Insights into the molecular regulation of FasL (CD178) biology

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

Inhibition and genetic ablation of the B7/CD28 T-cell costimulation axis prevents experimental hypertension

BACKGROUND

The pathogenesis of hypertension remains poorly understood, and treatment is often unsuccessful. Recent evidence suggests that the adaptive immune response plays an important role in this disease. Various hypertensive stimuli cause T-cell activation and infiltration into target organs such as the vessel and the kidney, which promotes vascular dysfunction and blood pressure elevation. Classically, T-cell activation requires T-cell receptor ligation and costimulation. The latter often involves interaction between B7 ligands (CD80 and CD86) on antigen-presenting cells with the T-cell coreceptor CD28. This study was therefore performed to examine the role of this pathway in hypertension.

METHODS AND RESULTS

Angiotensin II-induced hypertension increased the presence of activated (CD86(+)) dendritic cells in secondary lymphatic tissues. Blockade of B7-dependent costimulation with CTLA4-Ig reduced both angiotensin II- and deoxycorticosterone acetate (DOCA)-salt-induced hypertension. Activation of circulating T cells, T-cell cytokine production, and vascular T-cell accumulation caused by these hypertensive stimuli were abrogated by CTLA4-Ig. Furthermore, in mice lacking B7 ligands, angiotensin II caused minimal blood pressure elevation and vascular inflammation, and these effects were restored by transplantation with wild-type bone marrow.

CONCLUSIONS

T-cell costimulation via B7 ligands is essential for development of experimental hypertension, and inhibition of this process could have therapeutic benefit in the treatment of this disease.

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

CD95 is a dual-function receptor that exerts pro- or antiapoptotic effects depending on the cellular context, the state of activation, the signal threshold and the mode of ligation. In this study, we report that CD95 engagement modulates TCR/CD3-driven signaling pathways in resting T lymphocytes in a dose-dependent manner. While high doses of immobilized CD95 agonists silence T cells, lower concentrations augment activation and proliferation. We analyzed the co-stimulatory capacity of CD95 in detail in resting human CD4(+) T cells, and demonstrate that low-dose ligand-induced co-internalization of CD95 and TCR/CD3 complexes enables non-apoptotic caspase activation, the prolonged activation of MAP kinases, the upregulation of antiapoptotic proteins associated with apoptosis resistance, and the activation of transcription factors and cell-cycle regulators for the induction of proliferation and cytokine production. We propose that the levels of CD95L on antigen-presenting cells (APCs), neighboring T cells or epithelial cells regulate inhibitory or co-stimulatory CD95 signaling, which in turn is crucial for fine-tuning of primary T-cell activation.

Promoting effects of Ganoderma lucidum polysaccharides on B16F10 cells to activate lymphocytes

The immune system in patients with cancer often fails to control tumour growth because of deficient immunogenicity of tumour cells. Ganoderma lucidum polysaccharides (Gl-PS) are believed to have anti-tumour effects by boosting host immune function. Additionally, Gl-PS may have some direct effects on tumour cells in the activation of lymphocytes, thus enhancing the immunogenicity of tumour cells. We tested the effects of Gl-PS in lymphocyte activation by incubating Gl-PS with a tumour cell line deficient in antigen presentation. Our study showed that Gl-PS can promote B16F10 melanoma cells to induce lymphocyte proliferation, CD69 and FasL expression and IFN-γ production, indicating that Gl-PS can improve the nature of B16F10 cells to activate lymphocytes. Furthermore, H-2D(b) [a major histocompatibility (MHC) class I molecule], and B7-1 and B7-2 (two prominent co-stimulatory molecules expressed on B16F10 cells) were enhanced by Gl-PS, suggesting that these molecules may at least partially be involved in the process of Gl-PS on B16F10 cells to activate lymphocytes.

Therapeutic approaches to multiple sclerosis: an update on failed, interrupted, or inconclusive trials of immunomodulatory treatment strategies

Multiple sclerosis (MS) continues to be a therapeutic challenge, and much effort is being made to develop new and more effective immune therapies. Particularly in the past decade, neuroimmunologic research has delivered new and highly effective therapeutic options, as seen in the growing number of immunotherapeutic agents and biologics in development. However, numerous promising clinical trials have failed to show efficacy or have had to be halted prematurely because of unexpected adverse events. Some others have shown results that are of unknown significance with regard to a reliable assessment of true efficacy versus safety. For example, studies of the highly innovative monoclonal antibodies that selectively target immunologic effector molecules have not only revealed the impressive efficacy of such treatments, they have also raised serious concerns about the safety profiles of these antibodies. These results add a new dimension to the estimation of risk-benefit ratios regarding acute or long-term adverse effects. Therapeutic approaches that have previously failed in MS have indicated that there are discrepancies between theoretical expectations and practical outcomes of different compounds. Learning from these defeats helps to optimize future study designs and to reduce the risks to patients. This review summarizes trials on MS treatments since 2001 that failed or were interrupted, attempts to analyze the underlying reasons for failure, and discusses the implications for our current view of MS pathogenesis, clinical practice, and design of future studies. In order to maintain clarity, this review focuses on anti-inflammatory therapies and does not include studies on already approved and effective disease-modifying therapies, albeit used in distinct administration routes or under different paradigms. Neuroprotective and alternative treatment strategies are presented elsewhere.

The junctional adhesion molecule JAML is a costimulatory receptor for epithelial gammadelta T cell activation

Gammadelta T cells present in epithelial tissues provide a crucial first line of defense against environmental insults, including infection, trauma, and malignancy, yet the molecular events surrounding their activation remain poorly defined. Here we identify an epithelial gammadelta T cell-specific costimulatory molecule, junctional adhesion molecule-like protein (JAML). Binding of JAML to its ligand Coxsackie and adenovirus receptor (CAR) provides costimulation leading to cellular proliferation and cytokine and growth factor production. Inhibition of JAML costimulation leads to diminished gammadelta T cell activation and delayed wound closure akin to that seen in the absence of gammadelta T cells. Our results identify JAML as a crucial component of epithelial gammadelta T cell biology and have broader implications for CAR and JAML in tissue homeostasis and repair.

