-regulating kinase 1, leading to the activation of the MAPKs JNK and p38. Owing to the in utero lethality of daxx-deficient mice, the in vivo role of Daxx has been so far difficult to analyze. We have generated transgenic mice expressing a dominant-negative form of Daxx (Daxx-DN) in the T-cell lineage. We show that Daxx is recruited to the Fas receptor upon FasL engagement and that Daxx-DN expression protects activated T cells from Fas-induced cell death, by preventing the death-inducing signal complex to be properly formed. Normal lymphocyte development and homeostasis are nevertheless observed. Interestingly, we report that both in vitro and in vivo stimulation of Daxx-DN T-lymphocytes leads to increased proliferative T-cell responses. This increased proliferation is associated with a marked increase in tyrosine phosphorylation of LAT and ZAP70 as Daxx-DN favor their recruitment to the T-cell receptor (TCR) complex. These findings identify Daxx as a critical regulator of T-lymphocyte homeostasis by decreasing TCR-induced cell proliferation and by promoting Fas-mediated cell death.

In vitro generated human memory-like T cells are CD95 type II cells and resistant towards CD95-mediated apoptosis

An adaptive immune response implies expansion of activated T cells and subsequent elimination to maintain homeostasis in a process called activation-induced cell death. Some cells, however, differentiate into memory cells and ensure a strong secondary immune response. To analyze the apoptosis phenotype of memory T cells on a cellular and molecular level, we have established an in vitro model of T cell activation and generation of cells phenotypically and functionally similar to memory cells. These long-term cultured T cells show a CD95-resistant phenotype, although they are still sensitive towards TCR/CD3-mediated apoptosis. Biochemical analysis revealed that these cells shift from CD95 type I (direct signaling from the receptor) during the effector phase to CD95 type II cells (dependent on the mitochondrial amplification loop). Moreover, their mitochondria are protected, probably due to high expression levels of Bcl-x(L) and Bcl-2. Thus, our data suggest a mechanism how memory T cells acquire resistance towards bystander cell death via the CD95 system.

Apoptosis induced in HIV-1-exposed, resting CD4+T cells subsequent to signaling through homing receptors is Fas/Fas ligand-mediated

The hallmark of HIV-1 disease is the gradual disappearance of CD4+ T cells from the blood. The mechanism of this depletion, however, is still unclear. Evidence suggests that lymphocytes die in lymph nodes, not in blood, and that uninfected bystander cells are the predominant cells dying. Our and others' previous studies showed that the lymph node homing receptor, CD62 ligand (CD62L), and Fas are up-regulated on resting CD4+ T cells after HIV-1 binding and that these cells home to lymph nodes at an enhanced rate. During the homing process, signals are induced through various homing receptors, which in turn, induced many of the cells to undergo apoptosis after they entered the lymph nodes. The purpose of this study was to determine how the homing process induces apoptosis in HIV-1-exposed, resting CD4+ T cells. We found that signaling through CD62L up-regulated FasL. This resulted in apoptosis of only HIV-1-presignaled, resting CD4+ T cells, not normal CD4+ T cells. This homing receptor-induced apoptosis could be blocked by anti-FasL antibodies or soluble Fas, demonstrating that the Fas-FasL interaction caused the apoptotic event.

Cutting Edge: Abortive Proliferation of CD46-Induced Tr1-Like Cells due to a Defective Akt/Survivin Signaling Pathway

T regulatory cell 1 (Tr1) are low proliferating peripherally induced suppressive T cells. Engaging CD3 and CD46 on human CD4+ T cells induces a Tr1-like phenotype. In this study, we report that human Tr1-like cells do not sustain proliferation over time. The weak proliferation of these cells results first from their inability to sustain expression of various cell cycle-associated proteins, to efficiently degrade the inhibitor of cell cycle progression p27/Kip1 and, as a consequence, in their accumulation in the G0-G1 phase. Also, the reduced proliferation of Tr1-like cells results from their increased sensitivity to death as they divide, through a mechanism that is neither Fas-mediated nor Bcl2/Bcl-xL related. Both properties, impaired cell cycle and death sensitivity, are explained by a specific defective activation of Akt that impairs the expression of Survivin. Thus, our results show that CD3/CD46-induced Tr1-like cells die through a process of abortive proliferation.

Ex Vivo Soluble Fas Ligand Treatment of Donor Cells to Selectively Reduce Murine Acute Graft Versus Host Disease

BACKGROUND

Allogeneic bone marrow transplantation (BMT) and donor lymphocyte infusion (DLI) provide valuable treatments for a range of diseases. However, the therapeutic utility of BMT and DLI is reduced by the high incidence of graft-versus-host disease (GvHD) mediated by activated donor T lymphocytes directed against recipient alloantigens.

METHODS

Using mouse models, we developed and evaluated a strategy to selectively enhance activation-induced cell death (AICD) of anti-recipient T cells within transplant donor cell populations, with the goal of reducing GvHD. Responder T lymphocytes were incubated ex vivo with irradiated allogenic stimulator cells in a mixed lymphocyte reaction (MLR) in the presence of soluble Fas ligand (sFasL) to induce AICD in alloreactive cells.

RESULTS

This ex vivo sFasL treatment reduced proliferation to the allogeneic stimulator cells in vitro and abrogated acute GvHD capacity in vivo. In contrast, the secondary immune responsiveness of the ex vivo sFasL-treated responder T cells to an unrelated model antigen was preserved. Furthermore, upon adoptive transfer in a DLI model, ex vivo sFasL-treated T cells were able to reject a model tumor. Finally, ex vivo sFasL treatment of bone marrow cells did not reduce their hematopoietic engraftment capacity.

CONCLUSIONS

Thus, ex vivo treatment with sFasL appears to have potential for translation to clinical cell processing of BMT allografts and DLI infusions.

Immunohistochemical detection of CD 95 (Fas) & Fas ligand (Fas-L) in plasma cells of multiple myeloma and its correlation with survival

Multiple myeloma (MM) is a malignant disease resulting from an uncontrolled proliferation of a neoplastic plasma cell clone in the bone marrow, which might also be induced by the loss of control on apoptosis. Fas ligand (Fas-L), a member of the tumor necrosis factor family, induces apoptosis mediated via its transmembrane death receptor Fas (Apo-1/CD95) antigen. In the present study, immunostaining was performed on the initial diagnostic bone marrow biopsies of 36 MM patients (1 stage I, 5 stage II, 30 stage III), to evaluate the distribution of Fas receptor and Fas-L on malignant plasma cells. Both Fas and Fas-L were positive in 13 cases and negative in 3, whereas 10 cases were Fas-negative, Fas-L-positive and 10 were Fas-positive, Fas-L-negative. Although no association was found between the expression of Fas receptor or Fas-L and overall survival, Fas-L positivity was significantly associated with a shorter event-free survival (p = 0.0335). In this study, it has been shown that the expression of Fas-L, in malignant plasma cells of myeloma patients significantly shortens the event-free survival, indicating that the defect in apoptosis might be associated with disease progression in MM.

