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

Caspase family in autoimmune diseases

Programmed cell death (PCD) plays a crucial role in maintaining tissue homeostasis, with its primary forms including apoptosis, pyroptosis, and necroptosis. The caspase family is central to these processes, and its complex functions across different cell death pathways and other non-cell death roles have been closely linked to the pathogenesis of autoimmune diseases. This article provides a comprehensive review of the role of the caspase family in autoimmune diseases such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), type 1 diabetes (T1D), and multiple sclerosis (MS). It particularly emphasizes the intricate functions of caspases within various cell death pathways and their potential as therapeutic targets, thereby offering innovative insights and a thorough discussion in this field. In terms of therapy, strategies targeting caspases hold significant promise. We emphasize the importance of a holistic understanding of caspases in the overall concept of cell death, exploring their unique functions and interrelationships across multiple cell death pathways, including apoptosis, pyroptosis, necroptosis, and PANoptosis. This approach transcends the limitations of previous studies that focused on singular cell death pathways. Additionally, caspases play a key role in non-cell death functions, such as immune cell activation, cytokine processing, inflammation regulation, and tissue repair, thereby opening new avenues for the treatment of autoimmune diseases. Regulating caspase activity holds the potential to restore immune balance in autoimmune diseases. Potential therapeutic approaches include small molecule inhibitors (both reversible and irreversible), biological agents (such as monoclonal antibodies), and gene therapies. However, achieving specific modulation of caspases to avoid interference with normal physiological functions remains a major challenge. Future research must delve deeper into the regulatory mechanisms of caspases and their associated complexes linked to PANoptosis to facilitate precision medicine. In summary, this article offers a comprehensive and in-depth analysis, providing a novel perspective on the complex roles of caspases in autoimmune diseases, with the potential to catalyze breakthroughs in understanding disease mechanisms and developing therapeutic strategies.

Nr4a1 and Nr4a3 redundantly control clonal deletion and contribute to an anergy-like transcriptome in auto-reactive thymocytes to impose tolerance in mice

The Nr4a nuclear hormone receptors are transcriptionally upregulated in response to antigen recognition by the T cell receptor (TCR) in the thymus and are implicated in clonal deletion, but the mechanisms by which they operate are not clear. Moreover, their role in central tolerance is obscured by redundancy among the Nr4a family members and by their reported functions in Treg generation and maintenance. Here we take advantage of competitive bone marrow chimeras and the OT-II/RIPmOVA model to show that Nr4a1 and Nr4a3 are essential for the upregulation of Bcl2l11/BIM and thymic clonal deletion by self-antigen. Importantly, thymocytes lacking Nr4a1/3 acquire an anergy-like signature after escaping clonal deletion and Treg lineage diversion. We further show that the Nr4a family helps mediate a broad transcriptional program in self-reactive thymocytes that resembles anergy and may operate at the margins of canonical thymic tolerance mechanisms to restrain self-reactive T cells after thymic egress.

Interleukins 4 and 21 Protect Anti-IgM Induced Cell Death in Ramos B Cells: Implication for Autoimmune Diseases

Interleukins 4 (IL-4) and 21 (IL-21) belong to the common gamma chain cytokine family which are highly involved in the progression of autoimmune diseases. While IL-4 is well known to be involved in the suppression of apoptosis of autoreactive B cells, the role played by IL-21 remains unclear. In the current study, we activated the human Burkitt’s lymphoma Ramos B cells with anti-IgM to mimic B cell hyperactivation observed in patients of autoimmune diseases. Consistent with other reported findings, anti-IgM led to the downregulation of proteins involved in B cell survival and proliferation, as well as the activation of caspase 3 activity and DNA damage, resulting in apoptotic cell death after 48-hour treatment. Although both IL-4 and IL-21 reversed anti-IgM-induced apoptosis and cell cycle arrest, they did so via different mechanisms: while IL-4 could directly suppress anti-IgM-induced caspase 3 activation and marker indicative of DNA damage, IL-21 could induce B cell proliferation in the presence of anti-IgM. Importantly, IL-21 also suppressed activation induced cell death in human primary B cells. Pre-treatment with clinically validated JAK inhibitors completely reversed the effects of IL-4 and IL-21 to rescue anti-IgM induced cell death and DNA damage. The results indicate the underlying mechanisms of how IL-4 and IL-21 differentially promote survival of hyperactivated B cells and provide hints to treat autoimmune diseases.

Therapeutic approaches targeting CD95L/CD95 signaling in cancer and autoimmune diseases

Cell death plays a pivotal role in the maintenance of tissue homeostasis. Key players in the controlled induction of cell death are the Death Receptors (DR). CD95 is a prototypic DR activated by its cognate ligand CD95L triggering programmed cell death. As a consequence, alterations in the CD95/CD95L pathway have been involved in several disease conditions ranging from autoimmune diseases to inflammation and cancer. CD95L-induced cell death has multiple roles in the immune response since it constitutes one of the mechanisms by which cytotoxic lymphocytes kill their targets, but it is also involved in the process of turning off the immune response. Furthermore, beyond the canonical pro-death signals, CD95L, which can be membrane-bound or soluble, also induces non-apoptotic signaling that contributes to its tumor-promoting and pro-inflammatory roles. The intent of this review is to describe the role of CD95/CD95L in the pathophysiology of cancers, autoimmune diseases and chronic inflammation and to discuss recently patented and emerging therapeutic strategies that exploit/block the CD95/CD95L system in these diseases.

Prognostic features of the tumour microenvironment in oesophageal adenocarcinoma

Oesophageal adenocarcinoma (OAC) is a disease with an incredibly poor survival rate and a complex makeup. The growth and spread of OAC tumours are profoundly influenced by their surrounding microenvironment and the properties of the tumour itself. Constant crosstalk between the tumour and its microenvironment is key to the survival of the tumour and ultimately the death of the patient. The tumour microenvironment (TME) is composed of a complex milieu of cell types including cancer associated fibroblasts (CAFs) which make up the tumour stroma, endothelial cells which line blood and lymphatic vessels and infiltrating immune cell populations. These various cell types and the tumour constantly communicate through environmental cues including fluctuations in pH, hypoxia and the release of mitogens such as cytokines, chemokines and growth factors, many of which help promote malignant progression. Eventually clusters of tumour cells such as tumour buds break away and spread through the lymphatic system to nearby lymph nodes or enter the circulation forming secondary metastasis. Collectively, these factors need to be considered when assessing and treating patients clinically. This review aims to summarise the ways in which these various factors are currently assessed and how they relate to patient treatment and outcome at an individual level.

