Autoimmune lymphoproliferative syndromes: genetic defects of apoptosis pathways

Mechanistic insight on the role of iRhom2-TNF-α-BAFF signaling pathway in various autoimmune disorders

iRhom2 is a crucial cofactor involved in upregulation of TNF receptors (TNFRs) and the pro-inflammatory cytokine tumor necrosis factor (TNF-) from the cell surface by ADAM17. Tumor necrosis factor- α converting enzyme (TACE) is another name given to ADAM17. Many membrane attached biologically active molecules are cleaved by this enzyme which includes TNFRs and the pro-inflammatory cytokine tumor necrosis factor- α. The TNF receptors are of two types TNFR1 and TNFR2. iRhom2 belongs to the pseudo-protease class of rhomboid family, its abundance is observed in the immune cells. Biological activity of ADAM17 is affected in multiple levels by the iRhom2. ADAM17 is trafficked into the Golgi apparatus by the action of iRhom2, where it gets matured proteolytically and is stimulated to perform its function on the cell surface. This process of activation of ADAM17 results in the protection of the organism from the cascade of inflammatory reactions, as this activation blocks the TNF- α mediated secretion responsible for inflammatory responses produced. Present paper illustrates about the iRhom2-TNF-α-BAFF signaling pathway and its correlation with several autoimmune disorders such as Rheumatoid Arthritis, Systemic Lupus Erythematosus, Hemophilia Arthropathy, Alzheimer's disease and Tylosis with esophageal cancer etc.

[Mechanisms of immunological tolerance and their dysregulation in rheumatic diseases]

The major tasks of the immune system are protection against infectious agents, maintaining homeostasis by recognizing and neutralizing noxious substances from the environment, and monitoring pathological, e.g. neoplastic tissue changes. It accomplishes these tasks through complex interactions of cellular and humoral components of the innate and adaptive immune system. This review article focuses on a central problem of self versus non-self discrimination in the development of B and T lymphocytes as carriers of adaptive immunity. During maturation of the lymphocytes in the bone marrow, large repertoires of lymphocyte receptors are randomly generated by somatic recombination, which as a whole have the capability of recognizing any foreign antigen. In order to reduce the implicit risk of autoaggressive immunity that might arise from evolutionary conserved structural motifs in self and foreign antigens, the adaptive immune system must provide redundant mechanisms (clonal deletion, anergy, quiescence and suppression) to eliminate or inactivate lymphocytes expressing highly avid receptors for autoantigens. Thus, the provision of costimulatory signals resulting in a reduced activation threshold of potentially autoreactive anergic T cells through infection, molecular mimicry, disrupted apoptosis regulation, altered "self" by post-translational modification, genetic changes in transcription factors with critical importance for thymic tolerance induction or signaling components of apoptosis can lead to a disruption of self-tolerance and the induction of pathogenic autoimmunity.

A novel role of Fas in delaying cellular senescence

Fas-mediated apoptosis is a major player of many physiological and pathological cellular processes. Fas-regulated immune regulation exhibits either the beneficial or the harmful effects which is associated with the onset or development of immune disorders. Alterations in apoptosis may contribute to age-associated changes. However, the role of apoptosis in the ageing process remains ambiguous. Here we demonstrated Fas signaling-mediated premature senescence in young mouse embryonic fibroblast (MEF) cells. Activated Fas signaling by agonist Jo-2 resulted in declined senescence in young and aged MEFs. Premature senescence induced the early activation of senescence markers, including the increase in the percentage of SA-β-galactosidase (SA-β-gal) cells, the induction of p53 phosphorylation, and the enhanced expression of p16 and p21 protein and elevated IL-6 pro-inflammatory cytokine in the absence of Fas. The elevated production of reactive oxygen species (ROS) in Fas-deficient MEFs was associated with dysfunctional mitochondria. Further, we determined that the known ROS scavenger NAC (N-acetyl-l-cysteine) could reverse the process of premature senescence in absence of Fas. Therefore, this study signifies a novel role of Fas in the control of cellular senescence.

Thymus antibody-secreting cells: once forgotten but not lost

Antibody-secreting cells are essential contributors to the humoral response. This is due to multiple factors which include: 1) the ability to secrete thousands of antibodies per second, 2) the ability to regulate the immune response and 3) the potential to be long-lived. Not surprisingly, these cells can be found in numerous sites within the body which include organs that directly interface with potential pathogens (e.g., gut) and others that provide long-term survival niches (e.g., bone marrow). Even though antibody-secreting cells were first identified in the thymus of both humans and rodents in the 1960s, if not earlier, only recently has this population begun to be extensively investigated. In this article, we provide an update regarding the current breath of knowledge pertaining to thymus antibody-secreting cells and discuss the potential roles of these cells and their impact on health.

Mesenchymal stem cells empower T cells in the lymph nodes via MCP-1/PD-L1 axis

Mesenchymal stem cells (MSCs) are a type of immunosuppressive stromal cell found in multiple tissues and organs. However, whether MSCs possess immunosupportive characteristics remains unclear. In this study, we showed that the lymph nodes contain immunosupportive MSCs. They produce and secrete a high level of MCP-1 to promote T-cell proliferation and differentiation, in contrast to bone marrow MSCs (BMMSCs), which repress T-cell activation. Unlike BMMSCs, lymph node MSCs (LNMSCs) fail to respond to activated T-cell-induced production of PD-L1 to induce T-cell apoptosis. Mechanistically, MCP-1 activates phospho-Erk to sustain T-cell proliferation and activation while it represses NF-κB/PD-L1 pathway to avoid induction of T-cell apoptosis. Interestingly, inflammatory lymph node-derived LNMSCs abolish their immunosupportive function due to reduction of MCP-1 expression. Finally, we show that systemic infusion of LNMSCs rescues immunosuppression in cytoxan (CTX)-treated mice. This study reveals a previously unrecognized mechanism underlying MSC-based immunoregulation using the MCP-1/PD-L1 axis to energize T cells and suggests a potential to use MSCs to treat immunosuppressive disorders.

Enhancement of Neuroblastoma NK-Cell-Mediated Lysis through NF-kB p65 Subunit-Induced Expression of FAS and PVR, the Loss of Which Is Associated with Poor Patient Outcome

Simple Summary

Neuroblastoma (NB) cells adopt several molecular strategies to evade the Natural Killer (NK)-mediated response. Herein, we found that the overexpression of the NF-kB p65 subunit in NB cell lines upregulates the expression of both the death receptor FAS and the activating ligand PVR, thus rendering NB cells more susceptible to NK-cell-mediated apoptosis, recognition, and killing. These data could provide a clue for a novel NK-cell-based immunotherapy of NB. In addition, array CGH analysis performed in our cohort of NB patients showed that loss of both the FAS and PVR genes correlated with low survival, thus revealing a novel biomarker predicting the outcome of NB patients.