Selection of anti-double-stranded DNA B cells in autoimmune MRL-lpr/lpr mice

Abs to DNA and nucleoproteins are expressed in systemic autoimmune diseases, whereas B cells producing such Abs are edited, deleted, or inactivated in healthy individuals. Why autoimmune individuals fail to regulate is not well understood. In this study, we investigate the sources of anti-dsDNA B cells in autoimmune transgenic MRL-lpr/lpr mice. These mice are particularly susceptible to lupus because they carry a site-directed transgene, H76R that codes for an anti-DNA H chain. Over 90% of the B cells are eliminated in the bone marrow of these mice, and the few surviving B cells are associated with one of two Vkappa editors, Vkappa38c and Vkappa21D. Thus, it appears that negative selection by deletion and editing are intact in MRL-lpr/lpr mice. However, a population of splenic B cells in the H76R MRL-lpr/lpr mice produces IgG anti-nuclear Abs, and these mice have severe autoimmune organ damage. These IgG Abs are not associated with editors but instead use a unique Vkappa gene, Vkappa23. The H76R/Vkappa23 combination has a relatively high affinity for dsDNA and an anti-nuclear Ab pattern characteristic of lupus. Therefore, this Vkappa gene may confer a selective advantage to anti-DNA Abs in diseased mice.

Perforin, Granzyme B, and fas ligand for molecular diagnosis of acute renal-allograft rejection: analyses on serial biopsies suggest methodological issues

BACKGROUND

The Perforin-Granzyme B and Fas/Fas Ligand apoptotic mechanisms are involved in the development of acute renal rejection (AR). We describe our experience of analyzing the expression of cytotoxic T-lymphotoxins (CTL) in biopsies and peripheral blood leukocytes (PBL) for the diagnosis of AR.

METHODS

We analyzed Perforin (P), Granzyme B (GB) and Fas Ligand (FL) expression in 68 renal biopsies and 64 PBL using comparative kinetic RT-PCR and, for GAPDH and FL, we also replicated with real-time RT-PCR. The levels of expression were measured in different groups, such as T0 (biopsies before reperfusion and PBL in recipient before the transplant [Tx]), Td (biopsies and PBL collected for clinical purposes) and Tp (biopsies and PBL two months after Tx).

RESULTS

A higher CTL expression was seen in non-rejecting (NR) biopsies in the first 2 months after Tx. P and FL were significantly more expressed during AR in all biopsies and in Td, while P remained upregulated in Tp. In PBL, there was no significant increase in CTL transcription during AR. A variable expression of CTL emerged in all T0 biopsies.

CONCLUSIONS

Two lytic pathways are activated in biopsies when AR occurs shortly after Tx, whereas the P/GB mechanism prevails if it occurs later on. Only P and FL in biopsies might be able to predict AR diagnosis, but with a considerable variability in each sample, possibly due to the small portion of tissue core, which may be inadequate for molecular diagnosis. CTL expression in PBL does not correlate with histological AR.

Regulation of Apoptosis by Gram-Positive Bacteria: Mechanistic Diversity and Consequences for Immunity

Apoptosis, or programmed cell death (PCD), is an important physiological mechanism, through which the human immune system regulates homeostasis and responds to diverse forms of cellular damage. PCD may also be involved in immune counteraction to microbial infection. Over the past decade, the amount of research on bacteria-induced PCD has grown tremendously, and the implications of this mechanism on immunity are being elucidated. Some pathogenic bacteria actively trigger the suicide response in critical lineages of leukocytes that orchestrate both the innate and adaptive immune responses; other bacteria proactively prevent PCD to benefit their own survival and persistence. Currently, the microbial virulence factors, which represent the keys to unlocking the suicide response in host cells, are a primary focus of this field. In this review, we discuss these bacterial "apoptosis regulatory molecules" and the apoptotic events they either trigger or prevent, the host target cells of this regulatory activity, and the possible ramifications for immunity to infection. Gram-positive pathogens including Staphylococcus, Streptococcus, Bacillus, Listeria, and Clostridia species are discussed as important agents of human infection that modulate PCD pathways in eukaryotic cells.

Suppression of the cell-mediated immune response by a Fas-immunoglobulin fusion protein

INTRODUCTION

Immunosuppressive agents must not only be effective in impairing the host's allo-immune response, but should also be selective in targeting only those elements of the immune system activated by the allograft. The fact that allo-activated T cells express surface protein molecules that are not typically present on resting T cells can be exploited to specifically target this population. Fas ligand is one such molecule whose cell surface expression on T cells is dramatically up-regulated upon activation.

METHODS

We constructed a murine fusion protein by linking the extracellular domain of Fas to the Fc region of IgG2a. The rationale being to selectively target activated T cells via binding of its Fas moiety to cell surface Fas ligand, and then to allow the Fc moiety to invoke its usual effector mechanisms resulting in the destruction of the allo-activated T cell. Here, we describe the design and expression of Fas-IgG2a and characterize several key in vitro and in vivo properties of this fusion protein including its ability to impact on both cell-mediated immune responses and cellular apoptotic activity using a murine model of delayed-type hypersensitivity.

RESULTS

In vitro, our Fas-IgG2a construct bound activated T cells via FasL and invoked cytotoxicity. In vivo, it demonstrated a prolonged half-life characteristic of an immunoglobulin-like molecule. Most significantly, it suppressed the cell-mediated immune response and diminished cellular apoptotic activity in lymphoid tissue in our murine model.

CONCLUSION

Fas-IgG2a is a novel agent for delivering target-specific immunosuppression with potential applicability in the transplant setting.

Chronic activation in presymptomatic amyotrophic lateral sclerosis (ALS) mice of a feedback loop involving Fas, Daxx, and FasL

The reasons for the cellular specificity and slow progression of motoneuron diseases such as ALS are still poorly understood. We previously described a motoneuron-specific cell death pathway downstream of the Fas death receptor, in which synthesis of nitric oxide (NO) is an obligate step. Motoneurons from ALS model mice expressing mutant SOD1 showed increased susceptibility to exogenous NO as compared with controls. Here, we report a signaling mechanism whereby NO leads to death of mutant, but not control, motoneurons. Unexpectedly, exogenous NO triggers expression of Fas ligand (FasL) in cultured motoneurons. In mutant SOD1(G93A) and SOD1(G85R), but not in control motoneurons, this up-regulation results in activation of Fas, leading through Daxx to phosphorylation of p38 and further NO synthesis. This Fas/NO feedback amplification loop is required for motoneuron death in vitro. In vivo, mutant SOD1(G93A) and SOD1(G85R) mice show increased numbers of positive motoneurons and Daxx nuclear bodies weeks before disease onset. Moreover, FasL up-regulation is reduced in the presence of transgenic dominant-negative Daxx. We propose that chronic low-level activation of the Fas/NO feedback loop may underlie the motoneuron loss that characterizes familial ALS and may help to explain its slowly progressive nature.