Homeostatic apoptosis prevents competition-induced atrophy in follicular B cells

While the intrinsic apoptosis pathway is thought to play a central role in shaping the B cell lineage, its precise role in mature B cell homeostasis remains elusive. Using mice in which mature B cells are unable to undergo apoptotic cell death, we show that apoptosis constrains follicular B (FoB) cell lifespan but plays no role in marginal zone B (MZB) cell homeostasis. In these mice, FoB cells accumulate abnormally. This intensifies intercellular competition for BAFF, resulting in a contraction of the MZB cell compartment, and reducing the growth, trafficking, and fitness of FoB cells. Diminished BAFF signaling dampens the non-canonical NF-κB pathway, undermining FoB cell growth despite the concurrent triggering of a protective p53 response. Thus, MZB and FoB cells exhibit a differential requirement for the intrinsic apoptosis pathway. Homeostatic apoptosis constrains the size of the FoB cell compartment, thereby preventing competition-induced FoB cell atrophy.

PD-1/PDL-1 Inhibitors and Cardiotoxicity; Molecular, Etiological and Management Outlines

Background

The US Food and Drug Administration (FDA) has approved several immunotherapeutic drugs for cancer since 2010, and many more are still being evaluated in other clinical studies. These inhibitors significantly increase response rates and result in the treatment of patients with advanced cancer. However, cancer immunotherapy leads to essential cardiac toxicity properties that have become distinct from other cancer patients' care and are mostly related to their etiology.

Aim of review

As potential implications, the occurrence of cardiovascular adverse events is particularly challenging and needs a comprehensive understanding of overall cancer-related etiology, clinical outcomes with different variable severity, and management.

Key scientific concepts of review

In terms of improving the overall survival of patients with cancer, clinicians should be careful in selecting either programmed cell death-1 (PD-1) or its programmed cell death ligand (PDL-1) inhibitors by evaluating their risk and clinical benefit for early intervention and decrease the level of morbidity and mortality of their patients. This review focuses on the effectiveness of PD-1/PL-1 antibodies and associated cardiotoxicity adverse events, including etiological mechanisms, diagnosis, and treatment.

Identification of a genomic enhancer that enforces proper apoptosis induction in thymic negative selection

During thymic negative selection, autoreactive thymocytes carrying T cell receptor (TCR) with overtly strong affinity to self-MHC/self-peptide are removed by Bim-dependent apoptosis, but how Bim is specifically regulated to link TCR activation and apoptosis induction is unclear. Here we identify a murine T cell-specific genomic enhancer EBAB (Bub1-Acoxl-Bim), whose deletion leads to accumulation of thymocytes expressing high affinity TCRs. Consistently, EBAB knockout mice have defective negative selection and fail to delete autoreactive thymocytes in various settings, with this defect accompanied by reduced Bim expression and apoptosis induction. By contrast, EBAB is dispensable for maintaining peripheral T cell homeostasis via Bim-dependent pathways. Our data thus implicate EBAB as an important, developmental stage-specific regulator of Bim expression and apoptosis induction to enforce thymic negative selection and suppress autoimmunity. Our study unravels a part of genomic enhancer codes that underlie complex and context-dependent gene regulation in TCR signaling.

The multiple faces of CD5

Since its discovery, over 30 years ago, CD5 has been used as a marker to identify T cells, B1-a cells, and B cell chronic lymphocytic leukemia cells. Throughout the years, many studies have described the functional relevance of CD5 as a modulator of T and B cell receptor signaling. However, it has not been until recent years that CD5 has emerged as a functional receptor in other areas of the immune system. Here, we review some of the most important aspects of CD5 as a modulator of TCR and BCR signaling, cell survival receptor both in T and B cells during health and disease, as well as the newly discovered roles of this receptor in thymocyte selection, T cell effector differentiation, and immune tolerance. CD5 was found to promote T cell survival by protecting autoreactive T cell from activation-induced cell death, to promote de novo induction of regulatory T cells in the periphery, to modulate Th17 and Th2 differentiation, and to modulate immune responses by modulating dendritic cell functions. CD5 is overexpressed in Tregs and Bregs, which are fundamental to maintain immune homeostasis. The newly established roles of CD5 in modulating different aspects of immune responses identify this receptor as an immune checkpoint modulator, and therefore it could be used as a target for immune intervention in different pathologies such as cancer, autoimmune diseases or infections.

Cardiac Complications in Immune Checkpoint Inhibition Therapy

Immune checkpoint inhibitors (ICIs) have changed the treatment landscape of advanced cancers. Unfortunately, these agents can induce a wide spectrum of immune-related adverse events (irAEs) through activation of immune responses in non-target organs, including the heart. As the clinical use of ICI therapy increases rapidly, management of irAEs is becoming extremely important. The most commonly presented cardiac irAE is myocarditis. Histopathologically, T-cell (with a predominance of CD8⁺ cells) and macrophage infiltration in the myocardium is typically observed in ICI-associated myocarditis. Other presentations of cardiac irAEs include congestive heart failure, Takotsubo cardiomyopathy, pericardial disease, arrhythmias, and conduction disease. Although cardiac irAEs are relatively rare, they can be life-threatening. Hence, cardiologists and oncologists should be vigilant for these presentations.

Immune checkpoint inhibitor-related myocarditis

Immune checkpoint inhibitors have demonstrated significant clinical benefit in many cancers. The clinical benefit afforded by these treatments can be accompanied by a unique and distinct spectrum of adverse events. Recently, several fatal cases of immune checkpoint inhibitor-related myocarditis were reported. Although its frequency is comparatively lower than that of other immune-related adverse events, myocarditis can lead to circulatory collapse and lethal ventricular arrhythmia. Immune checkpoints, cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed cell death protein 1 (PD-1), play important roles in establishing peripheral tolerance to the heart. Evidence from studies using genetically engineered mouse models suggests that CTLA-4 signaling terminates proliferation and promotes anergy during the primary response to cardiac self-peptide recognition. PD-1 signaling restrains autoreactive T cells that enter the peripheral tissues and recognize cardiac-peptide, maintaining them in an anergic state. Patients affected by immune checkpoint inhibitor-related myocarditis often experience rapid onset of profound hemodynamic compromise progressing to cardiogenic shock. Early diagnosis is mandatory to address specific therapy and correct the timing of circulatory support. However, the diagnosis of myocarditis is challenging due to the heterogeneity of clinical presentations. Owing to its early onset, nonspecific symptomatology and fulminant progression, especially when these drugs are used in combination, oncologists should be vigilant for immune checkpoint inhibitor-related myocarditis. With many questions yet to be answered, from basic immune biology to clinical management, future research should aim to optimize the use of these drugs by identifying predictive biomarkers of either a response to therapy or the risks of myocarditis development.