Abstract

High-risk neuroblastoma (NB) is a rare childhood cancer whose aggressiveness is due to a variety of chromosomal genetic aberrations, including those conferring immune evasion. Indeed, NB cells adopt several molecular strategies to evade recognition by the immune system, including the downregulation of ligands for NK-cell-activating receptors. To date, while molecular strategies aimed at enhancing the expression of ligands for NKG2D- and DNAM-1-activating receptors have been explored, no evidence has been reported on the immunomodulatory mechanisms acting on the expression of death receptors such as Fas in NB cells. Here, we demonstrated that transient overexpression of the NF-kB p65 subunit upregulates the surface expression of Fas and PVR, the ligand of DNAM-1, thus making NB cell lines significantly more susceptible to NK-cell-mediated apoptosis, recognition, and killing. In contrast, IFNγ and TNFα treatment, although it induced the upregulation of FAS in NB cells and consequently enhanced NK-cell-mediated apoptosis, triggered immune evasion processes, including the strong upregulation of MHC class I and IDO1, both of which are involved in mechanisms leading to the impairment of a proper NK-cell-mediated killing of NB. In addition, high-resolution array CGH analysis performed in our cohort of NB patients revealed that the loss of FAS and/or PVR genes correlated with low survival independently of the disease stage. Our data identify the status of the FAS and PVR genes as prognostic biomarkers of NB that may predict the efficacy of NK-cell-based immunotherapy of NB. Overall, restoration of surface expression of Fas and PVR, through transient upregulation of NF-kB, may be a clue to a novel NK-cell-based immunotherapy of NB.

Cellular and molecular mechanisms breaking immune tolerance in inborn errors of immunity

In addition to susceptibility to infections, conventional primary immunodeficiency disorders (PIDs) and inborn errors of immunity (IEI) can cause immune dysregulation, manifesting as lymphoproliferative and/or autoimmune disease. Autoimmunity can be the prominent phenotype of PIDs and commonly includes cytopenias and rheumatological diseases, such as arthritis, systemic lupus erythematosus (SLE), and Sjogren's syndrome (SjS). Recent advances in understanding the genetic basis of systemic autoimmune diseases and PIDs suggest an at least partially shared genetic background and therefore common pathogenic mechanisms. Here, we explore the interconnected pathogenic pathways of autoimmunity and primary immunodeficiency, highlighting the mechanisms breaking the different layers of immune tolerance to self-antigens in selected IEI.

Neonatal Autoimmune Lymphoproliferative Syndrome: A Case Report and A Brief Review

The authors are reporting a case of autoimmune lymphoproliferative syndrome in a newborn who presented with massive hepatosplenomegaly, thrombocytopenia, and anemia at birth. Antenatal ultrasound revealed a fetus with hepatosplenomegaly. The infant was treated with steroids and sirolimus and is doing well at 4 years of age. This is the first case report of autoimmune lymphoproliferative syndrome presenting as hepatosplenomegaly during fetal life.

Long term follow-up of pediatric-onset Evans syndrome: broad immunopathological manifestations and high treatment burden

Pediatric-onset Evans syndrome (pES) is defined by both immune thrombocytopenic purpura (ITP) and autoimmune hemolytic anemia (AIHA) before the age of 18 years. There have been no comprehensive long-term studies of this rare disease, which can be associated to various immunopathological manifestations (IM). We report outcomes of the 151 patients with pES and more than 5 years of follow-up from the nationwide French prospective OBS’CEREVANCE cohort. Median age at final follow-up was 18.5 years (range, 6.8–50.0 years) and the median follow-up period was 11.3 years (range, 5.1–38.0 years). At 10 years, ITP and AIHA were in sustained complete remission in 54.5% and 78.4% of patients, respectively. The frequency and number of clinical and biological IM increased with age: at the age of 20 years, 74% had at least one clinical IM (cIM). A wide range of cIM occurred, mainly lymphoproliferation, dermatological, gastrointestinal/hepatic and pneumological IM. The number of cIM was associated with a subsequent increase in the number of second-line treatments received (other than steroids and immunoglobulins; hazard ratio 1.4, 95% Confidence Interval: 1.15–1.60, P=0.0002, Cox proportional hazards method). Survival at 15 years after diagnosis was 84%. Death occurred at a median age of 18 years (range, 1.7–31.5 years), and the most frequent cause was infection. The number of second-line treatments and severe/recurrent infections were independently associated with mortality. In conclusion, long-term outcomes of pES showed remission of cytopenias but frequent IM linked to high second-line treatment burden. Mortality was associated to drugs and/or underlying immunodeficiencies, and adolescents-young adults are a high-risk subgroup.

Key diagnostic markers for autoimmune lymphoproliferative syndrome with molecular genetic diagnosis

Autoimmune lymphoproliferative syndrome (ALPS) is a rare immunodeficiency caused by mutations in genes affecting the extrinsic apoptotic pathway (FAS, FASL, CASP10). This study evaluated the clinical manifestations, laboratory findings, and molecular genetic results of 215 patients referred as possibly having ALPS. Double-negative T-cell (DNT) percentage and in vitro apoptosis functional tests were evaluated by fluorescence-activated cell sorting; interleukin 10 (IL-10) and IL-18 and soluble FAS ligand (sFASL) were measured by enzyme-linked immunosorbent assay. Genetic analysis was performed by next-generation sequencing. Clinical background data were collected from patients’ records. Patients were categorized into definite, suspected, or unlikely ALPS groups, and laboratory parameters were compared among these groups. Of 215 patients, 38 met the criteria for definite ALPS and 17 for suspected ALPS. The definite and suspected ALPS patient populations showed higher DNT percentages than unlikely ALPS and had higher rates of lymphoproliferation. Definite ALPS patients had a significantly more abnormal in vitro apoptosis function, with lower annexin, than patients with suspected ALPS (P = .002) and patients not meeting ALPS criteria (P < .001). The combination of elevated DNTs and an abnormal in vitro apoptosis functional test was the most useful in identifying all types of ALPS patients; the combination of an abnormal in vitro apoptosis functional test and elevated sFASLs was a predictive marker for ALPS-FAS group identification. Lymphoproliferation, apoptosis functional test, and DNTs are the most sensitive markers; elevated IL-10 and IL-18 are additional indicators for ALPS. The combination of elevated sFASLs and abnormal apoptosis function was the most valuable prognosticator for patients with FAS mutations.