Distinct infiltration of neutrophils in lesion shoulders in ApoE-/- mice

Inflammation and activation of immune cells are key mechanisms in the development of atherosclerosis. Previous data indicate important roles for monocytes and T-lymphocytes in lesions. However, recent data suggest that neutrophils also may be of importance in atherogenesis. Here, we use apolipoprotein E (ApoE)-deficient mice with fluorescent neutrophils and monocytes (ApoE(-/-)/Lys(EGFP/EGFP) mice) to specifically study neutrophil presence and recruitment in atherosclerotic lesions. We show by flow cytometry and confocal microscopy that neutrophils make up for 1.8% of CD45(+) leukocytes in the aortic wall of ApoE(-/-)/Lys(EGFP/EGFP) mice and that their contribution relative to monocyte/macrophages within lesions is approximately 1:3. However, neutrophils accumulate at sites of monocyte high density, preferentially in shoulder regions of lesions, and may even outnumber monocyte/macrophages in these areas. Furthermore, intravital microscopy established that a majority of leukocytes interacting with endothelium on lesion shoulders are neutrophils, suggesting a significant recruitment of these cells to plaque. These data demonstrate neutrophilic granulocytes as a major cellular component of atherosclerotic lesions in ApoE(-/-) mice and call for further study on the roles of these cells in atherogenesis.

Positive T cell co-stimulation by TLR7/8 ligands is dependent on the cellular environment

Toll-like receptors (TLRs) are mediators of innate immune responses detecting conserved pathogen-associated molecules. Whereas most TLRs are expressed on the cell surface, TLR3, 7, 8 and 9 are predominantly localized in endosomal compartments. Recent studies reported that TLRs are also expressed by T lymphocytes, resulting in direct co-stimulation of isolated CD4(+) T cells for example by Pam3CSK4 (TLR2 ligand) or flagellin (TLR5 ligand). We here describe enhanced IFN-γ production and T cell proliferation by anti-CD3 T cell receptor (TCR) or antigenic stimulation of purified human CD4(+) T cells upon co-culture with TLR7/8 specific single-stranded oligoribonucleotides or small molecule ligands. Surprisingly, TLR7/8 stimulation of CD4(+) T cells within a whole peripheral mononuclear cell (PBMC) environment did not result in enhanced T cell proliferation, but in a lack of proliferation that was cell-cell contact dependent. Immune cell depletion assays pointed towards a monocyte-mediated effect. Different TLR ligands influenced T cell proliferation differently. The effect of inhibition of T cell proliferation was most prominently seen for TLR7 ligands whereas the effects were minimal for TLR8 and TLR9 ligands indicating that the suppressive phenotype is unique only for certain TLRs. Our results strongly suggest that co-stimulation of T cell proliferation by TLR7/8 agonists is dependent on the specific cellular context.

An immunological overview of allergen specific immunotherapy -- subcutaneous and sublingual routes

Allergen-specific immunotherapy remains the most likely effective treatment modality for allergic disorders by targeting the underlying immune mechanisms and possibly causing modifications in the disease course, as well as treating the symptoms. Treatment and compliance experiences been gained over nearly a century in injection-type allergen-specific immunotherapy have motivated the development of newer, alternative routes. Adverse events and safety concerns, efficacy and ease of application seem to be the stimulating factors for the development of a sublingual form of this treatment modality, wherein the principal factor is the capture of the antigen (allergen) by dendritic cells, in the location where oral tolerance arises. Due to the presence of high numbers of tolerogenic dendritic cell subsets in this region, programming of the immune system towards a regulatory state with unresponsiveness to specific allergens occurs. Induction of peripheral tolerance through the generation of regulatory T cells is the key event, with several functional modulations in the allergic immune response. With an increase in understanding of the mechanism of regulatory pathways, promising progresses in the field of allergen-specific immunotherapy will ensue and may provide new options for the treatment of allergic disorders.

Costimulatory molecule programmed death-1 in the cytotoxic response during chronic hepatitis C

Hepatitis C virus (HCV)-specific CD8⁺ T cells play an important role in the resolution of HCV infection. Nevertheless, during chronic hepatitis C these cells lack their effector functions and fail to control the virus. HCV has developed several mechanisms to escape immune control. One of these strategies is the up-regulation of negative co-stimulatory molecules such us programmed death-1 (PD-1). This molecule is up-regulated on intrahepatic and peripheral HCV-specific cytotoxic T cells during acute and chronic phases of the disease, whereas PD-1 expression is low in resolved infection. PD-1 expressing HCV-specific CD8⁺ T cells are exhausted with impairment of several effector mechanisms, such as: type-1 cytokine production, expansion ability after antigen encounter and cytotoxic ability. However, PD-1 associated exhaustion can be restored by blocking the interaction between PD-1 and its ligand (PD-L1). After this blockade, HCV-specific CD8⁺ T cells reacquire their functionality. Nevertheless, functional restoration depends on PD-1 expression level. High PD-1-expressing intrahepatic HCV-specific CD8⁺ T cells do not restore their effector abilities after PD-1/PD-L1 blockade. The mechanisms by which HCV is able to induce PD-1 up-regulation to escape immune control are unknown. Persistent TCR stimulation by a high level of HCV antigens could favour early PD-1 induction, but the interaction between HCV core protein and gC1q receptor could also participate in this process. The PD-1/PD-L1 pathway modulation could be a therapeutic strategy, in conjunction with the regulation of others co-stimulatory pathways, in order to restore immune response against HCV to succeed in clearing the infection.

Suppression of activation and costimulatory signaling in splenic CD4+ T cells after trauma-hemorrhage reduces T-cell function: a mechanism of post-traumatic immune suppression

Reduced immune function is frequently a consequence of serious injury such as trauma-hemorrhage (T-H). Injury may lead to reduced T-cell activation, resulting in decreased engagement of costimulatory molecules after antigen recognition and in subsequent immunological compromise and anergy. We hypothesized that inhibition of CD28 expression is one possible mechanism by which immune functions are suppressed after T-H. Male C3H/HeN mice (with or without ovalbumin immunization) were subjected to sham operation or T-H and sacrificed after 24 hours. Splenic T cells were then stimulated with concanavalin A or ovalbumin in vivo or in vitro, and CD28, cytotoxic T-lymphocyte antigen 4 (CTLA-4), CD69, and phospho-Akt expression was determined. T-cell proliferation/cytokine production was measured in vitro. Stimulation-induced CD69, CD28, and phospho-Akt up-regulation were significantly impaired after T-H compared with sham-operated animals; however, CTLA-4 expression was significantly higher in the T-H group. Over a 3-day span, stimulated T cells from sham-operated animals showed significantly higher proliferation compared with the T-H group. IL-2 and IFN-gamma were elevated in sham-operated animals, whereas IL-4 and IL-5 rose in the T-H group, revealing a shift from T(H)1 to T(H)2 type cytokine production after T-H. Dysregulation of the T-cell costimulatory pathway is therefore likely to be a significant contributor to post-traumatic immune suppression.

