Increased caspase-3 expression and activity contribute to reduced CD3zeta expression in systemic lupus erythematosus T cells

Distinct gene dysregulation patterns herald precision medicine potentiality in systemic lupus erythematosus

OBJECTIVES

We aimed at investigating the whole-blood transcriptome, expression quantitative trait loci (eQTLs), and levels of selected serological markers in patients with SLE versus healthy controls (HC) to gain insight into pathogenesis and identify drug targets.

METHODS

We analyzed differentially expressed genes (DEGs) and dysregulated gene modules in a cohort of 350 SLE patients and 497 HC from the European PRECISESADS project (NTC02890121), split into a discovery (60%) and a replication (40%) set. Replicated DEGs qualified for eQTL, pathway enrichment, regulatory network, and druggability analysis. For validation purposes, a separate gene module analysis was performed in an independent cohort (GSE88887).

RESULTS

Analysis of 521 replicated DEGs identified multiple enriched interferon signaling pathways through Reactome. Gene module analysis yielded 18 replicated gene modules in SLE patients, including 11 gene modules that were validated in GSE88887. Three distinct gene module clusters were defined i.e., "interferon/plasma cells", "inflammation", and "lymphocyte signaling". Predominant downregulation of the lymphocyte signaling cluster denoted renal activity. By contrast, upregulation of interferon-related genes indicated hematological activity and vasculitis. Druggability analysis revealed several potential drugs interfering with dysregulated genes within the "interferon" and "PLK1 signaling events" modules. STAT1 was identified as the chief regulator in the most enriched signaling molecule network. Drugs annotated to 15 DEGs associated with cis-eQTLs included bortezomib for its ability to modulate CTSL activity. Belimumab was annotated to TNFSF13B (BAFF) and daratumumab was annotated to CD38 among the remaining replicated DEGs.

CONCLUSIONS

Modulation of interferon, STAT1, PLK1, B and plasma cell signatures showed promise as viable approaches to treat SLE, pointing to their importance in SLE pathogenesis.

Investigating the molecular mechanism of iguratimod act on SLE using network pharmacology and molecular docking analysis

Objective: Iguratimod (IGU) is a novel small disease-modifying compound widely used in Asia for the treatment of rheumatic diseases. IGU is a methane sulfonanilide. We applied network pharmacology to investigate the pharmacological mechanisms of IGU act on SLE.

Methods: We used PharmMapper, UniProt, and OMIM databases to screen the potential targets of IGU, and the SLE-related disease targets were predicted. Hub target genes among the intersections of the potential targets (IGU) and related genes (SLE) were validated using the PPI network generated by the String database. GO and KEGG enrichment analyses were carried out using the David online platform. Finally, the molecular docking of hub targets and their corresponding compounds were completed through AutoDock Vina and PyMOL software for visualization.

Result: A total of 292 potential targets of IGU, 6501 related disease targets of SLE, and 114 cross targets were screened from the aforementioned database. Network topology analysis identified 10 hub targets, such as CASP3, AKT1, EGFR, MMP9, and IGF1. GO enrichment analysis mainly focuses on the negative regulation of the apoptotic process and signal transduction. KEGG enrichment analysis illustrated that the PI3K-AKT signaling pathway, MAPK signaling pathway, and FoxO signaling pathway might play a significant role in the pharmacological mechanisms of IGU act on SLE. Molecular docking confirmed that the IGU ligand had strong binding activity to the hub targets.

Conclusion: This study based on network pharmacology and molecular docking validation preliminarily revealed the protein targets affected by IGU acting on SLE through, and explored potential therapeutic mechanism role of IGU in SLE treatment by multi pathways.

Targets of Tripterygium glycosides in systemic lupus erythematosus treatment: A network-pharmacology study

OBJECTIVE

We aimed to explore the underlying mechanism of Tripterygium glycosides (TGs) in treating systemic lupus erythematosus (SLE) through network-pharmacology approach.

METHODS

The protein targets of TGs' three active ingredients (triptolide, tripterine, and wilforlide) and SLE were identified by database search. Then, the intersection of the two groups was studied. The drug-target network between the active ingredients of TGs and the overlapping genes was constructed, visualized, and analyzed with Cytoscape software. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment were performed to analyze these genes. Finally, we validated our predictions of the potential targets through docking study.

RESULTS

A total of 55 overlapping genes were discovered. Results suggested that the TGs' mechanism in SLE treatment was associated with heat shock protein family A member 5, heat shock protein family A member 8, eukaryotic translation elongation factor 1 alpha 1, and so forth with their related 4042 gene network, which regulated ribosome, spliceosome, viral carcinogenesis, Epstein-Barr virus infection signaling, and so forth. Molecular-docking analysis proved that hydrogen bonding was the main form of interaction.

CONCLUSIONS

Our research provided the protein targets affected by TGs in SLE treatment. The key targets (CASP3, MAPK1, HIF1A, and so forth) involving 4042 proteins became the multitarget mechanism of TGs in SLE treatment.

