Modulation of CD4+ T-cell activation by CD95 co-stimulation

Immune mechanisms and predictive biomarkers related to neoadjuvant immunotherapy response in stage III melanoma

The treatment for stage III melanoma has advanced significantly, nevertheless, a substantial proportion of patients experience relapse. Neoadjuvant immune checkpoint blockade has emerged as a promising approach, allowing early micrometastatic disease treatment, reduction of tumor burden before surgery, and enhanced tumor-specific T-cell responses. However, not all patients respond to treatment, highlighting the need for understanding immune mechanisms behind failure and identification of predictive markers. Here we performed a robust evaluation of systemic and tumoral immune profiles in a well-defined cohort of advanced melanoma patients treated with immune checkpoint inhibitors. Elevated CTACK and CXCL9 chemokines pre-treatment suggested their potential as predictive tools for treatment response. Furthermore, CD95 expression in CD8+ T lymphocytes surfaced as a favorable prognostic indicator, while PD-1, CD161, and PD-L2 exhibited correlations with worst outcomes. These findings shed light on the intricate interplay between immune markers and melanoma response to neoadjuvant immune checkpoint therapy, offering insights into personalized treatment strategies.

The abscopal effect of anti-CD95 and radiotherapy in melanoma

BACKGROUND

Radiotherapy (RT) is frequently adopted to control cancer cell proliferation, which is achieved by altering the tumor microenvironment (TME) and immunogenicity. Apoptosis of cancer cells is the major effect of radiation on tumor tissues. Fas/APO-1(CD95) receptors on the cell membrane are death receptors that can be activated by diverse factors, including radiation and integration with CD95L on CD8⁺ T cells. The abscopal effect is defined as tumor regression out of the local RT field, and it is produced through anti-tumor immunity. The immune response against the radiated tumor is characterized by the cross-presentation between antigen-presenting cells (APCs), which includes cytotoxic T cells (CTLs) and dendritic cells (DCs).

METHODS

The effect of activation and radiation of CD95 receptors on melanoma cell lines was examined in vivo and in vitro. In vivo, bilateral lower limbs were given a subcutaneous injection of a dual-tumor. Tumors in the right limb were radiated with a single dose of 10 Gy (primary tumor), while tumors in the left limb (secondary tumor) were spared.

RESULTS

The anti-CD95 treatment plus radiation (combination treatment) reduced growth rates of both primary and secondary tumors relative to the control or radiation groups. In addition, higher degrees of infiltrating CTLs and DCs were detected in the combination treatment compared to the other groups, but the immune response responsible for secondary tumor rejection was not proven to be tumor specific. In vitro, combination treatment combined with radiation resulted in further apoptosis of melanoma cells relative to controls or cells treated with radiation.

CONCLUSIONS

Targeting CD95 on cancer cells will induce tumor control and the abscopal effect.

Increased Expression of CD95 in CD4+ Effector Memory T Cells Promotes Th17 Response in Patients with Myasthenia Gravis

Emerging data have revealed that CD95 can evoke non-apoptotic signals, thereby promoting pro-inflammatory functions that link to the severity of autoimmune disorders. Here, we reported that the expression of CD95 in CD4⁺ effector memory T (CD4⁺ TEM) cells was increased in myasthenia gravis (MG) patients. We also found increased expression of CD95 in CD4⁺ TEM cells from MG patients correlated positively with clinical severity scores (QMGs), serum IL-17 levels and plasma cells (PCs) frequencies. Conventional treatment, such as glucocorticoid, could down-regulate the expression of CD95 in CD4⁺ TEM cells, QMGs, serum IL-17 levels and PCs frequencies from MG patients. In vitro, low-dose of agonistic anti-CD95 mAb could promote Th17 cell development. This effect was reversed by CD95 siRNA. Moverover, CD95 stimulation induced the phosphorylation of p38 and Erk1/2 and Th17 cell differentiation, and p38 specific inhibitor SB203580 or Erk1/2 specific inhibitor PD98059 could induce opposite changes. However, SB203580 or PD98059 do not abrogate the increase of CCR6⁺IL-17A⁺ cells, ROR-γt and IL-17 expression induced by CD95 triggering relatively to each corresponding control. This suggests that p38 and Erk1/2 MAPK pathway plays a role in expression of CCR6⁺IL-17A⁺ cells, ROR-γt and IL-17, but not in their increase induced by CD95 triggering. Taken together, this study revealed that increased expression of CD95 in CD4⁺ TEM cells promotes Th17 response under the microenvironment of MG.

Impact of human CD95 mutations on cell death and autoimmunity: a model

CD95/Fas/APO-1 can trigger apoptotic as well as nonapoptotic pathways in immune cells. CD95 signaling in humans can be inhibited by several mechanisms, including mutations in the gene encoding CD95. CD95 mutations lead to autoimmune disorders, such as autoimmune lymphoproliferative syndrome (ALPS). Gaining further insight into the reported mutations of CD95 and resulting alterations of its signaling networks may provide further understanding of their presumed role in certain autoimmune diseases. For illustrative purposes and to better understand the potential outcomes of CD95 mutations, here we assign their positions to the recently determined 3D structures of human CD95. Based on this, we make certain predictions and speculate on the putative role of CD95 mutation defects in CD95-mediated signaling for certain autoimmune diseases.

The three as: Alternative splicing, alternative polyadenylation and their impact on apoptosis in immune function

The latest advances in next-generation sequencing studies and transcriptomic profiling over the past decade have highlighted a surprising frequency of genes regulated by RNA processing mechanisms in the immune system. In particular, two control steps in mRNA maturation, namely alternative splicing and alternative polyadenylation, are now recognized to occur in the vast majority of human genes. Both have the potential to alter the identity of the encoded protein, as well as control protein abundance or even protein localization or association with other factors. In this review, we will provide a summary of the general mechanisms by which alternative splicing (AS) and alternative polyadenylation (APA) occur, their regulation within cells of the immune system, and their impact on immunobiology. In particular, we will focus on how control of apoptosis by AS and APA is used to tune cell fate during an immune response.