Gm614 Protects Germinal Center B Cells From Death by Suppressing Caspase-1 Transcription in Lupus-Prone Mice

Only a few signaling pathways have been reported in germinal center (GC) B-cell proliferation and death. In this study, we showed that a novel uncharacterized Gm614 protein is highly expressed in GC B cells from lupus-prone mice. Critically, ablation of this GC B-cell-specific Gm614 promoted GC B-cell death and mitigation of autoimmune symptoms, whereas overexpression protected GC B cells from death and exacerbated autoimmune symptoms. We demonstrated that mechanistically, nuclear-localized Gm614 reduced caspase-1 expression in GC B cells by binding with caspase-1 promoter to suppress its activation. Our results suggest that Gm614 protects GC B cells from death by suppressing caspase-1 transcription in autoimmune diseases. This may provide some hints for targeting the cell proliferation involved in autoimmune diseases.

Extracellular Vesicles Derived From Apoptotic Cells: An Essential Link Between Death and Regeneration

Apoptosis is a universal and continuous event during tissue development, restoration, repair, and regeneration. Mounting evidence has demonstrated that apoptosis is essential for the activation of tissue regeneration. However, the underlying mechanism remains elusive. A striking development in recent years comes from research on extracellular vesicles (EVs) derived from apoptotic cells. During apoptosis, cells secrete vesicles of various sizes containing various components. Apoptotic cell-derived EVs (ApoEVs) have been found to transit to neighboring cells or cells in distant tissues through the circulation. These vesicles could act as containers to transmit the nucleic acid, protein, and lipid signals to target cells. ApoEVs have been shown to promote regeneration in the cardiovascular system, skin, bone, muscle, kidney, etc. Moreover, several specific signaling pathways mediating the anabolic effects of ApoEVs have been classified. In this review, we comprehensively discussed the latest findings on the function of ApoEVs in tissue regeneration and disease prevention. These findings may reveal unexpected clues regarding the regulatory network between cell death and tissue regeneration and suggest novel targets for regenerative medicine. The findings discussed here also raise the question whether and to what extent ApoEVs contribute to embryonic development. This question is all the more urgent because the exact functions of apoptotic events during numerous developmental processes are still largely unclear.

Off-Label Use of Sirolimus and Everolimus in a Pediatric Center: A Case Series and Review of the Literature

BACKGROUND

It has been 15 years since sirolimus, an mTOR inhibitor, received Food and Drug Administration approval to prevent acute rejection in kidney transplantation, and 8 years since its analog everolimus acquired the same status. Since then, these drugs have become more and more utilized and their immunosuppressive and antiproliferative properties have been tested in a great variety of clinical conditions, often achieving excellent results. Despite such positive evidence, the on-label indications for these rapalogs are still very restrictive, especially in children.

AIMS

The aims of this study were to describe our center's experience with sirolimus and everolimus in managing rare pediatric conditions for which mTOR inhibitors have been reported as a therapeutic option, although without conclusive approval from regulatory agencies, and to evaluate safety and tolerability of the treatment at the prescribed doses.

METHODS

All the subjects who received off-label sirolimus or everolimus at the Pediatric Department of the IRCCS Burlo Garofolo in the last 13 years were included. For each disease found in our case series, we reviewed the current scientific literature.

RESULTS

Off-label treatment with rapalogs was prescribed in 16 children (11 males, 5 females, median age of 9.5 years, range 1-16 years). Seven had immunologic disorders: four autoimmune lymphoproliferative syndrome (ALPS), one multicentric Castleman disease (mCD), one activated PI3K delta kinase syndrome (APDS), and one immunodysregulation with polyendocrinopathy enteropathy X-linked (IPEX). Eight had proliferative disorders or vascular anomalies: one cystic lymphangioma, two Bannayan-Riley-Ruvalcaba syndrome (BRRS), one blue rubber bleb nevus syndrome (BRBNS), two tuberous sclerosis complex (TSC), and one low-flow mixed arterial and venous malformation. One case had congenital hyperinsulinism (CHI). The average dosage administered was 1 mg/m² for sirolimus and 7 mg/m² for everolimus. We experienced a good measurable clinical improvement in 14 patients. Nobody experienced serious adverse events (SAEs). The therapy was interrupted in two cases, for lack of efficacy and poor tolerance in one case and for occurrence of bacterial pneumonia in the other one. A review of the literature identified 101 published reports that met our inclusion criteria.

CONCLUSIONS

Although use of mTOR inhibitors has been considered to be complicated, our experience shows that, using low dosages, it is possible to obtain relevant clinical improvements, with a good profile of safety and tolerability.

Primary and Secondary Immune Cytopenias: Evaluation and Treatment Approach in Children

This review summarizes the evaluation and management of the autoimmune cytopenias, a heterogeneous group of conditions including, but not limited to, autoimmune hemolytic anemia, immune thrombocytopenia, and multilineage disorders in Evans syndrome. These diseases can be challenging to treat and there are limited data comparing second-line therapeutics. The understanding of the molecular cause of these conditions is improving with the goal of advancing therapies and making them more targeted.

Survivin induces defects in apoptosis in eosinophils in intestine with food allergy

Survivin is an anti-apoptosis protein that may be associated with the development of eosinophilia; the latter is associated with the pathogenesis of many immune disorders. Here we report that less apoptotic eosinophils (Eos) were induced in those isolated from mice suffering from food allergy (FA) than those from naive mice after treating with cisplatin in vitro. Exposure to cisplatin induced more Fas ligand (FasL) expression in Eos isolated from naive mice than in those of FA mouse. Survivin was detected in the intestinal tissue extracts in much higher amounts in the FA group than in the naive group. Immunohistochemistry showed that epithelial cells were the major source of survivin in the intestine. Exposure to IL-4 or IL-13 up-regulated the expression of survivin in intestinal epithelial cells. Survivin interfered with the expression of FasL in Eos. Inhibition of survivin attenuated the eosinophilia-related inflammation in the intestine. In conclusion, intestinal epithelial cell-produced survivin induced defects in apoptosis in Eos to contribute to eosinophilia in the intestine. Inhibition of survivin can suppress the eosinophilia-related intestinal inflammation. The data suggest that survivin may be a novel target for the treatment of FA.