Signaling by the inhibitory receptor CD200R is rewired by type I interferon

CD200 receptor 1 (CD200R) is an inhibitory immunoreceptor that suppresses Toll-like receptor (TLR)–induced cytokine production through the adaptor protein Dok2 and the GTPase activating protein (GAP) p120-RasGAP, which can be cleaved during mild cellular stress. We found that in the presence of cleaved p120-RasGAP, CD200R lost its capacity to inhibit phosphorylation of ribosomal S6 protein (rpS6), suggesting the reduced activity of mammalian target of rapamycin complex 1 (mTORC1). Furthermore, treatment of human peripheral blood mononuclear cells (PBMC) with interferon-α (IFN-α) resulted in increased amounts of cleaved p120-RasGAP. Upon pretreatment of cells with increasing concentrations of IFN-α, CD200R switched from inhibiting to potentiating the TLR7- and TLR8-induced expression of the gene encoding IFN-γ, a cytokine that is important for innate and adaptive immunity and is implicated in systemic lupus erythematosus (SLE) pathogenesis. PBMC from patients with SLE, a prototypic type I IFN disease, had an increased abundance of cleaved p120-RasGAP compared to that in cells from healthy controls. In a subset of SLE patients, CD200R stopped functioning as an inhibitory receptor or potentiated TLR-induced IFNG mRNA expression. Thus, our data suggest that type I IFN rewires CD200R signaling to be proinflammatory, which could contribute to the perpetuation of inflammation in patients with SLE.

Cellular Fragments in the Perivitelline Space Are Not a Predictor of Expanded Blastocyst Quality

The presence of cellular fragments in the perivitelline space is a commonly used parameter to determine quality before transfer of in vitro produced (IVP) embryos. However, this parameter is difficult to assess after blastocyst expansion. In this study, we used mechanical hatching to confirm the presence of cellular fragments in the perivitelline space of bovine IVP blastocysts. We further looked for associations between possible apoptosis within extruded cells/ cellular fragments and the quality of bovine blastocysts using quantitative RT-PCR and immunofluorescence. Surprisingly, more than 42% of expanded blastocysts had cellular fragments in the perivitelline space; however, more than 37% of extruded cells were TUNEL negative. We observed no significant difference in embryo quality between expanded blastocysts with and without cellular fragments in the perivitelline space. Overall, our data suggest that embryos extrude abnormal cells to maintain their developmental potential. The presence of fragmented cells is not an indicator of embryo quality.

Defects at the Posttranscriptional Level Account for the Low TCRζ Chain Expression Detected in Gastric Cancer Independently of Caspase-3 Activity

Background

Reduced TCRζ chain surface has been reported in T cells from patients with different inflammatory conditions and cancer. However, the causes of this diminished expression in cancer remain elusive.

Methods

T cell-enriched populations of blood or tissue (tumoral and nontumoral) origin from 44 patients with gastric adenocarcinoma and 33 healthy subjects were obtained. Samples were subjected to cytofluorimetry, Western blot analysis, TCRζ cDNA sequencing experiments, measurement of TCRζ mRNA levels, and caspase-3 activity assays.

Results

Cytofluorimetry revealed a decreased TCRζ expression in T cells of patients, assessed either as percentage of cells expressing this chain (blood: control subjects 99.8 ± 0.1%, patients 98.8 ± 1.1%P < 0.001; tissue: control subjects 96.7 ± 0.9%, patients tumoral tissue 67.9 ± 27.0%, patients nontumoral tissue 82.8 ± 12.6%, P = 0.019) or mean fluorescence intensity (MFI) value (blood: control subjects 102.2 ± 26.0; patients 58.0 ± 12.3, P = 0.001; tissue: control subjects 99.4 ± 21.4; patients tumoral tissue 41.6 ± 21.4; patients nontumoral tissue 62.3 ± 16.6, P = 0.001). Other chains pertaining to the TCR-CD3 complex (CD3ε) showed no significant differences (MFI values). Subsequent TCRζ cDNA sequencing experiments or measurements of TCRζ mRNA levels disclosed no differences between patients and control subjects. Evaluation of caspase-3 activity showed higher levels in T cell extracts of patients, and this activity could be decreased by 70% with the use of the inhibitor Ac-DEVD-FMK, although CD3ζ expression levels did not recover.

Conclusions

These results further place the defect responsible for the low TCRζ expression in cancer at the posttranscriptional level and suggests contrary to what has been proposed in other pathologies that elevated caspase-3 activity is not the causative agent.

Genetics of systemic sclerosis

Systemic sclerosis is an autoimmune disease characterized by generalized fibrosis in connective tissues and internal organs as consequences of microvascular dysfunction and immune dysfunctions, which leads to premature death in affected individuals. The etiology of systemic sclerosis is complex and poorly understood, but as with most autoimmune diseases, it is widely accepted that both environmental and genetic factors contribute to disease risk. During the last decade, the number of genetic markers convincingly associated with systemic sclerosis has exponentially increased. In this article, we briefly mention the genetic components of systemic sclerosis. Then, we review the classical and novel genetic associations with systemic sclerosis, analyzing the firmest and replicated signals within non-human leukocyte antigen genes, identified by both candidate gene approach and genome-wide association studies. We also provide an insight into the future perspectives that will shed more light into the complex genetic background of the disease. Despite the remarkable advance of systemic sclerosis genetics during the last decade, the use of the new genetic technologies such as next-generation sequencing, as well as the deep phenotyping of the study cohorts, to fully characterize the genetic component of this disease is imperative to identify causal variants, which leads to more targeted and effective treatment of systemic sclerosis.