Fas-threshold signalling in MSCs promotes pancreatic cancer progression and metastasis

Mesenchymal stem cells (MSCs) belong to the tumour microenvironment and have been implicated in tumour progression. We found that the number of MSCs significantly increased in tumour-burdened mice driven by Fas-threshold signalling. Consequently, MSCs lacking Fas lost their ability to induce metastasis development in a pancreatic cancer model. Mixing of MSCs with pancreatic cancer cells led to sustained production of the pro-metastatic cytokines CCL2 and IL6 by the stem cells. The levels of these cytokines were dependent on the number of MSCs, linking Fas-mediated MSC-proliferation to their capacity to promote tumour progression. Furthermore, we discovered that CCL2 and IL6 were induced by pancreatic cancer cell-derived IL1. Importantly, analysis of patient transcriptomic data revealed that high FasL expression correlates with high levels of MSC markers as well as increased IL6 and CCL2 levels in pancreatic tumours. Moreover, both FasL and CCL2 are linked to elevated levels of markers specific for monocytes known to possess further pro-metastatic activities. These results confirm our experimental findings of a FasL-MSC-IL1-CCL2/IL6 axis in pancreatic cancer and highlights the role of MSCs in tumour progression.

Fas/FasL Signaling Regulates CD8 Expression During Exposure to Self-Antigens

Activation of self-reactive CD8+ T cells induces a peripheral tolerance mechanism that involves loss of CD8 expression. Because genetic deficiency of Fas and Fasl causes the accumulation of double-negative (DN; CD3+ TCR-αβ+ CD4- CD8-) T cells that have been proposed to derive from CD8+ cells, we decided to explore the role of Fas and FasL in self-antigen-induced CD8 downregulation. To this end, we quantified Fas and FasL induction by different stimuli and analyzed the effects of Fas/FasL deficiency during a protective immune response and after exposure to self-antigens. Our data describes how Fas and FasL upregulation differs depending on the setting of CD8 T cell activation and demonstrates that Fas/FasL signaling maintains CD8 expression during repetitive antigen stimulation and following self-antigen encounter. Together, our results reveal an unexpected role of Fas/FasL signaling and offer a new insight into the role of these molecules in the regulation of immune tolerance.

Metabolic and Mitochondrial Functioning in Chimeric Antigen Receptor (CAR)-T Cells

Chimeric antigen receptor (CAR) T-cell therapy has revolutionized adoptive cell therapy with impressive therapeutic outcomes of >80% complete remission (CR) rates in some haematological malignancies. Despite this, CAR T cell therapy for the treatment of solid tumours has invariably been unsuccessful in the clinic. Immunosuppressive factors and metabolic stresses in the tumour microenvironment (TME) result in the dysfunction and exhaustion of CAR T cells. A growing body of evidence demonstrates the importance of the mitochondrial and metabolic state of CAR T cells prior to infusion into patients. The different T cell subtypes utilise distinct metabolic pathways to fulfil their energy demands associated with their function. The reprogramming of CAR T cell metabolism is a viable approach to manufacture CAR T cells with superior antitumour functions and increased longevity, whilst also facilitating their adaptation to the nutrient restricted TME. This review discusses the mitochondrial and metabolic state of T cells, and describes the potential of the latest metabolic interventions to maximise CAR T cell efficacy for solid tumours.

Critical Roles of Balanced T Helper 9 Cells and Regulatory T Cells in Allergic Airway Inflammation and Tumor Immunity

CD4⁺T helper (Th) cells are important mediators of immune responses in asthma and cancer. When counteracted by different classes of pathogens, naïve CD4⁺T cells undergo programmed differentiation into distinct types of Th cells. Th cells orchestrate antigen-specific immune responses upon their clonal T-cell receptor (TCR) interaction with the appropriate peptide antigen presented on MHC class II molecules expressed by antigen-presenting cells (APCs). T helper 9 (Th9) cells and regulatory T (Treg) cells and their corresponding cytokines have critical roles in tumor and allergic immunity. In the context of asthma and cancer, the dynamic internal microenvironment, along with chronic inflammatory stimuli, influences development, differentiation, and function of Th9 cells and Treg cells. Furthermore, the dysregulation of the balance between Th9 cells and Treg cells might trigger aberrant immune responses, resulting in development and exacerbation of asthma and cancer. In this review, the development, differentiation, and function of Th9 cells and Treg cells, which are synergistically regulated by various factors including cytokine signals, transcriptional factors (TFs), costimulatory signals, microenvironment cues, metabolic pathways, and different signal pathways, will be discussed. In addition, we focus on the recent progress that has helped to achieve a better understanding of the roles of Th9 cells and Treg cells in allergic airway inflammation and tumor immunity. We also discuss how various factors moderate their responses in asthma and cancer. Finally, we summarize the recent findings regarding potential mechanisms for regulating the balance between Th9 and Treg cells in asthma and cancer. These advances provide opportunities for novel therapeutic strategies that are aimed at reestablishing the balance of these cells in the diseases.

The FasLane to ocular pathology-metalloproteinase cleavage of membrane-bound FasL determines FasL function

Fas ligand (FasL) is best known for its ability to induce cell death in a wide range of Fas-expressing targets and to limit inflammation in immunoprivileged sites such as the eye. In addition, the ability of FasL to induce a much more extensive list of outcomes is being increasingly explored and accepted. These outcomes include the induction of proinflammatory cytokine production, T cell activation, and cell motility. However, the distinct and opposing functions of membrane-associated FasL (mFasL) and the C-terminal soluble FasL fragment (sFasL) released by metalloproteinase cleavage is less well documented and understood. Both mFasL and sFasL can form trimers that engage the trimeric Fas receptor, but only mFasL can form a multimeric complex in lipid rafts to trigger apoptosis and inflammation. By contrast, a number of reports have now documented the anti-apoptotic and anti-inflammatory activity of sFasL, pointing to a critical regulatory function of the soluble molecule. The immunomodulatory activity of FasL is particularly evident in ocular pathology where elimination of the metalloproteinase cleavage site and the ensuing increased expression of mFasL can severely exacerbate the extent of inflammation and cell death. By contrast, both homeostatic and increased expression of sFasL can limit inflammation and cell death. The mechanism(s) responsible for the protective activity of sFasL are discussed but remain controversial. Nevertheless, it will be important to consider therapeutic applications of sFasL for the treatment of ocular diseases such as glaucoma.