Distinct kinetics and dynamics of cross-presentation in liver sinusoidal endothelial cells compared to dendritic cells

Cross-presentation is an important function of immune competent cells, such as dendritic cells (DCs), macrophages, and an organ-resident liver cell population, i.e., liver sinusoidal endothelial cells (LSECs). Here, we characterize in direct comparison to DCs the distinct dynamics and kinetics of cross-presentation employed by LSECs, which promote tolerance induction in CD8 T cells. We found that LSECs were as competent in cross-presenting circulating soluble antigen ex vivo as DCs at a per-cell basis. However, antigen uptake in vivo was 100-fold more pronounced in LSECs, indicating distinct mechanisms of cross-presentation. In contrast to mannose-receptor-mediated antigen uptake and routing into stable endosomes dedicated to cross-presentation in DCs, we observed distinct antigen-uptake and endosomal routing with high antigen turnover in LSECs that resulted in short-lived cross-presentation. Receptor-mediated endocytosis did not always lead to cross-presentation, because immune-complexed antigen taken up by the Fc-receptor was not cross-presented by LSECs, indicating that induction of CD8 T cell tolerance by LSECs is impaired in the presence of preexisting immunity.

CONCLUSION

These results provide a mechanistic explanation how organ-resident LSECs accommodate continuous scavenger function with the capacity to cross-present circulating antigens using distinct kinetics and dynamics of antigen-uptake, routing and cross-presentation compared to DCs.

Targeting Costimulatory Pathways for Tumor Immunotherapy

Tumor immunotherapy harnesses the potential of the host immune system to recognize and eradicate neoplastic tissue. The efficiency of the immune system in mediating tumor regression depends on the induction of antigen-specific T-cell responses through physiologic immune surveillance, priming by vaccination, or following adoptive transfer of T-cells. Although a variety of tumor-associated antigens have been identified and many immunotherapeutic strategies have been tested, objective clinical responses are rare. The reasons for this include the inability of current immunotherapy approaches to generate efficient T-cell responses, the presence of regulatory cells that inhibit T-cell responses, and other tumor escape mechanisms. The activation of effector T-cells depends on interactions between the T-cell receptor (TCR) and cognate antigen presented as peptides within the major histocompatibility complex (MHC) and costimulatory signals delivered by CD28, which binds to B7.1 and B7.2. More recently, several new molecular receptors and ligands have been identified that integrate into stimulatory or inhibitory activity for T-cells. These signals have been loosely associated with the costimulatory molecules but actually represent a diverse group of molecular pathways that have unique and overlapping functions. This review will focus on these pathways and emphasize their role in mediating T-cell activation for the purpose of enhancing tumor immunotherapy. As we gain a better understanding of the molecular and cellular consequences of T-cell signaling through the costimulatory pathways, a more rational approach to the activation or inhibition of T-cell responses can be developed for the treatment of cancer and other immune-mediated diseases.

FasL expression and reverse signalling

FasL plays a central role in the induction of apoptosis within the immune system. It mediates activation-induced cell death (AICD) of T lymphocytes and contributes to the cytotoxic effector function of T and NK cells. Moreover, FasL is discussed as direct effector molecule for the establishment of immune privilege and tumour survival. Besides its death-promoting activity, FasL has been implicated in reverse signalling and might thus also play a role in T cell development and selection and the modulation of T cell activation. Considering these diverse functions, the overall FasL expression has to be tightly controlled to avoid unwanted damage. Based on an activation-associated transcriptional control, several post-transcriptional processes ensure a safe storage, a rapid mobilisation, a target-directed activity and a subsequent inactivation. Over the past years, the identification and characterisation of FasL-interacting proteins provided novel insight into the mechanisms of FasL transport, processing and reverse signalling, which might be exemplary also for the other members of the TNF family.

Proliferative signals mediated by CD28 superagonists require the exchange factor Vav1 but not phosphoinositide 3-kinase in primary peripheral T cells

Almost all responses of naive T cells require co-stimulation, i.e. engagement of the clonotypic TCR with relevant antigen/MHC and the co-stimulatory molecule CD28. How CD28 contributes to T-cell proliferation remains poorly understood, with widely conflicting reports existing which may reflect different methods of co-ligating receptors. Some CD28 mAb, however, can stimulate T-cell proliferation without the need for TCR co-ligation, and thus provide unique tools to dissect proliferative signals mediated through CD28 alone. Using primary peripheral T cells from CD28-transgenic mice, we show that both the YMNM and Lck-binding motifs, but not the Itk-binding motif, in CD28 are required for proliferation. Given that the YMNM motif recruits both phosphoinositide 3-kinase (PI3K) and the exchange factor Vav1, we investigated the role of these two molecules in CD28-mediated proliferation. In p110delta(D910A/D910A) transgenic T cells, which are defective in PI3K activation following CD28 ligation, proliferation was comparable to that in wild-type cells. By contrast, T-cell proliferation was abolished in Vav1(-/-) cells. Although we did not address the role of Grb2 in CD28 signalling, these results indicate that CD28 can mediate Lck- and Vav1-dependent proliferative signals independently of PI3K.

Modulation of NKT cell development by B7-CD28 interaction: an expanding horizon for costimulation

It has been demonstrated that the development of NKT cells requires CD1d. The contribution of costimulatory molecules in this process has not been studied. Here we show that in mice with targeted mutations of B7-1/2 and CD28, the TCRbeta(+)alpha-Galcer/CD1d(+) (iValpha14 NKT) subset is significantly reduced in the thymus, spleen and liver. This is mainly due to decreased cell proliferation; although increased cell death in the thymi of CD28-deficient mice was also observed. Moreover, in the B7-1/2- and CD28-deficient mice, we found a decreased percentage of the CD4(-)NK1.1(+) subset and a correspondingly increased portion of the CD4(+)NK1.1(-) subset. In addition, the mice with a targeted mutation of either B7 or CD28 had a reduced susceptibility to Con A induced hepatitis, which is known to be mediated by NKT cells. Our results demonstrate that the development, maturation and function of NKT cell are modulated by the costimulatory pathway and thus expand the horizon of costimulation into NKT, which is widely viewed as a bridge between innate and adaptive immunity. As such, costimulation may modulate all major branches of cell-mediated immunity, including T cells, NK cells and NKT cells.