Association of autoimmunity and cancer: An emphasis on proteolytic enzymes

Cancer and autoimmune diseases are the two devastating conditions that together constitute a leading health problem worldwide. The rising burden of these disorders in the developing world demands a multifaceted approach to address the challenges it poses. Understanding the root causes and specific molecular mechanisms by which the progression of the diseases takes place is need of the hour. A strong inflammatory background and common developmental pathways, such as activation of immune cells, proliferation, increased cell survival and migration which are controlled by growth factors and inflammatory cytokines have been considered as the critical culprits in the progression and complications of these disorders. Enzymes are the potential immune modulators which regulate various inflammatory events and can break the circulating immune complexes via macrophages production. In the current manuscript, we have uncovered the possible role of proteolytic enzymes in the pathogenesis and progression of cancer and autoimmune diseases. In the light of the available scientific literature, we advocate in-depth comprehensive studies which will shed light towards the role of proteolytic enzymes in the modulation of inflammatory responses in cancer and autoimmune diseases together.

SLE-Associated Defects Promote Altered T Cell Function

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease linked to profound defects in the function and phenotype of T lymphocytes. Here, we describe abnormal signaling pathways that have been documented in T cells from patients with SLE and discuss how they impact gene expression and immune function, in order to understand how they contribute to disease development and progression.

Downregulation of CD3ζ in NK Cells from Systemic Lupus Erythematosus Patients Confers a Proinflammatory Phenotype

Cytotoxic function and cytokine profile of NK cells are compromised in patients with systemic lupus erythematosus (SLE). CD3ζ, an important molecule for NK cell activation, is downregulated in SLE T cells and contributes to their altered function. However, little is known about the role of CD3ζ in SLE NK cells. We studied CD3ζ levels and its contribution to cytotoxic, degranulation, and cytokine production capacity of NK cells from patients with SLE. Furthermore, we studied the human NK cell line, NKL, in which manipulation of CD3ζ levels was achieved using small interfering RNA and NK cells from Rag2 mice deficient in CD3ζ. We found reduced CD3ζ expression in NK cells from SLE patients independent of disease activity. Downregulation of CD3ζ expression in NK cells is mediated, at least in part, by Caspase 3, the activity of which is higher in NK cells from patients with SLE compared with NK cells from healthy donors. CD3ζ levels correlated inversely with natural cytotoxicity and the percentage of cells capable of producing the proinflammatory cytokines IFN-γ and TNF. In contrast, CD3ζ levels showed a direct correlation with levels of Ab-dependent cellular cytotoxicity. Experiments performed in CD3ζ-silenced NKL and CD3ζ-deficient NK cells from Rag2 mice confirmed the dependence of NK cell function on CD3ζ levels. Our results demonstrate a differential role for CD3ζ in natural cytotoxicity and Ab-dependent cellular cytotoxicity. We conclude that downregulated CD3ζ confers a proinflammatory phenotype to SLE NK cells and contributes to their altered function in patients with SLE.

Systemic lupus erythematosus in the light of the regulatory effects of galectin-1 on T-cell function

Galectin-1 is an endogenous immunoregulatory lectin-type protein. Its most important effects are the inhibition of the differentiation and cytokine production of Th1 and Th17 cells, and the induction of apoptosis of activated T-cells. Galectin-1 has been identified as a key molecule in antitumor immune surveillance, and data are accumulating about the pathogenic role of its deficiency, and the beneficial effects of its administration in various autoimmune disease models. Initial animal and human studies strongly suggest deficiencies in both galectin-1 production and responsiveness in systemic lupus erythematosus (SLE) T-cells. Since lupus features widespread abnormalities in T-cell activation, differentiation and viability, in this review the authors wished to highlight potential points in T-cell signalling processes that may be influenced by galectin-1. These points include GM-1 ganglioside-mediated lipid raft aggregation, early activation signalling steps involving p56Lck, the exchange of the CD3 ζ-ZAP-70 to the FcRγ-Syk pathway, defective mitogen-activated protein kinase pathway activation, impaired regulatory T-cell function, the failure to suppress the activity of interleukin 17 (IL-17) producing T-cells, and decreased suppression of the PI3K-mTOR pathway by phosphatase and tensin homolog (PTEN). These findings place galectin-1 into the group of potential pathogenic molecules in SLE.