B-CD8+ T Cell Interactions in the Anti-Idiotypic Response against a Self-Antibody

P3 is a murine, germline, IgM mAb that recognizes N-glycolylated gangliosides and other self-antigens. This antibody is able to induce an anti-idiotypic IgG response and B-T idiotypic cascade, even in the absence of any adjuvant or carrier protein. P3 mAb immunization induces the expression of activation markers in a significant percentage of B-1a cells in vivo. Interestingly, transfer of both B-1a and B-2 to BALB/Xid mice was required to recover anti-P3 IgG response in this model. In fact, P3 mAb activated B-2 cells, in vitro, inducing secretion of IFN-γ and IL-4, although this activation was not detected ex vivo. Interestingly, naïve CD8+ T cells increased the expression of activation markers and IFN-γ secretion in the presence of B-1a cells isolated from P3 mAb-immunized mice, even without in vitro restimulation. In contrast, B-2 cells were able to stimulate CD8+ T cells only if P3 was added in vitro. Using bioinformatics, a MHC class I-binding peptide from P3 VH region was identified. P3 mAb was able to induce a specific CTL response in vivo against cells presenting this peptide. Both humoral and CTL anti-idiotypic responses could be mechanisms to protect against the self-reactive antibody, contributing to keeping the tolerance to self-antigens.

B-cell tolerance and autoimmunity

Self-reactive B cells are tolerized at various stages of B-cell development and differentiation, including the immature B-cell stage (central tolerance) and the germinal center (GC) B-cell stage, and B-cell tolerance involves various mechanisms such as deletion, anergy, and receptor editing. Self-reactive B cells generated by random immunoglobulin variable gene rearrangements are tolerized by central tolerance and anergy in the periphery, and these processes involve apoptosis regulated by Bim, a pro-apoptotic member of the Bcl-2 family, and regulation of B-cell signaling by various phosphatases, including SHIP-1 and SHP-1. Self-reactive B cells generated by somatic mutations during GC reaction are also eliminated. Fas is not directly involved in this process but prevents persistence of GC reaction that allows generation of less stringently regulated B cells, including self-reactive B cells. Defects in self-tolerance preferentially cause lupus-like disease with production of anti-nuclear antibodies, probably due to the presence of a large potential B-cell repertoire reactive to nucleic acids and the presence of nucleic acid-induced activation mechanisms in various immune cells, including B cells and dendritic cells. A feed-forward loop composed of anti-nuclear antibodies produced by B cells and type 1 interferons secreted from nucleic acid-activated dendritic cells plays a crucial role in the development of systemic lupus erythematosus.

POSH Regulates CD4+ T Cell Differentiation and Survival

The scaffold molecule POSH is crucial for the regulation of proliferation and effector function in CD8(+) T cells. However, its role in CD4(+) T cells is not known. In this study, we found that disruption of the POSH scaffold complex established a transcriptional profile that strongly skewed differentiation toward Th2, led to decreased survival, and had no effect on cell cycle entry. This is in stark contrast to CD8(+) T cells in which POSH regulates cell cycle and does not affect survival. Disruption of POSH in CD4(+) T cells resulted in the loss of Tak1-dependent activation of JNK1/2 and Tak1-mediated survival. However, in CD8(+) T cells, POSH regulates only JNK1. Remarkably, each type of T cell had a unique composition of the POSH scaffold complex and distinct posttranslational modifications of POSH. These data indicate that the mechanism that regulates POSH function in CD4(+) T cells is different from CD8(+) T cells. All together, these data strongly suggest that POSH is essential for the integration of cell-type-specific signals that regulate the differentiation, survival, and function of T cells.

Establishment and characterization of gemcitabine-resistant human cholangiocarcinoma cell lines with multidrug resistance and enhanced invasiveness

To establish and characterize the gemcitabine-resistant cholangiocarcinoma (CCA) cell lines, CCA KKU‑M139 and KKU‑M214 cell lines were exposed stepwisely to increasing gemcitabine (GEM). The resultant drug-resistant cell lines, KKU‑M139/GEM and KKU‑M214/GEM, retained the resistant phenotype in drug-free medium at least for 2 months. Sulforhodamine B assay demonstrated that KKU‑M139/GEM and KKU‑M214/GEM were 25.88- and 62.31-fold more resistant to gemcitabine than their parental cells. Both gemcitabine-resistant cell lines were cross-resistant to 5-fluorouracil (5-FU), doxorubicin and paclitaxel indicating their multidrug-resistant nature. Using reverse transcriptase-polymerase chain reaction (RT-PCR), real-time PCR and western blot analyses, gemcitabine-resistant cells showed upregulation of RRM1 and downregulation of hENT1 and dCK. In relation to multidrug resistance, these cell lines showed upregulation of multidrug resistance protein 1 (MRP1) leading to an increase of drug efflux. Using cell adhesion and Boyden chamber transwell assays, these cell lines also showed higher cell adhesion, migration and invasion capabilities via the activations of protein kinase C (PKC), focal adhesion kinase (FAK), extracellular signal-regulated kinase-1/2 (ERK1/2) and nuclear factor-κB (NF-κB). Higher activity of matrix metalloproteinase-9 (MMP-9) and urokinase plasminogen activator (uPA) was also observed by a gelatin zymography assay and a casein-plasminogen zymography assay. Flow cytometry analysis indicated the G2/M arrest regulated by downregulation of cyclin B1 and cyclin-dependent kinase 1 (Cdk1) resulted in an extended population doubling time. Using Annexin V/propidium iodide staining, evasion of apoptosis via an intrinsic pathway was observed in both cell lines in association with upregulation of Bcl-2 and downregulation of Bax. Interestingly, Fas was additionally downregulated in KKU‑M214/GEM supporting the view of its higher GEM resistant characteristics. These findings indicate that long-term exposure of CCA cell lines to gemcitabine induce not only multidrug resistance but also enhance their invasiveness.

