IRF4 Has a Unique Role in Early B Cell Development and Acts Prior to CD21 Expression to Control Marginal Zone B Cell Numbers.

Strict control of B lymphocyte development is required for the ability to mount humoral immune responses to diverse foreign antigens while remaining self-tolerant. In the bone marrow, B lineage cells transit through several developmental stages in which they assemble a functional B cell receptor in a stepwise manner. The immunoglobulin heavy chain gene is rearranged at the pro-B stage. At the large pre-B stage, cells with a functional heavy chain expand in response to signals from IL-7 and the pre-BCR. Cells then cease proliferation at the small pre-B stage and rearrange the immunoglobulin light chain gene. The fully formed BCR is subsequently expressed on the surface of immature B cells and autoreactive cells are culled by central tolerance mechanisms. Once in the periphery, transitional B cells develop into mature B cell subsets such as marginal zone and follicular B cells. These developmental processes are controlled by transcription factor networks, central to which are IRF4 and IRF8. These were thought to act redundantly during B cell development in the bone marrow, with their functions diverging in the periphery where IRF4 limits the number of marginal zone B cells and is required for germinal center responses and plasma cell differentiation. Because of IRF4's unique role in mature B cells, we hypothesized that it may also have functions earlier in B cell development that cannot be compensated for by IRF8. Indeed, we find that IRF4 has a unique role in upregulating the pre-B cell marker CD25, limiting IL-7 responsiveness, and promoting migration to CXCR4 such that IRF4-deficient mice have a partial block at the pre-B cell stage. We also find that IRF4 acts in early transitional B cells to restrict marginal zone B cell development, as deletion of IRF4 in mature B cells with CD21-cre impairs plasma cell differentiation but has no effect on marginal zone B cell numbers. These studies highlight IRF4 as the dominant IRF family member in early B lymphopoiesis.

Effect of a Synthetic Organoselenium Compound on Post-Vaccination Immunopoiesis in the Red Bone Marrow and Cell Composition of Peripheral Blood of White Mice Vaccinated with Yersinia pestis EV.

We studied the effect of an experimental synthetic organoselenium compound 2,6-dipyridinium- 9-selenabicyclo[3.3.1]nonane dibromide (974zh) on the cell composition of the red bone marrow and peripheral blood in white mice. The study drug co-administered with Yersinia pestis EV vaccine strain (103 CFU) potentiated maturation and migration of mature neutrophils from the bone marrow into the circulation. Reducing the dose of the live vaccine and the anti-inflammatory properties of the study drug made it possible to reduce the allergic reaction during the vaccination process.

The MS Remyelinating Drug Bexarotene (an RXR Agonist) Promotes Induction of Human Tregs and Suppresses Th17 Differentiation In Vitro.

The retinoid X receptor agonist bexarotene promotes remyelination in patients with multiple sclerosis. Murine studies have also demonstrated that RXR agonists have anti-inflammatory effects by enhancing the ability of all-trans-retinoic acid (atRA) to promote T-regulatory cell (Treg) induction and reduce Th17 differentiation in vitro. By stimulating human naïve CD4 T-cells in the presence of Treg or Th17 skewing cytokines, we show that bexarotene also tips the human Treg/Th17 axis in favor of Treg induction, but unlike murine cells this occurs independently of atRA and retinoic acid receptor signaling. Tregs induced in the presence of bexarotene express canonical markers of T-regulation and are functionally suppressive in vitro. Circulating Treg numbers did not increase in the blood of trial patients receiving bexarotene; we believe this is because Treg induction is likely to occur within tissues. These findings lend support to developing RXR agonists as treatments of autoimmune diseases, in particular multiple sclerosis.

Extracellular signal-regulated kinase (ERK) pathway control of CD8+ T cell differentiation.

