Regulatory defects in Cbl and mitogen-activated protein kinase (extracellular signal-related kinase) pathways cause persistent hyperexpression of CD40 ligand in human lupus T cells

Regulatory effect of curcumin on CD40:CD40L interaction and therapeutic implications

Natural compounds have garnered significant attention as potential therapeutic agents due to their inherent properties. Their notable qualities, including safety, efficacy, favorable pharmacokinetic properties, and heightened effectiveness against certain diseases, particularly inflammatory conditions, make them particularly appealing. Among these compounds, curcumin has attracted considerable interest for its unique therapeutic properties and has therefore been extensively studied as a potential therapeutic agent for treating various diseases. Curcumin exhibits diverse anti-inflammatory, antioxidant, and antimicrobial effects. Curcumin's immune system regulatory ability has made it a promising compound for treatment of various inflammatory diseases, such as psoriasis, atherosclerosis, asthma, colitis, IBD, and arthritis. Among the signaling pathways implicated in these conditions, the CD40 receptor together with its ligand, CD40L, are recognized as central players. Studies have demonstrated that the interaction between CD40 and CD40L interaction acts as the primary mediator of the immune response in inflammatory diseases. Numerous studies have explored the impact of curcumin on the CD40:CD40L pathway, highlighting its regulatory effects on this inflammatory pathway and its potential therapeutic use in related inflammatory conditions. In this review, we will consider the evidence concerning curcumin's modulatory effects in inflammatory disease and its potential therapeutic role in regulating the CD40:CD40L pathway.

Polygenic autoimmune disease risk alleles impacting B cell tolerance act in concert across shared molecular networks in mouse and in humans

Most B cells produced in the bone marrow have some level of autoreactivity. Despite efforts of central tolerance to eliminate these cells, many escape to periphery, where in healthy individuals, they are rendered functionally non-responsive to restimulation through their antigen receptor via a process termed anergy. Broad repertoire autoreactivity may reflect the chances of generating autoreactivity by stochastic use of germline immunoglobulin gene segments or active mechanisms may select autoreactive cells during egress to the naïve peripheral B cell pool. Likewise, it is unclear why in some individuals autoreactive B cell clones become activated and drive pathophysiologic changes in autoimmune diseases. Both of these remain central questions in the study of the immune system(s). In most individuals, autoimmune diseases arise from complex interplay of genetic risk factors and environmental influences. Advances in genome sequencing and increased statistical power from large autoimmune disease cohorts has led to identification of more than 200 autoimmune disease risk loci. It has been observed that autoantibodies are detectable in the serum years to decades prior to the diagnosis of autoimmune disease. Thus, current models hold that genetic defects in the pathways that control autoreactive B cell tolerance set genetic liability thresholds across multiple autoimmune diseases. Despite the fact these seminal concepts were developed in animal (especially murine) models of autoimmune disease, some perceive a disconnect between human risk alleles and those identified in murine models of autoimmune disease. Here, we synthesize the current state of the art in our understanding of human risk alleles in two prototypical autoimmune diseases - systemic lupus erythematosus (SLE) and type 1 diabetes (T1D) along with spontaneous murine disease models. We compare these risk networks to those reported in murine models of these diseases, focusing on pathways relevant to anergy and central tolerance. We highlight some differences between murine and human environmental and genetic factors that may impact autoimmune disease development and expression and may, in turn, explain some of this discrepancy. Finally, we show that there is substantial overlap between the molecular networks that define these disease states across species. Our synthesis and analysis of the current state of the field are consistent with the idea that the same molecular networks are perturbed in murine and human autoimmune disease. Based on these analyses, we anticipate that murine autoimmune disease models will continue to yield novel insights into how best to diagnose, prognose, prevent and treat human autoimmune diseases.

Post-translational modifications in T cells in systemic erythematosus lupus

Systemic erythematosus lupus (SLE) is a classic autoimmune disease characterized by multiple autoantibodies and immune-mediated tissue damage. The aetiology of this disease is still unclear. A new drug, belimumab, which acts against the B-lymphocyte stimulator (BLyS), can effectively improve the condition of SLE patients, but it cannot resolve all SLE symptoms. The discovery of novel, precise therapeutic targets is urgently needed. It is well known that abnormal T-cell function is one of the most crucial factors contributing to the pathogenesis of SLE. Protein post-translational modifications (PTMs), including phosphorylation, glycosylation, acetylation, methylation, ubiquitination and SUMOylation have been emphasized for their roles in activating protein activity, maintaining structural stability, regulating protein-protein interactions and mediating signalling pathways, in addition to other biological functions. Summarizing the latest data in this area, this review focuses on the potential roles of diverse PTMs in regulating T-cell function and signalling pathways in SLE pathogenesis, with the goal of identifying new targets for SLE therapy.

Curcumin modulation of the activation of PYK2 in peripheral blood mononuclear cells from patients with lupus nephritis

INTRODUCTION

Proline-rich tyrosine kinase 2 (PYK2) provides important signals during the activation of lymphocytes, which is essential in autoimmune diseases. Systemic lupus erythematosus (SLE) is a representative autoimmune disease, and lupus nephritis (LN) is one of its most severe complications. Although glucocorticoid-binding immuno-suppression is the first-line therapy for patients with LN, the common and severe side effects of such treatment call for new strategies to improve long-term prognosis and life quality for these patients. Curcumin has been used to treat autoimmune disease with good curative effect, but little is known about the effect of curcumin on LN patients. Our aim was to investigate the mechanism of curcumin for management of LN, specifically regarding the PYK2 pathways.

MATERIAL AND METHODS

Freshly isolated peripheral blood mononuclear cells (PBMCs) from 20 LN patients and 20 healthy individuals were cultured and stimulated with either PMA, PMA+TyrA9 (PYK2 specific inhibitor), or PMA+Curcumin, and with PBS as control. After 48 hours of incubation, cells were harvested and the expression of PYK2, p-PYK2, CD40L, CTLA-4, and PBMCs proliferation were measured. Then the expression and activation of PYK2 was evaluated using Western blot, the expression of costimulatory molecules CD40L and CTLA-4 protein was evaluated using flow cytometry, and PBMC proliferation was assessed using a [3H]-thymidine incorporation assay.

RESULTS

Curcumin inhibited the expression and activation of PYK2 in PBMCs in patients with LN in vitro. The inhibition rate of curcumin was negatively correlated with the level of serum complement, but positively correlated with 24-h proteinuria. Curcumin also suppressed the expression of costimulatory molecules CD40L and CTLA-4, as well as PBMC proliferation. Interestingly, these effects were not reproduced on PBMC cultures of healthy subjects.

CONCLUSIONS

The inhibition of PYK2 signalling protein may be one of the mechanisms underlying the action of curcumin in LN treatment.

Decreased SAP Expression in T Cells from Patients with Systemic Lupus Erythematosus Contributes to Early Signaling Abnormalities and Reduced IL-2 Production

T cells from patients with systemic lupus erythematosus (SLE) display a number of abnormalities, including increased early signaling events following engagement of the TCR. Signaling lymphocytic activation molecule family cell surface receptors and the X-chromosome-defined signaling lymphocytic activation molecule-associated protein (SAP) adaptor are important in the development of several immunocyte lineages and modulating the immune response. We present evidence that SAP protein levels are decreased in T cells and in their main subsets isolated from 32 women and three men with SLE, independent of disease activity. In SLE T cells, SAP protein is also subject to increased degradation by caspase-3. Forced expression of SAP in SLE T cells normalized IL-2 production, calcium (Ca(2+)) responses, and tyrosine phosphorylation of a number of proteins. Exposure of normal T cells to SLE serum IgG, known to contain anti-CD3/TCR Abs, resulted in SAP downregulation. We conclude that SLE T cells display reduced levels of the adaptor protein SAP, probably as a result of continuous T cell activation and degradation by caspase-3. Restoration of SAP levels in SLE T cells corrects the overexcitable lupus T cell phenotype.