Innate and Adaptive Immune Responses in HELLP Syndrome

Innate and adaptive immune involvement in hemolysis, elevated liver enzymes and low platelet (HELLP) syndrome is an understudied field, although it is of high clinical importance. This syndrome implies a risk of serious morbidity and mortality to both the mother and the fetus during pregnancy. It was proposed that HELLP syndrome occurs in a circulatory inflammatory milieu, that might in turn participate in a complex interplay between the secreted inflammatory immunomodulators and immune cell surface receptors. Meanwhile, reported immune cell attenuation during HELLP may consequently lead to a prolonged immunoactivation and tissue damage. In this regard, learning more about the immune components of this syndrome should widen the understanding of the HELLP pathophysiology and eventually enable development of novel immune-based therapeutics. This review aims to summarize and discuss the recent and previous findings of the innate and adaptive immune responses during HELLP in order to update the current knowledge of the immune involvement in HELLP pathogenesis.

Fas signaling-mediated TH9 cell differentiation favors bowel inflammation and antitumor functions

Fas induces apoptosis in activated T cell to maintain immune homeostasis, but the effects of non-apoptotic Fas signaling on T cells remain unclear. Here we show that Fas promotes T_H9 cell differentiation by activating NF-κB via Ca²⁺-dependent PKC-β activation. In addition, PKC-β also phosphorylates p38 to inactivate NFAT1 and reduce NFAT1-NF-κB synergy to promote the Fas^-induced T_H9 transcription program. Fas ligation exacerbates inflammatory bowel disease by increasing T_H9 cell differentiation, and promotes antitumor activity in p38 inhibitor-treated T_H9 cells. Furthermore, low-dose p38 inhibitor suppresses tumor growth without inducing systemic adverse effects. In patients with tumor, relatively high T_H9 cell numbers are associated with good prognosis. Our study thus implicates Fas in CD4⁺ T cells as a target for inflammatory bowel disease therapy. Furthermore, simultaneous Fas ligation and low-dose p38 inhibition may be an effective approach for T_H9 cell induction and cancer therapy.

Fas signalling induces apoptosis of activated T cells to maintain immune homeostasis. Here the authors show that Fas also induces PKC-β activation to promote NF-κB-mediated T_H9 cell differentiation, while p38 activation by PKC-β antagonizes this effect, thereby supporting a synergy between p38 inhibitor and Fas for T_H9 differentiation.

c-FLIP and CD95 signaling are essential for survival of renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is the most-prominent tumor type of kidney cancers. Resistance of renal cell carcinoma (RCC) against tumor therapy is often owing to apoptosis resistance, e.g., by overexpression of anti-apoptotic proteins. However, little is known about the role of the apoptosis inhibitor c-FLIP and its potential impact on death receptor-induced apoptosis in ccRCC cells. In this study, we demonstrate that c-FLIP is crucial for resistance against CD95L-induced apoptosis in four ccRCC cell lines. Strikingly, downregulation of c-FLIP expression by short hairpin RNA (shRNA)interference led to spontaneous caspase activation and apoptotic cell death. Of note, knockdown of all c-FLIP splice variants was required to induce apoptosis. Stimulation of ccRCC cells with CD95L induced NF-κB and MAP kinase survival pathways as revealed by phosphorylation of RelA/p65 and Erk1/2. Interestingly, CD95L surface expression was high in all cell lines analyzed, and CD95 but not TNF-R1 clustered at cell contact sites. Downstream of CD95, inhibition of the NF-κB pathway led to spontaneous cell death. Surprisingly, knockdown experiments revealed that c-FLIP inhibits NF-κB activation in the context of CD95 signaling. Thus, c-FLIP inhibits apoptosis and dampens NF-κB downstream of CD95 but allows NF-κB activation to a level sufficient for ccRCC cell survival. In summary, we demonstrate a complex CD95-FLIP-NF-κB-signaling circuit, in which CD95-CD95L interactions mediate a paracrine survival signal in ccRCC cells with c-FLIP and NF-κB both being required for inhibiting cell death and ensuring survival. Our findings might lead to novel therapeutic approaches of RCC by circumventing apoptosis resistance.

Fas Promotes T Helper 17 Cell Differentiation and Inhibits T Helper 1 Cell Development by Binding and Sequestering Transcription Factor STAT1

The death receptor Fas removes activated lymphocytes through apoptosis. Previous transcriptional profiling predicted that Fas positively regulates interleukin-17 (IL-17)-producing T helper 17 (Th17) cells. Here, we demonstrate that Fas promoted the generation and stability of Th17 cells and prevented their differentiation into Th1 cells. Mice with T-cell- and Th17-cell-specific deletion of Fas were protected from induced autoimmunity, and Th17 cell differentiation and stability were impaired. Fas-deficient Th17 cells instead developed a Th1-cell-like transcriptional profile, which a new algorithm predicted to depend on STAT1. Experimentally, Fas indeed bound and sequestered STAT1, and Fas deficiency enhanced IL-6-induced STAT1 activation and nuclear translocation, whereas deficiency of STAT1 reversed the transcriptional changes induced by Fas deficiency. Thus, our computational and experimental approach identified Fas as a regulator of the Th17-to-Th1 cell balance by controlling the availability of opposing STAT1 and STAT3 to have a direct impact on autoimmunity.

A genetic IFN/STAT1/FAS axis determines CD4 T stem cell memory levels and apoptosis in healthy controls and Adult T-cell Leukemia patients

Adult T-cell leukemia (ATL) is an aggressive, chemotherapy-resistant CD4+CD25+ leukemia caused by HTLV-1 infection, which usually develops in a minority of patients several decades after infection. IFN + AZT combination therapy has shown clinical benefit in ATL, although its mechanism of action remains unclear. We have previously shown that an IFN-responsive FAS promoter polymorphism in a STAT1 binding site (rs1800682) is associated to ATL susceptibility and survival. Recently, CD4 T stem cell memory (TSCM) Fashi cells have been identified as the hierarchical cellular apex of ATL, but a possible link between FAS, apoptosis, proliferation and IFN response in ATL has not been studied. In this study, we found significant ex vivo antiproliferative, antiviral and immunomodulatory effects of IFN-α treatment in short-term culture of primary mononuclear cells from ATL patients (n = 25). Bayesian Network analysis allowed us to integrate ex vivo IFN-α response with clinical, genetic and immunological data from ATL patients, thereby revealing a central role for FAS -670 polymorphism and apoptosis in the coordinated mechanism of action of IFN-α. FAS genotype-dependence of IFN-induced apoptosis was experimentally validated in an independent cohort of healthy controls (n = 20). The same FAS -670 polymorphism also determined CD4 TSCM levels in a genome-wide twin study (p = 7 × 10-11, n = 460), confirming a genetic link between apoptosis and TSCM levels. Transcriptomic analysis and cell type deconvolution confirmed the FAS genotype/TSCM link and IFN-α-induced downregulation of CD4 TSCM-specific genes in ATL patient cells. In conclusion, ex vivo IFN-α treatment exerts a pleiotropic effect on primary ATL cells, with a genetic IFN/STAT1/Fas axis determining apoptosis vs. proliferation and underscoring the CD4 TSCM model of ATL leukemogenesis.