A mathematical model for a T cell fate decision algorithm during immune response

We formulate and analyze an algorithm of cell fate decision that describes the way in which division vs. apoptosis choices are made by individual T cells during an infection. Such model involves a minimal number of known biochemical mechanisms: it basically relies on the interplay between cell division and cell death inhibitors on one hand, and membrane receptors on the other. In spite of its simplicity, the proposed decision algorithm is able to account for some significant facts in immune response. At the individual level, the existence of T cells that continue to replicate in the absence of antigen and the possible occurrence of T cell apoptosis in the presence of antigen are predicted by the model. Moreover, the latter is shown to yield an emergent collective behavior, the observed delay in clonal contraction with respect to the end of antigen stimulation, which is shown to arise just from individual T cell decisions made according to the proposed mechanism.

NR4A nuclear receptors in immunity and atherosclerosis

PURPOSE OF REVIEW

To understand chronic inflammatory diseases such as atherosclerosis, we require in-depth knowledge on immune-cell differentiation, function of specific immune-cell subsets and endothelial cell-mediated extravasation. In this review, we summarize a number of very recent observations on the pivotal function of NR4A nuclear receptors in immunity and atherosclerosis.

RECENT FINDINGS

NR4A nuclear receptors are involved in negative selection of thymocytes, Treg differentiation and the development of Ly6C monocytes. Nur77 and Nurr1 attenuate atherosclerosis in mice whereas NOR-1 aggravates vascular lesion formation.

SUMMARY

These exciting, novel insights on the function of NR4A nuclear receptors in immunity, vascular cells and atherosclerosis will initiate a plethora of studies to understand the underlying molecular mechanisms, which will culminate in the identification of novel NR4A targets to modulate chronic inflammatory disease.

Macrophages engulfing apoptotic thymocytes produce retinoids to promote selection, differentiation, removal and replacement of double positive thymocytes

The thymus provides the microenvironment in which thymocytes develop into mature T-cells, and interactions with thymic stromal cells are thought to provide the necessary signals for thymocyte maturation. Recognition of self-MHC by T-cells is a basic requirement for mature T-cell functions, and those thymocytes that do not recognize or respond too strongly to the peptide-loaded self-MHC molecules found in the thymus undergo apoptosis. As a result, 95% of the thymocytes produced will die and be subsequently cleared by macrophages. This review describes a complex crosstalk between developing thymocytes and engulfing macrophages which is mediated by retinoids produced by engulfing macrophages. The interaction results in the harmonization of the rate of cell death of dying double positive cells with their clearance and replacement, and in promotion of the differentiation of the selected cells in the thymus.

Thymoproteasome subunit-β5T generates peptide-MHC complexes specialized for positive selection

Cortical thymic epithelial cells (cTECs) express a unique thymoproteasome subunit-β5T that plays an essential role in the development of CD8 T cells. In contrast, the immunoproteasome subunit-β5i is expressed in other thymic antigen-presenting cells (APCs). The thymoproteasome may generate peptides that are specialized for positive selection, or it may simply serve to generate peptides that are distinct from other APCs that cause negative selection, thereby promoting an overall larger number of surviving clones to mature and function in the immune system. To distinguish these models, we genetically engineered mice to express distinct peptide repertoires in cTECs vs. other APCs without expressing β5T, by generating β5t(5i) knockin mice, in which β5i replaced β5T in cTECs. When such animals were crossed to β5i(-/-) mice, β5i was exclusively expressed in cTECs, whereas β5 was expressed in other cells. However, this mouse did not support normal positive selection, suggesting that β5T generates peptides that are intrinsically better for positive selection (i.e., β5i could not replace β5T) and not merely because these peptides are distinct from peptides presented by other APCs. Finally, using an Nur77(GFP) reporter, we show that the T cells generated in the absence of β5T have higher reactivity to self, generating predominantly CD44(hi) memory phenotype peripheral CD8(+) T cells. Altogether, our results suggest that the thymoproteasome supports positive selection by generating peptides that are optimized for the selection of weakly self-reactive, naïve T-cell clones.

Fatigue-related gene networks identified in CD(14)+ cells isolated from HIV-infected patients: part I: research findings

PURPOSE

Human immunodeficiency virus (HIV)-related fatigue (HRF) is multicausal and potentially related to mitochondrial dysfunction caused by antiretroviral therapy with nucleoside reverse transcriptase inhibitors (NRTIs).

METHODOLOGY

The authors compared gene expression profiles of CD14(+) cells of low versus high fatigued, NRTI-treated HIV patients to healthy controls (n = 5/group). The authors identified 32 genes predictive of low versus high fatigue and 33 genes predictive of healthy versus HIV infection. The authors constructed genetic networks to further elucidate the possible biological pathways in which these genes are involved. RELEVANCE FOR NURSING PRACTICE: Genes including the actin cytoskeletal regulatory proteins Prokineticin 2 and Cofilin 2 along with mitochondrial inner membrane proteins are involved in multiple pathways and were predictors of fatigue status. Previously identified inflammatory and signaling genes were predictive of HIV status, clearly confirming our results and suggesting a possible further connection between mitochondrial function and HIV. Isolated CD14(+) cells are easily accessible cells that could be used for further study of the connection between fatigue and mitochondrial function of HIV patients.

IMPLICATION FOR PRACTICE

The findings from this pilot study take us one step closer to identifying biomarker targets for fatigue status and mitochondrial dysfunction. Specific biomarkers will be pertinent to the development of methodologies to diagnosis, monitor, and treat fatigue and mitochondrial dysfunction.

Apoptotic and nonapoptotic caspase functions in animal development

A developing animal is exposed to both intrinsic and extrinsic stresses. One stress response is caspase activation. Caspase activation not only controls apoptosis but also proliferation, differentiation, cell shape, and cell migration. Caspase activation drives development by executing cell death or nonapoptotic functions in a cell-autonomous manner, and by secreting signaling molecules or generating mechanical forces, in a noncell autonomous manner.

Integrin signaling in cancer cell survival and chemoresistance

Resistance to apoptosis and chemotherapy is a hallmark of cancer cells, and it is a critical factor in cancer recurrence and patient relapse. Extracellular matrix (ECM) via its receptors, the integrins, has emerged as a major pathway contributing to cancer cell survival and resistance to chemotherapy. Several studies over the last decade have demonstrated that ECM/integrin signaling provides a survival advantage to various cancer cell types against numerous chemotherapeutic drugs and against antibody therapy. In this paper, we will discuss the major findings on how ECM/integrin signaling protects tumor cells from drug-induced apoptosis. We will also discuss the potential role of ECM in malignant T-cell survival and in cancer stem cell resistance. Understanding how integrins and their signaling partners promote tumor cell survival and chemoresistance will likely lead to the development of new therapeutic strategies and agents for cancer treatment.