Disturbed T Cell Signaling and Altered Th17 and Regulatory T Cell Subsets in the Pathogenesis of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the presence of autoantibodies against nuclear components. Circulating immune complexes of chromatin and autoantibodies deposit in various tissues leading to inflammation and tissue damage. It has been well documented that autoimmunity in SLE depends on autoreactive T cells. In this review, we summarize the literature that addresses the roles of T cell signaling, and Th17 and regulatory T cells (Tregs) in the development of SLE. T cell receptor (TCR) signaling appears to be aberrant in T cells of patients with SLE. In particular, defects in the TCRζ chain, Syk kinase, and calcium signaling molecules have been associated with SLE, which leads to hyperresponsive autoreactive T cells. Furthermore, in patients with SLE increased numbers of autoreactive Th17 cells have been documented, and Th17 cells appear to be responsible for tissue inflammation and damage. In addition, reduced numbers of Tregs as well as Tregs with an impaired regulatory function have been associated with SLE. The altered balance between the number of Tregs and Th17 cells in SLE may result from changes in the cytokine milieu that favors the development of Th17 cells over Tregs.

Dysregulation of anergy-related factors involved in regulatory T cells defects in Systemic Lupus Erythematosus patients: Rapamycin and Vitamin D efficacy in restoring regulatory T cells

AIM

Systemic Lupus Erythematosus (SLE) patients display dysfunctions in T cell activation and anergy. Therefore the aims of our study were to explore the expression of anergy-related factors in CD4⁺ T cells in relationship with regulatory T cells (Tregs) frequency in SLE patients and to identify strategies to redress these defects.

METHOD

Casitas B-cell lymphoma b (Cbl-b) and 'gene related to anergy in lymphocytes' (GRAIL) proteins were analyzed in peripheral blood mononuclear cells (PBMCs) from SLE patients and healthy donors (HD) by immunoblotting. cbl-b, grail, growth response factors (egr)2 and egr3 messenger RNAs (mRNAs) were evaluated by real-time polymerase chain reaction in SLE and HD PBMCs and CD4⁺ T cells. Phenotypic and functional characterization of CD4⁺ T cells was performed by flow cytometry. Tregs expansion protocol consisted in culturing CD4⁺ T cells for 14 or 21 days of experimental activation with anti-CD3 and anti-CD28 monoclonal antibodies, human recombinant interleukin (hrIL)-2, in the absence or presence of rapamycin (Rapa) or 1,25-(OH)2D3 (vitamin D: VitD).

RESULTS

SLE PBMCs expressed low levels of Cbl-b and GRAIL proteins. Both SLE PBMCs and CD4⁺ T cells expressed low levels of egr2/3 mRNAs. SLE patients had a reduced number of Tregs with impaired suppressive activity. An association between egr2 mRNA level in CD4⁺ T cells and Tregs percentage was identified. Experimental activation of CD4⁺ T cells in the presence of hrIL-2 and Rapa or VitD induced the expansion of SLE Tregs. However, on long-term, only Rapa exposure of SLE CD4⁺ T cells yielded high numbers of Tregs with sustained suppressive activity.

CONCLUSION

Our results suggest a new strategy to correct defects in CD4⁺ T cell tolerance mechanisms that may prove beneficial in SLE.

IL-15 prolongs CD154 expression on human CD4 T cells via STAT5 binding to the CD154 transcriptional promoter

Activation-induced CD154 expression on CD4 T cells is prolonged in systemic lupus erythematosus, but the mechanism(s) for its dysregulation are unknown. The studies reported herein demonstrate that interleukin-15 (IL-15) is capable of prolonging CD154 expression on phytohemagglutinin (PHA)-activated CD4 T cells. As IL-15 signals through signal transducer and activator of transcription 5 (STAT5), predicted STAT5 binding sites in the human CD154 transcriptional promoter were identified, and STAT5 binding to the proximal CD154 promoter in vitro and in vivo following primary CD4 T-cell activation was demonstrated. Moreover, overexpression of wild-type STAT5 in primary human CD4 T cells augmented CD154 transcription, whereas overexpression of a dominant-negative (DN) STAT5 protein inhibited CD154 transcription. Mutation of the most proximal STAT5 binding site in the CD154 promoter resulted in diminished DNA binding and reduced CD154 transcriptional activity. Interestingly, STAT5-specific small interfering RNA inhibited CD154 surface expression at 48 but not 24 h after T-cell activation. Thus, these findings provide some of the first evidence to support a possible mechanistic link to explain how the overexpression of IL-15 observed in lupus patients may be involved in the prolonged expression of CD154 that has also been observed on lupus CD4 T cells.

Aberrant B-lymphocyte responses in lupus: inherent or induced and potential therapeutic targets

BACKGROUND

Lupus is a prototype autoimmune disease of unknown aetiology. The disease is complex; manifest diverse clinical symptoms and disease mechanisms. This complexity has provided many leads to explore: from disease mechanisms to approaches for therapy. B-lymphocytes play a central role in the pathogenesis of the disease. However, the cause of aberrant B-lymphocyte responses in patients and, indeed, its causal relationship with the disease remain unclear.

DESIGN

This article provides a synopsis of current knowledge of immunological abnormalities in lupus with an emphasis on abnormalities in the B-lymphocyte compartment.

RESULTS

There is evidence for abnormalities in most compartments of the immune system in animal models and patients with lupus including an ever expanding list of abnormalities within the B-lymphocyte compartment. In addition, recent genome-wide linkage analyses in large cohorts of patients have identified new sets of genetic association factors some with potential links with defective B-lymphocyte responses although their full pathophysiological effects remain to be determined. The accumulating knowledge may help in the identification and application of new targeted therapies for treating lupus disease.

CONCLUSIONS

Cellular, molecular and genetic studies have provided significant insights into potential causes of immunological defects associated with lupus. Most of this insight relate to defects in B- and T-lymphocyte tolerance, signalling and responses. For B-lymphocytes, there is evidence for altered regulation of inter and intracellular signalling pathways at multiple levels. Some of these abnormalities will be discussed within the context of potential implications for disease pathogenesis and targeted therapies.

Casitas B lineage lymphoma b is a key regulator of peripheral tolerance in systemic lupus erythematosus

OBJECTIVE

To analyze whether the expression and modulation of T cell receptor (TCR) signaling is dependent on Casitas B lineage lymphoma b (Cbl-b) in T cells from patients with systemic lupus erythematosus (SLE) upon stimulation with a tolerogenic substance.

METHODS

Peripheral blood mononuclear cells were obtained from 20 patients with SLE (active disease or in remission) and 20 healthy controls. Levels of Cbl-b expression were measured using reverse transcription-polymerase chain reaction and Western blotting in peripheral CD4+ T cells from SLE patients and healthy controls upon anergy induction. Cell proliferation was measured using the carboxyfluorescein diacetate succinimidyl ester dilution method. Cytokine production was analyzed by luminometry, and surface expression of activation markers was assessed by flow cytometry. Transfection assays were performed to induce overexpression of Cbl-b, and phosphorylation of TCR-associated kinases was evaluated.

RESULTS

CD4+ T cells from SLE patients displayed resistance to anergy (as evidenced by increased cell proliferation, interleukin-2 production, and expression of activation and costimulatory markers), and this was associated with altered Cbl-b expression. Upon ionomycin treatment, primary T cells showed enhanced MAPK activity and decreased Akt phosphorylation, which was representative of the anergic state. In T cells from lupus patients, Cbl-b overexpression led to increased expression of phosphorylated MAPK, thus indicating the reversibility of anergy resistance.