Role of Exosomes in the Regulation of T-cell Mediated Immune Responses and in Autoimmune Disease

: T-cell mediated immune responses should be regulated to avoid the development of autoimmune or chronic inflammatory diseases. Several mechanisms have been described to regulate this process, namely death of overactivated T cells by cytokine deprivation, suppression by T regulatory cells (Treg), induction of expression of immune checkpoint molecules such as CTLA-4 and PD-1, or activation-induced cell death (AICD). In addition, activated T cells release membrane microvesicles called exosomes during these regulatory processes. In this review, we revise the role of exosome secretion in the different pathways of immune regulation described to date and its importance in the prevention or development of autoimmune disease. The expression of membrane-bound death ligands on the surface of exosomes during AICD or the more recently described transfer of miRNA or even DNA inside T-cell exosomes is a molecular mechanism that will be analyzed.

Apoptosis and apoptotic body: disease message and therapeutic target potentials

Apoptosis is widely known as programmed cell death eliciting no inflammatory responses. The intricacy of apoptosis has been a focus of an array of researches, accumulating a wealth of knowledge which led to not only a better understanding of the fundamental process, but also potent therapies of diseases. The classic intrinsic and extrinsic signaling pathways of apoptosis, along with regulatory factors have been well delineated. Drugs and therapeutic measures designed based on current understanding of apoptosis have long been employed. Small-molecule apoptosis inducers have been clinically used for eliminating morbid cells and therefore treating diseases, such as cancer. Biologics with improved apoptotic efficacy and selectivity, such as recombinant proteins and antibodies, are being extensively researched and some have been approved by the FDA. Apoptosis also produces membrane-bound vesicles derived from disassembly of apoptotic cells, now known as apoptotic bodies (ApoBDs). These little sealed sacs containing information as well as substances from dying cells were previously regarded as garbage bags until they were discovered to be capable of delivering useful materials to healthy recipient cells (e.g., autoantigens). In this review, current understandings and knowledge of apoptosis were summarized and discussed with a focus on apoptosis-related therapeutic applications and ApoBDs.

Elevated Soluble Fas and FasL in Cerebrospinal Fluid and Serum of Patients With Anti-N-methyl-D-aspartate Receptor Encephalitis

Objective: Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is a severe autoimmune disorder that mainly affects children and young women. The Fas system contains both membrane-bound versions of Fas (mFas) and Fas ligand (mFasL), and soluble versions (sFas and sFasL), which play important roles in apoptosis and regulation of the immune system. Both the levels of sFas and sFasL and the role they play in anti-NMDAR disease pathogenesis remain unclear. Methods: Forty-eight pairs of cerebrospinal fluid (CSF) and serum were collected from patients with anti-NMDAR encephalitis, encephalitis of other causes or peripheral neuropathy. The CSF and serum concentrations of sFas and sFasL were determined with enzyme-linked immunosorbent assay. Results: CSF concentrations of sFas and sFasL were both increased in anti-NMDAR encephalitis patients compared with controls patients. Serum sFas levels were also elevated in anti-NMDAR encephalitis patients relative to controls. sFas and sFasL concentrations in CSF positively correlated with the modified Rankin scale (mRS) both at onset and 6-months follow-up. Conclusion: CSF sFas and sFasL levels were elevated in anti-NMDAR encephalitis patients, and reflect the disease severity of anti-NMDAR encephalitis.

Molecular Classification of Primary Immunodeficiencies of T Lymphocytes

Proper regulation of the immune system is required for protection against pathogens and preventing autoimmune disorders. Inborn errors of the immune system due to inherited or de novo germline mutations can lead to the loss of protective immunity, aberrant immune homeostasis, and the development of autoimmune disease, or combinations of these. Forward genetic screens involving clinical material from patients with primary immunodeficiencies (PIDs) can vary in severity from life-threatening disease affecting multiple cell types and organs to relatively mild disease with susceptibility to a limited range of pathogens or mild autoimmune conditions. As central mediators of innate and adaptive immune responses, T cells are critical orchestrators and effectors of the immune response. As such, several PIDs result from loss of or altered T cell function. PID-associated functional defects range from complete absence of T cell development to uncontrolled effector cell activation. Furthermore, the gene products of known PID causal genes are involved in diverse molecular pathways ranging from T cell receptor signaling to regulators of protein glycosylation. Identification of the molecular and biochemical cause of PIDs can not only guide the course of treatment for patients, but also inform our understanding of the basic biology behind T cell function. In this chapter, we review PIDs with known genetic causes that intrinsically affect T cell function with particular focus on perturbations of biochemical pathways.

Caspase-8: regulating life and death

Roles for cell death in development, homeostasis, and the control of infections and cancer have long been recognized. Although excessive cell damage results in passive necrosis, cells can be triggered to engage molecular programs that result in cell death. Such triggers include cellular stress, oncogenic signals that engage tumor suppressor mechanisms, pathogen insults, and immune mechanisms. The best-known forms of programmed cell death are apoptosis and a recently recognized regulated necrosis termed necroptosis. Of the two best understood pathways of apoptosis, the extrinsic and intrinsic (mitochondrial) pathways, the former is induced by the ligation of death receptors, a subset of the TNF receptor (TNFR) superfamily. Ligation of these death receptors can also induce necroptosis. The extrinsic apoptosis and necroptosis pathways regulate each other and their balance determines whether cells live. Integral in the regulation and initiation of death receptor-mediated activation of programmed cell death is the aspartate-specific cysteine protease (caspase)-8. This review describes the role of caspase-8 in the initiation of extrinsic apoptosis execution and the mechanism by which caspase-8 inhibits necroptosis. The importance of caspase-8 in the development and homeostasis and the way that dysfunctional caspase-8 may contribute to the development of malignancies in mice and humans are also explored.

Dual Role of Fas/FasL-Mediated Signal in Peripheral Immune Tolerance

Fas-mediated apoptosis contributes to physiological and pathological cellular processes, such as differentiation and survival. In particular, the roles of Fas in immune cells are complex and critical for the maintenance of immune tolerance. The precise pathways and unique functions associated with Fas/FasL-mediated signaling in the immune system are known. The dual character of Fas/FasL-mediated immune regulation that induces beneficial or harmful effects is associated with the onset or development of immune disorders. Studies on mutations in genes encoding Fas and FasL gene of humans and mice contributed to our understanding of the pathogenesis of autoimmune diseases. Here, we review the opposing functions of Fas/FasL-mediated signaling, bilateral effects of Fas/FasL on in immune cells, and complex pathogenesis of autoimmunity mediated by Fas/FasL.