The integration of multiple signalling pathways that co-ordinate T cell metabolism and transcriptional reprogramming is required to drive T cell differentiation and proliferation. One key T cell signalling module is mediated by extracellular signal-regulated kinases (ERKs) which are activated in response to antigen receptor engagement. The activity of ERKs is often used to report antigen receptor occupancy but the full details of how ERKs control T cell activation is not understood. Accordingly, we have used mass spectrometry to explore how ERK signalling pathways control antigen receptor driven proteome restructuring in CD8+ T cells to gain insights about the biological processes controlled by ERKs in primary lymphocytes. Quantitative analysis of >8000 proteins identified 900 ERK regulated proteins in activated CD8+ T cells. The data identify both positive and negative regulatory roles for ERKs during T cell activation and reveal that ERK signalling primarily controls the repertoire of transcription factors, cytokines and cytokine receptors expressed by activated T cells. It was striking that a large proportion of the proteome restructuring that is driven by triggering of the T cell antigen receptor is not dependent on ERK activation. However, the selective targets of the ERK signalling module include the critical effector molecules and the cytokines that allow T cell communication with other immune cells to mediate adaptive immune responses.

STAT1 Isoforms Differentially Regulate NK Cell Maturation and Anti-tumor Activity.

Natural killer (NK) cells are important components of the innate immune defense against infections and cancers. Signal transducer and activator of transcription 1 (STAT1) is a transcription factor that is essential for NK cell maturation and NK cell-dependent tumor surveillance. Two alternatively spliced isoforms of STAT1 exist: a full-length STAT1α and a C-terminally truncated STAT1ß isoform. Aberrant splicing is frequently observed in cancer cells and several anti-cancer drugs interfere with the cellular splicing machinery. To investigate whether NK cell-mediated tumor surveillance is affected by a switch in STAT1 splicing, we made use of knock-in mice expressing either only the STAT1α (Stat1α/α) or the STAT1ß (Stat1ß/ß ) isoform. NK cells from Stat1α/α mice matured normally and controlled transplanted tumor cells as efficiently as NK cells from wild-type mice. In contrast, NK cells from Stat1ß/ß mice showed impaired maturation and effector functions, albeit less severe than NK cells from mice that completely lack STAT1 (Stat1-/- ). Mechanistically, we show that NK cell maturation requires the presence of STAT1α in the niche rather than in NK cells themselves and that NK cell maturation depends on IFNγ signaling under homeostatic conditions. The impaired NK cell maturation in Stat1ß/ß mice was paralleled by decreased IL-15 receptor alpha (IL-15Rα) surface levels on dendritic cells, macrophages and monocytes. Treatment of Stat1ß/ß mice with exogenous IL-15/IL-15Rα complexes rescued NK cell maturation but not their effector functions. Collectively, our findings provide evidence that STAT1 isoforms are not functionally redundant in regulating NK cell activity and that the absence of STAT1α severely impairs, but does not abolish, NK cell-dependent tumor surveillance.

Development of Proliferative Response of Thymic Lymphocytes to T-Cell Mitogen in Rats Exposed to Endocrine Disrupter DDT during Ontogeny.

We studied the formation of proliferative response of thymic lymphocytes to T-cell mitogen in rats exposed to endocrine disrupter DDT during prenatal and postnatal ontogeny. Developmental exposure to the endocrine disruptor was found to attenuate proliferative response during puberty and adulthood due to maintenance of higher proliferation rate of thymic lymphocytes in comparison with age-matched controls. Insufficient proliferative response to mitogens in rats developmentally exposed to the endocrine disrupter increases the risk of impairment of cell-mediated reactions of adaptive immunity.

Prednisolone in early pregnancy inhibits regulatory T cell generation and alters fetal and placental development in mice.

Corticosteroids have been utilised in the assisted reproduction setting with the expectation of suppressing aberrant immune activation and improving fertility in women. However, the effects of corticosteroids on fertility, and on pregnancy and offspring outcomes, are unclear. In this study, mice were administered prednisolone (1 mg/kg) or PBS daily in the pre-implantation phase, and effects on the adaptive immune response, the implantation rate, fetal development and postnatal outcomes were investigated. Prednisolone disrupted the expected expansion of CD4+ T cells in early pregnancy, inhibiting generation of both regulatory T cells (Treg cells) and effector T cells and suppressing IFNG required for T cell functional competence. Prednisolone caused an 8-20% increase in the embryo implantation rate and increased the number of viable pups per litter. In late gestation, fetal and placental weights were reduced in a litter size-dependent manner, and the canonical inverse relationship between litter size and fetal weight was lost. The duration of pregnancy was extended by ~ 0.5 day and birth weight was reduced by ~ 5% after prednisolone treatment. Viability of prednisolone-exposed offspring was comparable to controls, but body weight was altered in adulthood, particularly in male offspring. Thus, while prednisolone given in the pre-implantation phase in mice increases maternal receptivity to implantation and resource investment in fetal growth, there is a trade-off in long-term consequences for fetal development, birth weight and offspring health. These effects are associated with, and likely caused by, prednisolone suppression of the adaptive immune response at the outset of pregnancy.