CONCLUSION

These findings suggest that abnormal peripheral tolerance in SLE is caused by a deficiency in Cbl-b, and that this ubiquitin ligase plays a key role in regulating TCR signaling during the induction of peripheral tolerance.

Estradiol differentially regulates calreticulin: a potential link with abnormal T cell function in systemic lupus erythematosus?

OBJECTIVE

Systemic lupus erythematosus (SLE) is an autoimmune disease that affects women nine times more often than men. The present study investigates estradiol-dependent control of the calcium-buffering protein, calreticulin, to gain further insight into the molecular basis of abnormal T cell signaling in SLE T cells.

METHODS

T cells were purified from blood samples obtained from healthy females and SLE patients. Calreticulin expression was quantified by real-time polymerase chain amplification. Calreticulin and estrogen receptor-α were co-precipitated and analyzed by Western blotting to determine if the proteins associate in T cells.

RESULTS

Calreticulin expression increased (p = 0.034) in activated control T cells, while estradiol decreased (p = 0.044) calreticulin in resting T cells. Calreticulin expression decreased in activated SLE T cell samples and increased in approximately 50% of resting T cell samples. Plasma estradiol was similar (p > 0.05) among SLE patients and control volunteers. Estrogen receptor-α and calreticulin co-precipitated from nuclear and cytoplasmic T cell compartments.

CONCLUSIONS

The results indicate that estradiol tightly regulates calreticulin expression in normal human T cells, and the dynamics are different between activated and resting T cells. The absence of this tight regulation in SLE T cells could contribute to abnormal T cell function.

Lupus autoimmunity altered by cellular methylation metabolism

Modifications of both DNA and protein by methylation are key factors in normal T and B cell immune responses as well as in the development of autoimmune disease. For example, the failure to maintain the methylation status of CpG dinucleotides in DNA triggers T cell autoreactivity. Methylated proteins are known targets of autoimmunity, including the symmetrical dimethylarginine residues of SmD1 and SmD3 in SLE. Herein, we demonstrate that altering the metabolism of S-adenosylmethionine (SAM), the major methyl donor for transmethylation reactions, can suppress T cell immunity. A by-product of SAM metabolism, 5'-deoxy-5'-methylthioadenosine (MTA), and an indirect inhibitor of methyltransferases, inhibits T cell responses including T cell activation markers, Th1/Th2 cytokines and TCR-related signaling events. Moreover, treatment of the lupus-prone MRL/lpr mouse with MTA markedly ameliorates splenomegaly, lymphadenopathy, autoantibody titers as well as IgG deposition and cellular infiltration in the kidney. Incubation of cells with SAM, which increases intracellular MTA levels, inhibits both TCR-mediated T cell proliferation and BCR (anti-IgM)-triggered B cell proliferation in a dose-dependent manner. These studies define the central role of MTA and SAM in immune responses and provide a simple approach to altering lymphocyte transmethylation and T cell mediated autoimmune syndromes.

Megakaryocyte progenitors are the main APCs inducing Th17 response to lupus autoantigens and foreign antigens

In search of autoantigen-presenting cells that prime the pathogenic autoantibody-inducing Th cells of lupus, we found that CD41(+)CD151(+) cells among Lineage(-) (Lin(-)) CD117(+) (c-Kit(+)) CX3CR1(-) splenocytes depleted of known APCs were most proficient in presenting nuclear autoantigens from apoptotic cells to induce selectively an autoimmune Th17 response in different lupus-prone mouse strains. The new APCs have properties resembling megakaryocyte and/or bipotent megakaryocyte/erythroid progenitors of bone marrow, hence they are referred to as MM cells in this study. The MM cells produce requisite cytokines, but they require contact for optimal Th17 induction upon nucleosome feeding, and can induce Th17 only before undergoing differentiation to become c-Kit(-)CD41(+) cells. The MM cells expand up to 10-fold in peripheral blood of lupus patients and 49-fold in spleens of lupus mice preceding disease activity; they accelerate lupus in vivo and break tolerance in normal mice, inducing autoimmune Th17 cells. MM cells also cause Th17 skewing to foreign Ag in normal mice without Th17-polarizing culture conditions. Several molecules in MM cells are targets for blocking of autoimmunization. This study advances our understanding of lupus pathogenesis and Th17 differentiation biology by characterizing a novel category of APC.

Preformed CD40L is stored in Th1, Th2, Th17, and T follicular helper cells as well as CD4+ 8- thymocytes and invariant NKT cells but not in Treg cells

CD40L is essential for the development of adaptive immune responses. It is generally thought that CD40L expression in CD4⁺ T cells is regulated transcriptionally and made from new mRNA following antigen recognition. However, imaging studies show that the majority of cognate interactions between effector CD4⁺ T cells and APCs in vivo are too short to allow de novo CD40L synthesis. We previously showed that Th1 effector and memory cells store preformed CD40L (pCD40L) in lysosomal compartments and mobilize it onto the plasma membrane immediately after antigenic stimulation, suggesting that primed CD4⁺ T cells may use pCD40L to activate APCs during brief encounters. Indeed, our recent study showed that pCD40L is sufficient to mediate selective activation of cognate B cells and trigger DC activation in vitro. In this study, we show that pCD40L is present in Th1 and follicular helper T cells developed during infection with lymphocytic choriomeningitis virus, Th2 cells in the airway of asthmatic mice, and Th17 cells from the CNS of animals with experimental autoimmune encephalitis (EAE). pCD40L is nearly absent in both natural and induced Treg cells, even in the presence of intense inflammation such as occurs in EAE. We also found pCD40L expression in CD4 single positive thymocytes and invariant NKT cells. Together, these results suggest that pCD40L may function in T cell development as well as an unexpectedly broad spectrum of innate and adaptive immune responses, while its expression in Treg cells is repressed to avoid compromising their suppressive activity.

Linker for activation of T cells is displaced from lipid rafts and decreases in lupus T cells after activation via the TCR/CD3 pathway

Systemic lupus erythematosus (SLE) is characterized by abnormal signal transduction mechanisms in T lymphocytes. Linker for activation of T cells (LAT) couples TCR/CD3 activation with downstream signaling pathways. We reported diminished ERK 1/2 kinase activity in TCR/CD3 stimulated lupus T cells. In this study we evaluated the expression, phosphorylation, lipid raft and immunological synapse (IS) localization and colocalization of LAT with key signalosome molecules. We observed a diminished expression and an abnormal localization of LAT in lipid rafts and at the IS in activated lupus T cells. LAT phosphorylation, capture by GST-Grb2 fusion protein, and coupling to Grb2 and PLCγ1, was similar in healthy control and lupus T cells. Our results suggest that an abnormal localization of LAT within lipid rafts and its accelerated degradation after TCR/CD3 activation may compromise the assembly of the LAT signalosome and downstream signaling pathways required for full MAPK activation in lupus T cells.

Expression and function of Cbl-b in T cells from patients with systemic lupus erythematosus, and detection of the 2126 A/G Cblb gene polymorphism in the Mexican mestizo population

Systemic lupus erythematosus (SLE) is characterized by abnormalities in the function of T and B lymphocytes and in the signaling pathways induced through their receptors. Cbl-b is an intracellular adaptor protein that plays a key role in the negative regulation of lymphocyte activity. We explored the expression and function of Cbl-b in T lymphocytes from SLE patients. In addition, the possible association of SLE and a single nucleotide polymorphism (SNP) of the Cblb gene was determined. We studied 150 SLE patients, 163 healthy individuals, and 14 patients with rheumatoid arthritis (RA). The expression of Cbl-b was analyzed in the peripheral blood mononuclear cells, and the negative regulatory function of Cbl-b was assessed by analyzing actin polymerization and the phosphorylation of JNK and c-Jun induced through CD3. Furthermore, the 2126(A/G) SNP of the Cblb gene was detected by real-time polymerase chain reaction. We found a significant small reduction in the expression of Cbl-b as well as increased levels of activation of c-Jun and actin polymerization in T lymphocytes from patients with SLE compared with healthy controls or RA patients. In addition, a significant association between the 2126(A/G) SNP and SLE was detected. Our data suggest that Cbl-b may contribute to the deregulated activation of T lymphocytes observed in SLE.