In Vitro Evaluation of the Apoptosis Function in Human Activated T Cells

The apoptosis function can be monitored on human lymphocytes by quantifying the induced-death upon apoptotic stimuli involving either the extrinsic or the intrinsic pathway on in vitro activated T cells. Her, we describe an in vitro assay allowing the monitoring of three different apoptosis pathways: (1) the FAS-induced pathway, (2) the activation-induced cell death (AICD), and (3) the death induced by starvation of the cells, called activated-cell autonomous death (ACAD).

Dietary n-3 PUFAs augment caspase 8 activation in Staphylococcal aureus enterotoxin B stimulated T-cells

Epidemiological studies have linked consumption of n-3 PUFAs with a variety of beneficial health benefits, particularly with respect to putative anti-inflammatory effects. Unfortunately, many of these results remain somewhat controversial because in most instances there has not been a linkage to specific molecular mechanisms. For instance, dietary exposure to low levels of mercury has been shown to be damaging to neural development, but concomitant ingestion of n-3 PUFAs as occurs during consumption of fish, has been shown to counteract the detrimental effects. As the mechanisms mediating the neurotoxicity of environmental mercury are not fully delineated, it is difficult to conceptualize a testable molecular mechanism explaining how n-3 PUFAs negate its neurotoxic effects. However, environmental exposure to mercury also has been linked to increased autoimmunity. By way of a molecular understanding of this immuno-toxic association, disruption of CD95 signaling is well established as a triggering factor for autoimmunity, and we have previously shown that environmentally relevant in vitro and dietary exposures to mercury interfere with CD95 signaling. In particular we have shown that activation of caspase 8, as well as downstream activation of caspase 3, in response to CD95 agonist stimulation is depressed by mercury. More recently we have shown in vitro that the n-3 PUFA docosahexaenoic acid counteracts the negative effect of mercury on CD95 signaling by restoring caspase activity. We hypothesized that concomitant ingestion of n-3 PUFAs with mercury might be protective from the immuno-toxic effects of mercury, as it is with mercury's neuro-toxic effects, and in the case of immuno-toxicity this would be related to restoration of CD95 signal strength. We now show that dietary ingestion of n-3 PUFAs generally promotes CD95 signaling by upregulating caspase 8 activation. Apart from accounting for the ability of n-3 PUFAs to specifically counteract autoimmune sequelae of mercury exposure, this novel finding for the first time suggests a testable molecular mechanism explaining the overall anti-inflammatory properties of n-3 PUFAs.

Defective Function of the Fas Apoptotic Pathway in Type 1 Diabetes Mellitus Correlates with Age at Onset

The Fas death receptor triggers lymphocyte apoptosis through an extrinsic and an intrinsic pathway involving caspase-8 and -9 respectively. Inherited defects of Fas function are displayed by a proportion of patients with Type 1 diabetes mellitus (T1DM) especially those with a second autoimmunity (T1DM-p). This study assesses activation of both pathways in Fas-resistant (FasR) patients to localize the defect. 21/28 (75%) T1DM-p, 14/50 (38%) T1DM, and 7/150 (5%) controls were FasR. Analysis of the 35 FasR patients and 20 Fas-sensitive (FasS) controls showed that caspase-9 activity was lower in T1DM-p and T1DM than in controls, whereas caspase-8 activity was lower in T1DM-p than in T1DM and the controls. Single patient analysis showed that 16/35 patients displayed defective activity of one (FasR1), whereas 19 displayed normal activity of both caspases (FasR2) Ages at onset of diabetes mellitus in T1DM and the second autoimmune disease in T1DM-p were lower in FasR than in FasS patients. All FasR1 patients developed diabetes mellitus before the age of 9 years, whereas a later onset was displayed by 26% FasR2 and 53% FasS patients. These data show that defective Fas function may involve both the extrinsic and intrinsic pathway in T1DM and severity correlates with the precocity of the autoimmune attack and its tissue polyreactivity.

The intersection of immune deficiency and autoimmunity

PURPOSE OF REVIEW

Immune deficiency and autoimmunity have been recognized as cotravelers for decades. This clinically oriented review brings together our evolving mechanistic understanding to highlight associations of particular relevance to rheumatologists.

RECENT FINDINGS

Conceptually, all autoimmunity derives from a loss of tolerance. This distinguishes it from autoinflammation in which the innate immune system is dysregulated without necessarily affecting tolerance. Studies have demonstrated the profound effects of signaling defects, apoptotic pathways and the ramifications of homeostatic proliferation on tolerance. This foundation has translated into an improved understanding of the specific associations of autoimmune diseases with immune deficiencies. This important foundation paves the way for personalized treatment strategies.

SUMMARY

This review identifies critical mechanisms important to conceptualize the association of primary immune deficiencies and autoimmunity. It highlights a growing appreciation of the hidden single gene defects affecting T-cells within the group of patients with early-onset pleomorphic autoimmunity.

Regulation of proximal T cell receptor signaling and tolerance induction by deubiquitinase Usp9X

The T cell hyperproliferation and autoimmune phenotypes that manifest in mice lacking E3 ubiquitin ligases such as Cbl, ITCH, or GRAIL highlight the importance of ubiquitination for the maintenance of peripheral T cell tolerance. Less is known, however, about the deubiquitinating enzymes that regulate T cell proliferation and effector function. Here, we define a cell intrinsic role for the deubiquitinase Usp9X during proximal TCR signaling. Usp9X-deficient T cells were hypoproliferative, yet mice with T cell-specific Usp9x deletion had elevated numbers of antigen-experienced T cells and expanded PD-1 and OX40-expressing populations consistent with immune hyperactivity. Aged Usp9x KO mice developed lupus-like autoimmunity and lymphoproliferative disease, indicating that ubiquitin ligases and deubiquitinases maintain the delicate balance between effective immunity and self-tolerance.

Silica exposure and altered regulation of autoimmunity

Silica particles and asbestos fibers, which are known as typical causatives of pneumoconiosis, induce lung fibrosis. Moreover, silicosis patients often complicate with autoimmune diseases, and asbestos-exposed patients suffer from malignant diseases such as pleural mesothelioma and lung cancer. We have been conducting experimental studies to investigate altered regulation of self-tolerance caused by silica exposure, including analyses using specimens such as plasma and immunocompetent cells obtained from silicosis patients, as a means of examining the supposition that silica exposure induces molecular and cellular biological alterations of immune cells. These approaches have resulted in the detection of several specific autoantibodies, alterations of CD95/Fas and its related molecules, and evidence of chronic activation of responder T cells and regulatory T cells following silica exposure. In this review, we present details of our investigations as an introduction to scientific approaches examining the immunological effects of environmental and occupational substances.