IL-4 together with IL-1ß induces antitumor Th9 cell differentiation in the absence of TGF-ß signaling.

IL-9-producing CD4+ (Th9) cells are a subset of CD4+ T-helper cells that are endowed with powerful antitumor capacity. Both IL-4 and TGF-ß have been reported to be indispensable for Th9 cell-priming and differentiation. Here we show, by contrast, that Th9 cell development can occur in the absence of TGF-ß signaling. When TGF-ß was replaced by IL-1ß, the combination of IL-1ß and IL-4 efficiently promoted IL-9-producing T cells (Th9IL-4+IL-1ß). Th9IL-4+ IL-1ß cells are phenotypically distinct T cells compared to classic Th9 cells (Th9IL-4+TGF-ß) and other Th cells, and are enriched for IL-1 and NF-κB gene signatures. Inhibition of NF-κB but not TGF-ß-signaling negates IL-9 production by Th9IL-4+IL-1ß cells. Furthermore, when compared with classic Th9IL-4+TGF-ß cells, Th9IL-4+IL-1ß cells are less exhausted, exhibit cytotoxic T effector gene signature and tumor killing function, and exert a superior antitumor response in a mouse melanoma model. Our study thus describes an alternative pathway for Th9 cell differentiation and provides a potential avenue for antitumor therapies.

Signaling Lymphocytic Activation Molecule Family Member 1 Engagement Inhibits T Cell-B Cell Interaction and Diminishes Interleukin-6 Production and Plasmablast Differentiation in Systemic Lupus Erythematosus.

OBJECTIVE: Signaling lymphocytic activation molecule family member 1 (SLAMF1) homophilic interactions promote immunoglobulin production and T cell-B cell cross-talk. SLAMF1 is overexpressed on T and B cells in patients with systemic lupus erythematosus (SLE). This study was undertaken to determine the role of SLAMF1 monoclonal antibody (mAb) in modulating T cell-B cell interaction and B cell activation. METHODS: Anti-IgM-prestimulated naive or total B cells from either healthy donors or patients with SLE were cocultured with autologous T cells under CD3/CD28 stimulation, in the presence or absence of the SLAMF1 mAb. Naive B cells were stimulated with anti-IgM and CD40L in the presence of the SLAMF1 antibody. Cytokine production by CD4+ T cells and B cells was examined by flow cytometry and/or quantitative polymerase chain reaction. Plasmablast formation and T cell and B cell conjugates were assessed by flow cytometry. IgG and antinuclear antibody production was determined by enzyme-linked immunosorbent assay. RESULTS: SLAMF1 ligation in a human peripheral blood T cell-B cell culture system reduced the following in both healthy controls and patients with SLE: conjugate formation, interleukin-6 (IL-6) production by B cells, IL-21 and IL-17A production by T cells, and Ig and autoantibody production. Whereas the SLAMF1 mAb directly affected the function of isolated peripheral B cells by decreasing IL-6 and Ig production in vitro, it did not affect cytokine production by isolated T cells stimulated in vitro. CONCLUSION: The SLAMF1 antibody inhibits T cell-B cell interaction and suppresses B cell cytokine production and differentiation, thereby acting as a potential therapeutic tool in the treatment of patients with SLE.

Glucocorticoid susceptibility and in vivo ABCB1 activity differ in murine B cell subsets.