Changes in T Cell and Dendritic Cell Phenotype from Mid to Late Pregnancy Are Indicative of a Shift from Immune Tolerance to Immune Activation

During pregnancy, the mother allows the immunologically distinct fetoplacental unit to develop and grow. Opinions are divided as to whether this represents a state of fetal-specific tolerance or of a generalized suppression of the maternal immune system. We hypothesized that antigen-specific T cell responses are modulated by an inhibitory T cell phenotype and modified dendritic cell (DC) phenotype in a gestation-dependent manner. We analyzed changes in surface markers of peripheral blood T cells, ex vivo antigen-specific T cell responses, indoleamine 2,3-dioxygenase (IDO) activity (kynurenine/tryptophan ratio, KTR), plasma neopterin concentration, and the in vitro expression of progesterone-induced blocking factor (PIBF) in response to peripheral blood mononuclear cell culture with progesterone. We found that mid gestation is characterized by reduced antigen-specific T cell responses associated with (1) predominance of effector memory over other T cell subsets; (2) upregulation of inhibitory markers (programmed death ligand 1); (3) heightened response to progesterone (PIBF); and (4) reduced proportions of myeloid DC and concurrent IDO activity (KTR). Conversely, antigen-specific T cell responses normalized in late pregnancy and were associated with increased markers of T cell activation (CD38, neopterin). However, these changes occur with a simultaneous upregulation of immune suppressive mechanisms including apoptosis (CD95), coinhibition (TIM-3), and immune regulation (IL-10) through the course of pregnancy. Together, our data suggest that immune tolerance dominates in the second trimester and that it is gradually reversed in the third trimester in association with immune activation as the end of pregnancy approaches.

Longitudinal peripheral blood transcriptional analysis of a patient with severe Ebola virus disease

The 2013-2015 outbreak of Ebola virus disease in Guinea, Liberia, and Sierra Leone was unprecedented in the number of documented cases, but there have been few published reports on immune responses in clinical cases and their relationships with the course of illness and severity of Ebola virus disease. Symptoms of Ebola virus disease can include severe headache, myalgia, asthenia, fever, fatigue, diarrhea, vomiting, abdominal pain, and hemorrhage. Although experimental treatments are in development, there are no current U.S. Food and Drug Administration-approved vaccines or therapies. We report a detailed study of host gene expression as measured by microarray in daily peripheral blood samples collected from a patient with severe Ebola virus disease. This individual was provided with supportive care without experimental therapies at the National Institutes of Health Clinical Center from before onset of critical illness to recovery. Pearson analysis of daily gene expression signatures revealed marked gene expression changes in peripheral blood leukocytes that correlated with changes in serum and peripheral blood leukocytes, viral load, antibody responses, coagulopathy, multiple organ dysfunction, and then recovery. This study revealed marked shifts in immune and antiviral responses that preceded changes in medical condition, indicating that clearance of replicating Ebola virus from peripheral blood leukocytes is likely important for systemic viral clearance.

Role of caspases in CD95-induced biphasic activation of acid sphingomyelinase

Acid sphingomyelinase (A-SMase) plays an important role in the initiation of CD95 signaling by forming ceramide-enriched membrane domains that enable clustering and activation of the death receptors. In TNF-R1 and TRAIL-R1/R2 signaling, A-SMase also contributes to the lysosomal apoptosis pathway triggered by receptor internalization. Here, we investigated the molecular mechanism of CD95-mediated A-SMase activation, demonstrating that A-SMase is located in internalized CD95-receptosomes and is activated by the CD95/CD95L complex in a biphasic manner.Since several caspases have been described to be involved in the activation of A-SMase, we evaluated expression levels of caspase-8, caspase-7 and caspase-3 in CD95-receptosomes. The occurrence of cleaved caspase-8 correlated with the first peak of A-SMase activity and translocation of the A-SMase to the cell surface which could be blocked by the caspase-8 inhibitor IETD.Inhibition of CD95-internalization selectively reduced the second phase of A-SMase activity, suggesting a fusion between internalized CD95-receptosomes and an intracellular vesicular pool of A-SMase. Further analysis demonstrated that caspase-7 activity correlates with the second phase of the A-SMase activity, whereas active caspase-3 is present at early and late internalization time points. Blocking caspases-7/ -3 by DEVD reduced the second phase of A-SMase activation in CD95-receptosomes suggesting the potential role of caspase-7 or -3 for late A-SMase activation.In summary, we describe a biphasic A-SMase activation in CD95-receptosomes indicating (I.) a caspase-8 dependent translocation of A-SMase to plasma membrane and (II.) a caspase-7 and/or -3 dependent fusion of internalized CD95-receptosomes with intracellular A-SMase-containing vesicles.

Dysregulation of the Fas/FasL system in an experimental animal model of HELLP syndrome

INTRODUCTION

Placental FasL is up-regulated in women with HELLP (hemolysis elevated liver enzyme and low platelet) syndrome and has been proposed to contribute to the liver damage seen in these patients.

OBJECTIVE

This study aimed to determine if an experimental rodent model of HELLP also had dysregulation of Fas/FasL compared to normal pregnant (NP) rats. We also set out to determine if blockade of the endothelin system regulated Fas/FasL expression in HELLP rats.

STUDY DESIGN

On gestational day (GD) 12, sEng (7ug/kg) and sFlt-1 (4.7ug/kg) infusion began via mini-osmotic pump into NP rats. On GD19 plasma and tissue were collected and FasL and Fas were measured via enzyme linked immunosorbent assay and gene expression via real-time PCR.