Bryostatin analogue-induced apoptosis in mantle cell lymphoma cell lines

The anti-cancer effects of bryostatin-1, a potent diacylglycerol analogue, have traditionally been attributed to its action on protein kinase C. However, we previously documented apoptosis in a B non-Hodgkin lymphoma cell line involving diacylglycerol analogue stimulation of Ras guanyl-releasing protein, a Ras activator, and Bim, a proapoptotic Bcl-2 family protein. To further explore the role of Bim, we examined several Bim-deficient B non-Hodgkin lymphoma cells for their responses to pico, a synthetic bryostatin-1-like compound. The Bim(-) mantle cell lymphoma cell lines Jeko-1, Mino, Sp53, UPN1, and Z138 and the Bim(+) cell line Rec-1, as well as the Burkitt lymphoma cells lines BL2 (Bim(-)) and Daudi (Bim(+)), were examined for their response to pico using assays for proliferation and apoptosis as well as biochemical methods for Ras guanyl-releasing proteins and Bcl-2 family members. With the exception of UPN1, mantle cell lymphoma cell lines underwent pico-induced apoptosis, as did BL2. In some cases, hallmarks of apoptosis were substantially diminished in the presence of mitogen-activated protein kinase kinase inhibitors. Pico treatment generally led to increased expression of proapoptotic Bik, although the absolute levels of Bik varied considerably between cell lines. A pico-resistant variant of Z138 exhibited decreased Bik induction compared to parental Z138 cells. Pico also generally decreased expression of anti-apoptotic Bcl-XL and Mcl1. Although, these changes in Bcl-2 family members seem unlikely to fully account for the differential behavior of the cell lines, our demonstration of a potent apoptotic process in most cell lines derived from mantle cell lymphoma encourages a re-examination of diacylglycerol analogues in the treatment of this subset of B non-Hodgkin lymphoma cases.

Proapoptotic protein Bim is differentially required during thymic clonal deletion to ubiquitous versus tissue-restricted antigens

Positive and negative selection of thymocytes in the thymus are critical for the development of a mature and self-tolerant T-cell repertoire. The proapoptotic Bcl-2 family member Bim is important for negative selection by inducing apoptosis in thymocytes receiving a strong signal through their antigen receptor. However, in the case of ubiquitous self-antigens (UbA), Bim is not required for the clonal deletion of self-reactive thymocytes, suggesting the existence of nonapoptotic clonal deletion mechanisms. Unlike UbA, clonal deletion to tissue-restricted antigens (TRAs) requires positive selection and CCR7-mediated migration to the medulla. This led us to hypothesize that Bim is required for the latter. To study the role of Bim in clonal deletion to TRA, we constructed bone marrow (BM) chimeras using OT-I Bim-deficient or -sufficient donor bone marrow and recipients that express membrane bound chicken ovalbumin under control of the rat insulin promoter (Rip-mOVA). We found that clonal deletion to TRA was completely abrogated in the absence of Bim and large numbers of mature OT-I CD8 T cells survived in the periphery. Despite the large numbers of autoreactive T cells, the chimeras did not develop diabetes and OT-I Bim-deficient T cells from these chimeras were functionally impaired. Collectively, these data provide unique evidence of a differential, thymocyte-intrinsic, molecular requirement downstream of the T-cell receptor (TCR) for clonal deletion to UbA versus TRA and highlight the profound ability of other tolerance mechanisms to control T-cell autoreactivity in the absence of thymic clonal deletion.

Immunologic similarities between selected autoimmune diseases and peanut allergy: possible new therapeutic approaches

Food allergies are an important medical problem in Westernized countries. Allergy to peanuts is a dramatic example of a food allergy that tends to be particularly severe and long-lived. This article examines food allergy-specifically peanut allergy-from the perspective that tolerance to foods is a normal state, just as tolerance to self-proteins is a normal state. From this vantage point, loss of tolerance to foods in food-allergic individuals can be viewed as parallel to the loss of tolerance to self-proteins in those with autoimmune diseases. Although our knowledge base is far from satisfactory, there are important similarities in the immunologic abnormalities that are characteristic of both peanut allergy and several autoimmune diseases. Delineation of these similarities may open the door to new therapeutic approaches for the treatment of severe food allergies.

IFN-α is constitutively expressed in the human thymus, but not in peripheral lymphoid organs

Type I interferons have been typically studied for their effects in the context of bacterial or viral infections. However in this report, we provide evidence that Interferon-alpha (IFN-α) expressing cells are present in the thymus in the absence of infection. We show that pDC express the highest level of IFN-α and that MxA, which is exclusively expressed after engagement of the type I IFN receptor by IFN-α/β, is expressed in normal fetal and post-natal thymus, but not in the periphery. The highest level of MxA is expressed in mature thymocytes and pDC located in the medulla and at the cortico-medullary junction. The anti-microbial peptide LL-37, which is expressed in the thymus, when complexed with eukaryotic nucleic acids, induces the secretion of IFN-α by thymic pDC. This results in the upregulation of MxA expression in responsive thymocytes. We propose that the secretion of IFN-α in the thymus may function to regulate the rate of T cell development and modulate the requirements for the selection of developing T cells.

Inflammation-inducing Th1 and Th17 cells differ in their expression patterns of apoptosis-related molecules

Th1 cells are remarkably more susceptible to activation induced cell death than Th17. Here, we compared cultures of these two cell subpopulations for their expression of apoptosis-related molecules when re-exposed to their specific antigen. We also compared the expression of apoptosis-related molecules in the mouse eye with inflammation induced by Th1 or Th17 cells. Using qPCR we found that the mRNA transcript levels of the majority of tested apoptosis-related molecules were higher in the Th1 cultures, and in eyes with Th1-induced inflammation. Apoptotic intrinsic pathway molecules played minor roles in the processes in vitro or in vivo, whereas extrinsic pathway molecules, as well as PD-1, its ligands and Tim3, were heavily involved.

Who lives and who dies: Role of apoptosis in quashing developmental errors

Apoptosis is essential for normal development. Large numbers of cells are eliminated by apoptosis in early neural development and during the formation of neural connections. However, our understanding of this life-or-death decision is incomplete, because it is difficult to identify dying cells by conventional strategies. Live imaging is powerful for studying apoptosis, because it can trace a death-fated cell throughout its lifetime. The Drosophila sensory organ development is a convenient system for studying neural-cell selection via lateral inhibition. We recently showed that about 20% of the differentiating neuronal cells die during sensory organ development, which results in the characteristic spatial patterning of the sensory organs. The eliminated differentiating neurons expressed neurogenic genes and high levels of activated Notch. Thus, live imaging allowed us to document the role of apoptosis in neural progenitor selection, and revealed that Notch activation is the mechanism determining which cells die during sensory organ development.