Glucocorticoids are produced and released by the adrenal gland and become elevated in response to stress. Although glucocorticoids are well known for their immunosuppressive effects, less is known about their effects on B cells. ABCB1 is an efflux pump expressed in both cancer and normal cells, modulating the gradient of various metabolites, including hydrocortisone. Our goal was to evaluate the effect of this glucocorticoid on murine B cell differentiation and whether sensitivity to hydrocortisone could be related to ABCB1 activity in vivo. C57BL/6 mice received one or three consecutive i.p. injections of hydrocortisone (70, 140 and 200 mg/kg/day). ABCB1 activity was evaluated via the rhodamine-123 transport and inhibited by cyclosporin A in hydrocortisone-treated and control mice. Cells from bone marrow, spleen and blood were counted, incubated with antibodies and analyzed by flow cytometry. A single hydrocortisone injection did not alter the number of bone marrow subsets. Conversely, three daily injections were able to reduce the cell number of most bone marrow subsets, excepting c-kit-sca-1+ and mature B cells. This treatment reduced marginal zone, follicular and transitional B cells, though splenic subsets were more resistant than bone marrow B cells. Recirculating follicular B cells in the blood were resistant to hydrocortisone. With the exception of follicular B cells, all subpopulations exhibited ABCB1 activity. However, hydrocortisone treatment did not affect ABCB1 activity in most subsets analyzed. Results suggest that hydrocortisone is able to regulate B cell lymphopoiesis although ABCB1 activity is not related to the susceptibility to that glucocorticoid in B cell subsets.

NLRP3 inflammasome regulates Th17 differentiation in rheumatoid arthritis.

Rheumatoid arthritis (RA) is one of the most common autoimmune diseases. Th17 has been shown to play am important role in the pathogenesis of RA. Accumulating data suggest the involvement of NLRP3 inflammasome in Th17 differentiation in autoimmune diseases. In the current study, we found that NLRP3 inflammasome is activated in CD4 T cells from RA patients. The activation of NLRP3 inflammasome was correlated with disease activities and IL-17A concentration in RA sera. Knockdown of NLRP3 suppressed Th17 differentiation. In addition, caspase-1 or IL-1 receptor inhibitor inhibits Th17 differentiation significantly. Further, ROS production is increased in CD4 T cells from RA patients. The inhibition of ROS production decreased NLRP3 inflammasome activation and IL-1ß production in CD4 T cells, leading to the suppression of Th17 differentiation. These findings suggest a pathogenic role of NLRP3 inflammasome in RA by promoting Th17 cell differentiation. NLRP3 inflammasome could be a potential therapeutic target for the treatment of RA.

Humanized mice reveal an essential role for human hepatocytes in the development of the liver immune system.

The liver is an immunological organ with a distinct immune cell profile. Although the composition and function of liver immune cells have been widely investigated, the mechanisms regulating the development and homeostasis of the specialized immune system, especially in humans, remain largely unknown. Herein, we address this question in humanized mice (hu-mice) that were constructed by transplantation of human fetal thymus and CD34+ hematopoietic stem/progenitor cells in immunodeficient mice with or without autologous human hepatocyte engraftment. Although the levels of human immune cell reconstitution in peripheral blood and spleen were comparable between hu-mice with and without human hepatocyte engraftment, the former group showed that human immune cell reconstitution in the liver was significantly improved. Notably, human immune cells, including Kupffer cells, dendritic cells and natural killer cells, were shown to be closely colocalized with human hepatocytes in the liver. Human hepatocytes engrafted in the mouse liver were found to produce IL-3, IL-15, GM-CSF, M-CSF, MCP-1, CXCL-1 and CXCL-10, which are known to be important for immune cell development, differentiation, tissue migration and retention, and have no or poor cross-reaction between humans and mice. Furthermore, human hepatocytes were able to support human immune cell survival and expansion in an in vitro co-culture assay. This study demonstrates an essential role for hepatocytes in the development and maintenance of the liver immune cell profile. The hu-mouse model with human autologous immune cell and hepatocyte reconstitution has potential for use in studies of the pathogenesis of liver immune disorders such as hepatotropic virus infections.

New therapeutic opportunities from dissecting the pre-B leukemia bone marrow microenvironment.