Genetic risk factors for sclerotic graft-versus-host disease

Sclerotic graft-versus-host disease (GVHD) is a distinctive phenotype of chronic GVHD after allogeneic hematopoietic cell transplantation, characterized by fibrosis of skin or fascia. Sclerotic GVHD has clinical and histopathological similarities with systemic sclerosis, an autoimmune disease whose risk is influenced by genetic polymorphisms. We examined 13 candidate single-nucleotide polymorphisms (SNPs) that have a well-documented association with systemic sclerosis to determine whether these SNPs are also associated with the risk of sclerotic GVHD. The study cohort included 847 consecutive patients who were diagnosed with chronic GVHD. Genotyping was performed using microarrays, followed by imputation of unobserved SNPs. The donor rs10516487 (BANK1: B-cell scaffold protein with ankyrin repeats 1) TT genotype was associated with lower risk of sclerotic GVHD (hazard ratio [HR], 0.43; 95% confidence interval [CI], 0.21-0.87; P = .02). Donor and recipient rs2056626 (CD247: T-cell receptor ζ subunit) GG or GT genotypes were associated with higher risk of sclerotic GVHD (HR, 1.57; 95% CI, 1.13-2.18; P = .007 and HR, 1.66; 95% CI, 1.19-2.32; P = .003, respectively). Donor and recipient rs987870 (5'-flanking region of HLA-DPA1) CC genotypes were associated with higher risk of sclerotic GVHD (HR, 2.50; 95% CI, 1.22-5.11; P = .01 and HR, 2.13; 95% CI, 1.00-4.54; P = .05, respectively). In further analyses, the recipient DPA1*01:03∼DPB1*04:01 haplotype and certain amino acid substitutions in the recipient P1 peptide-binding pocket of the HLA-DP heterodimer were associated with risk of sclerotic GVHD. Genetic components associated with systemic sclerosis are also associated with sclerotic GVHD. HLA-DP-mediated antigen presentation, T-cell response, and B-cell activation have important roles in the pathogenic mechanisms of both diseases.

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.

Treatment of low doses curcumin could modulate Th17/Treg balance specifically on CD4+ T cell cultures of systemic lupus erythematosus patients

Introduction

The balance between T helper 17 (Th17) and regulatory T cells (Treg) is a new paradigm in the pathogenesis of systemic lupus erythematosus (SLE). Currently, there are no drugs that able to modulate Th17/Treg balance specifically in SLE. Curcumin is a bioactive agent that has a specific action against hyperproliferative cells. However, its role in modulating Th17/Treg balance in SLE is still unknown. This research aimed to investigate the role of curcumin in modulating Th17/Treg balance on CD4+ T cell cultures of SLE patients.

Material and methods

CD4+ T cells from SLE 6 untreated patients and 6 healthy subjects were collected, stimulated with Th17 differentiating factors, and curcumin 0.1 and 1 µg/ml was added on cultures. After 72 hours incubation, cells were harvested and measured for Th17 and Treg percentages using flow cytometry and interleukin-17A (IL-17A) and transforming growth factor-β1 (TGF-β1) levels using ELISA.

Results

Administration of low doses of curcumin (0.1 and 1 µg/ml) could decrease Th17 percentages (p = 0.000 and p = 0.000 compared to control), reduce IL-17A productions (p = 0.000 and p = 0.000 compared to control), increase Treg percentages (p = 0.001 and p = 0.000 compared to control), and increase TGF-β1 productions (p = 0.001 and p = 0.000 compared to control) on CD4+ T cells of SLE patients. Interestingly, these effects were not reproduced on CD4+ T cells cultures of healthy subjects.

Conclusions

These data suggest that curcumin can modulate Th17/Treg balance specifically on CD4+ T cells of SLE patients without affecting healthy subjects.

Extracellular 2'5'-oligoadenylate synthetase 2 mediates T-cell receptor CD3-ζ chain down-regulation via caspase-3 activation in oral cancer

Decreased expression of CD3-ζ chain, an adaptor protein associated with T-cell signalling, is well documented in patients with oral cancer, but the mechanistic justifications are fragmentary. Previous studies in patients with oral cancer have shown that decreased expression of CD3-ζ chain was associated with decreased responsiveness of T cells. Tumours are known to induce localized as well as systemic immune suppression. This study provides evidence that oral tumour-derived factors promote immune suppression by down-regulating CD3-ζ chain expression. 2'5'-Oligoadenylate synthetase 2 (OAS2) was identified by the proteomic approach and our results established a causative link between CD3-ζ chain down-regulation and OAS2 stimulation. The surrogate situation was established by over-expressing OAS2 in a HEK293 cell line and cell-free supernatant was collected. These supernatants when incubated with T cells resulted in down-regulation of CD3-ζ chain, which shows that the secreted OAS2 is capable of regulating CD3-ζ chain expression. Incubation of T cells with cell-free supernatants of oral tumours or recombinant human OAS2 (rh-OAS2) induced caspase-3 activation, which resulted in CD3-ζ chain down-regulation. Caspase-3 inhibition/down-regulation using pharmacological inhibitor or small interfering RNA restored down-regulated CD3-ζ chain expression in T cells induced by cell-free tumour supernatant or rh-OAS2. Collectively these results show that OAS2 leads to impairment in CD3-ζ chain expression, so offering an explanation that might be applicable to the CD3-ζ chain deficiency observed in cancer and diverse disease conditions.

In HIV-positive patients, myeloid-derived suppressor cells induce T-cell anergy by suppressing CD3ζ expression through ELF-1 inhibition

OBJECTIVE

During HIV infection, a down-modulation of CD3ζ was found on T cells, contributing to T-cell anergy. In this work, we studied the correlation between myeloid-derived suppressor cells (MDSC) frequency and T-cell CD3ζ expression. Moreover, we investigated the mechanisms of CD3ζ decrease exploited by MDSC.