Cyclosporine-resistant, Rab27a-independent mobilization of intracellular preformed CD40 ligand mediates antigen-specific T cell help in vitro

CD40L is critically important for the initiation and maintenance of adaptive immune responses. It is generally thought that CD40L expression in CD4(+) T cells is regulated transcriptionally and made from new mRNA following Ag recognition. However, recent studies with two-photon microscopy revealed that most cognate interactions between effector CD4(+) T cells and APCs are too short for de novo synthesis of CD40L. Given that effector and memory CD4(+) T cells store preformed CD40L (pCD40L) in lysosomal compartments and that pCD40L comes to the cell surface within minutes of antigenic stimulation, we and others have proposed that pCD40L might mediate T cell-dependent activation of cognate APCs during brief encounters in vivo. However, it has not been shown that this relatively small amount of pCD40L is sufficient to activate APCs, owing to the difficulty of separating the effects of pCD40L from those of de novo CD40L and other cytokines in vitro. In this study, we show that pCD40L surface mobilization is resistant to cyclosporine or FK506 treatment, while de novo CD40L and cytokine expression are completely inhibited. These drugs thus provide a tool to dissect the role of pCD40L in APC activation. We find that pCD40L mediates selective activation of cognate but not bystander APCs in vitro and that mobilization of pCD40L does not depend on Rab27a, which is required for mobilization of lytic granules. Therefore, effector CD4(+) T cells deliver pCD40L specifically to APCs on the same time scale as the lethal hit of CTLs but with distinct molecular machinery.

Prolonged expression of CD154 on CD4 T cells from pediatric lupus patients correlates with increased CD154 transcription, increased nuclear factor of activated T cell activity, and glomerulonephritis

OBJECTIVE

To assess CD154 expression in patients with pediatric systemic lupus erythematosus (SLE) and to explore a transcriptional mechanism that may explain dysregulated expression of CD154.

METHODS

Cell surface CD154 expression (pre- and postactivation) in peripheral blood CD4 T cells from 29 children with lupus and 29 controls matched for age, sex, and ethnicity was examined by flow cytometry. CD154 expression was correlated with clinical features, laboratory parameters, and treatments received. Increased CD154 expression on CD4 T cells from the SLE patients was correlated with CD154 message and transcription rates by real-time reverse transcription-polymerase chain reaction (RT-PCR) and nuclear run-on assays, respectively. Nuclear factor of activated T cell (NF-AT) transcription activity and mRNA levels in CD4 T cells from SLE patients were explored by reporter gene analysis and real-time RT-PCR, respectively.

RESULTS

CD154 surface protein levels were increased 1.44-fold in CD4 T cells from SLE patients as compared with controls in cells evaluated 1 day postactivation ex vivo. This increase correlated clinically with the presence of nephritis and an elevated erythrocyte sedimentation rate. Increased CD154 protein levels also correlated with increased CD154 mRNA levels and with CD154 transcription rates, particularly at later time points following T cell activation. Reporter gene analyses revealed a trend for increased NF-AT, but decreased activator protein 1 and similar NF-kappaB, activity in CD4 T cells from SLE patients as compared with controls. Moreover, NF-AT1 and, in particular, NF-AT2 mRNA levels were notably increased in CD4 T cells from SLE patients as compared with controls.

CONCLUSION

Following activation, cell surface CD154 is increased on CD4 T cells from pediatric lupus patients as compared with controls, and this increase correlates with the presence of nephritis, increased CD154 transcription rates, and increased NF-AT activity. These results suggest that NF-AT/calcineurin inhibitors, such as tacrolimus and cyclosporine, may be beneficial in the treatment of lupus nephritis.

Activation signal transduction by proline-rich tyrosine kinase 2 (PYK2) in peripheral blood mononuclear cells from patients with systemic lupus erythematosus

To explore the role of proline-rich tyrosine kinase 2 (PYK2) in systemic lupus erythematosus (SLE), we studied the expression, activation, and function of PYK2 in peripheral blood mononuclear cells (PBMC) from 36 SLE patients. As controls, samples from 19 patients with rheumatoid arthritis and 15 healthy individuals were studied simultaneously. We found a significant increase of both the total PYK2 protein and its activated/phosphorylated form in PBMCs from patients with SLE, particularly those with the complication of nephritis (WHO class IV). There is a clear correlation between the activation of PYK2 and the level of serum complements. In active SLE patients, activation of PYK2 in PBMCs accompanies the increased cell proliferation and the induced expression of co-stimulatory molecules CD40L and CTLA4. These results indicate that phosphorylated PYK2 may induce the expression of CD40L and CTLA4, and subsequently the cell proliferation. PYK2 signaling enhances the autoreactive lymphocyte activation and plays an important role in the pathogenesis of SLE.

Systems biology of lupus: mapping the impact of genomic and environmental factors on gene expression signatures, cellular signaling, metabolic pathways, hormonal and cytokine imbalance, and selecting targets for treatment

Systemic lupus erythematosus (SLE) is characterized by the dysfunction of T cells, B cells, and dendritic cells, the release of pro-inflammatory nuclear materials from necrotic cells, and the formation of antinuclear antibodies (ANA) and immune complexes of ANA with DNA, RNA, and nuclear proteins. Activation of the mammalian target of rapamycin (mTOR) has recently emerged as a key factor in abnormal activation of T and B cells in SLE. In T cells, increased production of nitric oxide and mitochondrial hyperpolarization (MHP) were identified as metabolic checkpoints upstream of mTOR activation. mTOR controls the expression T-cell receptor-associated signaling proteins CD4 and CD3zeta through increased expression of the endosome recycling regulator Rab5 and HRES-1/Rab4 genes, enhances Ca2+ fluxing and skews the expression of tyrosine kinases both in T and B cells, and blocks the expression of Foxp3 and the generation of regulatory T cells. MHP, increased activity of mTOR, Rab GTPases, and Syk kinases, and enhanced Ca2+ flux have emerged as common T and B cell biomarkers and targets for treatment in SLE.

Functional activation of proline-rich tyrosine kinase2 (PYK2) in peripheral blood mononuclear cells from patients with systemic lupus erythematosus

Background

Systemic lupus erythematosus (SLE) is a representative systemic autoimmune disease characterized by activated T cells and polyclonally activated B cells that produce autoantibodies. Activation of autoreactive T and B cells plays a pivotal role in the pathogenesis of this disease. A role of focal adhesion kinase (FAK) in the pathogenesis has been suggested. Proline-rich tyrosine kinase2 (PYK2) is structurally related to FAK, however, the functional activation of PYK2 in SLE remains unclear. In the present study, we showed that PYK2 is significantly increased and activated in peripheral blood mononuclear cells (PBMCs) of patients with SLE. In addition, we showed the involvement of PYK2 proteins in the up-regulation of CD40L and CTLA4 expression and PBMC proliferation.

Methods

Freshly isolated PBMCs from 48 SLE patients, 32 patients with rheumatoid arthritis(RA) and 24 healthy individuals were analyzed for the expression and activation of PYK2 by western-blotting and immunocytochemistry. The other isolated PBMCs from patients with this condition were cultured and stimulated with PMA or TyrA9, and then the expression of costimulatory molecules CD40L and CTLA4 was evaluated using flow cytometry, PBMCs proliferation was determined with [³H]-thymidine incorporation (CPM).