The microenvironments of leukemia and cancer are critical for multiple stages of malignancies, and they are an attractive therapeutic target. While skeletal abnormalities are commonly seen in children with acute lymphoblastic leukemia (ALL) prior to initiating osteotoxic therapy, little is known about the alterations to the bone marrow microenvironment during leukemogenesis. Therefore, in this study, we focused on the development of precursor-B cell ALL (pre-B ALL) in an immunocompetent BCR-ABL1+ model. Here we show that hematopoiesis was perturbed, B lymphopoiesis was impaired, collagen production was reduced, and the number of osteoblastic cells was decreased in the bone marrow microenvironment. As previously found in children with ALL, the leukemia-bearing mice exhibited severe bone loss during leukemogenesis. Leukemia cells produced high levels of receptor activator of nuclear factor κB ligand (RANKL), sufficient to cause osteoclast-mediated bone resorption. In vivo administration of zoledronic acid rescued leukemia-induced bone loss, reduced disease burden and prolonged survival in leukemia-bearing mice. Taken together, we provide evidence that targeting leukemia-induced bone loss is a therapeutic strategy for pre-B ALL.

Detection and Characterization of CD8+ Autoreactive Memory Stem T Cells in Patients With Type 1 Diabetes.

Stem memory T cells (Tscm) constitute the earliest developmental stage of memory T cells, displaying stem cell-like properties, such as self-renewal capacity. Their superior immune reconstitution potential has sparked interest in cancer immune therapy, vaccine development, and immune reconstitution, whereas their role in autoimmunity is largely unexplored. Here we show that autoreactive CD8+ Tscm specific for ß-cell antigens GAD65, insulin, and IGRP are present in patients with type 1 diabetes (T1D). In vitro, the generation of autoreactive Tscm from naive precursors required the presence of the homeostatic cytokine interleukin-7 (IL-7). IL-7 promotes glucose uptake via overexpression of GLUT1 and upregulation of the glycolytic enzyme hexokinase 2. Even though metabolism depends on glucose uptake, the subsequent oxidation of pyruvate in the mitochondria was necessary for Tscm generation from naive precursors. In patients with T1D, high expression of GLUT1 was a hallmark of circulating Tscm, and targeting glucose uptake via GLUT1 using the selective inhibitor WZB117 resulted in inhibition of Tscm generation and expansion. Our results suggest that autoreactive Tscm are present in patients with T1D and can be selectively targeted by inhibition of glucose metabolism.

Roles of activating functions 1 and 2 of estrogen receptor α in lymphopoiesis.

Apart from the role of sex steroids in reproduction, sex steroids are also important regulators of the immune system. 17ß-estradiol (E2) represses T and B cell development, but augments B cell function, possibly explaining the different nature of immune responses in men and women. Both E2 and selective estrogen receptors modulators (SERM) act via estrogen receptors (ER). Activating functions (AF)-1 and 2 of the ER bind to coregulators and thus influence target gene transcription and subsequent cellular response to ER activation. The importance of ERαAF-1 and AF-2 in the immunomodulatory effects of E2/SERM has previously not been reported. Thus, detailed studies of T and B lymphopoiesis were performed in ovariectomized E2-, lasofoxifene- or raloxifene-treated mice lacking either AF-1 or AF-2 domains of ERα, and their wild-type littermate controls. Immune cell phenotypes were analyzed with flow cytometry. All E2 and SERM-mediated inhibitory effects on thymus cellularity and thymic T cell development were clearly dependent on both ERαAFs. Interestingly, divergent roles of ERαAF-1 and ERαAF-2 in E2 and SERM-mediated modulation of bone marrow B lymphopoiesis were found. In contrast to E2, effects of lasofoxifene on early B cells did not require functional ERαAF-2, while ERαAF-1 was indispensable. Raloxifene reduced early B cells partly independent of both ERαAF-1 and ERαAF-2. Results from this study increase the understanding of the impact of ER modulation on the immune system, which can be useful in the clarification of the molecular actions of SERMs and in the development of new SERM.

IFN-ß regulates Th17 differentiation partly through the inhibition of osteopontin in experimental autoimmune encephalomyelitis.