DESIGN AND METHOD

CD3ζ expression and MDSC frequency were evaluated by flow cytometry on peripheral blood mononuclear cells from 105 HIV-positive (HIV+) patients. The role of MDSC in the modulation of the HIV-specific T-cell response was evaluated. The level of CD3ζ mRNA and ELF-1 protein were analysed by real-time-PCR and western blot, respectively.

RESULTS

We found that granulocytic-MDSC (Gr-MDSC) were expanded in HIV+ patients compared with healthy donors; in particular, in cART-treated individuals a higher Gr-MDSC frequency was observed in patients with a CD4 T-cell count below 400 cells/μl. We found an inverse correlation between the percentage of Gr-MDSC and CD3ζ level. Moreover, in-vitro MDSC depletion induced the up-regulation of CD3ζ in T cells, restoring the functionality of αβ, but not γδ T cells. The in-vitro effect of isolated MDSC on CD3ζ expression was found cell contact-dependent, and was not mediated by previously described molecules. CD3ζ down-modulation corresponds to the decrease of its mRNA induced by silencing the transcription factor ELF-1.

CONCLUSION

Our data provide new knowledge on mechanisms used by Gr-MDSC in immune-modulation and on their role in the immune reconstitution during antiviral treatments.

Serine Arginine-Rich Splicing Factor 1 (SRSF1) Contributes to the Transcriptional Activation of CD3ζ in Human T Cells

T lymphocytes from many patients with systemic lupus erythematosus (SLE) express decreased levels of the T cell receptor (TCR)-associated CD3 zeta (ζ) signaling chain, a feature directly linked to their abnormal phenotype and function. Reduced mRNA expression partly due to defective alternative splicing, contributes to the reduced expression of CD3ζ chain. We previously identified by oligonucleotide pulldown and mass spectrometry approaches, the serine arginine-rich splicing factor 1 (SRSF1) binding to the 3’ untranslated region (UTR) of CD3ζ mRNA. We showed that SRSF1 regulates alternative splicing of the 3’UTR of CD3ζ to promote expression of the normal full length 3`UTR over an unstable splice variant in human T cells. In this study we show that SRSF1 regulates transcriptional activation of CD3ζ. Specifically, overexpression and silencing of SRSF1 respectively increases and decreases CD3ζ total mRNA and protein expression in Jurkat and primary T cells. Using promoter-luciferase assays, we show that SRSF1 enhances transcriptional activity of the CD3ζ promoter in a dose dependent manner. Chromatin immunoprecipitation assays show that SRSF1 is recruited to the CD3ζ promoter. These results indicate that SRSF1 contributes to transcriptional activation of CD3ζ. Thus our study identifies a novel mechanism whereby SRSF1 regulates CD3ζ expression in human T cells and may contribute to the T cell defect in SLE.

T cell signaling abnormalities contribute to aberrant immune cell function and autoimmunity

Systemic lupus erythematosus (SLE) is a prototype systemic autoimmune disease that results from a break in immune tolerance to self-antigens, leading to multi-organ destruction. Autoantibody deposition and inflammatory cell infiltration in target organs such as kidneys and brain lead to complications of this disease. Dysregulation of cellular and humoral immune response elements, along with organ-defined molecular aberrations, form the basis of SLE pathogenesis. Aberrant T lymphocyte activation due to signaling abnormalities, linked to defective gene transcription and altered cytokine production, are important contributors to SLE pathophysiology. A better understanding of signaling and gene regulation defects in SLE T cells will lead to the identification of specific novel molecular targets and predictive biomarkers for therapy.

T cell receptor-associated protein tyrosine kinases: the dynamics of tolerance regulation by phosphorylation and its role in systemic lupus erythematosus

There are different abnormalities that lead to the autoreactive phenotype in T cells from systemic lupus erythematosus (SLE) patients. Proximal signaling, involving the T-cell receptor (TCR) and its associated protein tyrosine kinases (PTKs), is significantly affected in SLE. This ultimately leads to aberrant responses, which include enhanced tyrosine phosphorylation and calcium release, as well as decreased IL-2 secretion. Lck, ZAP70 and Syk, which are PTKs with a major role in proximal signaling, all present abnormal functioning that contributes to an altered T cell response in these patients. A number of other molecules, especially regulatory proteins, are also involved. This review will focus on the PTKs that participate in proximal signaling, with specific emphasis on their relevance in maintaining peripheral tolerance, their abnormalities in SLE and how these contribute to an altered T cell response.

The pathology of T cells in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterized by the production of a wide array of autoantibodies. Thus, the condition was traditionally classified as a "B-cell disease". Compelling evidence has however shown that without the assistance of the helper T lymphocytes, it is indeed difficult for the "helpless" B cells to become functional enough to trigger SLE-related inflammation. T cells have been recognized to be crucial in the pathogenicity of SLE through their capabilities to communicate with and offer enormous help to B cells for driving autoantibody production. Recently, a number of phenotypic and functional alterations which increase the propensity to trigger lupus-related inflammation have been identified in lupus T cells. Here, potential mechanisms involving alterations in T-cell receptor expressions, postreceptor downstream signalling, epigenetics, and oxidative stress which favour activation of lupus T cells will be discussed. Additionally, how regulatory CD4+, CD8+, and γδ T cells tune down lupus-related inflammation will be highlighted. Lastly, while currently available outcomes of clinical trials evaluating therapeutic agents which manipulate the T cells such as calcineurin inhibitors indicate that they are at least as efficacious and safe as conventional immunosuppressants in treating lupus glomerulonephritis, larger clinical trials are undoubtedly required to validate these as-yet favourable findings.