Fas ligand is localized to membrane rafts, where it displays increased cell death–inducing activity

Fas ligand (FasL), a member of the TNF protein family, potently induces cell death by activating its matching receptor Fas. Fas-mediated killing plays a critical role in naturally and pathologically occurring cell death, including development and homeostasis of the immune system. In addition to its receptor-interacting and cell death–inducing extracellular domain, FasL has a well-conserved intracellular portion with a proline-rich SH3 domain–binding site probably involved in non-apoptotic functions. We report here that, as with the Fas receptor, a fraction of FasL is constitutively localized in rafts. These dynamic membrane microdomains, enriched in sphingolipids and cholesterol, are important for cell signaling and trafficking processes. We show that FasL is partially localized in rafts and that increased amounts of FasL are found in rafts after efficient FasL/Fas receptor interactions. Raft disorganization after cholesterol oxidase treatment and deletions within the intracellular FasL domain diminish raft partitioning and, most important, lead to decreased FasL killing. We conclude that FasL is recruited into lipid rafts for maximum Fas receptor contact and cell death–inducing potency. These findings raise the possibility that certain pathologic conditions may be treated by altering the cell death–inducing capability of FasL with drugs affecting its raft localization.

Distinct mechanisms control human naive and antigen-experienced CD8+ T lymphocyte proliferation

Human Ag-specific CD8(+) T lymphocytes are heterogeneous and include functionally distinct populations. In this study, we report that at least two distinct mechanisms control the expansion of circulating naive, memory, and effector CD8(+) T lymphocytes when exposed to mitogen or Ag stimulation. The first one leads to apoptosis and occurs shortly after in vitro stimulation. Susceptibility to cell death is prominent among primed T cell subsets, and it is inversely correlated with the size of the ex vivo Bcl-2(high) population within these subsets. Importantly, the Bcl-2(high) phenotype is associated to the proportion of responsive CD8(+) T cells, independently of their differentiation stage. The second one depends on the expression of newly synthesized cyclin-dependent kinase inhibitor p16(INK4a) that occurs in a significant fraction of T cells that had been actively cycling, leading to their cell cycle arrest upon stimulation. Strikingly, accumulation of p16(INK4a) protein preferentially occurs in naive as opposed to primed derived T lymphocytes and is not related to apoptosis. Significant levels of p16 are readily detectable in a small number of ex vivo CD8(+) T cells. Our observations reveal that activation-induced p16 expression represents an alternative process to apoptosis, limiting the proliferation potential of activated naive derived T lymphocytes.

HIV-1 gp120-mediated apoptosis of T cells is regulated by the membrane tyrosine phosphatase CD45

The molecular mechanism of the human immunodeficiency virus type 1 (HIV-1) gp120-induced apoptosis of bystander T cells is not well defined. Here, we demonstrate that CD45, a key component of the T cell receptor pathway, plays a crucial role in apoptosis induced by HIV-1 gp120. We observed that HIV-1 gp120-induced apoptosis was significantly reduced in a CD45-deficient cell line and that reconstitution of CD45 in these cells restored gp120-induced apoptosis. However, expression of a chimeric protein containing only the intracellular phosphatase domain was not able to restore the apoptotic function in the CD45-negative clone, indicating an important role for the extracellular domain of CD45 in this function. The role of CD45 in gp120-induced apoptosis was further confirmed in T cell lines and peripheral blood mononuclear cells using a selective CD45 inhibitor as well as CD45-specific small interfering RNA. We also observed that gp120 treatment induced CD45 association with the HIV coreceptor CXCR4. Further elucidation of downstream signaling events revealed that CD45 modulates HIV-1 gp120-induced apoptosis by regulating Fas ligand induction and activation of the phosphoinositide 3-kinase/Akt pathway. These results suggest a novel CD45-mediated mechanism for the HIV envelope-induced apoptosis of T cells.

Short communication: impairment of membrane markers on peripheral blood mononuclear cells and imbalance of cytokine secretion in the pathogenesis of multiple sclerosis active phases

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS). In active disease, a transmigration of autoreactive T cells to myelin antigens recruited from the peripheral blood (PBMC) to the CNS occurs, and there these cells prolong their survival and contribute to the perpetuation of the inflammation. In the active local lesions of MS patients, these cells display activation and apoptosis surface markers and secrete a range of cytokines. The aim of this research is to study on PBMCs and in the serum of stable and active MS subjects (1) the behavior of the CD40/CD40L system and the consequent balance of Th1 and Th2 cytokines and (2) the apoptosis marker system CD95/CD95L and tumor necrosis factor (TNF)- binding receptors, TNFRI and TNFRII. A possible excess of activation marker expression affecting and driving Th1 cytokine production or a parallel impairment of apoptosis may contribute to MS relapses. Our results may indicate that a dysregulation of early activation and apoptosis receptor systems and a profound and complex imbalance of cytokine production occurred in the peripheral blood of MS patients. This impairment could account for active phases of the disease.

Phosphatidylinositol-3-phosphate kinase pathway activation protects leukemic large granular lymphocytes from undergoing homeostatic apoptosis

T-cell large granular lymphocytic leukemia (T-LGL) is characterized by chronic clonal lymphoproliferation of cytotoxic T lymphocytes (CTLs). Despite exhibiting phenotypic properties of antigen-activated cells, including expression of Fas and FasL, T-LGL cells accumulate and demonstrate resistance to apoptosis. We propose that increased activity of a prosurvival signaling pathway in T-LGL is responsible for attenuated apoptosis in T-LGL. Given the importance of the phosphatidylinositol-3 kinase (PI3K)-AKT pathway in regulating the balance between survival and apoptosis, we analyzed AKT activity in T-LGL cells. Compared with resting CTLs from healthy donors, patients' T-LGL cells showed higher levels of phosphorylated AKT. We demonstrate that phospho-AKT induction is dependent on the upstream activity of a Src family kinase. Since the PI3K-AKT pathway can antagonize the ability of Fas to initiate apoptosis, we hypothesized that inhibition of PI3K would lead to reacquisition of Fas sensitivity in T-LGL. Inhibition of the PI3K-AKT pathway alone led to brisk spontaneous apoptosis of T-LGL. These results suggest that T-LGL pathogenesis is dependent on activity of the PI3K-AKT pathway, without which the leukemic cells will begin to undergo spontaneous apoptosis. We propose that novel therapeutics inhibiting the PI3K-AKT axis may provide effective treatment for T-LGL.