RESULTS

HELLP rats had significantly more circulating and placental FasL compared to NP rats, whereas hepatic FasL was decreased and placental Fas was increased compared to NP rats. Administration of an endothelin A receptor antagonist (ET_A) beginning on GD12 significantly decreased placental expression of Fas in HELLP rats. Liver mRNA transcript of Fas was significantly increased in HELLP rats compared to NP rats.

CONCLUSION

These data suggest that rats in this experimental model of HELLP syndrome have abnormal expression of the Fas/FasL system. Future studies will examine the sources of Fas/FasL dysregulation in this model and if blockade could reduce some of the inflammation and hypertension associated with HELLP syndrome.

A20 Curtails Primary but Augments Secondary CD8+ T Cell Responses in Intracellular Bacterial Infection

The ubiquitin-modifying enzyme A20, an important negative feedback regulator of NF-κB, impairs the expansion of tumor-specific CD8⁺ T cells but augments the proliferation of autoimmune CD4⁺ T cells. To study the T cell-specific function of A20 in bacterial infection, we infected T cell-specific A20 knockout (CD4-Cre A20^fl/fl) and control mice with Listeria monocytogenes. A20-deficient pathogen-specific CD8⁺ T cells expanded stronger resulting in improved pathogen control at day 7 p.i. Imaging flow cytometry revealed that A20-deficient Listeria-specific CD8⁺ T cells underwent increased apoptosis and necroptosis resulting in reduced numbers of memory CD8⁺ T cells. In contrast, the primary CD4⁺ T cell response was A20-independent. Upon secondary infection, the increase and function of pathogen-specific CD8⁺ T cells, as well as pathogen control were significantly impaired in CD4-Cre A20^fl/fl mice. In vitro, apoptosis and necroptosis of Listeria-specific A20-deficient CD8⁺ T cells were strongly induced as demonstrated by increased caspase-3/7 activity, RIPK1/RIPK3 complex formation and more morphologically apoptotic and necroptotic CD8⁺ T cells. In vitro, A20 limited CD95L and TNF-induced caspase3/7 activation. In conclusion, T cell-specific A20 limited the expansion but reduced apoptosis and necroptosis of Listeria-specific CD8⁺ T cells, resulting in an impaired pathogen control in primary but improved clearance in secondary infection.

Mycobacterium tuberculosis-specific and MHC class I-restricted CD8+ T-cells exhibit a stem cell precursor-like phenotype in patients with active pulmonary tuberculosis

The nature and longevity of the T-cell response directed against Mycobacterium tuberculosis (MTB) are important for effective pathogen containment. We analyzed ex vivo the nature of MTB antigen-specific T-cell responses directed against the MTB secreted antigens Rv0288, Rv1886c, Rv3875, the antigens Rv2958c, Rv2957, and Rv0447c (intracellular, non-secreted enzymes) in blood from Korean patients with active tuberculosis (TB). MTB-specific T-cell function was defined by intracellular cytokine production (interleukin (IL)-2, interferon gamma, tumour necrosis factor alpha, and IL-17) and by multimer-guided (HLA-A*02:01 and HLA-A*24:02) analysis of epitope-specific CD8+ T-cells, along with phenotypic markers (CD45RA and CCR7), CD107a, a marker for degranulation, and CD127 co-staining for T-cell differentiation and homing. Cytokine production analysis underestimated the frequencies of MTB antigen-specific T-cells defined by major histocompatibility complex (MHC) class I-peptide multimer analysis. We showed that MTB antigen-specific CD8+ T-cells exhibit a distinct marker profile associated with the nature of the MTB antigens, i.e., Rv0288, Rv1886c, and Rv3875-reactive T-cells clustered in the precursor T-cell compartment, whereas Rv2958c, Rv2957, and Rv0447c-reactive T-cells were associated with the terminally differentiated T-cell phenotype, in the patient cohort. Rv0288, Rv1886c, and Rv3875-specific CD8+ T-cells were significantly enriched for CD107a+ T-cells in HLA-A*02:01 (p<0.0001) and HLA-A*24:02 (p=0.0018) positive individuals, as compared to Rv2958c, Rv2957, and Rv0447c antigens. CD127 (IL-7 receptor)-expressing T-cells were enriched in HLA-A*02:01-positive individuals for the Rv0288, Rv1886c, and Rv3875 specificities (p=0.03). A high proportion of antigen-specific T-cells showed a precursor-like phenotype (CD45RA+CCR7+) and expressed the stem cell-associated markers CD95 and c-kit. These data show that MTB-specific T-cells can express stem cell-like features; this is associated with the nature of the MTB antigen and the genetic background of the individual.

Sodium benzoate, a food preservative, affects the functional and activation status of splenocytes at non cytotoxic dose

Sodium benzoate (SB) is a widely used food preservative due to its bacteriostatic and fungistatic properties. The acceptable daily intake of SB is 5 mg/kg-bw, however, it has been found to be used in the food commodities at relatively high levels (2119 mg/kg). Earlier studies on SB have shown its immunosuppressive properties, but comprehensive immunotoxicity data is lacking. Our studies have shown that SB was non cytotoxic in splenocytes up to 1000 μg/ml for 72 h, however at 2500 μg/ml it was found to be cytotoxic. Thus, 1000 μg/ml dose of SB was chosen for the subsequent experiments. SB significantly suppresses the proliferation of Con A and LPS stimulated splenocytes at 72 h, while allogenic response of T cells was significantly decreased after 96 h. SB did not affect the relative expression of CD3e or CD4 molecules following 72 h exposure, however, it downregulated the relative expression of CD8 co-receptor. Further, exposure of splenocytes to SB for 72 h led to reduced expression of CD28 and CD95, which play a vital role in T cell activation. SB also suppresses the relative expression of CD19, CD40 and CD95 receptors on B cells after 72 h. In addition to the functional responses, SB lowered the expression of IL4, IL6, IFNγ and IL17 cytokines in Con A stimulated splenocytes; and IL6, IFNγ and TNFα in LPS stimulated splenocytes following 48 h of exposure. Taken together, the present study is suggestive of the immunomodulatory potential of SB.