Transplantation immunology: what the clinician needs to know for immunotherapy

The liver is unique among transplanted organs with respect to its interaction with the host immune system. There is evidence, both anecdotal and documented, that some liver recipients who cease taking immunosuppressive drugs maintain allograft function, suggesting robust tolerance is in place. Moreover, recipients of human liver allografts require less immunosuppression than do other organ recipients, and liver transplants confer protection on other organ grafts from the same donor. Hence, the liver shows features of immune privilege. Still, the liver can display destructive immunologic processes such as rejection in approximately one quarter of patients. The understanding of the cellular and molecular mechanisms operant in tolerance vs allograft rejection is important for developing new agents to improve long-term outcome, minimize infectious complications (including recurrence of hepatotropic viruses), and deliver immunosuppression without long-term toxicity. This review describes the unique aspects of the hepatic immune response, the pathways involved in T-cell activation and alloantigen recognition, effector cells and pathways mediating liver allograft rejection, the role of regulatory T cells, and targets of current and future immunosuppressive agents.

Transcriptional regulation by poly(ADP-ribose) polymerase-1 during T cell activation

Background

Accumulating evidence suggests an important role for the enzyme poly(ADP-ribose) polymerase-1 (PARP-1) as an integral part of the gene expression regulatory machinery during development and in response to specific cellular signals. PARP-1 might modulate gene expression through its catalytic activity leading to poly(ADP-ribosyl)ation of nuclear proteins or by its physical association with relevant proteins. Recently, we have shown that PARP-1 is activated during T cell activation. However, the proposed role of PARP-1 in reprogramming T cell gene expression upon activation remains largely unexplored.

Results

In the present study we use oligonucleotide microarray analysis to gain more insight into the role played by PARP-1 during the gene expression reprogramming that takes place in T cells upon activation with anti-CD3 stimulation alone, or in combination with anti-CD28 co-stimulation. We have identified several groups of genes with expression modulated by PARP-1. The expression of 129 early-response genes to anti-CD3 seems to be regulated by PARP-1 either in a positive (45 genes) or in a negative manner (84 genes). Likewise, in the presence of co-stimulation (anti-CD3 + anti-CD28 stimulation), the expression of 203 genes is also regulated by PARP-1 either up (173 genes) or down (30 genes). Interestingly, PARP-1 deficiency significantly alters expression of genes associated with the immune response such as chemokines and genes involved in the Th1/Th2 balance.

Conclusion

This study provides new insights into changes in gene expression mediated by PARP-1 upon T cell activation. Pathway analysis of PARP-1 as a nuclear signalling molecule in T cells would be of relevance for the future development of new therapeutic approaches targeting PARP-1 in the acquired immune response.

NKG2D receptor signaling enhances cytolytic activity by virus-specific CD8+ T cells: evidence for a protective role in virus-induced encephalitis

Inoculation with the neurotropic JHM strain of mouse hepatitis virus (JHMV) into the central nervous system (CNS) of mice results in an acute encephalitis associated with an immune-mediated demyelinating disease. During acute disease, infiltrating CD8(+) T cells secrete gamma interferon (IFN-gamma) that controls replication in oligodendrocytes, while infected astrocytes and microglia are susceptible to perforin-mediated lysis. The present study was undertaken to reveal the functional contributions of the activating NKG2D receptor in host defense and disease following JHMV infection. NKG2D ligands RAE-1, MULT1, and H60 were expressed within the CNS following JHMV infection. The immunophenotyping of infiltrating cells revealed that NKG2D was expressed on approximately 90% of infiltrating CD8(+) T cells during acute and chronic disease. Blocking NKG2D following JHMV infection resulted in increased mortality that correlated with increased viral titers within the CNS. Anti-NKG2D treatment did not alter T-cell infiltration into the CNS or the generation of virus-specific CD8(+) T cells, and the expression of IFN-gamma was not affected. However, cytotoxic T-lymphocyte (CTL) activity was dependent on NKG2D expression, because anti-NKG2D treatment resulted in a dramatic reduction in lytic activity by virus-specific CD8(+) T cells. Blocking NKG2D during chronic disease did not affect either T-cell or macrophage infiltration or the severity of demyelination, indicating that NKG2D does not contribute to virus-induced demyelination. These findings demonstrate a functional role for NKG2D in host defense during acute viral encephalitis by selectively enhancing CTL activity by infiltrating virus-specific CD8(+) T cells.

Gene transfer of antisense B7.1 attenuates acute rejection against splenic allografts in rats

Blockade of CD80-CD28 costimulatory pathway induces unresponsiveness of T cells to alloantigens and protects allografts against immune rejection in numerous animal models. The aim of this study was to investigate whether blocking expression of B7.1 (CD80) on donor splenocytes by an antisense technique protected splenic allografts against immune rejection. Splenic grafts from Wistar-Furth rats were intra-arterially transfused with an antisense B7.1 expression vector, before they were transplanted into Sprague-Dawley rats. The rats were sacrificed at scheduled times, and the splenic allografts histologically examined. Antisense gene transfer resulted in marked down-regulation of B7.1 in donor spleens, hyporesponsiveness of recipient T cells, and attenuated acute immune rejection against splenic allografts. No obvious damage to skin, liver, or gut due to graft-versus-host disease was detected in the recipients. In conclusion, blocking expression of B7.1 in donor spleens by antisense gene therapy represented a potential alloantigen-specific immunosuppressive strategy to inhibit acute rejection against splenic allografts.

New therapies for treatment of rheumatoid arthritis

Rheumatoid arthritis is characterised by pain, swelling, and destruction of joints, with resultant disability. Only disease-modifying antirheumatic drugs can interfere with the disease process. In the past few years, biological agents, especially inhibitors of tumour necrosis factor, have allowed for hitherto unseen therapeutic benefit, although even with these drugs the frequency and degree of responses are restricted. Therefore, new agents are needed, and three novel biological compounds for treatment of rheumatoid arthritis have already been used in practice or are on the horizon: rituximab (anti-CD20), abatacept (cytotoxic T-lymphocyte antigen 4 immunoglobulin), and tocilizumab (anti-interleukin 6 receptor). We discuss the targets of these drugs, the roles of these targets in the pathogenesis of rheumatoid arthritis, and the efficacy and adverse effects of these agents from clinical trial data. Novel therapeutic strategies in conjunction with optimised disease assessment for better treatment of rheumatoid arthritis and an outlook into potential future targets are also presented.