Cytometry on a chip: cellular phenotypic and functional analysis using grating-coupled surface plasmon resonance

Grating-coupled surface plasmon resonance imaging (GCSPRI) is a method for the accurate assessment of both cell phenotype and function. In GCSPRI, cells and/or proteins of interest are flowed across antibodies immobilized on a gold-coated sensor chip. The surface of the chip is illuminated with monochromatic light that couples with surface plasmons in the gold. At a specific angle of incidence, the GCSPR angle, the maximum amount of coupling occurs. Shifts in the GCSPR angle can be correlated with refractive index changes following cell or analyte capture by the immobilized antibodies. In addition, GCSPRI can image the cells as they are being captured. GCSPRI's multiplexed format allows for the parallel assessment of up to 400 individual antibody regions. In this paper, we demonstrate GCSPRI's ability to identify cells and proteins of interest and compare results to a traditional flow cytometry system. This technology represents a fast and powerful method for the simultaneous assessment of cell phenotype and function.

A functional role of flip in conferring resistance of Crohn's disease lamina propria lymphocytes to FAS-mediated apoptosis

BACKGROUND & AIMS

There is evidence that, in Crohn's disease (CD), lamina propria T lymphocytes (LPLs) are resistant to FAS-mediated apoptosis and that this defect contributes to the mucosal T-cell accumulation. In this study we examined the functional role of Flip, a Flice inhibitor protein, in the resistance of CD LPL to FAS-mediated apoptosis.

METHODS

Biopsy specimens and LPLs were taken from CD and ulcerative colitis (UC) patients and normal controls and analyzed for Flip by Western blotting. We also examined whether inhibition of Flip by antisense oligonucleotide restored the susceptibility of CD LPLs to FAS-induced apoptosis. LPL apoptosis was assessed by flow cytometry.

RESULTS

After FAS stimulation, the rate of apoptosis of CD3+ LPLs was higher in normal controls and patients with UC than in patients with CD. Enhanced expression of both long and short Flip isoforms was seen in biopsy specimens and purified CD3+ and CD45RO+ LPLs of CD patients in comparison with UC patients and normal controls. No increase in Flip was documented in untreated celiac disease mucosa, thus suggesting the possibility that induction of Flip in the gut does not simply rely on the ongoing inflammation. Finally, we showed that inhibition of Flip by antisense oligonucleotide reverted the resistance of CD LPLs to FAS-induced apoptosis.

CONCLUSIONS

Data suggest a role for Flip in the resistance of CD LPLs to FAS-mediated apoptosis.

The role of FAS to ezrin association in FAS-mediated apoptosis

The acquisition of a cell polarity is a crucial requirement for a number of cellular functions, including apoptosis. Cell polarization is an actin cytoskeleton-driven process, through a connection between actin and an increasing number of membrane proteins. The major actors in this connection are ezrin, radixin and moesin, a family of proteins with a high level of homology. Their structure includes an epitope that links to membrane proteins and the other that binds to the actin molecule. In this review we discuss recent data showing that the Fas linkage to the actin cytoskeleton is ezrin mediated and it is an essential requirement for susceptibility to the Fas-mediated apoptosis. The ezrin region responsible of Fas binding consists of 18 aminoacids mapped on the median lobe of the ezrin FERM domain. This binding is specific and of key importance in the control of cell homeostasis. Moreover, Fas-ezrin co-localization, ezrin phosphorylation and early acquisition of susceptibility to Fas-mediated apoptosis, may have a role in some human diseases in which programmed cell death seems to be a central pathogenetic mechanism, such as AIDS.

Genomic approach of AIDS pathogenesis: exhaustive genotyping of the TNFR1 gene in a French AIDS cohort

Large-scale genomic studies in cohorts have been made possible for the last few years thanks to the progress of molecular biology and bioinformatics. This systematic approach allows a better understanding of the molecular mechanisms of disease development and as a consequence can contribute to the rational design of new diagnostic and therapeutic tools. We present here the exhaustive genotyping of a candidate gene, tumor necrosis factor receptor 1 (TNFR1), in the genetic of resistance to immunodeficiency virus (GRIV) AIDS cohort. This gene was chosen because it is likely to be involved in the apoptosis pathways of CD4+ and CD8+ T-cells during human immunodeficiency virus 1 (HIV-1) infection. Seven frequent polymorphisms were characterized in 319 HIV-1 seropositive patients from the GRIV cohort with extreme disease progression phenotypes, slow progression or rapid progression, and in 427 healthy controls. The TNFR1 gene locus does not appear to be part of any haploblock and contains only a small haploblock of two successive SNPs. One promoter SNP (TNFR1_17444594, position -581) and one intronic SNP (TNFR1_27223241, position +11511) gave weak positive signals of association (resp. P=0.03 and P=0.04) as well as two haplotypes. To our knowledge, this is the first genetic association study dealing with the TNFR1 gene in AIDS and the putative associations identified will need to be validated through other AIDS cohort analyses or by further biological experimentation.

Activated CD4+CD25+ T cells selectively kill B lymphocytes

The suppressive capacity of naturally occurring mouse CD4+CD25+ T cells on T-cell activation has been well documented. The present study is focused on the interaction of CD4+CD25+ T cells and B cells. By coculturing preactivated CD4+CD25+ T cells with B cells in the presence of polyclonal B-cell activators, we found that B-cell proliferation was significantly suppressed. The suppression of B-cell proliferation was due to increased cell death caused by the CD4+CD25+ T cells in a cell-contact-dependent manner. The induction of B-cell death is not mediated by Fas-Fas ligand pathway, but surprisingly, depends on the up-regulation of perforin and granzymes in the CD4+CD25+ T cells. Furthermore, activated CD4+CD25+ T cells preferentially killed antigen-presenting but not bystander B cells. Our results demonstrate that CD4+CD25+ T cells can act directly on B cells and suggest that the prevention of autoimmunity by CD4+CD25+ T cells can be explained, at least in part, by the direct regulation of B-cell function.