Bcl-2 knockdown accelerates T cell receptor-triggered activation-induced cell death in jurkat T cells

Cell death and survival are tightly controlled through the highly coordinated activation/inhibition of diverse signal transduction pathways to insure normal development and physiology. Imbalance between cell death and survival often leads to autoimmune diseases and cancer. Death receptors sense extracellular signals to induce caspase-mediated apoptosis. Acting upstream of CED-3 family proteases, such as caspase-3, Bcl-2 prevents apoptosis. Using short hairpin RNAs (shRNAs), we suppressed Bcl-2 expression in Jurkat T cells, and this increased TCR-triggered AICD and enhanced TNFR gene expression. Also, knockdown of Bcl-2 in Jurkat T cells suppressed the gene expression of FLIP, TNF receptor-associated factors 3 (TRAF3) and TRAF4. Furthermore, suppressed Bcl-2 expression increased caspase-3 and diminished nuclear factor kappa B (NF-κB) translocation.

Diagnosis and management of autoimmune cytopenias in childhood

The diagnosis and management of children with autoimmune cytopenias can be challenging. Children can present with immune-mediated destruction of a single-cell lineage or multiple cell lineages, including platelets (immune thrombocytopenia [ITP]), erythrocytes (autoimmune hemolytic anemia), and neutrophils (autoimmune neutropenia). Immune-mediated destruction can be primary or secondary to a comorbid immunodeficiency, malignancy, rheumatologic condition, or lymphoproliferative disorder. Treatment options generally consist of nonspecific immune suppression or modulation. This nonspecific approach is changing as recent insights into disease biology have led to targeted therapies, including the use of thrombopoietin mimetics in ITP and sirolimus for cytopenias associated with autoimmune lymphoproliferative syndrome.

[Advances in the knowledge and management of autoimmune lymphoproliferative syndrome]

Autoimmune lymphoproliferative syndrome (ALPS) represents a failure of apoptotic mechanisms to maintain lymphocyte homeostasis. ALPS often manifest in childhood with cytopenias, chronic non-malignant lymphoproliferation and autoimmune complications. A number of new insights have improved the understanding of the genetics and biology of ALPS. The treatment of the disease has changed and mycophenolate mofetil and sirolimus have been demonstrated to have marked activity against the disease, improving quality of life for many patients. These will be discussed in this review.

Causes and consequences of the autoimmune lymphoproliferative syndrome

Autoimmune lymphoproliferative syndrome (ALPS) is the first autoimmune hematological disease whose genetic basis has been defined. It is a disorder of apoptosis in which the inability of lymphocytes to die leads to lymphadenopathy, hypersplenism, and autoimmune cytopenias of childhood onset. More than 200 ALPS patients have been studied over the last 15 years and followed by our colleagues and ourselves at the Clinical Center of the National Institutes of Health. Based upon this experience we have determined that patients with germline mutations of the intracellular domain of Fas protein, the most frequent single genetic cause of ALPS, have a significantly increased risk of developing Hodgkin and non-Hodgkin lymphoma (NHL), underscoring the critical role played by cell surface receptor-mediated apoptosis in eliminating redundant proliferating lymphocytes with autoreactive and oncogenic potential. The major determinants of morbidity and mortality in ALPS are the severity of the autoimmune disease, hypersplenism, asplenia-related sepsis, and the risk of lymphoma, which in itself requires long-term surveillance. Though most episodes of cytopenias respond to courses of conventional immunomodulatory agents, some ALPS patients, especially those with massive splenomegaly and hypersplenism, may require splenectomy and/or ongoing immunosuppressive treatment. Thus, ALPS highlights the importance of cell death pathways in health and disease.

Microarray analysis reveals the molecular basis of antiarthritic activity of huo-luo-xiao-ling dan

Rheumatoid arthritis (RA) is a chronic inflammatory disease of autoimmune origin. Huo-luo-xiao-ling dan (HLXL) is an herbal mixture that has been used in traditional Chinese medicine over several decades to treat chronic inflammatory diseases including RA. However, the mechanism of the anti-arthritic action of this herbal remedy is poorly understood at the molecular level. In this study, we determined by microarray analysis the effects of HLXL on the global gene expression profile of the draining lymph node cells (LNC) in the rat adjuvant arthritis (AA) model of human RA. In LNC restimulated in vitro with the disease-related antigen mycobacterial heat-shock protein 65 (Bhsp65), 84 differentially expressed genes (DEG) (64 upregulated and 20 downregulated) versus 120 DEG (94 upregulated and 26 downregulated) were identified in HLXL-treated versus vehicle (Water)-treated rats, respectively, and 62 DEG (45 upregulated and 17 downregulated) were shared between the two groups. The most affected pathways in response to HLXL treatment included immune response, inflammation, cellular proliferation and apoptosis, and metabolic processes, many of which are directly relevant to arthritis pathogenesis. These results would advance our understanding of the mechanisms underlying the anti-arthritic activity of HLXL.

Somatic loss of heterozygosity, but not haploinsufficiency alone, leads to full-blown autoimmune lymphoproliferative syndrome in 1 of 12 family members with FAS start codon mutation

We describe a family with 12 members carrying a heterozygous germline FAS c.3G>T start codon mutation leading to FAS haploinsufficiency. One patient had autoimmune lymphoproliferative syndrome (ALPS), one had recovered from ALPS, and ten mutation-positive relatives (MPRs) were healthy. FAS-mediated apoptosis and surface expression of FAS in single-positive T cells were lower for MPRs but did not discriminate between them and the ALPS patient. However, double-negative (DN) T cells of the ALPS patient had no FAS expression due to somatic loss of heterozygosity. Our results in this kindred suggest that FAS haploinsufficiency does not cause ALPS-FAS, but that modifying genetic events are crucial for its pathogenesis. FAS surface expression on DN T cells should be assessed routinely and FAS haploinsufficient patients should be followed as its potential for lymphomagenesis is not well defined and a second hit might occur later on.