Stimulation of N-methyl-d-aspartate receptors modulates Jurkat T cell growth and adhesion to fibronectin

The aims of this study were to investigate the expression and the functional roles of N-methyl-d-aspartate (NMDA) receptors in leukemic Jurkat T cells. RT-PCR and immunofluorescence/confocal microscopy analysis showed that Jurkat T cells express the NR1 and NR2B subunits of the NMDA receptors. Exposure of Jurkat cells to either (5S,10R)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,b]cyclohepten-5,10-imine [(+)-MK 801] or D-(-)-2-amino-5-phosphonopentanoic acid (D-AP5), two selective NMDA receptor antagonists, limited cell growth by inhibiting cell cycle progression and inducing apoptosis, whereas l-glutamate (1 microM) and NMDA (10 microM) significantly increased (137.2+/-22.0%; P<0.01) Jurkat T cell adhesion to fibronectin. In conclusion, our results demonstrate that Jurkat T cells express NMDA receptors functionally active in controlling cell growth and adhesion to fibronectin.

Analysis of expression and function of the inhibitory receptor ILT2 (CD85j/LILRB1/LIR-1) in peripheral blood mononuclear cells from patients with systemic lupus erythematosus (SLE)

The aim of this work was to study the expression and function of the inhibitory receptor ILT2/CD85j in peripheral blood mononuclear cells (PBMC) from patients with systemic lupus erythematosus (SLE). We studied 23 SLE patients as well as 17 patients with rheumatoid arthritis, 10 with fibromyalgia, and 23 healthy individuals. We found a variable level of expression of ILT2 in the PBMC from both SLE patients and controls, with no significant differences among them. However, when the expression of this receptor was assessed in cell subsets, significantly lower levels were detected in CD19+ lymphocytes from SLE patients compared with healthy controls. Functional assays performed in unfractionated PBMC, showed a significant diminished inhibitory activity of ILT2 in CD4+ and CD8+ cell subsets from SLE patients compared to either rheumatoid arthritis or fibromyalgia patients, and healthy individuals. Our results show that the PBMC from some patients with SLE show a defective expression of ILT2, and that most of them exhibit a poor function of this inhibitory receptor.

[Update on pathophysiologic and immunotherapeutic approaches for the treatment of multiple sclerosis]

Multiple sclerosis (MS) is a chronic disabling disease with significant implications for patients and society. The individual disease course is difficult to predict due to the heterogeneity of clinical presentation and of radiologic and pathologic findings. Although its etiology still remains unknown, the last decade has brought considerable understanding of the underlying pathophysiology of MS. In addition to its acceptance as a prototypic inflammatory autoimmune disorder, recent data reveal the importance of primary and secondary neurodegenerative mechanisms such as oligodendrocyte death, axonal loss, and ion channel dysfunction. The deepened understanding of its immunopathogenesis and the limited effectiveness of currently approved disease-modifying therapies have led to a tremendous number of trials investigating potential new drugs. Emerging treatments take into account the different immunopathological mechanisms and strategies, to protect against axonal damage and promote remyelination. This review provides a compilation of novel immunotherapeutic strategies and recently uncovered aspects of known immunotherapeutic agents. The pathogenetic rationale of these novel drugs for the treatment of MS and accompanying preclinical and clinical data are highlighted.

Prion protein resides in membrane microclusters of the immunological synapse during lymphocyte activation

Expression of prion protein (PrP) has been reported for a variety of cell types including neuronal cells, haematopoietic stem cells, antigen-presenting cells, as well as lymphocytes. However, besides this widespread occurrence little is known about the physiological roles exhibited by this enigmatic protein. In this study, the contribution of PrP to the classical T-lymphocyte activation process was characterized by clustering the T-cell receptor component CD3epsilon as well as PrP with soluble and surface-immobilized antibodies, respectively. We present evidence that PrP is a component of signaling structures recently described as plasma membrane microclusters established during T-lymphocyte activation. The formation of immunological synapses, however, did not depend on the presence of PrP as proven by siRNA knockdown experiments, indicating very subtle physiological roles of PrP in vivo within the immune system.

CD28-mediated regulation of multiple myeloma cell proliferation and survival

Although interactions with bone marrow stromal cells are essential for multiple myeloma (MM) cell survival, the specific molecular and cellular elements involved are largely unknown, due in large part to the complexity of the bone marrow microenvironment itself. The T-cell costimulatory receptor CD28 is also expressed on normal and malignant plasma cells, and CD28 expression in MM correlates significantly with poor prognosis and disease progression. In contrast to T cells, activation and function of CD28 in myeloma cells is largely undefined. We have found that direct activation of myeloma cell CD28 by anti-CD28 mAb alone induces activation of PI3K and NFkappaB, suppresses MM cell proliferation, and protects against serum starvation and dexamethasone (dex)-induced cell death. Coculture with dendritic cells (DCs) expressing the CD28 ligands CD80 and CD86 also elicits CD28-mediated effects on MM survival and proliferation, and DCs appear to preferentially localize within myeloma infiltrates in primary patient samples. Our findings suggest a previously undescribed myeloma/DC cell-cell interaction involving CD28 that may play an important role in myeloma cell survival within the bone marrow stroma. These data also point to CD28 as a potential therapeutic target in the treatment of MM.

IMGT Colliers de Perles and IgSF domain standardization for T cell costimulatory activatory (CD28, ICOS) and inhibitory (CTLA4, PDCD1 and BTLA) receptors

T cell activation depends on the specific recognition by their T cell receptors (TR) of antigenic peptides bound to major histocompatibility complex (pMHC). Optimal T cell responses occur when T cells not only receive antigen-specific signals through the TR but also non-antigen-specific costimulatory activatory or inhibitory signals through costimulatory receptors. The activatory CD28/B7-1 (or B7-2), inhibitory CTLA4/B7-1 (or B7-2), activatory ICOS/B7H2 and inhibitory PDCD1/B7H1 (or B7DC) pathways involve the interaction of the V-LIKE-DOMAIN of the receptor with a B7 family member. The BTLA/HVEM pathway involves the interaction of the BTLA receptor C-LIKE-DOMAIN with HVEM, a TNFR family member. The human and mouse CD28, CTLA4, ICOS, PDCD1 and BTLA genes, alleles and alternative transcripts and the IMGT Colliers de Perles of the IgSF domains, based on the IMGT unique numbering, are described according to the IMGT-ONTOLOGY concepts of IMGT, the international ImMunoGeneTics information system, http://imgt.cines.fr).