Ubiquitination regulates expression of the serine/arginine-rich splicing factor 1 (SRSF1) in normal and systemic lupus erythematosus (SLE) T cells

T cells from patients with systemic lupus erythematosus (SLE) exhibit reduced expression of the critical T cell receptor (TCR)-associated CD3ζ signaling chain and are poor producers of the vital cytokine IL-2. By oligonucleotide pulldown and mass spectrometry discovery approaches, we identified the splicing regulator serine/arginine-rich splicing factor (SRSF) 1 or splicing factor 2/alternative splicing factor (SF2/ASF) to be important in the expression of CD3ζ chain. Importantly, increases in the expression of SRSF1 rescued IL-2 production in T cells from patients with SLE. In this study, we investigated the regulation of SRSF1 expression in resting and activated human T cells. We found that T cell stimulation induced a rapid and significant increase in mRNA expression of SRSF1; however, protein expression levels did not correlate with this increase. Co-engagement of CD28 induced a similar mRNA induction and reduction in protein levels. Proteasomal but not lysosomal degradation was involved in this down-regulation as evidenced by blocking with specific inhibitors MG132 and bafilomycin, respectively. Immunoprecipitation studies showed increased ubiquitination of SRSF1 in activated T cells. Interestingly, T cells from patients with SLE showed increased ubiquitination of SRSF1 when compared with those from healthy individuals. Our results demonstrate a novel mechanism of regulation of the splicing factor SRSF1 in human T cells and a potential molecular mechanism that controls its expression in SLE.

CREMα suppresses spleen tyrosine kinase expression in normal but not systemic lupus erythematosus T cells

OBJECTIVE

T cells from patients with systemic lupus erythematosus (SLE) display increased amounts of spleen tyrosine kinase (Syk), which is involved in the aberrant CD3/T cell receptor-mediated signaling process, and increased amounts of CREMα, which suppresses the production of interleukin-2. Syk expression can be suppressed by CREMα. This study was undertaken to investigate why CREMα fails to suppress Syk expression in SLE T cells.

METHODS

CREMα was overexpressed in healthy T cells by transfection with CREMα expression vector, and Syk expression and phosphorylation were measured. A newly identified cAMP response element (CRE) site on the SYK promoter was characterized by chromatin immunoprecipitation (ChIP) and electrophoretic mobility shift assay. The CREMα-mediated repression of Syk expression was further evaluated by analyzing SYK promoter activity. T cells from SLE patients and healthy individuals were subjected to ChIP to evaluate CREMα binding and histone H3 acetylation.

RESULTS

Increased CREMα levels suppressed Syk expression by direct binding to a CRE site of the SYK promoter in T cells from healthy individuals but failed to do so in T cells from SLE patients. The failure of CREMα to suppress Syk expression in SLE T cells was due to weaker binding to the CRE site of the SYK promoter compared to healthy T cells because the promoter site is hypoacetylated in SLE T cells and therefore of limited access to transcription factors.

CONCLUSION

Our findings indicate that epigenetic alteration of the SYK promoter in SLE T cells results in the inability of the transcriptional repressor CREMα to bind and suppress the expression of Syk, resulting in aberrant T cell signaling.

The role of endocytic recycling in autoimmunity

Abnormalities in T cell signal transduction underlie pathology in systemic lupus erythematosus. Lupus T cells are more sensitive to stimulation, yet have reduced expression of T cell antigen receptor (TCR) at the surface. The amount of TCR expressed at the surface of a T cell directly determines the ability of a T cell to become activated. The endocytic recycling machinery regulates transport of T cell receptors to the plasma membrane, internalization of surface receptors, and recycling to the cell surface, which determines the ability of a T cell to become activated. Increased recycling of CD3 and CD4 receptors occurs in lupus T cells, and could represent a mechanism by which T cells are sensitized to stimulation. This chapter explains methods used to investigate endocytic recycling of the TCR, CD4, and CD8 co-receptors in peripheral blood lymphocytes, T cells, and in splenocytes from lupus-prone murine models. The assays described will allow the study of surface receptor turnover in live untouched lymphocytes by flow cytometry.

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.

Abnormalities of T cell signaling in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease resulting from a loss of tolerance to multiple self antigens, and characterized by autoantibody production and inflammatory cell infiltration in target organs, such as the kidneys and brain. T cells are critical players in SLE pathophysiology as they regulate B cell responses and also infiltrate target tissues, leading to tissue damage. Abnormal signaling events link to defective gene transcription and altered cytokine production, contributing to the aberrant phenotype of T cells in SLE. Study of signaling and gene transcription abnormalities in SLE T cells has led to the identification of novel targets for therapy.