Results

Compared with RA patients and healthy donors, PBMCs from SLE patients expressed more of both the total PYK2 protein and its activated/phosphorylated form. The increase of activated PYK2 protein in SLE PBMCs was correlated with the complication of nephritis and inversly associated the level of serum complements. In active SLE patients, activation of PYK2 in PBMCs is accompanying the increased cell proliferation and the induced expression of costimulatory molecules CD40L and CTLA4.

Conclusion

Our findings indicate that phosphorylated PYK2 in SLE PBMCs may induce the expression of CD40L and CTLA4, and subsequently the cell proliferation. PYK2 signaling enhances the autoreactive lymphocyte activation and plays an important role in the pathogenesis of SLE.

Regulatory T cell (Treg) subsets return in patients with refractory lupus following stem cell transplantation, and TGF-beta-producing CD8+ Treg cells are associated with immunological remission of lupus

Compared with conventional drug therapy, autologous hemopoietic stem cell transplantation (HSCT) can induce very-long-term remission in refractory lupus patients. Herein, we show that in posttransplant patients, both CD4(+)CD25(high)FoxP3(+) and an unusual CD8(+)FoxP3(+) Treg subset return to levels seen in normal subjects; accompanied by almost complete inhibition of pathogenic T cell response to critical peptide autoepitopes from histones in nucleosomes, the major lupus autoantigen from apoptotic cells. In addition to a stably sustained elevation of FoxP3, posttransplant CD8 T cells also maintained markedly higher expression levels of latency-associated peptide (LAP), CD103, PD-1, PD-L1, and CTLA-4, as compared with pretransplant CD8 T cells that were identically treated by a one-time activation and rest in short-term culture. The posttransplant CD8 regulatory T cells (Treg) have autoantigen-specific and nonspecific suppressive activity, which is contact independent and predominantly TGF-beta dependent. By contrast, the pretransplant CD8 T cells have helper activity, which is cell contact dependent. Although CD4(+)CD25(high) Treg cells return during clinical remission of conventional drug-treated lupus, the posttransplant patient's CD8 Treg cells are considerably more potent, and they are absent in drug-treated patients in whom CD4 T cell autoreactivity to nucleosomal epitopes persists even during clinical remission. Therefore, unlike conventional drug therapy, hemopoietic stem cell transplantation generates a newly differentiated population of LAP(high)CD103(high) CD8(TGF-beta) Treg cells, which repairs the Treg deficiency in human lupus to maintain patients in true immunological remission.

T-cell and B-cell signaling biomarkers and treatment targets in lupus

PURPOSE OF REVIEW

Systemic lupus erythematosus is characterized by the production of antinuclear autoantibodies and dysfunction of T-cells, B-cells, and dendritic cells. Here, we review newly recognized genetic factors and mechanisms that underlie abnormal intracellular signal processing and intercellular communication within the immune system in systemic lupus erythematosus.

RECENT FINDINGS

Activation of the mammalian target of rapamycin plays a pivotal role in abnormal activation of T and B-cells in systemic lupus erythematosus. In T-cells, increased production of nitric oxide and mitochondrial hyperpolarization were identified as metabolic checkpoints upstream of mammalian target of rapamycin activation. Mammalian target of rapamycin controls the expression T-cell receptor-associated signaling proteins CD4 and CD3zeta through increased expression of the endosome recycling regulator HRES-1/Rab4 gene, mediates enhanced Ca2+ fluxing and skews the expression of tyrosine kinases both in T and B-cells, and blocks the expression of Foxp3 and the expansion of regulatory T-cells. Mitochondrial hyperpolarization and the resultant ATP depletion predispose T-cells to necrosis, thus promoting the dendritic cell activation, antinuclear autoantibody production, and inflammation.

SUMMARY

Mitochondrial hyperpolarization, increased activity of mammalian target of rapamycin and Syk kinases, enhanced receptor recycling and Ca2+ flux have emerged as common T and B-cell biomarkers and targets for treatment in systemic lupus erythematosus.

Ubiquitin ligase Cbl-b sensitizes leukemia and gastric cancer cells to anthracyclines by activating the mitochondrial pathway and modulating Akt and ERK survival signals

The present study reported that the ubiquitin ligase Cbl-b was up-regulated during anthracycline-induced apoptosis in two cell lines, RBL-2H3 leukemia cells and MGC803 gastric cancer cells. Overexpression of Cbl-b strongly promoted the cytotoxic and apoptosis-inducing effects of anthracyclines, while a dominant negative (DN) Cbl-b mutation abolished these effects in both cell lines. Further investigation revealed that mitochondrial depolarization was enhanced by Cbl-b and decreased by Cbl-b (DN) in RBL-2H3 cells. Moreover, overexpression of Cbl-b significantly suppressed ERK activation, and Cbl-b (DN) strongly enhanced both ERK and Akt activation. Altogether, these results indicate that Cbl-b sensitized both leukemia and gastric cancer cells to anthracyclines by activating the mitochondrial apoptotic pathway and modulating the ERK and Akt survival pathways.

Lupus and T cells

T-cell abnormalities and aberrant T helper cytokine profiles have been implicated in the loss of immune tolerance to nuclear and cytoplasmic antigens and linked to a variety of clinical manifestations in systemic lupus erythematosus (SLE). Here, we review the role of T cells in promoting and maintaining SLE in relation to their cellular and molecular abnormalities and provide an update on recent T cell-targeted therapeutic approaches for the restoration of T cell homeostasis in the disease.

The spliceosomal phosphopeptide P140 controls the lupus disease by interacting with the HSC70 protein and via a mechanism mediated by gammadelta T cells

The phosphopeptide P140 issued from the spliceosomal U1-70K snRNP protein is recognized by lupus CD4(+) T cells, transiently abolishes T cell reactivity to other spliceosomal peptides in P140-treated MRL/lpr mice, and ameliorates their clinical features. P140 modulates lupus patients' T cell response ex vivo and is currently included in phase IIb clinical trials. Its underlying mechanism of action remains elusive. Here we show that P140 peptide binds a unique cell-surface receptor, the constitutively-expressed chaperone HSC70 protein, known as a presenting-protein. P140 induces apoptosis of activated MRL/lpr CD4(+) T cells. In P140-treated mice, it increases peripheral blood lymphocyte apoptosis and decreases B cell, activated T cell, and CD4(-)CD8(-)B220(+) T cell counts via a specific mechanism strictly depending on gammadelta T cells. Expression of inflammation-linked genes is rapidly regulated in CD4(+) T cells. This work led us to identify a powerful pathway taken by a newly-designed therapeutic peptide to immunomodulate lupus autoimmunity.

Apigenin, a dietary flavonoid, sensitizes human T cells for activation-induced cell death by inhibiting PKB/Akt and NF-kappaB activation pathway

Resistance of T cells to activation-induced cell death (AICD) is associated with autoimmunity and lymphoproliferation. We found that apigenin (4',5,7-trihydroxyflavone), a non-mutagenic dietary flavonoid, augmented both extrinsic and intrinsic pathways of apoptosis in recurrently activated, but not in primarily stimulated, human blood CD4+ T cells. Apigenin potentiated AICD by inhibiting NF-kappaB activation and suppressing NF-kappaB-regulated anti-apoptotic molecules, cFLIP, Bcl-x(L), Mcl-1, XIAP and IAP, but not Bcl-2. Apigenin suppressed NF-kappaB translocation to nucleus and inhibited IkappaBalpha phosphorylation and degradation in response to TCR stimulation in reactivated peripheral blood CD4 T cells, as well as in leukemic Jurkat T cell lines. Among the pathways that lead to NF-kappaB activation upon TCR stimulation, apigenin selectively inhibited PI3K-PKB/Akt, but not PKC-theta activation in the human T cells, and synergized with a PI3K inhibitor to markedly augment AICD. Apigenin also suppressed expression of anti-apoptotic cyclooxygenase 2 (COX-2) protein in activated human T cells, but it did not affect activation of Erk MAPKinase. Thus, in chronically activated human T cells, relatively non-toxic apigenin can suppress anti-apoptotic pathways involving NF-kappaB activation, and especially cFLIP and COX-2 expression that are important for functioning and maintenance of immune cells in inflammation, autoimmunity and lymphoproliferation.