Anti-cytotoxic T lymphocyte antigen-4 (CTLA-4) immunotherapy for the treatment of prostate cancer

Costimulatory pathway ligands and receptors can deliver either positive or negative signals to help determine the ultimate fate of activated T lymphocytes. Cytotoxic T lymphocyte antigen-4 (CTLA-4) represents one of the most extensively studied receptors in the costimulatory pathway and has recently been shown to function as a potent inhibitor of T cell-mediated immunity. T-cell expression of CTLA-4 indirectly facilitates tumor progression by restraining host antitumoral immunity. In contrast, administration of a monoclonal antibody to block CTLA-4 function can alleviate restraints on T-cell activity to promote immune-mediated tumor regression. We review the preclinical and clinical experience with CTLA-4 blockade as a promising immunotherapeutic approach to treat patients with advanced prostate cancer.

CD28 costimulation provided through a CD19-specific chimeric antigen receptor enhances in vivo persistence and antitumor efficacy of adoptively transferred T cells

Chimeric antigen receptors (CAR) combine an antigen-binding domain with a CD3-zeta signaling motif to redirect T-cell specificity to clinically important targets. First-generation CAR, such as the CD19-specific CAR (designated CD19R), may fail to fully engage genetically modified T cells because activation is initiated by antigen-dependent signaling through chimeric CD3-zeta, independent of costimulation through accessory molecules. We show that enforced expression of the full-length costimulatory molecule CD28 in CD8(+)CD19R(+)CD28(-) T cells can restore fully competent antigen-dependent T-cell activation upon binding CD19(+) targets expressing CD80/CD86. Thus, to provide costimulation to T cells through a CD19-specific CAR, independent of binding to CD80/CD86, we developed a second-generation CAR (designated CD19RCD28), which includes a modified chimeric CD28 signaling domain fused to chimeric CD3-zeta. CD19R(+) and CD19RCD28(+) CD8(+) T cells specifically lyse CD19(+) tumor cells. However, the CD19RCD28(+) CD8(+) T cells proliferate in absence of exogenous recombinant human interleukin-2, produce interleukin-2, propagate, and up-regulate antiapoptotic Bcl-X(L) after stimulation by CD19(+) tumor cells. For the first time, we show in vivo that adoptively transferred CD19RCD28(+) T cells show an improved persistence and antitumor effect compared with CD19R(+) T cells. These data imply that modifications to the CAR can result in improved therapeutic potential of CD19-specific T cells expressing this second-generation CAR.

Molecules involved in T-B co-stimulation and B cell homeostasis: possible targets for an immunological intervention in autoimmunity

The deepened knowledge of co-stimulatory mechanisms within the immunological synapse and the emerging biological principles governing B cell homeostasis provide a plethora of new possibilities to selectively block or enhance immune responses. These mechanisms are highly relevant to the development of new treatment modalities for autoimmune diseases. Here we review approaches to antagonise members of the CD28-B7 superfamily as well as the TNF receptor ligand superfamily members, BAFF and APRIL, and their corresponding receptors on B cells (BAFF-R, TACI and BCMA). The proof of principle that such manipulations have indeed profound consequences for the human immune response comes from genetically manipulated mouse models, and, more importantly, from human immunodeficiency syndromes. Thus, the recent discovery of deletions in the ICOS, BAFF-R and TACI genes leading to disturbances in late B cell differentiation and hypogammaglobulinaemia underline the potential impact of targeting these molecules for therapeutic strategies in autoimmune disorders.

Regulation of mouse inducible costimulator (ICOS) expression by Fyn-NFATc2 and ERK signaling in T cells

The inducible costimulator (ICOS), a member of the CD28 family of costimulatory molecules, is rapidly induced upon T cell activation. Although the critical role of ICOS in costimulating T cell responses is well documented, little is known of the intracellular signaling pathways and mechanisms that regulate ICOS expression. Here, we report that Fyn, NFAT, and ERK signaling influence ICOS expression as various chemical inhibitors, such as PP2 that targets Src kinases, U0126 that targets MEK1/2, and cyclosporin A or FK506 that targets calcineurin and thereby affects NFAT, attenuate T cell receptor-mediated ICOS induction. Moreover, ectopic expression of NFATc2 or a constitutively active MEK2 amplifies ICOS transcription and transactivates a 288-bp core region of the icos promoter in luciferase reporter assays. We also identify a site on the icos promoter that is sensitive to ERK signaling and further show that NFATc2 can bind the icos promoter in vivo and that this binding is diminished when Fyn signaling is ablated. The normal activation of ERK but reduced nuclear translocation of NFATc2 in Fyn(-/-) CD4(+) T cells further suggest that Fyn and NFATc2 act in a common axis, separate from that involving ERK, to drive ICOS transcription. Taken together, our findings indicate that Fyn-calcineurin-NFATc2 and MEK2-ERK1/2 are two independent signaling pathways that cooperate to control T cell receptor-mediated ICOS induction.

Modification of accessory molecule signaling

The concept of costimulation, the requirement for an independent accessory cellular activation signal that supplements the signal delivered to a lymphocyte by antigen, has been a focal point of progress in understanding the regulation of the immune system. While considerable attention has been directed to new developments related to the activation of cells of the innate immune system through Toll-like receptors, resulting in the production of soluble mediators, augmented expression of cell surface costimulatory molecules on antigen-presenting cells is arguably the most significant early outcome of immune system activation. It is those cell surface molecules that provide the essential afferent costimulatory signals to T cells of the adaptive immune response. Once fully activated, T cells express their own cell surface accessory molecules that permit those T cells to instruct interacting B cells, macrophages, and dendritic cells to further implement an effective immune response. Significantly for patients with autoimmune diseases, the manipulation of costimulatory signals represents a rational and effective approach to modulating the chronic immune system activation that characterizes those diseases. Further elucidation of the complexities of members of the accessory molecule families and their functions should lead to an ever greater capacity for therapeutic modulation of the immune response in autoimmune and inflammatory diseases.

Pathogenic T cells in cerebral malaria

Malaria remains a major global health problem and cerebral malaria (CM) is one of the most serious complications of this disease. Recent years have seen important advances in our understanding of the pathogenesis of cerebral malaria. Parasite sequestration, a hallmark of this syndrome, is thought to be solely responsible for the pathological process. However, this phenomenon cannot explain all aspects of the pathogenesis of CM. The use of an animal model, Plasmodium berghei ANKA in mice, has allowed the identification of specific pathological components of CM. Although multiple pathways may lead to CM, an important role for CD8+ T cells has been clarified. Other cells, including platelets, and mediators such as cytokines also have an important role. In this review we have focused on the role of T cells, and discuss what remains to be studied to understand the pathways by which these cells mediate CM.