Auto-immune lymphoproliferative disorder and other secondary immune thrombocytopenias in childhood

Primary immune thrombocytopenia (ITP) in childhood, typically presents as an acute self-limiting illness. However, secondary ITP is often a chronic disorder due to an underlying disease. Combined cytopenias in childhood, that is, secondary ITP occurring with auto-immune hemolytic anemia and/or auto-immune neutropenia, are often associated with disorders characterized by immune dysregulation. Such disorders include systemic lupus erythematosus, auto-immune lymphoproliferative syndrome, and common variable immune deficiency. Evans syndrome describes the combination of ITP, autoimmune hemolytic anemia, and/or autoimmune neutropenia. However, it is now clear that some patients with Evans syndrome have an underlying immunodeficiency. This report focuses on combined auto-immune cytopenias and highlights the challenges in their diagnosis and management.

Probiotic-induced apoptosis and its potential relevance to mucosal inflammation of gastrointestinal tract

In this short review we attempt to establish and/or strengthen connections between probiotics administration and apoptotic pathway in gastrointestinal tract. The disturbance of apoptosis is mainly deliberated in the framework of insufficient removal of immuno-effector cells that may cause autoimmunity. In the context of the inflammatory bowel disease (IBD) and necrotizing enterocolitis (NEC), the commensal bacteria and their products effect on gut and immune cell survival are illustrated. The multitude of mechanisms of probiotics to induce cell death is shortly summarized and some aspects of it are being discussed in greater detail. The mechanism of intestinal cell death induced by probiotic administration and its influence on the immune system and potential benefits of apoptosis induction during probiotic therapy is indicated.

Epigenetics, autoimmunity and hematologic malignancies: a comprehensive review

The relationships between immunological dysfunction, loss of tolerance and hematologic malignancies have been a focus of attention in attempts to understand the appearance of a higher degree of autoimmune disease and lymphoma in children with congenital immunodeficiency. Although multiple hypotheses have been offered, it is clear that stochastic processes play an important role in the immunopathology of these issues. In particular, accumulating evidence is defining a role of epigenetic mechanisms as being critical in this continuous spectrum between autoimmunity and lymphoma. In this review, we focus attention predominantly on the relationships between T helper 17 (Th17) and T regulatory populations that alter local microenvironments and ultimately the expression or transcription factors involved in cell activation and differentiation. Abnormal expression in any of the molecules involved in Th17 and/or Treg development alter immune homeostasis and in genetically susceptible hosts may lead to the appearance of autoimmunity and/or lymphoma. These observations have clinical significance in explaining the discordance of autoimmunity in identical twins. They are also particularly important in the relationships between primary immune deficiency syndromes, immune dysregulation and an increased risk of lymphoma. Indeed, defining the factors that determine epigenetic alterations and their relationships to immune homeostasis will be a challenge greater or even equal to the human genome project.

Altered regulatory mechanisms governing cell survival in children affected with clustering of autoimmune disorders

Clustering of Autoimmune Diseases (CAD) is now emerging as a novel clinical entity within monogenic immune defects with a high familial occurrence. Aim of this study is to evaluate the regulatory mechanisms governing cell survival, paying a particular attention to Fas-induced apoptosis, in a cohort of 23 children affected with CAD. In 14 patients, Fas stimulation failed to induce cell apoptosis and in 1 case it was associated with Fas gene mutation. Our study highlights the importance to evaluate cell apoptosis in the group of children with CAD, which, with this regard, represents a distinct clinical entity.

Autoimmune lymphoproliferative syndrome caused by a homozygous null FAS ligand (FASLG) mutation

BACKGROUND

Autoimmune lymphoproliferative syndrome (ALPS) is characterized by chronic nonmalignant lymphoproliferation, accumulation of double-negative T cells, hypergammaglobulinemia G and A, and autoimmune cytopenia.

OBJECTIVES

Although mostly associated with FAS mutations, different genetic defects leading to impaired apoptosis have been described in patients with ALPS, including the FAS ligand gene (FASLG) in rare cases. Here we report on the first case of complete FAS ligand deficiency caused by a homozygous null mutant.

METHODS

Double-negative T-cell counts and plasma IL-10 and FAS ligand concentrations were determined as ALPS markers. The FASLG gene was sequenced, and its expression was analyzed by means of Western blotting. FAS ligand function was assessed based on reactivation-induced cell death.

RESULTS

We describe a patient born to consanguineous parents who presented with a severe form of ALPS caused by FASLG deficiency. Although the clinical presentation was compatible with a homozygous FAS mutation, FAS-induced apoptosis was normal, and plasma FAS ligand levels were not detectable. This patient carries a homozygous, germline, single-base-pair deletion in FASLG exon 1, leading to a premature stop codon (F87fs x95) and a complete defect in FASLG expression. The healthy parents were each heterozygous for the mutation, confirming its recessive trait.

CONCLUSION

FAS ligand deficiency should be screened in patients presenting with ALPS features but lacking the usual markers, including plasma soluble FAS ligand and an in vitro apoptotic defect. An activation-induced cell death test could help in discrimination.

Up-regulation of fas and fasL pro-apoptotic genes expression in type 1 diabetes patients after autologous haematopoietic stem cell transplantation

Type 1 diabetes (T1D) is a chronic autoimmune disease characterized by T cell-mediated destruction of pancreatic β cells, resulting in insulin deficiency and hyperglycaemia. Recent studies have described that apoptosis impairment during central and peripheral tolerance is involved in T1D pathogenesis. In this study, the apoptosis-related gene expression in T1D patients was evaluated before and after treatment with high-dose immunosuppression followed by autologous haematopoietic stem cell transplantation (HDI-AHSCT). We also correlated gene expression results with clinical response to HDI-AHSCT. We observed a decreased expression of bad, bax and fasL pro-apoptotic genes and an increased expression of a1, bcl-x(L) and cIAP-2 anti-apoptotic genes in patients' peripheral blood mononuclear cells (PBMCs) compared to controls. After HDI-AHSCT, we found an up-regulation of fas and fasL and a down-regulation of anti-apoptotic bcl-x(L) genes expression in post-HDI-AHSCT periods compared to pre-transplantation. Additionally, the levels of bad, bax, bok, fasL, bcl-x(L) and cIAP-1 genes expression were found similar to controls 2 years after HDI-AHSCT. Furthermore, over-expression of pro-apoptotic noxa at 540 days post-HDI-AHSCT correlated positively with insulin-free patients and conversely with glutamic acid decarboxylase autoantibodies (GAD65) autoantibody levels. Taken together, the results suggest that apoptosis-related genes deregulation in patients' PBMCs might be involved in breakdown of immune tolerance and consequently contribute to T1D pathogenesis. Furthermore, HDI-AHSCT modulated the expression of some apoptotic genes towards the levels similar to controls. Possibly, the expression of these apoptotic molecules could be applied as biomarkers of clinical remission of T1D patients treated with HDI-AHSCT therapy.