Multiple sclerosis (MS) and the corresponding animal model, experimental autoimmune encephalomyelitis (EAE), are chronic neuroinflammatory autoimmune diseases. Increased activation of CD4+T cells, especially the Th1 and Th17 subsets, is thought to play a causal role in this disease. IFN-ß is widely used in the treatment of MS and is found to decrease IL-17 and OPN production in MS patients and EAE mice. However, a definitive molecular mechanism has not yet been fully elucidated. In this study, we investigated the immunomodulatory effect of IFN-ß on the EAE model. We observed disease progression and determined the percentage of Th1/Th17 cells in the peripheral immune organs, brain, and spinal cord of mice. Furthermore, the levels of related cytokines and transcription factors were measured in splenocytes, and the effects of IFN-ß on Th17 differentiation were assessed in vitro. Compared to the control group, IFN-ß treatment significantly reduced the incidence of EAE and the associated pathological damage. Th1 and Th17 cells in IFN-ß-treated mice were significantly reduced, and the levels of cytokines, such as IFN-γ, IL-17, and OPN, were significantly decreased in splenocyte supernatants as well as the levels of corresponding transcription factors. IFN-ß inhibited downstream inflammatory cytokines through the inhibition of PI3K/AKT/NF-κB axis and p38, JNK-MAPK, as well as the regulation of mTOR complexes. Moreover, IFN-ß inhibited Th17 differentiation and neutralizing OPN antibodies offset the inhibitory effect of IFN-ß on Th17 cells. Meanwhile, IFN-ß influenced the acetylation of the Il17a and Opn gene promoters. The findings described herein provide novel evidence for the role of IFN-ß in Th17 differentiation partly through the inhibition of OPN.

Effects of a tissue-selective estrogen complex on B lymphopoiesis and B cell function.

BACKGROUND/OBJECTIVE: 17ß-estradiol (E2) has major effects on the immune system. It induces thymic atrophy, inhibits both T and B lymphopoiesis and stimulates antibody production treatment with E2 has protective effects on the skeleton but is associated with negative side effects in reproductive organs. A tissue-selective estrogen complex (TSEC) comprise of estrogens combined with a selective estrogen receptor modulator (SERM). TSEC therapy displays the bone-protective effects of estrogen, while the negative side effects on reproductive organs are blocked by the SERM. In a recent publication we showed that treatment with the TSEC E2+bazedoxifene (bza) potently inhibits experimental arthritis and associated osteoporosis. In order to elucidate immunological mechanisms involved in those effects, the aim of this study was to investigate how E2+bza treatment affects the healthy immune system. METHODS: Ovariectomized C57BL/6N mice were treated with vehicle, E2, bza or E2+bza. Weights of uterus and thymus were determined and fluorescence-activated cell sorting was used to analyze B cell populations in bone marrow and spleen. Immunoglobulin production from B cells in bone marrow and spleen were determined using ELISPOT. RESULTS: Addition of bza to E2-treatment totally antagonized the E2-mediated proliferative effect on uterus. On the contrary, addition of bza to E2-treatment did not block the E2-induced thymic atrophy or inhibition of B lymphopoiesis, and did not block the E2-induced increase in immunoglobulin secretion from bone marrow B cells. CONCLUSIONS: Addition of bza to E2-treatment blocks E2-induced uteroproliferation but does not alter E2-mediated effects on thymus, B lymphopoiesis or B cell function.

Inflammatory Changes in Bone Marrow Microenvironment Associated with Declining B Lymphopoiesis.

B lymphopoiesis arrests precipitously in rabbits such that by 2-4 mo of age, before sexual maturity, little to no B lymphopoiesis occurs in the bone marrow (BM). Previously, we showed that in mice, adipocytes inhibit B lymphopoiesis in vitro by inducing inflammatory myeloid cells, which produce IL-1ß. In this study, we characterized rabbit BM after the arrest of B lymphopoiesis and found a dramatic increase in fat, increased CD11b+ myeloid cells, and upregulated expression of the inflammatory molecules, IL-1ß and S100A9, by the myeloid cells. We added BM fat, CD11b+ myeloid cells, and recombinant S100A9 to B lymphopoiesis cultures and found that they inhibited B lymphopoiesis and enhanced myelopoiesis. Unlike IL-1ß, which inhibits B lymphopoiesis by acting on early lymphoid progenitors, S100A9 inhibits B lymphopoiesis by acting on myeloid cells and promoting the release of inflammatory molecules, including IL-1ß. Many molecules produced by adipocytes activate the NLRP3 inflammasome, and the NLRP3 inhibitor, glibenclamide, restored B lymphopoiesis and minimized induction of myeloid cells induced by adipocyte-conditioned medium in vitro. We suggest that fat provides an inflammatory microenvironment in the BM and promotes/activates myeloid cells to produce inflammatory molecules such as IL-1ß and S100A9, which negatively regulate B lymphopoiesis.