Cytokine receptor signalling and aging

With ageing the immune system is deregulated and this leads to the development of immunosenescence mainly affecting the adaptive immune response. There is much knowledge accumulated concerning various receptor functions and signalling with ageing such as TCR, FcRs, TLRs. Cytokines are playing a major role in haematopoietic cell functions and in the harmonious and integrated coordination of the innate and adaptive immune response. There exists a large amount of data on cytokine production changes with ageing, as IL-2 production is decreasing, while IL-6 production is increasing. In contrast, there is only scarce knowledge concerning the cytokine receptors and their signalling in ageing. However, there is some evidence that the signalling of IL-2 receptors is altered in T cells and macrophages, mainly in relation to the JAK/STAT pathway. We present here evidence that the IL-6 induced signalling is also altered in T cells with ageing. An alteration in the JAKs and STATs activations in T cells and macrophages was demonstrated. The exact cause of these altered activations is not known and future studies are needed to elucidate them. In this review we summarise our present knowledge on cytokine signalling with ageing, mainly focusing on IL-2 and IL-6 receptors signalling.

Involvement of phosphatidylinositol-3 kinase–Akt and nuclear factor kappa-B pathways in the effect of frutalin on human lymphocyte

The mechanisms involved in the mitogenic effect of lectins are not fully understood and are thought to involve a cascade of intracellular signals related to T cell receptor activation. This study shows that frutalin, the alpha-D-galactose-binding lectin from Artocarpus incisa seeds, is a potent mitogenic activator of human lymphocytes. This effect is inhibited by D-galactose and PI3K inhibitors, and is accompanied by an increase in IL-2 receptor expression and by a PI3K-dependent IL-2 gene expression and IL-2 protein synthesis. Frutalin also induces Akt-phosphorylation and activates NF-kappaB, inducing its translocation from the cytosol to the nucleus. Both effects are blocked in the presence of D-galactose or by PI3K inhibitors. In summary, frutalin, interacting with alpha-D-galactose, activates signaling pathways related to TCR, and thereby triggers PI3K/Akt and NF-kappaB pathway, which modulates T cell proliferation, IL-2 synthesis and IL-2R expression. Frutalin might be a useful tool to study intracellular mechanisms following T cell activation that link upstream signaling pathways to downstream events.

CD4+ T cells contribute to postischemic liver injury in mice by interacting with sinusoidal endothelium and platelets

The mechanisms by which T cells contribute to the hepatic inflammation during antigen-independent ischemia/reperfusion (I/R) are not fully understood. We analyzed the recruitment of T cells in the postischemic hepatic microcirculation in vivo and tested the hypothesis that T cells interact with platelets and activate sinusoidal endothelial cells, resulting in microvascular dysfunction followed by tissue injury. Using intravital videofluorescence microscopy, we show in mice that warm hepatic I/R (90/30-140 min) induces accumulation and transendothelial migration of CD4+, but not CD8+ T cells in sinusoids during early reperfusion. Simultaneous visualization of fluorescence-labeled CD4+ T cells and platelets showed that approximately 30% of all accumulated CD4+ T cells were colocalized with platelets, suggesting an interaction between both cell types. Although interactions of CD4+/CD40L-/- T cells with CD40L-/- platelets in wild-type mice were slightly reduced, they were almost absent if CD4+ T cells and platelets were from CD62P-/- mice. CD4 deficiency as well as CD40-CD40L and CD28-B7 disruption attenuated postischemic platelet adherence in the same manner as platelet inactivation with a glycoprotein IIb/IIIa antagonist and reduced neutrophil transmigration, sinusoidal perfusion failure, and transaminase activities. Treatment with an MHC class II antibody, however, did not affect I/R injury. In conclusion, we describe the type, kinetic, and microvascular localization of T cell recruitment in the postischemic liver. CD4+ T cells interact with platelets in postischemic sinusoids, and this interaction is mediated by platelet CD62P. CD4+ T cells activate endothelium, increase I/R-induced platelet adherence and neutrophil migration via CD40-CD40L and CD28-B7-dependent pathways, and aggravate microvascular/hepatocellular injury.

Differential expression of NF-kappaB pathway genes among peripheral T-cell lymphomas

Nuclear factor kappa B (NF-kappaB) is one important pathway in T-cell proliferation and survival. In a previously reported microarray study, we found NF-kappaB pathway genes differentially expressed between peripheral (PTCL) and lymphoblastic lymphomas. Here, we investigated the expression of NF-kappaB pathway genes using cDNA microarrays in a group of 62 PTCL and in reactive lymph nodes. We found two different subgroups of PTCL based on the expression of NF-kappaB pathway genes. One-third of PTCL showed clearly reduced expression of NF-kappaB genes, while the other group was characterized by high expression of these genes. This distinction was found among all T-cell lymphoma categories analyzed (PTCL unspecified, angioimmunoblastic, cutaneous and natural killer/T lymphomas) with the exception of anaplastic lymphomas (ALCL), which were characterized by reduced NF-kappaB expression in anaplastic cells. Quantitative RT-PCR and immunohistochemical analysis of NF-kappaB-p65 protein confirmed these differences among PTCL subgroups. Importantly, we found that differentiation between NF-kappaB-positive and -negative PTCL could be of clinical interest. The expression profile associated to reduced expression of NF-kappaB genes was significantly associated with shorter survival of patients and seems to be an independent prognostic factor in a multivariate analysis.

Controlling NF-κB activation in T cells by costimulatory receptors

Full and productive activation of T lymphocytes relies on the simultaneous delivery of T cell receptor (TCR)- and coreceptor-derived signals. In naïve T cells engagement of the TCR alone causes anergy, while TCR triggering of preactivated T cells results in activation-induced cell death. Costimulatory signals are prominently mirrored by the activation of NF-kappaB, which needs input from the TCR as well as from coreceptors in order to be fully activated and to fulfil its crucial function in the immune response. Coreceptor-generated signals tightly control the duration and amplitude of the NF-kappaB response. The activation of IkappaB kinase (IKK) complex at the contact zone between a T cell and an antigen-presenting cell offers the unique opportunity to study the spatial organization of IKK activation. Recent studies indicate that coreceptor pathways influence the threshold activities of many signalling mediators and thus act on multiple layers of the NF-kappaB pathway.