Evaluation of the Bcl-2 family antagonist ABT-737 in collagen-induced arthritis

Therapeutic manipulation of cellular apoptosis holds great promise for malignant and potentially nonmalignant diseases. A relative resistance to apoptosis in RA synovium is associated with increased expression of prosurvival Bcl-2 family members. In this study, we demonstrate that treatment of DBA/1 mice, prior to the onset of CIA with ABT-737, a BH3 mimetic targeting Bcl-2, Bcl-w, and Bcl-x(L), ameliorated disease development. In contrast, treatment of mice with ABT-737 in established CIA did not alter the course of disease. ABT-737 induced lymphopenia, however pathogenic lymphoid populations in CIA mice were less affected, as shown by relatively normal T and B cell responses to CII. Naïve lymphocytes were highly sensitive to apoptosis after culture with ABT-737, but synovial macrophages and neutrophils were not. Mcl-1 was detected in synovial monocyte/macrophages and neutrophils and strikingly, its expression, rather than Bcl-2 and Bcl-x(L), increased in the affected paws and lymphoid organs of mice with CIA. These observations implicate Mcl-1, which is not targeted by ABT-737, in the survival of inflammatory cells in established CIA and suggest that antagonism of Mcl-1 may be more effective in diseases such as RA.

Fraternal twins: Swiprosin-1/EFhd2 and Swiprosin-2/EFhd1, two homologous EF-hand containing calcium binding adaptor proteins with distinct functions

Changes in the intracellular calcium concentration govern cytoskeletal rearrangement, mitosis, apoptosis, transcriptional regulation or synaptic transmission, thereby, regulating cellular effector and organ functions. Calcium binding proteins respond to changes in the intracellular calcium concentration with structural changes, triggering enzymatic activation and association with downstream proteins. One type of calcium binding proteins are EF-hand super family proteins. Here, we describe two recently discovered homologous EF-hand containing adaptor proteins, Swiprosin-1/EF-hand domain containing 2 (EFhd2) and Swiprosin-2/EF-hand domain containing 1 (EFhd1), which are related to allograft inflammatory factor-1 (AIF-1). For reasons of simplicity and concision we propose to name Swiprosin-1/EFhd2 and Swiprosin-2/EFhd1 from now on EFhd2 and EFhd1, according to their respective gene symbols. AIF-1 and Swiprosin-1/EFhd2 are already present in Bilateria, for instance in Drosophila melanogaster and Caenhorhabditis elegans. Swiprosin-2/EFhd1 arose later from gene duplication in the tetrapodal lineage. Secondary structure prediction of AIF-1 reveals disordered regions and one functional EF-hand. Swiprosin-1/EFhd2 and Swiprosin-2/EFhd1 exhibit a disordered region at the N-terminus, followed by two EF-hands and a coiled-coil domain. Whereas both proteins are similar in their predicted overall structure they differ in a non-homologous stretch of 60 amino acids just in front of the EF-hands. AIF-1 controls calcium-dependent cytoskeletal rearrangement in innate immune cells by means of its functional EF-hand. We propose that Swiprosin-1/EFhd2 as well is a cytoskeleton associated adaptor protein involved in immune and brain cell function. Pro-inflammatory conditions are likely to modulate expression and function of Swiprosin-1/EFhd2. Swiprosin-2/EFhd1, on the other hand, modulates apoptosis and differentiation of neuronal and muscle precursor cells, probably through an association with mitochondria. We suggest furthermore that Swiprosin-2/EFhd1 is part of a cellular response to oxidative stress, which could explain its pro-survival activity in neuronal, muscle and perhaps some malignant tissues.

Protein kinase C regulates mitochondrial targeting of Nur77 and its family member Nor-1 in thymocytes undergoing apoptosis

Nur77 orphan steroid receptor and its family member Nor-1 are required for apoptosis of developing T cells. In thymocytes, signals from the TCR complex induce Nur77 and Nor-1 expression followed by translocation from the nucleus to mitochondria. Nur77 and Nor-1 associate with Bcl-2 in the mitochondria, resulting in a conformation change that exposes the Bcl-2 BH3 domain, a presumed pro-apoptotic molecule of Bcl-2. As Nur77 and Nor-1 are heavily phosphorylated, we examined the requirement of Nur77 and Nor-1 phosphorylation in mitochondria translocation and Bcl-2 BH3 exposure. We found that HK434, a PKC agonist, in combination with calcium ionophore, can induce Nur77 and Nor-1 phosphorylation, translocation, Bcl-2 BH3 exposure and thymocyte apoptosis. Inhibitors of both classical and novel forms of PKC were able to block this process. In contrast, only the general but not classical PKC-specific inhibitors were able to block the same process initiated by PMA, a commonly used PKC agonist. These data demonstrate a differential activation of PKC isoforms by PMA and HK434 in thymocytes, and show the importance of PKC in mitochondria translocation of Nur77/Nor-1 and Bcl-2 conformation change during TCR-induced thymocyte apoptosis.

Peripheral lymphocyte subset and serum cytokine profiles of patients with West syndrome

OBJECTIVE

To clarify the immune pathophysiology of West syndrome (WS).

STUDY DESIGN

We measured peripheral blood lymphocyte subset and serum cytokine profiles in 76 WS patients and 26 age-matched controls. Adrenocorticotropic hormone (ACTH) is one of the most effective therapy for WS and presumably immune-modulating; therefore, we compared the measured parameters between before ACTH (pre-ACTH) WS patients and controls, between cryptogenic and symptomatic WS patients before ACTH (pre-ACTH), and between before (pre-ACTH) and after (post-ACTH) ACTH WS patients. The post-ACTH group included those who received the last ACTH dose within 1 month of sampling.

RESULTS

CD3+ CD25+, CD19+, and CD19+ CD95+ cells were found to be significantly lower in the pre-ACTH group than in the controls. Interleukin (IL)-1 receptor antagonist (RA), 5, 6, and 15; eotaxin; basic fibroblast growth factor (bFGF); and interferon gamma-inducible protein (IP)-10 levels were higher in pre-ACTH group than in the controls. No significant differences were found between the pre-ACTH cryptogenic and symptomatic groups. CD4+ cells, CD3+ cells, CD4+/8+ ratio, IL-1 beta, IL-12, and macrophage inflammatory protein (MIP)-1 beta were significantly higher in pre-ACTH group than in the post-ACTH group.