Identification and characterization of DEDDL, a human-specific isoform of DEDD

Death effector domain (DED) containing molecules are usually involved in the intracellular apoptosis cascade as executioners or regulators. One of these molecules, DEDD, was identified as a final target of the CD95 signaling pathway by which it would be transferred into the nucleolus to inhibit RNA polymerase I-dependent transcription. Here we describe a longer isoform of DEDD, DEDDL, produced by alternatively splicing, as an immune cell-specific DED-containing molecule. It is only expressed in human T lymphocytes and dendritic cells (DCs), and the mRNA expression in DCs was elevated upon inductive maturation. In cell lines MCF-7 and Jurkat, the overexpression of DEDDL could induce apoptosis more potently than that of DEDD. That DEDDL could bind FADD and cFLIP more potently than DEDD in vivo was revealed by cotransfection and immunoprecipitation. This may explain why DEDDL is a more potent apoptosis inducer, because DED-containing proteins usually induce apoptosis through DED binding. Finally, why DEDD and DEDDL are unstable in the overexpression and other studies may be explained by the finding that they are potential substrates of active caspases.

The apoptotic and proliferative fate of cytokine-induced killer cells after redirection to tumor cells with bispecific Ab

BACKGROUND

Cytokine-induced killer (CIK) cells are ex vivo expanded T cells with co-expression of CD3 and CD56 and NK activity. They have recently been evaluated in a phase I/II clinical trial against malignant lymphoma. Bispecific Ab (bsAb) redirect CIK cells to tumor targets, thus enhancing their cytotoxicity. While bsAb may improve T-cell mediated anti-tumor activity, little is known about the fate of effector cells upon redirection to tumor targets using a bsAb.

METHODS

Using ex vivo-activated CIK cells, Her2/neu expressing breast and ovarian cell lines and a F(ab')2 Her2/neu x CD3 bsAb, we investigated the anti-tumor activity and the proliferative and apoptotic outcome of CIK cells.

RESULTS

When redirected to tumor targets with bsAb, there was a significant increase in anti-tumor activity as well as an increase in both CIK cell proliferation and apoptosis. The addition of agonistic Ab against CD28 did not significantly increase proliferation or apoptosis of CIK cells redirected to CD80- and CD86- tumor targets. To attempt to reduce T-cell apoptosis, we incubated CIK cells in the presence of the pan-caspase inhibitor z-VAD-fmk, which led to a partial reduction in T-cell apoptosis without increasing cellular cytotoxicity.

DISCUSSION

bsAb are effective in redirecting activated T cells to tumor targets and such redirection leads to both T-cell proliferation and apoptosis that are not altered by co-stimulation through CD28. Effector cell apoptosis can be reduced by using a caspase inhibitor but this does not increase CIK cell cytotoxicity.

The ratio between dendritic cells and T cells determines the outcome of their encounter: Proliferationversus deletion

Dendritic cells (DC) either induce T cell tolerance or contribute to the initiation and modulation of T and B cell responses. Since many of the variables determining the thresholds of naive T cell priming were defined in vitro using a homogeneously matured DC population, we here focused on partially mature DC which might reflect the occurrence of tumor-infiltrating and thymic DC. To predict how those DC regulate the induction of antigen-specific T cell proliferation and T cell tolerance, we co-cultured ovalbumin-pulsed murine DC at different ratios with antigen-specific DO11.10 transgenic T cells. Whereas partially mature DC at a DC/T cell ratio of 1:10 supported proliferation, a DC/T cell ratio of 1:2 induced proliferation arrest in naive CD4+ T cells. The acquisition of the NK cell inhibitory markers NK1.1 and KLRG on T cells exposed to high numbers of DC suggests a role for these molecules in the protection of antigen-responsive T cells from exhaustion by overstimulation. Mechanistically, abortive T cell proliferation upon encounter of high numbers of partially mature DC is caused by an apoptosis-related pathway, suggesting that excessive antigen density without sufficient costimulation results in activation-induced cell death.

Amplification of Fas-mediated apoptosis in type II cells via microdomain recruitment

Fas triggers apoptosis via the caspase cascade when bound to its ligand FasL. In type I cells, Fas is concentrated into the plasma membrane lipid rafts, and these domains are required for the apoptotic signal to occur. In contrast, Fas is excluded from the microdomains in type II cells. We report that the coligation with Fas of the membrane receptor CD28 strongly increases Fas-induced apoptosis in type II T lymphocytes, whereas it has no effect in a type I cell line. The effect of CD28 is independent of its intracellular region and requires the recruitment of the microdomains. Indeed, upon CD28 costimulation, Fas is redistributed in the lipid rafts, and their disruption with a cholesterol chelator abrogates the effect of CD28. The microdomain-mediated cell death amplification does not alter death-induced signaling complex formation and is mediated by the enhancement of the mitochondrial apoptotic pathway. These findings indicate that the sensitivity to Fas-induced apoptosis of type II cells can be amplified in vivo by the recruitment of lipid rafts following interactions between nonapoptotic ligand/receptor pairs during cell-to-cell contacts.

Atrophy of mesenteric lymph nodes in experimental Chagas' disease: differential role of Fas/Fas-L and TNFRI/TNF pathways

It is currently accepted that experimental acute infection by Trypanosoma cruzi promotes changes in secondary lymphoid organs, with general T and B lymphocyte polyclonal activation. Here we show that mesenteric lymph nodes (MLN) of acutely infected mice show severe atrophy due to extensive lymphocyte apoptosis. Accordingly, clusters of apoptotic cells are detected in the initial phase of infection in MLN but not in subcutaneous nodes. Moreover, such atrophy is independent of the infection route, parasite load or the mouse strain used. Studies in Fas-L deficient (BALB gld/gld+/+) and in TNF type 1 receptor (p55-/-) knockout mice indicate that both molecules are involved in MLN atrophy: Fas-L participates in cell death of CD4+ as well as B lymphocytes, whereas the TNF type 1 receptor is important for the apoptosis of CD4+ and CD8+ T lymphocytes. In contrast, perforin does not play a role, as lymph nodes from perforin-deficient mice do not behave differently from the corresponding wild types. Our data support the concept that, even in a systemic infection, differential (even opposing) responses can be found in different lymph node chains.

An epistatic effect of the female specific loci on the development of autoimmune vasculitis and antinuclear autoantibody in murine lupus

OBJECTIVE

To identify the genetic loci regulating the incidence and severity of renal autoimmune vasculitis developed in murine lupus.

METHODS

Vasculitis of renal arteries was histopathologically evaluated in MRL/Mp-Fas(lpr) (MRL/lpr), C57BL/6-Fas(lpr) (B6/lpr), (MRL/lpr x B6/lpr) F1, and MRL/lpr x (MRL/lpr x B6/lpr) F1 backcross mice. Using genomic DNA samples of the backcross mice, genome-wide scans, association studies, and linkage analyses were carried out based on genotypes of polymorphic microsatellite markers. Correlations of vasculitis grade and levels of various autoantibodies were also evaluated.