Chemokine receptors expression on peripheral CD4-lymphocytes in rheumatoid arthritis: Coexpression of CCR7 and CD95 is associated with disease activity

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial inflammation triggered by infiltrating CD4 lymphocytes. The positioning and activation of lymphocyte in inflamed synovial tissues are dependent on a number of factors including their chemokine receptor expression profile. We aimed to investigate which chemokine receptors pattern correlate with serum cytokine levels and with disease activity. Forty patients with RA (34 female and 6 male) with age range from 21 to 68 years were included. Twenty healthy volunteers (16 female and 4 male) with matched age (range 21-48 years) were served as healthy controls (HCs). Expression of chemokine receptors (CCR5, CX3CR1 and CCR7) together with the apoptosis-related marker (CD95) was analyzed using three-color flow cytometry analysis after gating on CD4(+) peripheral blood lymphocytes. Plasma levels of IL-6, IL-10, IL-12 and TNF-α cytokines were measured in all participants using ELISA. Disease activity score (DAS28-CRP) system was assessed and active disease was defined as DAS28 ⩾3.2. Twenty-five (62.4%) patients were classified as active RA (ARA) and 15 (37.5%) patients with inactive RA (IRA). Percentages of CD4(+) lymphocytes expressing CD95 with either of CCR7 or CCR5 were significantly higher in ARA compared to IRA and HCs groups, while the expression of CX3CR1 on T-cells was found significantly lower in both CD95(-) and CD95(+) T-cells in RA groups than HC. Percentages of CD4(+)CD95(+)CCR7(+) cells correlated positively with IL-6 (r = 0.390). Whereas CD4(+)CD95(+)CX3CR1(+) were negatively correlated with TNF-α (r = -0.261). Correlation of CD4(+)CD95(+)CCR7(+) T cell subset with disease activity and inflammatory cytokines suggests a role for this cell subset in the pathogenesis of RA. Further investigation will be required to fully characterize this cell subset and its role in disease progression.

Effect of CD95 on inflammatory response in rheumatoid arthritis fibroblast-like synoviocytes

OBJECTIVE

Many CD95-expressing cells don't always undergo apoptosis after stimulation with CD95 ligation. The purpose of this paper is to investigate the role of expression of CD95 (Fas/Apo1) on inflammatory response in fibroblast-like synoviocytes (FLS) obtained from rheumatoid arthritis (RA) and to evaluate the role of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB or Akt) pathways within this process.

METHODS

The expression levels of CD95 were monitored by immunohistochemistry and reverse transcription polymerase chain reaction (RT-PCR). Apoptotic cells were detected by in situ apoptosis detection (TUNEL) assay. The RA-FLS were treated with agonistic anti-CD95 antibody or CD95 siRNA. Then the proliferation was detected by CCK-8, and mRNA level of inflammatory cytokines was detected by RT-PCR. After the RA-FLS were treated with agonistic anti-CD95 antibody, the total Akt and pAkt protein expression was analyzed by Western blot, and the changes mentioned above were observed while pre-incubated with the PI3K inhibitor LY294002.

RESULTS

A significant increase of CD95 antigen was found in RA compared with osteoarthritis (OA) samples, while apoptosis in RA synovial tissue was not obvious. Low concentrations of agonistic anti-CD95 antibody could promote RA-FLS growth and interleukin-6 (IL-6) mRNA expression, while high concentrations could induce apoptosis. And both of these phenomena could be inhibited by CD95 siRNA. Agonistic anti-CD95 antibody could stimulate the expression of pAkt, and PI3K specific inhibitor LY294002 could induce opposite changes.

CONCLUSION

Stimulation of CD95 could promote RA-FLS proliferation and inflammation, and activation of the PI3K/Akt signaling pathway might be the possible mechanism.

Tumour necrosis factor superfamily members in the pathogenesis of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the gastrointestinal tract of unclear aetiology of which two major forms are Crohn's disease (CD) and ulcerative colitis (UC). CD and UC are immunologically distinct, although they both result from hyperactivation of proinflammatory pathways in intestines and disruption of intestinal epithelial barrier. Members of the tumour necrosis factor superfamily (TNFSF) are molecules of broad spectrum of activity, including direct disruption of intestinal epithelial barrier integrity and costimulation of proinflammatory functions of lymphocytes. Tumour necrosis factor (TNF) has a well-established pathological role in IBD which also serves as a target in IBD treatment. In this review we discuss the role of TNF and other TNFSF members, notably, TL1A, FasL, LIGHT, TRAIL, and TWEAK, in the pathogenesis of IBD.

Life in the Fas lane: differential outcomes of Fas signaling

Fas, also known as CD95 or APO-1, is a member of the tumor necrosis factor/nerve growth factor superfamily. Although best characterized in terms of its apoptotic function, recent studies have identified several other cellular responses emanating from Fas. These responses include migration, invasion, inflammation, and proliferation. In this review, we focus on the diverse cellular outcomes of Fas signaling and the molecular switches identified to date that regulate its pro- and anti-apoptotic functions. Such switches occur at different levels of signal transduction, ranging from the receptor through to cross-talk with other signaling pathways. Factors identified to date including other extracellular signals, proteins recruited to the death-inducing signaling complex, and the availability of different intracellular components of signal transduction pathways. The success of therapeutically targeting Fas will require a better understanding of these pathways, as well as the regulatory mechanisms that determine cellular outcome following receptor activation.

Metabolic profiling of human CD4+ cells following treatment with methotrexate and anti-TNF-α infliximab

The autoimmune process in rheumatoid arthritis depends on activation of immune cells, which utilize intracellular kinases to respond to external stimuli such as cytokines, immune complexes, and antigens. CD4+ T cells comprise a large proportion of the inflammatory cells that invade the synovial tissue and may therefore be a cell type of pathogenic importance. Both methotrexate and infliximab are effective in the treatment of inflammatory arthritis; however, the biological effects triggered by these treatments and the biochemical mechanisms underlining the cell response are still not fully understood. Thus, in this study the global metabolic changes associated with methotrexate or infliximab treatment of isolated human CD4+ T cells were examined using gas chromatography/mass spectrometry or liquid chromatography/mass spectrometry. In total 148 metabolites involved in selective pathways were found to be significantly altered. Overall, the changes observed are likely to reflect the effort of CD4+ cells to increase the production of cellular reducing power to offset the cellular stress exerted by treatment. Importantly, analysis of the global metabolic changes associated with MTX or infliximab treatment of isolated human CD4+ T cells suggested that the toxicity associated with these agents is minimal when used at clinically relevant concentrations.