Extracellular signal-regulated kinase 1/2 signalling in SLE T cells is influenced by oestrogen and disease activity

Systemic lupus erythematosus (SLE) is an autoimmune disease that occurs primarily in women of reproductive age. The disease is characterized by exaggerated T-cell activity and abnormal T-cell signalling. The mitogen-activated protein kinase (MAPK) pathway is involved in the maintenance of T-cell tolerance that fails in patients with SLE. Oestrogen is a female sex hormone that binds to nuclear receptors and alters the rate of gene transcription. Oestrogen can also act through the plasma membrane and rapidly stimulate second messengers including calcium flux and kinase activation. In this study, we investigated whether oestrogen influences the activation of MAPK signalling through the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in activated SLE T cells. SLE and control T cells were cultured in serum-free medium without and with oestradiol (10(-7) M) for 18 h. The T cells were activated with phorbol 12 myristate 13-acetate and ionomycin for various time points (0-60 min), and the amount of phosphorylated ERK1/2 was measured by immunoblotting. There were no differences in ERK1/2 phosphorylation between SLE and control T cells at 5 and 15 min after the activation stimulus. However, comparison between the amount of phosphorylated ERK1/2 in SLE T cells from the same patients cultured without and with oestradiol showed a significant oestrogen-dependent suppression (P=0.48) of ERK1/2 in patients with inactive/mild systemic lupus erythematosus disease activity index (SLEDAI) (0-2) compared with patients with moderate (4-6) or active (8-12) SLEDAI scores. These results suggest that the suppression of MAPK through ERK1/2 phosphorylation is sensitive to oestradiol in patients with inactive or mild disease, but the sensitivity is not maintained when disease activity increases. Furthermore, studies are now necessary to understand the mechanisms by which oestrogen influences MAPK activation in SLE T cells.

Hyperexpression of cyclooxygenase 2 in the lupus immune system and effect of cyclooxygenase 2 inhibitor diet therapy in a murine model of systemic lupus erythematosus

OBJECTIVE

To investigate the role of cyclooxygenase 2 (COX-2) in the functioning of different cell types involved in the lupus autoimmune response, and to examine the therapeutic effect of COX-2 inhibitors in mice prone to spontaneously develop systemic lupus erythematosus (SLE).

METHODS

Lupus-prone (SWR x NZB)F(1) mice were fed with a diet containing different doses of the COX-2-specific inhibitor celecoxib or the nonspecific inhibitor aspirin, or a combination of both, and the effects of the therapy on autoantibody production, development of lupus nephritis, and mortality were determined. Expression of COX-2 by different cells of the lupus immune system and the effect of COX-2 inhibitors on the function of these cells in vitro and in vivo were assessed.

RESULTS

The immune cells of mice with SLE spontaneously hyperexpressed COX-2, and COX-2 inhibitors could cause cell apoptosis. Treatment with COX-2 inhibitors resulted in decreased autoantibody production and inhibition of the T cell response to the major lupus autoantigen, nucleosome, and its presentation by antigen-presenting cells. Surprisingly, a significant increase in survival occurred only in mice receiving intermittent therapy with the lowest dose of celecoxib (500 parts per million), approximating <100 mg of celecoxib/day in humans. A continuous diet, but not intermittent feeding, with the combination of celecoxib and aspirin delayed development of nephritis temporarily, but failed to prolong survival. Indeed, treatment with aspirin alone increased mortality.

CONCLUSION

The contributions of the major players in the pathogenic autoimmune response, namely, T cells, B cells, dendritic cells, and macrophages that are abnormally hyperactive in lupus, depend on the increased expression and activity of COX-2, similar to inflammatory cells in target organs. Intermittent pulse therapy with low doses of select COX-2 inhibitors would be of value in the treatment of lupus.

Shared signaling networks active in B cells isolated from genetically distinct mouse models of lupus

Though B cells play key roles in lupus pathogenesis, the molecular circuitry and its dysregulation in these cells as disease evolves remain poorly understood. To address this, a comprehensive scan of multiple signaling axes using multiplexed Western blotting was undertaken in several different murine lupus strains. PI3K/AKT/mTOR (mTOR, mammalian target of rapamycin), MEK1/Erk1/2, p38, NF-kappaB, multiple Bcl-2 family members, and cell-cycle molecules were observed to be hyperexpressed in lupus B cells in an age-dependent and lupus susceptibility gene-dose-dependent manner. Therapeutic targeting of the AKT/mTOR axis using a rapamycin (sirolimus) derivative ameliorated the serological, cellular, and pathological phenotypes associated with lupus. Surprisingly, the targeting of this axis was associated with the crippling of several other signaling axes. These studies reveal that lupus pathogenesis is contingent upon the activation of an elaborate network of signaling cascades that is shared among genetically distinct mouse models and raise hope that targeting pivotal nodes in these networks may offer therapeutic benefit.

Activation signal transduction by beta1 integrin in T cells from patients with systemic lupus erythematosus

OBJECTIVE

Beta 1 integrin is a representative adhesion molecule for cell-cell and cell-extracellular matrix interactions, and it provides costimulatory signals to T cells. However, the relevance of beta1 integrin to T cell activation in systemic lupus erythematosus (SLE) remains unclear. We undertook this study to perform a quantitative and functional analysis of beta1 integrin-mediated signaling to T cells in patients with SLE.

METHODS

Expression of cell surface molecules was assessed by flow cytometric analysis. Engagement of beta1 integrins was performed by crosslinking using a specific monoclonal antibody. To assess tyrosine kinases in beta1 integrin-mediated signaling, the cells were transfected with a wild-type (WT) focal adhesion kinase (FAK), a dominant-negative truncation of the FAK, or a WT PTEN expression plasmid via nucleofection.

RESULTS

Beta 1 integrin expression was significantly up-regulated on peripheral blood T cells from patients with active SLE, particularly those with the complication of World Health Organization class IV nephritis, whereas CD28 was significantly decreased in patients with active SLE compared with normal individuals. Beta 1 integrin expression closely correlated with serum hypocomplementemia. Engagement of beta1 integrin on T cells from patients with active SLE, but not on those from normal individuals, induced cell proliferation as well as CD40L expression on T cells. Up-regulation of CD40L expression and T cell proliferation, induced by beta1 integrin stimulation, were completely inhibited by transfection of the dominant-negative truncations of FAK or WT PTEN.

CONCLUSION

These results suggest that engagement of beta1 integrins on SLE T cells could induce FAK-mediated signaling and subsequent CD40L expression and proliferation. Thus, the beta1 integrin signaling cascade might serve to enhance autoreactive T cell activation.

Dendritic cells from lupus-prone mice are defective in repressing immunoglobulin secretion

Autoimmunity results from a breakdown in tolerance mechanisms that regulate autoreactive lymphocytes. We recently showed that during innate immune responses, secretion of IL-6 by dendritic cells (DCs) maintained autoreactive B cells in an unresponsive state. In this study, we describe that TLR4-activated DCs from lupus-prone mice are defective in repressing autoantibody secretion, coincident with diminished IL-6 secretion. Reduced secretion of IL-6 by MRL/lpr DCs reflected diminished synthesis and failure to sustain IL-6 mRNA production. This occurred coincident with lack of NF-kappaB and AP-1 DNA binding and failure to sustain IkappaBalpha phosphorylation. Analysis of individual mice showed that some animals partially repressed Ig secretion despite reduced levels of IL-6. This suggests that in addition to IL-6, DCs secrete other soluble factor(s) that regulate autoreactive B cells. Collectively, the data show that MRL/lpr mice are defective in DC/IL-6-mediated tolerance, but that some individuals maintain the ability to repress autoantibody secretion by an alternative mechanism.