RESULTS

Two recessive susceptibility loci of the MRL allele were identified on chromosomes 4 and 1, which had previously been defined as the autoimmune related loci termed Arvm1 and Sle-1/Nba2, respectively. The former was epistatic to the latter in a female specific manner. The titre of antinuclear autoantibody (ANA) in IgG class, but not ANA in IgM class or anti-dsDNA in either IgG or IgM class, correlated significantly with vasculitis grade.

CONCLUSIONS

The present loci have been reported in previous studies using a different set of murine strains, suggesting that they are of importance in the development of autoimmune vasculitis in murine models. The concomitance of autoimmune vasculitis and IgG ANA suggests a shared genetic factor regulating these traits.

Life and death of lymphocytes: a role in immunesenescence

Human aging is associated with progressive decline in immune functions, increased frequency of infections. Among immune functions, a decline in T cell functions during aging predominates. In this review, we will discuss the molecular signaling in two major pathways of apoptosis, namely death receptor pathway and mitochondrial pathway, and their alterations in both T and B lymphocytes in human aging with a special emphasis on naïve and different memory subsets of CD8+ T cells. We will also discuss a possible role of lymphocyte apoptosis in immune senescence.

Death receptor-mediated suicide: a novel target of autoimmune disease treatment

In the thymus, based on the reactivity of their T-cell receptor with self-MHC and antigenic peptides, developing immature T-cells undergo positive and negative selection. Cells recognising self-peptides and MHC with high affinity are considered autoreactive, and thus potentially harmful, and are eliminated by induction of apoptotic cell death. Thymic negative selection is, however, only incomplete and autoreactive T-cells escape into the periphery. It is not the presence of autoreactive mature T- and B-lymphocytes as the underlying cause of tissue destruction and development of autoimmune diseases, but their uncontrolled and excessive clonal expansion upon activation by self-antigen. Thus, potent regulatory mechanisms must keep these autoreactive cells under control to avoid their inappropriate activation. Recent evidence indicates that death receptors of the tumour necrosis factor receptor family play a central role in mediating antigen receptor-induced suicide of autoreactive T-lymphocytes. Defects in these apoptosis-inducing regulatory mechanisms may result in the development of autoimmune diseases. Therefore, enhancing the cell's own suicide program, offers a most attractive therapeutic target for the treatment of autoimmune diseases.

Glucocorticoids inhibit activation-induced cell death (AICD) via direct DNA-dependent repression of the CD95 ligand gene by a glucocorticoid receptor dimer

Glucocorticoids (GCs) play an important role in the regulation of peripheral T-cell survival. Their molecular mechanism of action and the question of whether they have the ability to inhibit apoptosis in vivo, however, are not fully elucidated. Signal transduction through the glucocorticoid receptor (GR) is complex and involves different pathways. Therefore, we used mice with T-cell-specific inactivation of the GR as well as mice with a function-selective mutation in the GR to determine the signaling mechanism. Evidence is presented for a functional role of direct binding of the GR to 2 negative glucocorticoid regulatory elements (nGREs) in the CD95 (APO-1/Fas) ligand (L) promoter. Binding of GRs to these nGREs reduces activation-induced CD95L expression in T cells. These in vitro results are fully supported by data obtained in vivo. Administration of GCs to mice leads to inhibition of activation-induced cell death (AICD). Thus, GC-mediated inhibition of CD95L expression of activated T cells might contribute to the anti-inflammatory function of steroid drugs. (Blood. 2005;106:617-625)

Preclinical evaluation of superantigen (staphylococcal enterotoxin B) in the intravesical immunotherapy of superficial bladder cancer

Superantigens are potent activators of T lymphocytes; therefore, their characteristics can be exploited in diseases where immunomodulation is known to be effective. In this study, we evaluated a new approach for the intravesical therapy of superficial bladder cancer. We investigated in coculture experiments if staphylococcal enterotoxin B (SEB)-activated PBMCs are able to induce apoptosis in human transitional cell carcinoma (TCC) cells. Additionally, we tested the toxicity and efficacy of SEB dissolved in NaCl 0.9% administered intravesically once weekly for 6 weeks in a rat bladder cancer model. To validate the coculture in vitro findings, we evaluated tumor stage, grade, apoptotic cells in the urothelium and stroma of the bladder and infiltration of the bladder wall by lymphocytes, macrophages and mononuclear cells. Coculture experiments revealed that SEB-activated PBMCs are able to kill TCC cells by inducing apoptosis. The intravesical toxicity study with a maximum dose of 100 microg/ml SEB demonstrated no side effects. In the intravesically SEB-treated animals (10 microg/ml), only 3 tumors remained vs. 15 persisting tumors in the control group. The remaining tumors of the therapy group showed a significant amount of apoptosis and granulocytes, mainly in the urothelium, whereas no relevant apoptosis or infiltration of the bladder with lymphocytes or macrophages was found in the control group. These preclinical findings suggest that SEB might be an interesting candidate for further clinical evaluation.

Selective up-regulation of caspase-3 gene expression following TCR engagement

Activation-induced cell death (AICD) in T lymphocytes depends on the expression of Fas-ligand, which triggers the apoptotic process after binding to its receptor Fas. This leads to the activation of cysteine proteases of the caspase family and especially of caspase-3, a critical effector protein during AICD. We have previously observed the up-regulation of caspase-3 expression in effector but not memory T cells stimulated in vivo. In this study, we further characterized the regulation of caspase expression following T cell receptor (TCR) signaling and demonstrate that a three-fold increase in caspase-3 mRNA levels was observed by semi-quantitative and real-time RT-PCR analysis. Caspase-3 expression was selectively increased among five different caspases following TCR stimulation, as assessed by RNase protection assay. Real-time RT-PCR analysis demonstrated that a three-fold up-regulation in caspase-3 mRNA levels was observed following TCR triggering, whereas caspase-8 mRNA levels remained unchanged. The increase in caspase-3 mRNA levels occurred before cleavage and activation of caspase-3 and in the absence of apoptosis. TCR-mediated induction in caspase-3 expression was not dependent on STAT1 activation, since following stimulation of KOX-14 cells the transcription factor was not phosphorylated. Together, these results show that TCR activation triggers the selective increase in caspase-3 mRNA levels, independently of caspase activity and the induction of apoptosis.