Feline B7.1 and B7.2 proteins produced from swinepox virus vectors are natively processed and biologically active: potential for use as nonchemical adjuvants

Costimulatory ligands, B7.1 and B7.2, have been incorporated into viral and DNA vectors as potential nonchemical adjuvants to enhance CTL and humoral immune responses against viral pathogens. In addition, soluble B7 proteins, minus their transmembrane and cytoplasmic domains, have been shown to block the down regulation of T-cell activation through blockade of B7/CTLA-4 interactions in mouse tumor models. Recently, we developed swinepox virus (SPV) vectors for delivery of feline leukemia antigens for vaccine use in cats [Winslow, B.J., Cochran, M.D., Holzenburg, A., Sun, J., Junker, D.E., Collisson, E.W., 2003. Replication and expression of a swinepox virus vector delivering feline leukemia virus Gag and Env to cell lines of swine and feline origin. Virus Res. 98, 1-15]. To explore the use of feline B7.1 and B7.2 ligands as nonchemical adjuvants, SPV vectors containing full-length feline B7.1 and B7.2 ligands were constructed and analyzed. Full-length feline B7.1 and B7.2 produced from SPV vectors were natively processed and costimulated Jurkat cells to produce IL-2, in vitro. In addition, we explored the feasibility of utilizing SPV as a novel expression vector to produce soluble forms of feline B7.1 (sB7.1) and B7.2 (sB7.2) in tissue culture. The transmembrane and cytoplasmic regions of the B7.1 and B7.2 genes were replaced with a poly-histidine tag and purified via a two-step chromatography procedure. Receptor binding and costimulation activity was measured. Although feline sB7.1-his and sB7.2-his proteins bound to the human homolog receptors, CTLA-4 and CD28, both soluble ligands possessed greater affinity for CTLA-4, compared to CD28. However, both retained the ability to partially block CD28-mediated costimulation in vitro. Results from these studies establish the use of SPV as a mammalian expression vector and suggest that full-length-vectored and purified soluble feline B7 ligands may be valuable, nonchemical immune-modulators.

Primary Cutaneous T-Cell Lymphomas Show a Deletion or Translocation AffectingNAV3, the HumanUNC-53Homologue

Multicolor fluorescent in situ hybridization (FISH) was used to identify acquired chromosomal aberrations in 12 patients with mycosis fungoides or Sézary syndrome, the most common forms of primary cutaneous T-cell lymphoma (CTCL). The most frequently affected chromosome was 12, which showed clonal deletions or translocations with a break point in 12q21 or 12q22 in five of seven consecutive Sézary syndrome patients and a clonal monosomy in the sixth patient. The break point of a balanced translocation t(12;18)(q21;q21.2), mapped in the minimal common region of two deletions, fine mapped to 12q2. By locus-specific FISH, the translocation disrupted one gene, NAV3 (POMFIL1), a human homologue of unc-53 in Caenorhabditis elegans. A missense mutation in the remaining NAV3 allele was found in one of six cases with a deletion or translocation. With locus-specific FISH, NAV3 deletions were found in the skin lesions of four of eight (50%) patients with early mycosis fungoides (stages IA-IIA) and in the skin or lymph node of 11 of 13 (85%) patients with advanced mycosis fungoides or Sézary syndrome. Preliminary functional studies with lentiviral small interfering RNA-based NAV3 silencing in Jurkat cells and in primary lymphocytes showed enhanced interleukin 2 expression (but not CD25 expression). Thus, NAV3 may contribute to the growth, differentiation, and apoptosis of CTCL cells as well as to the skewing from Th1-type to Th2-type phenotype during disease progression. NAV3, a novel putative haploinsufficient tumor suppressor gene, is disrupted in most cases of the commonest types of CTCL and may thus provide a new diagnostic tool.

Treatment of glomerulonephritis: will we ever have options other than steroids and cytotoxics?

Glomerulonephritis refers to a collection of primary renal disorders and those secondary to a systemic disease, all characterized by inflammation within the glomerulus. Given the underlying immunologic nature of these disorders, they are routinely treated with corticosteriods and various cytotoxic agents. Although in many instances such therapies are successful, they are associated with significant morbidity; as such, alternatives are clearly necessary. Our understanding of the pathogenesis of immunologic glomerular diseases has grown remarkably, in large part from the study of rodent disease models. Fundamental to each disorder is the development of an antigen-specific immune response followed by the effector stage of inflammation. To block the immune response, antigen-specific therapy can be used to induce tolerance, such as through the use of double-stranded DNA molecules in lupus nephritis. Since other antigen systems are less well characterized, inducing a more generalized impairment in the immune response by blocking costimulatory molecules CD40-CD154 and CD28-CD80/86 is a growing approach to treat various immunologic disorders and transplantation. To reduce glomerular inflammation, a variety of effector systems have been targeted, including complement, cytokines/chemokines, adhesion molecules, and mediators of cellular proliferation. Of these, antibodies targeting C5 in the complement system, and antibody and receptor antagonists of tumor necrosis factor-alpha (TNF-alpha) have already been used in glomerular disorders with some promise. Less specific blockade of receptor-mediated events stimulated by platelet-derived growth factors and cell cycle proteins may soon be applied to glomerulonephritis. Finally, interruption of fibrosing pathways, which lead to glomerulosclerosis and interstitial fibrosis common to the end-stage of all glomerulonephritis, is the subject of intense effort which may yield effective biologic therapies. In spite of all these advances, we still are dependent on steroids and cytotoxics to treat glomerulonephritis. To get past this, we must devote significant resources to take observations made in basic research laboratories to develop therapeutics and prove their utility in human disease.

Block and tackle: CTLA4Ig takes on lupus

Blockade of antigen nonspecific costimulatory signals is a promising approach for the treatment of autoimmune diseases including systemic lupus erythematosus (SLE). CTLA4Ig, an antagonist of the CD28/B7 costimulatory interaction, effectively prevents SLE onset in several murine models and, when used in combination with cyclophosphamide, can induce remission of active SLE nephritis. In this review we describe the known mechanisms of action of CTLA4Ig both in normal immunity and in autoimmune disease models and address issues about its activity that still need to be resolved. We discuss the preclinical use of CTLA4Ig in murine SLE models and the rationale for a clinical trial in SLE patients.