Increased levels of NF-ATc2 differentially regulate CD154 and IL-2 genes in T cells from patients with systemic lupus erythematosus

T cells from patients with systemic lupus erythematosus (SLE) are characterized by heightened TCR-initiated free intracytoplasmic calcium responses. We demonstrate that activated T cells from SLE patients, but not from rheumatoid arthritis patients, displayed higher levels of the calcineurin-dependent transcription factor NF-ATc2 in the nucleus compared with control T cells. DNA NF-AT-binding activity was also increased, as was the amount of NF-ATc2 bound to the promoters of CD154 (CD40L) and IL-2 genes. Nevertheless, although high NF-ATc2 levels translated into higher CD154 transcription in SLE, IL-2 transcription was decreased. The absence of important transcriptional activators (AP-1, NF-kappaBeta) and the presence of transcriptional repressors (cAMP response element modulator) on the IL-2 promoter explain this dichotomous effect.

Estrogen does not regulate CD154 mRNA stability in systemic lupus erythematosus T cells

Previous studies in our laboratory showed a dose-dependent and hormone-specific increase in CD154 expression in T cells from females with systemic lupus erythematosus (SLE). This present study investigates if the estrogen-dependent increase in CD154 expression is due to stabilization of the messenger RNA. T cells from female SLE patients and controls were cultured for 18 h in serum-free medium without and with estradiol 17-beta (10(-7) M). T cells were either unstimulated (resting) or were activated by further culture on anti-CD3 coated plates. Actinomycin D (25 microg/mL) was added to parallel cultures to inhibit new messenger RNA synthesis. CD154 messenger RNA stability was assessed by reverse-transcription polymerase chain amplification. Resting SLE (n = 10, P = 0.88) and normal (n = 7, P = 0.65) T cells showed no significant differences in message stability in response to estradiol. CD154 messenger RNA was also not significantly stabilized in activated SLE (n = 10, P = 0.15) or activated normal (n = 6, P = 0.077) T cells in response to estradiol. These findings indicate that the estrogen-dependent increase in CD154 in SLE T cells is not due to stability of the mRNA. These data are consistent with the postulate that estradiol stimulates CD154 transcription in SLE T cells.

Atorvastatin restores Lck expression and lipid raft-associated signaling in T cells from patients with systemic lupus erythematosus

Loss of tolerance to self-Ags in patients with systemic lupus erythematosus (SLE), a prototypic autoimmune disease, is associated with dysregulation of T cell signaling, including the depletion of total levels of lymphocyte-specific protein kinase (Lck) from sphingolipid-cholesterol-enriched membrane microdomains (lipid rafts). Inhibitors of 3-hyroxy-3-methylgluteryl CoA reductase (statins) can modify the composition of lipid rafts, resulting in alteration of T cell signaling. In this study, we show that atorvastatin targets the distribution of signaling molecules in T cells from SLE patients, by disrupting the colocalization of total Lck and CD45 within lipid rafts, leading to a reduction in the active form of Lck. Upon T cell activation using anti-CD3/anti-CD28 in vitro, the rapid recruitment of total Lck to the immunological synapse was inhibited by atorvastatin, whereas ERK phosphorylation, which is decreased in SLE T cells, was reconstituted. Furthermore, atorvastatin reduced the production of IL-10 and IL-6 by T cells, implicated in the pathogenesis of SLE. Thus, atorvastatin reversed many of the signaling defects characteristic of SLE T cells. These findings demonstrate the potential for atorvastatin to target lipid raft-associated signaling abnormalities in autoreactive T cells and provide a rationale for its use in therapy of autoimmune disease.

FR180204, a novel and selective inhibitor of extracellular signal-regulated kinase, ameliorates collagen-induced arthritis in mice

Extracellular signal-regulated kinase (ERK), a serine/threonine protein kinase of the mitogen-activated protein kinase superfamily, is activated by various stimuli in inflammatory cells. We recently described FR180204 (5-(2-phenylpyrazolo[1,5-a]pyridin-3-yl)-1H-pyrazolo[3,4-c]pyridazin-3-amine), a novel selective ERK inhibitor. In this paper, we investigated the effect of FR180204 on collagen-induced arthritis (CIA) in DBA/1 mice, an animal model of rheumatoid arthritis (RA) mediated by type II collagen (CII)-reactive T cells and anti-CII antibodies. Preventive administration of FR180204 (100 mg/kg, i.p., b.i.d.) significantly ameliorated the clinical arthritis and body weight loss occurring in the CIA mice. Further, FR180204-treated mice showed a significant decrease in plasma anti-CII antibody levels (62%). FR180204 also attenuated delayed-type hypersensitivity in CII-immunized DBA/1 mice, an inflammatory response elicited by CII-reactive T cells, in a dose-dependent manner (52 and 62% inhibition at 32 and 100 mg/kg, respectively). Moreover, FR180204 inhibited in vitro CII-induced proliferation of lymph node cells prepared from CII-immunized mice, in which CII-specific T cells are known to undergo specific proliferation. In conclusion, our results suggest that ERK regulates both the cell-mediated and humoral immune responses in the development of CIA. ERK inhibitors may be useful as therapeutic reagents for the treatment of RA.

Intracellular protein modification associated with altered T cell functions in autoimmunity

Posttranslational protein modifications influence a number of immunologic responses ranging from intracellular signaling to protein processing and presentation. One such modification, termed isoaspartyl (isoAsp), is the spontaneous nonenzymatic modification of aspartic acid residues occurring at physiologic pH and temperature. In this study, we have examined the intracellular levels of isoAsp residues in self-proteins from MRL(+/+), MRL/lpr, and NZB/W F(1) mouse strains compared with nonautoimmune B10.BR mice. In contrast to control B10.BR or NZB/W mice, the isoAsp content in MRL autoimmune mice increased and accumulated with age in erythrocytes, brain, kidney, and T lymphocytes. Moreover, T cells that hyperproliferate to antigenic stimulation in MRL mice also have elevated intracellular isoAsp protein content. Protein l-isoaspartate O-methyltransferase activity, a repair enzyme for isoAsp residues in vivo, remains stable with age in all strains of mice. These studies demonstrate a role for the accumulation of intracellular isoAsp proteins associated with T cell proliferative defects of MRL autoimmune mice.

Transcription factors TFE3 and TFEB are critical for CD40 ligand expression and thymus-dependent humoral immunity

TFE3 and TFEB are broadly expressed transcription factors related to the transcription factor Mitf. Although they have been linked to cytokine signaling pathways in nonlymphoid cells, their function in T cells is unknown. TFE3-deficient mice are phenotypically normal, whereas TFEB deficiency causes early embryonic death. We now show that combined inactivation of TFE3 and TFEB in T cells resulted in a hyper-immunoglobulin M syndrome due to impaired expression of CD40 ligand by CD4(+) T cells. Native TFE3 and TFEB bound to multiple cognate sites in the promoter of the gene encoding CD40 ligand (Cd40lg), and maximum Cd40lg promoter activity and gene expression required TFE3 or TFEB. Thus, TFE3 and TFEB are direct, physiological and mutually redundant activators of Cd40lg expression in activated CD4(+) T cells critical for T cell-dependent antibody responses.