The antiproliferative ELF2 isoform, ELF2B, induces apoptosis in vitro and perturbs early lymphocytic development in vivo.

BACKGROUND: ELF2 (E74-like factor 2) also known as NERF (new Ets-related factor), a member of the Ets family of transcription factors, regulates genes important in B and T cell development, cell cycle progression, and angiogenesis. Conserved ELF2 isoforms, ELF2A, and ELF2B, arising from alternative promoter usage can exert opposing effects on target gene expression. ELF2A activates, whilst ELF2B represses, gene expression, and the balance of expression between these isoforms may be important in maintaining normal cellular function. METHODS: We compared the function of ELF2 isoforms ELF2A and ELF2B with other ELF subfamily proteins ELF1 and ELF4 in primary and cancer cell lines using proliferation, colony-forming, cell cycle, and apoptosis assays. We further examined the role of ELF2 isoforms in haemopoietic development using a Rag1 -/-murine bone marrow reconstitution model. RESULTS: ELF2B overexpression significantly reduced cell proliferation and clonogenic capacity, minimally disrupted cell cycle kinetics, and induced apoptosis. In contrast, ELF2A overexpression only marginally reduced clonogenic capacity with little effect on proliferation, cell cycle progression, or apoptosis. Deletion of the N-terminal 19 amino acids unique to ELF2B abrogated the antiproliferative and proapoptotic functions of ELF2B thereby confirming its crucial role. Mice expressing Elf2a or Elf2b in haemopoietic cells variously displayed perturbations in the pre-B cell stage and multiple stages of T cell development. Mature B cells, T cells, and myeloid cells in steady state were unaffected, suggesting that the main role of ELF2 is restricted to the early development of B and T cells and that compensatory mechanisms exist. No differences in B and T cell development were observed between ELF2 isoforms. CONCLUSIONS: We conclude that ELF2 isoforms are important regulators of cellular proliferation, cell cycle progression, and apoptosis. In respect to this, ELF2B acts in a dominant negative fashion compared to ELF2A and as a putative tumour suppressor gene. Given that these cellular processes are critical during haemopoiesis, we propose that the regulatory interplay between ELF2 isoforms contributes substantially to early B and T cell development.

[Systemic lupus erythematosus and lymphopenia: Clinical and pathophysiological features]. / Lupus érythémateux systémique et lymphopénie : aspects cliniques et physiopathologiques.

Lymphopenia is frequent in systemic lupus erythematosus (SLE) and profound (<500/mm3) in 10% of cases. T lymphocytes, especially CD4+, are more affected than B cells. The pathophysiological mechanisms are complex, involving lymphocytotoxic antibodies, excess of apoptosis, increased susceptibility of T cells to complement mediated cytolysis, as well as lymphopoiesis impairment and lymphocyte sequestration. Lymphopenia in SLE is independent from other cytopenia and immunosuppressive drug regiments, and associated with disease activity, risk of flare and damage scores. Infectious risk is mostly bacterial, and lymphopenia <1 G/L is an independent risk factor for severe bacterial infections occurrence. The T cellular deficiency is associated with less control of viral replication, but severe and symptomatic infections are scarce. Although exceptional in SLE, pneumocystis is more severe than in HIV+ patients, and risk of progressive multifocal leukoencephalopathy seems increased compared to other rheumatic diseases. To date, there are no specific recommendations for management of SLE with lymphopenia. Infectious prophylaxis should remain exceptional and discussed on a case by case basis. Further studies are needed to assess the clinical characteristics and outcomes of patients with SLE and profound lymphopenia (<500/mm3), which are probably a subset of SLE with primary immunodeficiency and require specific management.