FcRγ controls the fas-dependent regulatory function of lymphoproliferative double negative T cells

Patients with autoimmune lymphoproliferative syndrome (ALPS) and lymphoproliferation (LPR) mice are deficient in Fas, and accumulate large numbers of αβ-TCR⁺, CD4⁻, CD8⁻ double negative (DN) T cells. The function of these DN T cells remains largely unknown. The common γ subunit of the activating Fc receptors, FcRγ, plays an important role in mediating innate immune responses. We have shown previously that a significant proportion of DN T cells express FcRγ, and that this molecule is required for TCR transgenic DN T cells to suppress allogeneic immune responses. Whether FcRγ plays a critical role in LPR DN T cell-mediated suppression of immune responses to auto and allo-antigens is not known. Here, we demonstrated that FcRγ⁺, but not FcRγ⁻ LPR DN T cells could suppress Fas⁺ CD4⁺ and CD8⁺ T cell proliferation in vitro and attenuated CD4⁺ T cell-mediated graft-versus host disease. Although FcRγ expression did not allow LPR DN T cells to inhibit the expansion of Fas-deficient cells within the LPR context, adoptive transfer of FcRγ⁺, but not FcRγ⁻, DN T cells inhibited lymphoproliferation in generalized lymphoproliferative disease (GLD) mice. Furthermore, FcRγ acted in a cell-intrinsic fashion to limit DN T cell accumulation by increasing the rate of apoptosis in proliferated cells. These results indicate that FcRγ can confer Fas-dependent regulatory properties on LPR DN T cells, and suggest that FcRγ may be a novel marker for functional DN Tregs.

Immunomodulation and T helper TH₁/TH₂ response polarization by CeO₂ and TiO₂ nanoparticles

Immunomodulation by nanoparticles, especially as related to the biochemical properties of these unique materials, has scarcely been explored. In an in vitro model of human immunity, we demonstrate two catalytic nanoparticles, TiO₂ (oxidant) and CeO₂ (antioxidant), have nearly opposite effects on human dendritic cells and T helper (T_H) cells. For example, whereas TiO₂ nanoparticles potentiated DC maturation that led towards T_H1-biased responses, treatment with antioxidant CeO₂ nanoparticles induced APCs to secrete the anti-inflammatory cytokine, IL-10, and induce a T_H2-dominated T cell profile. In subsequent studies, we demonstrate these results are likely explained by the disparate capacities of the nanoparticles to modulate ROS, since TiO₂, but not CeO₂ NPs, induced inflammatory responses through an ROS/inflammasome/IL-1β pathway. This novel capacity of metallic NPs to regulate innate and adaptive immunity in profoundly different directions via their ability to modulate dendritic cell function has strong implications for human health since unintentional exposure to these materials is common in modern societies.

Low FasL levels promote proliferation of human bone marrow-derived mesenchymal stem cells, higher levels inhibit their differentiation into adipocytes

Mesenchymal stem cells (MSCs) are multipotent progenitor cells that can differentiate into several cell types. Bone marrow (BM)-MSCs mainly differentiate into osteoblasts or adipocytes. MSC interactions with their microenvironment directly affect their self-renewal/differentiation program. Here, we show for the first time that Fas ligand (FasL), a well-explored proapoptotic cytokine, can promote proliferation of BM-derived MSCs in vitro and inhibits their differentiation into adipocytes. BM-MSCs treated with a low FasL dose (0.5 ng/ml) proliferated more rapidly than untreated cells without undergoing spontaneous differentiation or apoptosis, whereas higher doses (25 ng/ml) induced significant though not massive BM-MSC death, with surviving cells maintaining a stem cell phenotype. At the molecular level, 0.5 ng/ml FasL induced ERK1/2 phosphorylation and survivin upregulation, whereas 25 ng/ml FasL induced caspase activation. Importantly, 25 ng/ml FasL reversibly prevented BM-MSC differentiation into adipocytes by modulating peroxisome proliferator-activated receptor gamma (PPARγ) and FABP4/aP2 expression induced by adipogenic medium. All such effects were inhibited by anti-Fas neutralizing antibody. The in vitro data regarding adipogenesis were confirmed using Fas(lpr) mutant mice, where higher PPARγ and FABP4/aP2 mRNA and protein levels were documented in whole tibia. These data show for the first time that the FasL/Fas system can have a role in BM-MSC biology via regulation of both proliferation and adipogenesis, and may have clinical relevance because circulating Fas/FasL levels decline with age and several age-related conditions, including osteoporosis, are characterized by adipocyte accumulation in BM.

Expression of Th17-related genes in PHA/IL-2-activated human T cells by Fas signaling via caspase-1- and Stat3-dependent pathway

T helper 17 (Th17) cells, which produce interleukin 17 (IL-17), are involved in the pathogenesis of autoimmune diseases and inflammatory conditions. Th17 cells have been detected in many Fas ligand-positive tumors. This study investigates the expression of Th17-related genes in PHA/IL-2-activated human T cells upon Fas ligation. Activated T cells transiently express RORγt, IL-17A, and IL-17F. A subsequent Fas receptor stimulation or contact with FasL-expressing glioma cells significantly prolongs the induction of RORγt and Th17-related cytokines. Treatments with inhibitors of caspase-1 and Stat3 reduce the Fas-signal-associated induction of RORγt, IL-17A, and IL-17F, as well as the phosphorylation of Stat3. Although the ligation of Fas results in caspase-8 cleavage and ERK1/2 phosphorylation, inhibitors for caspase-8 and MEK have no effect on the expressions of RORγt, IL-17A, and IL-17F. The results suggest that the Fas signal favors the Th17-phenotypic features of human T cells through the caspase-1/Stat3 signaling pathway.