Regulatory T cells in lupus

Naturally occurring, CD4+ CD25+ regulatory T cells that are exported from the thymus early in life play an important role in controlling organ-specific autoimmune diseases, but they may not be critical for suppressing systemic autoimmunity in lupus. On the other hand, lupus-prone subjects appear to be deficient in generation of adaptive T-regulatory cells that can be induced by various means. We review autoantigen-specific therapeutic approaches that induce such regulatory T cells. Of particular interest are TGF-ss producing CD4+ CD25+ and CD8+ regulatory T cells that are induced by low dose tolerance therapy of lupus-prone mice with nucleosomal histone peptide epitopes, administered subcutaneously in subnanomolar doses. These regulatory T cells are not only efficient in suppressing autoantigen recognition and autoantibody production, but they also inhibit migration/accumulation of pathogenic autoimmune cells in the target organ, such as the kidneys of mice prone to develop lupus nephritis. We discuss why and under what conditions such therapeutic approaches would be beneficial in lupus patients and lupus-prone subjects.

Regulating the regulator: negative regulation of Cbl ubiquitin ligases

Cbl proteins are regulators of signal transduction through many pathways and, consequently, regulate cell function and development. They are ubiquitin ligases that ubiquitinate and target many signaling molecules for degradation. The Cbl proteins themselves are regulated by an increasingly complex network of interactions that fine-tune the effects that Cbl proteins have on signaling. The negative regulation of Cbl protein function can occur via cis-acting structural elements that prevent inappropriate ubiquitin ligase activity, degradation of the Cbl proteins, inhibition without degradation owing to interaction with other signaling proteins, deubiquitination of Cbl substrates, and regulation of assembly of the endosomal ESCRT-I complex. Defects in the regulatory mechanisms that control Cbl function are implicated in the development of immunological and malignant diseases.

Altered regulation of IL-2 production in systemic lupus erythematosus: an evolving paradigm

In systemic lupus erythematosus (SLE), IL-2 production by T lymphocytes in vitro is impaired. Deficient IL-2 production may be an outcome of a primary SLE T cell disorder that is due to impaired signal transduction. In this issue of the JCI, evidence is presented that an anti-TCR/CD3 complex autoantibody present in SLE sera can bind to T cells and activate the Ca(2+)-calmodulin kinase IV (CaMKIV) signaling cascade, resulting in downregulation of IL-2 transcription and IL-2 production. Because IL-2 may contribute to the maintenance of T cell tolerance, deficient IL-2 production could promote a breach of T cell tolerance that results in autoantibody production in SLE.

MRL/Mp CD4+,CD25- T cells show reduced sensitivity to suppression by CD4+,CD25+ regulatory T cells in vitro: a novel defect of T cell regulation in systemic lupus erythematosus

OBJECTIVE

To investigate the hypothesis that loss of suppression mediated by peripheral CD4+,CD25+ regulatory T cells is a hallmark of systemic lupus erythematosus (SLE).

METHODS

Mice of the MRL/Mp strain were studied as a polygenic model of SLE. Following immunomagnetic selection, peripheral lymphoid CD25+ and CD25- CD4+ T cells were cultured independently or together in the presence of anti-CD3/CD28 monoclonal antibody-coated beads. Proliferation was assessed by measuring the incorporation of tritiated thymidine.

RESULTS

While MRL/Mp CD4+,CD25+ regulatory T cells showed only subtle abnormalities of regulatory function in vitro, syngeneic CD4+,CD25- T cells showed significantly reduced sensitivity to suppression, as determined by crossover experiments in which MRL/Mp CD4+,CD25- T cells were cultured with H-2-matched CBA/Ca CD4+,CD25+ regulatory T cells in the presence of a polyclonal stimulus.

CONCLUSION

Our findings highlight a novel defect of peripheral tolerance in SLE. Identification of this defect could open new opportunities for therapeutic intervention.

Very low-dose tolerance with nucleosomal peptides controls lupus and induces potent regulatory T cell subsets

We induced very low-dose tolerance by injecting lupus prone (SWR x NZB)F1 (SNF1) mice with 1 mug nucleosomal histone peptide autoepitopes s.c. every 2 wk. The subnanomolar peptide therapy diminished autoantibody levels and prolonged life span by delaying nephritis, especially by reducing inflammatory cell reaction and infiltration in kidneys. H4(71-94) was the most effective autoepitope. Low-dose tolerance therapy induced CD8+, as well as CD4+ CD25+ regulatory T (Treg) cell subsets containing autoantigen-specific cells. These adaptive Treg cells suppressed IFN-gamma responses of pathogenic lupus T cells to nucleosomal epitopes at up to a 1:100 ratio and reduced autoantibody production up to 90-100% by inhibiting nucleosome-stimulated T cell help to nuclear autoantigen-specific B cells. Both CD4+ CD25+ and CD8+ Treg cells produced and required TGF-beta1 for immunosuppression, and were effective in suppressing lupus autoimmunity upon adoptive transfer in vivo. The CD4+ CD25+ T cells were partially cell contact dependent, but CD8+ T cells were contact independent. Thus, low-dose tolerance with highly conserved histone autoepitopes repairs a regulatory defect in systemic lupus erythematosus by generating long-lasting, TGF-beta-producing Treg cells, without causing allergic/anaphylactic reactions or generalized immunosuppression.

Naive CD4+ T Cells from Lupus-Prone Fas-Intact MRL Mice Display TCR-Mediated Hyperproliferation Due to Intrinsic Threshold Defects in Activation

Autoreactive T cell activation is a consistent feature of murine lupus; however, the mechanism of such activation remains unclear. We hypothesized that naive CD4+ T cells in lupus have a lower threshold of activation through their TCR-CD3 complex that renders them more susceptible to stimulation with self-Ags. To test this hypothesis, we compared proliferation, IL-2 production, and single cell calcium signaling of naive CD4+ T cells isolated from Fas-intact MRL/+(Fas-lpr) mice with H-2k-matched B10.BR and CBA/CaJ controls, following anti-CD3 stimulation in the presence or absence of anti-CD28. We also assessed the responsiveness of naive CD4+ T cells isolated from Fas-intact MRL and control mice bearing a rearranged TCR specific for amino acids 88-104 of pigeon cytochrome c to cognate and low affinity peptide Ags presented by bone marrow-matured dendritic cells. TCR transgenic and wild-type CD4+ T cells from MRL mice displayed a lower threshold of activation than control cells, a response that was class II MHC dependent. The rise in intracellular calcium in MRL vs controls was enhanced and prolonged following anti-CD3 triggering, suggestive of proximal defects in TCR-engendered signaling as the mechanism for the observed hyperactivity. These findings were observed as early as 1-2 mo postweaning and, based on analysis of F1 T cells, appeared to be dominantly expressed. This genetically altered threshold for activation of MRL T cells, a consequence of a proximal defect in CD3-mediated signal transduction, may contribute to the abrogation of T cell tolerance to self-Ags in lupus.

T-helper cell intrinsic defects in lupus that break peripheral tolerance to nuclear autoantigens

Special populations of T helper cells drive B cells to produce IgG class switched, pathogenic autoantibodies in lupus. The major source of antigenic determinants (epitopes) that trigger interactions between lupus T and B cells is nucleosomes of apoptotic cells. These epitopes can be used for antigen-specific therapy of lupus. Secondly, the autoimmune T cells of lupus are sustained because they resist anergy and activation-induced programmed cell death by markedly upregulating cyclooxygenase (COX) 2 along with the antiapoptotic molecule c-FLIP. Only certain COX-2 inhibitors block pathogenic anti-DNA autoantibody production in lupus by causing death of autoimmune T helper cells. Hence COX-2 inhibitors may work independently of their ability to block the enzymatic function of COX-2, and structural peculiarities of these select inhibitors may lead to better drug discovery and design.