CONCLUSIONS

Our study revealed immunological alterations in WS patients, and these responses were modified by ACTH therapy. Further study is needed to elucidate whether or how the immune system alteration is involved in the pathophysiology of WS.

Effects and regulation of autoreactive CD8+ T cells in a transgenic mouse model of autoimmune hepatitis

BACKGROUND & AIMS

Autoimmune hepatitis (AIH) is a chronic inflammatory liver disease of unknown etiology. Autoreactive T cells are thought to mediate liver injury, but the pathogenesis of AIH is poorly understood because of the lack of suitable animal models. We established a mouse model to investigate liver-specific T-cell responses and assess the effects and regulation of autoreactive CD8(+) T cells in the pathogenesis of AIH.

METHODS

We generated transgenic mice expressing the influenza virus hemagglutinin (HA) autoantigen under control of mouse albumin regulatory elements and alpha-fetoprotein enhancers (Alb) specifically in the liver (Alb-HA mice); they were crossed with mice that express a specific T-cell receptor (TCR) (CL4-TCR). CL4-TCR transgenic CD8(+) T cells were also adoptively transferred into Alb-HA mice. We investigated immunologic mechanisms of CD8(+) T cell-induced liver damage and of counteracting peripheral tolerance.

RESULTS

The double-transgenic mice (Alb-HA/CL4-TCR) spontaneously developed chronic, autoimmune-mediated hepatitis, characterized by necroinflammatory lesions, hepatic fibrosis, and increased levels of aminotransferase; these features resembled those of AIH. Interestingly, most liver-infiltrating, HA-specific CD8(+) T cells had an anergic phenotype; regulatory CD4(+)CD25(+)Foxp3(+) T cells accumulated in the inflamed liver.

CONCLUSIONS

The continuous development of a few, HA-specific CD8(+) effector T cells is sufficient to induce chronic hepatitis. Peripheral tolerance mechanisms such as induction of T-cell anergy and accumulation of regulatory CD4(+)CD25(+)Foxp3(+) T cells protect the liver from severe damage. Our mouse model that spontaneously develops chronic autoimmune-mediated hepatitis provides a new tool to investigate autoantigen-specific T-cell responses and regulatory mechanisms involved in the prevention and pathogenesis of AIH.

Interleukin-7 promotes the survival of human CD4+ effector/memory T cells by up-regulating Bcl-2 proteins and activating the JAK/STAT signalling pathway

SUMMARY

Interleukin-7 (IL-7) is a crucial cytokine involved in T-cell survival and development but its signalling in human T cells, particularly in effector/memory T cells, is poorly documented. In this study, we found that IL-7 protects human CD4(+) effector/memory T cells from apoptosis induced upon the absence of stimulation and cytokines. We show that IL-7 up-regulates not only Bcl-2 but also Bcl-xL and Mcl-1 as well. Interleukin-7-induced activation of the janus kinase/signal transducer and activator of transcription (JAK/STAT) signalling pathway is sufficient for cell survival and up-regulation of Bcl-2 proteins. In contrast to previous studies with naive T cells, we found that IL-7 is a weak activator of the phosphatidylinositol 3 kinase (PI3K)/AKT (also referred as protein kinase B) pathway and IL-7-mediated cell survival occurs independently from the PI3K/AKT pathway as well as from activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway. Considering the contribution of both IL-7 and CD4(+) effector/memory T cells to the pathogenesis of autoimmune diseases such as rheumatoid arthritis and colitis, our study suggests that IL-7 can contribute to these diseases by promoting cell survival. A further understanding of the mechanisms of IL-7 signalling in effector/memory T cells associated with autoimmune inflammatory diseases may lead to potential new therapeutic avenues.

c-Cbl promotes T cell receptor-induced thymocyte apoptosis by activating the phosphatidylinositol 3-kinase/Akt pathway

The ability of thymocytes to assess T cell receptor (TCR) signaling strength and initiate the appropriate downstream response is crucial for determining their fate. We have previously shown that a c-Cbl RING finger mutant knock-in mouse, in which the E3 ubiquitin ligase activity of c-Cbl is inactivated, is highly sensitive to TCR-induced death signals that cause thymic deletion. This high intensity signal involves the enhanced tyrosine phosphorylation of the mutant c-Cbl protein promoting a marked increase in the activation of Akt. Here we show that this high intensity signal in c-Cbl RING finger mutant thymocytes also promotes the enhanced induction of two mediators of TCR-directed thymocyte apoptosis, Nur77 and the pro-apoptotic Bcl-2 family member, Bim. In contrast, a knock-in mouse harboring a mutation at Tyr-737, the site in c-Cbl that activates phosphatidylinositol 3-kinase, shows reduced TCR-mediated responses including suppression of Akt activation, a reduced induction of Nur77 and Bim, and greater resistance to thymocyte death. These findings identify tyrosine-phosphorylated c-Cbl as a critical sensor of TCR signal strength that regulates the engagement of death-promoting signals.

A novel TCR transgenic model reveals that negative selection involves an immediate, Bim-dependent pathway and a delayed, Bim-independent pathway

A complete understanding of negative selection has been elusive due to the rapid apoptosis and clearance of thymocytes in vivo. We report a TCR transgenic model in which expression of the TCR during differentiation occurs only after V(D)J-like recombination. TCR expression from this transgene closely mimics expression of the endogenous TCRalpha locus allowing for development that is similar to wild type thymocytes. This model allowed us to characterize the phenotypic changes that occurred after TCR-mediated signaling in self-reactive thymocytes prior to their deletion in a highly physiological setting. Self-reactive thymocytes were identified as being immature, activated and CD4(lo)CD8(lo). These cells had upregulated markers of negative selection and were apoptotic. Elimination of Bim reduced the apoptosis of self-reactive thymocytes, but it did not rescue their differentiation and the cells remained at the immature CD4(lo)CD8(lo) stage of development. These cells upregulate Nur77 and do not contribute to the peripheral T cell repertoire in vivo. Remarkably, development past the CD4(lo)CD8(lo) stage was possible once the cells were removed from the negatively selecting thymic environment. In vitro development of these cells occurred despite their maintenance of high intracellular levels of Nur77. Therefore, in vivo, negatively selected Bim-deficient thymocytes are eliminated after prolonged developmental arrest via a Bim-independent pathway that is dependent on the thymic microenvironment. These data newly reveal a layering of immediate, Bim-dependent, and delayed Bim-independent pathways that both contribute to elimination of self-reactive thymocytes in vivo.