Molecular mechanisms of apoptosis in the cells of the immune system in human aging

Aging is associated with progressive decline in immune functions and increased frequency of infections, autoimmunity, and cancer. Among immune functions, a decline in T-cell functions during aging predominates. In this review, I discuss the molecular signaling of three distinct pathways of apoptosis, namely the death receptor pathway, the mitochondrial pathway, and the most recently described endoplasmic reticulum stress pathway, and the relative sensitivity of naive, central memory, and effector memory CD8(+) T-cell subsets to apoptosis. In addition, I review apoptosis, especially via death receptor pathway, in naive and various memory subsets of CD4(+) and CD8(+) T cells (with primary emphasis on CD8(+) naive and memory subsets) in human aging and discuss the role of apoptosis in immune senescence.

Pathophysiology of polytrauma

Immediate and early trauma deaths are determined by primary brain injuries, or significant blood loss (haemorrhagic shock), while late mortality is caused by secondary brain injuries and host defence failure. First hits (hypoxia, hypotension, organ and soft tissue injuries, fractures), as well as second hits (e.g. ischaemia/reperfusion injuries, compartment syndromes, operative interventions, infections), induce a host defence response. This is characterized by local and systemic release of pro-inflammatory cytokines, arachidonic acid metabolites, proteins of the contact phase and coagulation systems, complement factors and acute phase proteins, as well as hormonal mediators: it is defined as systemic inflammatory response syndrome (SIRS), according to clinical parameters. However, in parallel, anti-inflammatory mediators are produced (compensatory anti-inflammatory response syndrome (CARS). An imbalance of these dual immune responses seems to be responsible for organ dysfunction and increased susceptibility to infections. Endothelial cell damage, accumulation of leukocytes, disseminated intravascular coagulation (DIC) and microcirculatory disturbances lead finally to apoptosis and necrosis of parenchymal cells, with the development of multiple organ dysfunction syndrome (MODS), or multiple organ failure (MOF). Whereas most clinical trials with anti-inflammatory, anti-coagulant, or antioxidant strategies failed, the implementation of pre- and in-hospital trauma protocols and the principle of damage control procedures have reduced post-traumatic complications. However, the development of immunomonitoring will help in the selection of patients at risk of post-traumatic complications and, thereby, the choice of the most appropriate treatment protocols for severely injured patients.

The role of BH3-only proteins in the immune system

Programmed cell death--also known as apoptosis--has a crucial role in the immune system of mammals and other animals. It removes useless cells and potentially dangerous cells, including lymphocytes, and is involved in killing pathogen-infected or damaged cells. Defects in this process have been found to cause or contribute to diseases of the immune system, including immunodeficiency, autoimmunity, lymphoma and leukaemia. This review describes BH3-only proteins, a pro-apoptotic subgroup of the BCL-2 family, and their role in the development and function of the immune system.

Human Immunodeficiency virus type 1 Nef potently induces apoptosis in primary human brain microvascular endothelial cells via the activation of caspases

The lentiviral protein Nef plays a major role in the pathogenesis of human immunodeficiency virus type I (HIV-1) infection. Although the exact mechanisms of its actions are not fully understood, Nef has been shown to be essential for the maintenance of high-titer viral replication and disease pathogenesis in in vivo models of simian immunodeficiency virus infection of monkeys. Nef has also been suggested to play a pivotal role in the depletion of T cells by promoting apoptosis in bystander cells. In this context, we investigated the ability of extracellular and endogenously expressed HIV-1 Nef to induce apoptosis in primary human brain microvascular endothelial cells (MVECs). Human brain MVECs were exposed to baculovirus-expressed HIV-1 Nef protein, an HIV-1-based vector expressing Nef, spleen necrosis virus (SNV)-Nef virus (i.e., SNV vector expressing HIV-1 Nef as a transgene), and the HIV-1 strain ADA and its Nef deletion mutant, ADADeltaNef. We observed that ADA Nef, the HIV-1 vector expressing Nef, and SNV-Nef were able to induce apoptosis in a dose-dependent manner. The mutant virus with a deletion in Nef was able to induce apoptosis in MVECs to modest levels, but the effects were not as pronounced as with the wild-type HIV-1 strain, ADA, the HIV-1-based vector expressing Nef, or SNV-Nef viruses. We also demonstrated that relatively high concentrations of exogenous HIV-1 Nef protein were able to induce apoptosis in MVECs. Gene microarray analyses showed increases in the expression of several specific proapoptotic genes. Western blot analyses revealed that the various caspases involved with Nef-induced apoptosis are processed into cleavage products, which occur only during programmed cell death. The results of this study demonstrate that Nef likely contributes to the neuroinvasion and neuropathogenesis of HIV-1, through its effects on select cellular processes, including various apoptotic cascades.

Gene Expression of Perforin by Peripheral Blood Lymphocytes as a Marker of Acute Rejection

BACKGROUND

Previous findings have demonstrated that the expression of cytotoxic effector molecules is increased in acute rejection of renal allografts. In the present study, we serially examined the gene expression of perforin, granzyme B and Fas ligand (FasL) in peripheral blood lymphocytes (PBLs) of renal allograft recipients to assess the potential of their expression as a marker of acute rejection.

METHODS

PBLs were isolated from blood samples taken on days 2, 4, 6, 8, 10 and 12 after transplantation. Competitive PCR was performed to evaluate the abundance of mRNA of perforin, granzyme B and FasL. The mean value + 2 SD of each molecule in the control group was set as a discriminatory level for that particular molecule.

RESULTS

When all measured samples were compared, perforin expression was significantly higher in patients with acute rejection than in the control group (1.84 +/- 3.01 vs. 0.71 +/- 0.48, p = 0.01). The percentage of perforin expression exceeding the discriminatory level was also significantly higher in patients with acute rejection (p = 0.0003). Five patients in the rejection group (5/7, 71.4%) showed perforin expression exceeding the discriminatory level, while only 1 patient in the control group did so (1/8, 12.5%) (p = 0.02). Perforin expressions of days 0 and 1 of rejection crisis were the highest over the study period. No consistent pattern of granzyme B and FasL expression was identified in relation to rejection crisis.

CONCLUSION

Gene expression of perforin by PBLs was upregulated in accordance with acute rejection, thus offering the possibility that it may be utilized as a marker of acute rejection.

Correlation of CD95 and soluble CD95 expression with acute rejection status of liver transplantation

AIM: To analyze the expression levels of soluble form of CD95, CD95 ligand (sCD95 and sCD95L, respectively) in plasma and CD95 expression on CD3⁺ cells in liver-transplanted recipients with acute rejection (AR).

METHODS: Peripheral blood mononuclear cells (PBMCs) were isolated from 30 clinically liver transplanted recipients. CD95 expression on CD3⁺ cells was quantitatively measured by two-color fluorescence activated cell sorter (FACS) analysis. Lymphocyte surface phenotypes of CD4, CD8, CD16 and CD56 were determined by flow cytometry. Plasma levels of sCD95 and sCD95L were detected by Enzyme Linked-Immuno-Sorbent Assay (ELISA). The results were compared with that from normal healthy volunteers (n = 15 individuals).