Pathogen-induced proapoptotic phenotype and high CD95 (Fas) expression accompany a suboptimal CD8+ T-cell response: reversal by adenoviral vaccine

MHC class Ia-restricted CD8⁺ T cells are important mediators of the adaptive immune response against infections caused by intracellular microorganisms. Whereas antigen-specific effector CD8⁺ T cells can clear infection caused by intracellular pathogens, in some circumstances, the immune response is suboptimal and the microorganisms survive, causing host death or chronic infection. Here, we explored the cellular and molecular mechanisms that could explain why CD8⁺ T cell-mediated immunity during infection with the human protozoan parasite Trypanosoma cruzi is not optimal. For that purpose, we compared the CD8⁺ T-cell mediated immune responses in mice infected with T. cruzi or vaccinated with a recombinant adenovirus expressing an immunodominant parasite antigen. Several functional and phenotypic characteristics of specific CD8⁺ T cells overlapped. Among few exceptions was an accelerated expansion of the immune response in adenoviral vaccinated mice when compared to infected ones. Also, there was an upregulated expression of the apoptotic-signaling receptor CD95 on the surface of specific T cells from infected mice, which was not observed in the case of adenoviral-vaccinated mice. Most importantly, adenoviral vaccine provided at the time of infection significantly reduced the upregulation of CD95 expression and the proapoptotic phenotype of pathogen-specific CD8⁺ cells expanded during infection. In parallel, infected adenovirus-vaccinated mice had a stronger CD8 T-cell mediated immune response and survived an otherwise lethal infection. We concluded that a suboptimal CD8⁺ T-cell response is associated with an upregulation of CD95 expression and a proapoptotic phenotype. Both can be blocked by adenoviral vaccination.

Killer lymphocytes are important mediators of the immunological resistance against infections caused by virus, bacteria and parasites. In some circumstances, however, these lymphocytes are unable to properly eliminate the microorganisms which survive, causing death or establishing chronic infections. The purpose of our study was to understand why these killer cells do not succeed during infection with a human protozoan parasite. For that purpose, we compared the immune responses in animals infected or vaccinated. Many characteristics of these killer cells were similar. Among few exceptions was an accelerated immune response in vaccinated animals when compared to infected ones. Also, we observed on the surface of the killer lymphocytes from infected, but not from vaccinated animals, an increased expression of a protein involved in signaling cell death. Most importantly, vaccine significantly reduced the higher expression of this cell-death receptor. In parallel, these animals had a stronger immune response and cured infection. We concluded that a deficient killer cell response observed during infection was associated with an upregulation of this cell-death receptor and it was changed by vaccination.

Combination of biological screening in a cellular model of viral latency and virtual screening identifies novel compounds that reactivate HIV-1

Although highly active antiretroviral therapy (HAART) has converted HIV into a chronic disease, a reservoir of HIV latently infected resting T cells prevents the eradication of the virus from patients. To achieve eradication, HAART must be combined with drugs that reactivate the dormant viruses. We examined this problem in an established model of HIV postintegration latency by screening a library of small molecules. Initially, we identified eight molecules that reactivated latent HIV. Using them as templates, additional hits were identified by means of similarity-based virtual screening. One of those hits, 8-methoxy-6-methylquinolin-4-ol (MMQO), proved to be useful to reactivate HIV-1 in different cellular models, especially in combination with other known reactivating agents, without causing T-cell activation and with lower toxicity than that of the initial hits. Interestingly, we have established that MMQO produces Jun N-terminal protein kinase (JNK) activation and enhances the T-cell receptor (TCR)/CD3 stimulation of HIV-1 reactivation from latency but inhibits CD3-induced interleukin-2 (IL-2) and tumor necrosis factor alpha (TNF-α) gene transcription. Moreover, MMQO prevents TCR-induced cell cycle progression and proliferation in primary T cells. The present study documents that the combination of biological screening in a cellular model of viral latency with virtual screening is useful for the identification of novel agents able to reactivate HIV-1. Moreover, we set the bases for a hypothetical therapy to reactivate latent HIV by combining MMQO with physiological or pharmacological TCR/CD3 stimulation.

Pro- and anti-apoptotic CD95 signaling in T cells

The TNF receptor superfamily member CD95 (Fas, APO-1, TNFRSF6) is known as the prototypic death receptor in and outside the immune system. In fact, many mechanisms involved in apoptotic signaling cascades were solved by addressing consequences and pathways initiated by CD95 ligation in activated T cells or other "CD95-sensitive" cell populations. As an example, the binding of the inducible CD95 ligand (CD95L) to CD95 on activated T lymphocytes results in apoptotic cell death. This activation-induced cell death was implicated in the control of immune cell homeostasis and immune response termination. Over the past years, however, it became evident that CD95 acts as a dual function receptor that also exerts anti-apoptotic effects depending on the cellular context. Early observations of a potential non-apoptotic role of CD95 in the growth control of resting T cells were recently reconsidered and revealed quite unexpected findings regarding the costimulatory capacity of CD95 for primary T cell activation. It turned out that CD95 engagement modulates TCR/CD3-driven signal initiation in a dose-dependent manner. High doses of immobilized CD95 agonists or cellular CD95L almost completely silence T cells by blocking early TCR-induced signaling events. In contrast, under otherwise unchanged conditions, lower amounts of the same agonists dramatically augment TCR/CD3-driven activation and proliferation. In the present overview, we summarize these recent findings with a focus on the costimulatory capacity of CD95 in primary T cells and discuss potential implications for the T cell compartment and the interplay between T cells and CD95L-expressing cells including antigen-presenting cells.

Insights into the molecular regulation of FasL (CD178) biology

Fas ligand (FasL, CD95L, APO-1L, CD178, TNFSF6, APT1LG1) is the key death factor of receptor-triggered programmed cell death in immune cells. FasL/Fas-dependent apoptosis plays a pivotal role in activation-induced cell death, termination of immune responses, elimination of autoreactive cells, cytotoxic effector function of T and NK cells, and the establishment of immune privilege. Deregulation or functional impairment of FasL threatens the maintenance of immune homeostasis and defense and results in severe autoimmunity. In addition, FasL has been implicated as an accessory or costimulatory receptor in T cell activation. The molecular mechanisms underlying this reverse signaling capacity are, however, poorly understood and still controversially discussed. Many aspects of FasL biology have been ascribed to selective protein-protein interactions mediated by a unique polyproline region located in the membrane-proximal intracellular part of FasL. Over the past decade, we and others identified a large number of putative FasL-interacting molecules that bind to this polyproline stretch via Src homology 3 or WW domains. Individual interactions were analyzed in more detail and turned out to be crucial for the lysosomal storage, the transport and the surface appearance of the death factor and potentially also for reverse signaling. This review summarizes the work in the framework of the Collaborative Research Consortium 415 (CRC 415) and provides facts and hypotheses about FasL-interacting proteins and their potential role in FasL biology.