Antigen-specific tolerance inhibits autoimmune uveitis in pre-sensitized animals by deletion and CD4+CD25+ T-regulatory cells

The objective of the present study was to inhibit experimental autoimmune anterior uveitis (EAAU) by establishing antigen specific immune tolerance in animals pre-sensitized with melanin associated antigen (MAA). Intravenous administration of MAA on day 6, 7, 8 and 9 post-immunization induced tolerance and inhibited EAAU in all Lewis rats. Number of cells (total T cells, CD4⁺ T cells and CD8⁺ T cells) undergoing apoptosis dramatically increased in the popliteal lymph nodes (LNs) of the tolerized animals compared to non-tolerized animals. Additionally, FasL, TNFR1 and caspase-8 were upregulated in tolerized rats. Proliferation of total lymphocytes, CD4⁺T cells and CD8+ T cells (harvested from the popliteal LNs) in response to antigenic stimulation was drastically reduced in the state of tolerance compared to the cells from non-tolerized animals. Level of IFN-γ and IL-2 decreased while TGF-β2 was elevated in the state of tolerance. Furthermore, the number of CD4⁺CD25⁺FoxP3⁺ Tregs increased in the popliteal LNs of tolerized animals compared to non-tolerized animals. In conclusion, our results suggest that deletion of antigen specific T cells via apoptosis and active suppression mediated by Tregs plays an important role in the induction of antigen specific immune tolerance in animals with an established immune response against MAA.

BH3-only proteins and their roles in programmed cell death

The Bcl-2 family of proteins controls the mitochondrial pathway to apoptosis. It consists of pro-survival and pro-apoptotic members, and their interactions decide whether apoptogenic factor confined to the mitochondrial intermembrane space can leak to the cytosol. Despite the intense efforts to understand the molecular mechanisms that lead to the permeabilization of the mitochondrial membrane, this particular issue remains a matter of intense controversy. It is well accepted that pro-apoptotic Bax and Bak are directly responsible for the damage to the mitochondria, but pro-survival family members prevent them from doing so. It is also accepted that stress signals activate selected Bcl-2 homology (BH)3-only proteins. But do these BH3-only proteins bind and activate Bax and Bak directly, or do they inhibit the pro-survival family members?

How does Epstein-Barr virus (EBV) complement the activation of Myc in the pathogenesis of Burkitt's lymphoma?

A defining characteristic of the aggressive B cell tumour Burkitt's lymphoma (BL) is a reciprocal chromosomal translocation that activates the Myc oncogene by juxtaposing it to one of the immunoglobulin gene loci. The consequences of activating Myc include cell growth and proliferation that can lead to lymphomagenesis; however, as part of a fail-safe mechanism that has evolved in metazoans to reduce the likelihood of neoplastic disease, activated oncogenes such as Myc may also induce cell death by apoptosis and/or an irreversible block to proliferation called senescence. For lymphoma to develop it is necessary that these latter processes are repressed. More than 95% of a subset of BL – known as endemic (e)BL because they are largely restricted to regions of equatorial Africa and similar geographical regions – carry latent Epstein–Barr virus (EBV) in the form of nuclear extra-chromosomal episomes. Although EBV is not generally regarded as a driving force of BL cell proliferation, it plays an important role in the pathogenesis of eBL. Latency-associated EBV gene products can inhibit a variety of pathways that lead to apoptosis and senescence; therefore EBV probably counteracts the proliferation-restricting activities of deregulated Myc and so facilitates the development of BL.

Learning to be tolerant: how T cells keep out of trouble

A pool of immature T cells with a seemingly unrestricted repertoire of antigen specificities is generated life-long in the thymus. Amongst these cells are, however, thymocytes that express a strongly self-reactive antigen receptor and hence hold the potential to trigger autoimmunity. To prevent such an outcome, the thymus employs several independent but functionally related strategies that act in parallel to enforce self-tolerance. The deletion of strongly self-reactive thymocytes and the generation of regulatory T cells constitute the two most efficient mechanisms to induce and maintain immunological tolerance. Thymic epithelial cells of the medulla express for this purpose tissue-restricted self-antigens. This review will focus on the cellular and molecular mechanisms operative in the thymus to shape a repertoire of mature T cells tolerant to self-antigens.

The Bcl-2 family in autoimmune and degenerative disorders

Members of the Bcl-2 family are essential regulators of programmed cell death and thus play a major role in the development and function of many tissues. The balance between pro-survival and pro-apoptotic members of the family decides whether a cell will live or die. This mechanism allows organisms to get rid of cells that are no longer needed or have become dangerous. Deregulation of apoptosis is a major contributing factor in the development of many diseases. A deeper understanding of how the Bcl-2 family proteins orchestrate death in normal and pathologic conditions is thus relevant not only for disease etiology, but also to try to prevent these various disorders. Experiments with transgenic and gene-ablated mice have helped elucidate the function of the different members of the Bcl-2 family and their physiological roles. The present review highlights the role of Bcl-2 family members in autoimmune and degenerative disorders, with a particular focus on the mouse models that have been used to study their function.

T cell leukemia/lymphoma 1 and galectin-1 regulate survival/cell death pathways in human naive and IgM+ memory B cells through altering balances in Bcl-2 family proteins

BCR signaling plays a critical role in purging the self-reactive repertoire, or in rendering it anergic to establish self-tolerance in the periphery. Differences in self-reactivity between human naive and IgM(+) memory B cells may reflect distinct mechanisms by which BCR signaling dictates their survival and death. Here we demonstrate that BCR stimulation protected naive B cells from apoptosis with induction of prosurvival Bcl-2 family proteins, Bcl-x(L) and Mcl-1, whereas it rather accelerated apoptosis of IgM(+) memory B cells by inducing proapoptotic BH3-only protein Bim. We found that BCR-mediated PI3K activation induced the expression of Mcl-1, whereas it inhibited Bim expression in B cells. Phosphorylation of Akt, a downstream molecule of PI3K, was more sustained in naive than IgM(+) memory B cells. Abundant expression of T cell leukemia/lymphoma 1 (Tcl1), an Akt coactivator, was found in naive B cells, and enforced expression of Tcl1 induced a high level of Mcl-1 expression, resulting in prolonged B cell survival. In contrast, Galectin-1 (Gal-1) was abundantly expressed in IgM(+) memory B cells, and inhibited Akt phosphorylation, leading to Bim up-regulation. Enforced expression of Gal-1 induced accelerated apoptosis in B cells. These results suggest that a unique set of molecules, Tcl1 and Gal-1, defines distinct BCR signaling cascades, dictating survival and death of human naive and IgM(+) memory B cells.