RESULTS: FACS analysis showed that CD95 expression on CD3⁺ T cells was significantly increased in liver transplanted recipients with AR compared to that in stable recipients without rejection and infection or healthy individuals who did not undergo transplantation (18676.93±11588.34/molecule, 6848.20±1712.96/molecule, 6418.01±2001.95/molecule, respectively, P<0.01). Whereas no significant difference was seen between liver-transplanted stable recipients and healthy individuals. Furthermore, no significant differences were detected between each group with CD4/CD8 ratio or the percentage of CD16⁺56⁺ cells. Plasma levels of sCD95 were significantly higher in transplanted recipients with AR compared to that in stable recipients or healthy individuals (391.88±196.00, 201.37±30.30, 148.83±58.25 pg/mL, respectively, P<0.01). In contrast, the plasma levels of sCD95L in liver- transplanted recipients were not significantly different from that in healthy individuals.

CONCLUSION: The present results indicate that the increased CD95 expression on CD3⁺ cells and the increased levels of sCD95 in plasma may modify the immunological situation of the recipients after transplantation or represent the ongoing graft rejection.

Evidence for increased apoptosis of duodenal intraepithelial lymphocytes in cow's milk sensitive enteropathy

OBJECTIVES

Enterocyte apoptosis induced by activated intraepithelial lymphocytes (IELs) is increased in celiac disease (CD). A lesser increment in intraepithelial lymphocytes associated with normal villous structure is also characteristic of cow's milk sensitive enteropathy (CMSE), but no information is available about the apoptosis rate of this condition.

METHODS

Endoscopic biopsy samples of 21 children with untreated CMSE were compared with samples from 15 children with CD and 18 controls. Apoptosis was analyzed using the TUNEL technique and the M30 antibody from duodenal bulb and mid-duodenum samples. Ki-67 was used to detect the proliferation rate and CD3(+) to count the overall number of T lymphocytes.

RESULTS

In the mid-duodenum, CMSE patients showed a significantly increased intraepithelial and lamina propria density of TUNEL(+) cells, but no difference in the density of M30(+) epithelial cells was seen compared with controls. In CD subjects, TUNEL(+) counts in mid-duodenal villous epithelium were increased. CD3(+) intraepithelial lymphocytes were increased in both CMSE and CD and correlated with TUNEL(+) and M30(+) counts among all patients. No increase in proliferation rate was seen in CMSE, and no significant correlations between apoptosis and proliferation rates were detected.

CONCLUSIONS

The observed increase in TUNEL(+) counts and the absence of any increase in M30(+) cells suggest that the apoptosis rate of intraepithelial lymphocytes, but not of enterocytes, is increased in the small IELs in CMSE. However, the number of intraepithelial lymphocytes is still elevated in CMSE, indicating that a disturbance of homeostasis of intraepithelial lymphocytes is important in its pathogenesis.

Low soluble Fas (sFas) and sFas ligand (sFasL) content in breast milk after preterm as opposed to term delivery

AIM

Various mechanisms of innate immunity and gastrointestinal integrity are potentially affected by soluble Fas (sFas) and sFas ligand (sFasL). Assuming that sFas and sFasL in milk reflect cellular events during lactogenesis, we aimed to assess the impact of premature parturition and duration of lactation on the concentrations of sFas and sFasL in human milk.

PATIENTS AND METHODS

The content of the soluble form of the cell surface receptor Fas (sFas) and its natural ligand (sFasL) was measured in human breast milk of 44 healthy mothers after preterm (<35 wk, n=21) and term (>37 wk, n=23) delivery. Milk was furthermore classified as immature breast milk (days 4-7 of lactation) or mature breast milk (days 35-45 of lactation). Breast milk (2-3 ml) was sampled 5 min after the start of breastfeeding by manual expression or milk pump, and stored at -20 degrees C until analysis by an ELISA.

RESULTS

sFas and sFasL concentrations were lower in immature milk after preterm compared to term delivery (sFas: 1.71; 1.38-2.47 ng/ml vs 3.03; 2.02-4.30 ng/ml, p < 0.001; sFasL: 0.13; 0.07-0.21 ng/ml vs 0.29; 0.15-0.60 ng/ml, p < 0.001 [median +/- interquartile range]). Mature milk samples, taken 1 mo later from both gestational groups, did not differ in sFas/sFasL content. Soluble Fas was positively correlated with sFasL in the same sample of immature (p < 0.001) and mature human milk (p < 0.05). A positive correlation was found between sFas and sFasL in immature and mature milk samples of the same mother (p < 0.01). The body mass index of the mothers and duration of pregnancy were positively correlated with the sFas and sFasL content in immature milk (p < 0.05 and p < 0.01, respectively) but not in mature milk.

CONCLUSION

Preterm newborn infants fed with breast milk have a lower intake of sFas and sFasL compared to term neonates. Our results demonstrate that preterm delivery affects breast milk composition.

Antiapoptotic microenvironment of acute myeloid leukemia

We showed previously that tumor-derived supernatant (TSN) from acute myeloid leukemia (AML) myeloblasts inhibits peripheral blood T cell activation and proliferation, rendering the T cells functionally incompetent. We show here that the AML TSN also significantly delays apoptosis of both resting and stimulated T cells, as judged by reduction in annexin V/propidium iodide staining. In addition, we show that this is not unique to T cells and that AML TSN inhibits apoptosis of peripheral B cells, neutrophils, and monocytes. Furthermore, it also enhances the survival of other AML myeloblasts with lower viability. Investigations into the mechanism demonstrate a reduction in the cleavage of procaspase-3, -8, and -9 and the caspase substrate, poly(ADP-ribose)polymerase (PARP). This may be due to Bcl-2, which is normally down-regulated in CD3/CD28-stimulated T cells, but is maintained in the presence of AML TSN. We conclude that AML cells generate an antiapoptotic microenvironment that favors the survival of malignant cells, but also inhibits apoptosis of other normal hemopoietic cells. Reversal of these immunosuppressive effects and restoration of normal immune responses in patients with AML would improve the success of immunotherapy protocols.

An introduction to death receptors in apoptosis

Apoptosis is a source of much research interest across many fields, including developmental biology, immunology and oncology. As the exact pathways of this process are identified, so too are potential avenues for therapeutic application. Death receptors are important in inducing apoptosis and together with their ligands have become a source of attention as potential therapeutic agents. This review provides an introduction to the role of death receptors in apoptosis, together with a look at possible areas where this information may be applied therapeutically.