Differential expression of factors involved in the intrinsic and extrinsic apoptotic pathways in juvenile systemic lupus erythematosus

Dysregulated neutrophil apoptosis may result in the development of autoimmune disease by contributing to nuclear autoantigen exposure, leading to autoantibody generation and a breakdown in immune tolerance. It has previously been shown that neutrophil apoptosis is increased in juvenile-onset systemic lupus erythematosus (JSLE). This study aims to investigate the pathways involved in JSLE serum-induced apoptosis. Caspases 3, 7–9, IAP1/2, XIAP and FADD mRNA levels and TRAIL R2, BID/tBID, caspase 8 and 9 protein expression were measured in neutrophils from JSLE patients ( n = 14) and controls ( n = 10). The mRNA levels of caspases 7–9 were significantly higher in JSLE neutrophils than in controls, whereas the mRNA levels of IAP1, IAP2 and XIAP were decreased ( p < 0.05). A decrease in neutrophil apoptosis induced by JSLE serum was observed in the presence of caspase 8 and 9 inhibitors ( p < 0.05), and the activity of caspases 8 and 9 increased over time. tBID protein expression increased following incubation with JSLE serum. These data focus specifically on the expression and activity of the main caspases in the intrinsic and extrinsic apoptotic pathways. Increased expression of factors involved in the downstream signalling of the extrinsic apoptotic pathway indicates a prominent involvement of this pathway in JSLE serum-induced apoptosis.

NKG2D initiates caspase-mediated CD3zeta degradation and lymphocyte receptor impairments associated with human cancer and autoimmune disease

Deficiencies of the T cell and NK cell CD3ζ signaling adapter protein in patients with cancer and autoimmune diseases are well documented, but mechanistic explanations are fragmentary. The stimulatory NKG2D receptor on T and NK cells mediates tumor immunity but can also promote local and systemic immune suppression in conditions of persistent NKG2D ligand induction that include cancer and certain autoimmune diseases. In this paper, we provide evidence that establishes a causative link between CD3ζ impairment and chronic NKG2D stimulation due to pathological ligand expression. We describe a mechanism whereby NKG2D signaling in human T and NK cells initiates Fas ligand/Fas-mediated caspase-3/-7 activation and resultant CD3ζ degradation. As a consequence, the functional capacities of the TCR, the low-affinity Fc receptor for IgG, and the NKp30 and NKp46 natural cytotoxicity receptors, which all signal through CD3ζ, are impaired. These findings are extended to ex vivo phenotypes of T and NK cells among tumor-infiltrating lymphocytes and in peripheral blood from patients with juvenile-onset lupus. Collectively, these results indicate that pathological NKG2D ligand expression leads to simultaneous impairment of multiple CD3ζ-dependent receptor functions, thus offering an explanation that may be applicable to CD3ζ deficiencies associated with diverse disease conditions.

Genome-wide association study of systemic sclerosis identifies CD247 as a new susceptibility locus

Systemic sclerosis (SSc) is an autoimmune disease characterized by fibrosis of the skin and internal organs that leads to profound disability and premature death. To identify new SSc susceptibility loci, we conducted the first genome-wide association study in a population of European ancestry including a total of 2,296 individuals with SSc and 5,171 controls. Analysis of 279,621 autosomal SNPs followed by replication testing in an independent case-control set of European ancestry (2,753 individuals with SSc (cases) and 4,569 controls) identified a new susceptibility locus for systemic sclerosis at CD247 (1q22-23, rs2056626, P = 2.09 x 10(-7) in the discovery samples, P = 3.39 x 10(-9) in the combined analysis). Additionally, we confirm and firmly establish the role of the MHC (P = 2.31 x 10(-18)), IRF5 (P = 1.86 x 10(-13)) and STAT4 (P = 3.37 x 10(-9)) gene regions as SSc genetic risk factors.

Zeta chain expression in T and NK cells in peripheral blood of children with nephrotic syndrome

The idiopathic nephrotic syndrome (INS) has been related to cellular immune disturbances. The zeta (zeta) chain, a component of the T-cell receptor/CD3 (TCR) complex and CD16 heterodimer in NK cells, plays a crucial role in T and NK cell activation and proliferation. The aim of our study was to examine zeta chain expression in CD4+, CD8+ T lymphocytes and NK cells in the peripheral blood of children with INS and to evaluate the effect of anti-CD3+rIL-2 stimulation on the level of zeta chain expression in the INS pediatric population. The study group consisted of 15 children with INS in relapse, 16 patients with INS in clinical remission, and 17 controls. The percentage of zeta-positive cells and the values of mean fluorescence intensity (MFI) were determined by flow cytometry. Compared with that in the controls, the percentage of zeta+ freshly isolated NK cells in children with INS in relapse was significantly lower, whereas, in CD3+/CD4+ and CD3+/CD8+ populations, no alteration was observed. There were no differences in the MFI values between the populations of freshly isolated cells either. Stimulation with anti-CD3+rIL-2 decreased the percentage of zeta+/CD4+ T cells and NKzeta+ cells in a significant way in all the groups analysed, whereas the percentage of zeta+/CD8+ T cells decreased significantly only in patients with INS in relapse. The altered pattern of zeta expression in fresh NK cells from children with INS in relapse, and the disturbed response of zeta+/CD8+ T cells to anti-CD3+rIL-2 stimulation in relapse, suggests the possible role of this chain in immune dysregulation in INS, particularly with regard to cytotoxic cells.