Mutual antagonism of TGF-beta and Interleukin-2 in cell survival and lineage commitment of induced regulatory T cells

Transforming growth factor beta (TGF-β)- and Interleukin-2 (IL-2)-mediated signaling enables the generation and expansion of induced regulatory T (iTreg) cells that carry high hopes for the treatment of chronic inflammatory and autoimmune diseases. Knowledge about factors stabilizing their lineage commitment and lifespan, however, is limited. Here, we investigated the behavior of iTreg cells, derived from apoptosis-defective mouse mutants, during activated cell autonomous cell death, triggered by cytokine-deprivation, or activation-induced cell death (AICD) after restimulation of the T-cell receptor, and compared these responses with those of effector T cells. We observed that iTreg cells were much more sensitive to IL-2-deprivation but poorly susceptible to AICD. In fact, when apoptosis was compromised, T-cell receptor (TCR)-religation resulted in methylation-independent, ERK- and PI3K/mTOR-mediated loss of Foxp3 expression, impaired suppressive capacity and effector cytokine production. Although iTreg cells prevented colitis induction they rapidly lost Foxp3-GFP expression and gained ability to produce effector cytokines thereby imposing Th1 cell fate on resident effector cells. Surprisingly, iTreg cell conversion itself was limited by TGF-β-mediated Bim/Bcl2L11-dependent apoptosis. Hence, the very same cytokine that drives the generation of iTreg cells can trigger their demise. Our results provide novel insights in iTreg cell biology that will assist optimization of iTreg-based therapy.

New advances in the diagnosis and treatment of autoimmune lymphoproliferative syndrome

PURPOSE OF REVIEW

Autoimmune lymphoproliferative syndrome (ALPS) is a disorder of disrupted lymphocyte homeostasis, resulting from mutations in the Fas apoptotic pathway. Clinical manifestations include lymphadenopathy, splenomegaly, and autoimmune cytopenias. A number of new insights have improved the understanding of the genetics and biology of ALPS. These will be discussed in this review.

RECENT FINDINGS

A number of key observations have been made recently that better define the pathophysiology of ALPS, including the characterization of somatic FAS variant ALPS, the identification of haploinsufficiency as a mechanism of decreased Fas expression, and the description of multiple genetic hits in FAS in some families that may explain the variable penetrance of the disease. In addition, ALPS has been shown to be a more common condition, as patients diagnosed with other disorders, including Evans syndrome and common variable immune deficiency, have been found to have ALPS. Finally, the treatment of the disease has changed as splenectomy and rituximab have been shown to have unexpected ALPS-specific toxicities, and mycophenolate mofetil and sirolimus have been demonstrated to have marked activity against the disease.

SUMMARY

On the basis of novel advances, the diagnostic algorithm and recommended treatment for ALPS have changed significantly, improving quality of life for many patients.

Defective cell death signalling along the Bcl-2 regulated apoptosis pathway compromises Treg cell development and limits their functionality in mice

The Bcl-2 regulated apoptosis pathway is critical for the elimination of autoreactive lymphocytes, thereby precluding autoimmunity. T cells escaping this process can be kept in check by regulatory T (Treg) cells expressing the transcription and lineage commitment factor Foxp3. Despite the well-established role of Bcl-2 family proteins in shaping the immune system and their frequent deregulation in autoimmune pathologies, it is poorly understood how these proteins affect Treg cell development and function. Here we compared the relative expression of a panel of 40 apoptosis-associated genes in Treg vs. conventional CD4⁺ T cells. Physiological significance of key-changes was validated using gene-modified mice lacking or overexpressing pro- or anti-apoptotic Bcl-2 family members. We define a key role for the Bim/Bcl-2 axis in Treg cell development, homeostasis and function but exclude a role for apoptosis induction in responder T cells as relevant suppression mechanism. Notably, only lack of the pro-apoptotic BH3-only protein Bim or Bcl-2 overexpression led to accumulation of Treg cells while loss of pro-apoptotic Bad, Bmf, Puma or Noxa had no effect. Remarkably, apoptosis resistant Treg cells showed reduced suppressive capacity in a model of T cell-driven colitis, posing a caveat for the use of such long-lived cells in possible therapeutic settings.

A thermodynamic perspective of immune capabilities

We consider the mutual interactions, via cytokine exchanges, among helper lymphocytes, B lymphocytes and killer lymphocytes, and we model them as a unique system by means of a tripartite network. Each part includes all the different clones of the same lymphatic subpopulation, whose couplings to the others are either excitatory or inhibitory (mirroring elicitation and suppression by cytokine). First of all, we show that this system can be mapped into an associative neural network, where helper cells directly interact with each other and are able to secrete cytokines according to "strategies" learn by the system and profitable to cope with possible antigenic stimulation; the ability of such a retrieval corresponds to a healthy reaction of the immune system. We then investigate the possible conditions for the failure of a correct retrieval and distinguish between the following outcomes: massive lymphocyte expansion/suppression (e.g. lymphoproliferative syndromes), subpopulation unbalance (e.g. HIV, EBV infections) and ageing (thought of as noise growth); the correlation of such states to autoimmune diseases is also highlighted. Lastly, we discuss how self-regulatory effects within each effector branch (i.e. B and killer lymphocytes) can be modeled in terms of a stochastic process, ultimately providing a consistent bridge between the tripartite-network approach introduced here and the immune networks developed in the last decades.

KLHDC8B in Hodgkin lymphoma and possibly twinning

A key feature of Hodgkin lymphoma is that the malignant cells are binucleated, as a consequence of failed cytokinesis. We recently ascertained a family in which multiple cases of Hodgkin lymphoma had occurred among individuals who inherited a balanced chromosomal translocation. We cloned the translocation breakpoints and found that it disrupted a previously uncharacterized gene, KLHDC8B, encoding a Kelch family protein whose deficiency impairs cytokinesis and leads to binucleated cells. In other families we found a rare single nucleotide polymorphism affecting mitotic translation of KLHDC8B that was associated with and linked to Hodgkin lymphoma. Interestingly, the index family demonstrated an unusual frequency of twins, and there is a previously reported association between Hodgkin lymphoma and twins. Here we review the unusual genetic features of Hodgkin lymphoma, including gender concordance among siblings, and genetically test the hypothesis that KLHDC8B may participate in twinning by disrupting cytokinesis through impediment of polar body separation from oocytes.

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.