New CD3zeta allele showing a 9-bp deletion in the 3'-UT region of the gene

We report here a non-previously described 9-bp deletion in the 3'-UT region of the CD3zeta gene, located in between two AREs.

Activation of mammalian target of rapamycin controls the loss of TCRzeta in lupus T cells through HRES-1/Rab4-regulated lysosomal degradation

Persistent mitochondrial hyperpolarization (MHP) and enhanced calcium fluxing underlie aberrant T cell activation and death pathway selection in systemic lupus erythematosus. Treatment with rapamycin, which effectively controls disease activity, normalizes CD3/CD28-induced calcium fluxing but fails to influence MHP, suggesting that altered calcium fluxing is downstream or independent of mitochondrial dysfunction. In this article, we show that activity of the mammalian target of rapamycin (mTOR), which is a sensor of the mitochondrial transmembrane potential, is increased in lupus T cells. Activation of mTOR was inducible by NO, a key trigger of MHP, which in turn enhanced the expression of HRES-1/Rab4, a small GTPase that regulates recycling of surface receptors through early endosomes. Expression of HRES-1/Rab4 was increased in CD4(+) lupus T cells, and in accordance with its dominant impact on the endocytic recycling of CD4, it was inversely correlated with diminished CD4 expression. HRES-1/Rab4 overexpression was also inversely correlated with diminished TCRzeta protein levels. Pull-down studies revealed a direct interaction of HRES-1/Rab4 with CD4 and TCRzeta. Importantly, the deficiency of the TCRzeta chain and of Lck and the compensatory up-regulation of FcepsilonRIgamma and Syk, which mediate enhanced calcium fluxing in lupus T cells, were reversed in patients treated with rapamcyin in vivo. Knockdown of HRES-1/Rab4 by small interfering RNA and inhibitors of lysosomal function augmented TCRzeta protein levels in vitro. The results suggest that activation of mTOR causes the loss of TCRzeta in lupus T cells through HRES-1/Rab4-dependent lysosomal degradation.

Growth defects in mouse telomerase RNA-deficient cells expressing a template-mutated mouse telomerase RNA

Cellular viability requires telomere maintenance, which, in mammals, is mainly mediated by the reverse transcriptase telomerase. Telomerase core components are a catalytic subunit TERT and an RNA subunit TR (hTR in humans, mTR in mouse) that carries the template to generate telomeres de novo. Telomere dysfunction can lead to senescence or apoptosis and impairs the continued growth of immortal cancerous cell lines. The introduction of a template-mutated hTR in telomerase-positive and telomerase-negative human cell lines results in dramatic growth defects. No study has addressed the consequences of expressing a template-mutated mTR in mouse immortal cell lines. Therefore, we analyzed the effects of long-term expression of a template-mutated mTR in the telomerase-positive and telomerase-negative murine cell lines CB17 and DKO301, respectively. Whereas the CB17 clones expressing the template-mutated mTR did not demonstrate any growth impairment, many of the DKO301 clones expressing the template-mutated mTR underwent growth and cell cycle defects and eventual cell death. These results suggest that in the absence of wild-type telomerase, the expression of the template-mutated mTR likely perturbs telomere function, leading to decreased cellular viability. Furthermore, whereas the expression of template-mutated hTR in telomerase-negative human cell lines leads to immediate cellular toxicity, the expression of the template-mutated mTR in the telomerase-negative mouse cell line did not.

PP2A dephosphorylates Elf-1 and determines the expression of CD3zeta and FcRgamma in human systemic lupus erythematosus T cells

T cells from patients with systemic lupus erythematosus are characterized by decreased expression of CD3zeta-chain and increased expression of FcRgamma-chain, which becomes part of the CD3 complex and contributes to aberrant signaling. Elf-1 enhances the expression of CD3zeta, whereas it suppresses the expression of FcRgamma gene and lupus T cells have decreased amounts of DNA-binding 98 kDa form of Elf-1. We show that the aberrantly increased PP2A in lupus T cells dephosphorylates Elf-1 at Thr-231. Dephosphorylation results in limited expression and binding of the 98 kDa Elf-1 form to the CD3zeta and FcRgamma promoters. Suppression of the expression of the PP2A leads to increased expression of CD3zeta and decreased expression of FcRgamma genes and correction of the early signaling response. Therefore, PP2A serves as a central determinant of abnormal T cell function in human lupus and may represent an appropriate treatment target.

Altered T and B lymphocyte signaling pathways in lupus

Systemic lupus erythematosus (SLE) has long been recognized to be characterized by dysregulated signaling pathways in T and B lymphocytes, beginning with observations of cellular hyperactivity and hyperresponsiveness, and evolving to recent studies focused upon the genetic and molecular bases of such phenomena. This review focuses on recently elucidated signaling abnormalities currently thought to be intrinsic to T and/or B cells in human SLE.

Functional skewing of the global CD8 T cell population in chronic hepatitis B virus infection

The inflamed liver in chronic hepatitis B virus (HBV) infection (CHB) is characterized by a large influx of non–virus-specific CD8 T cells. Little is known about the functional capacity of these lymphocytes, which could provide insights into mechanisms of failure of viral control and liver damage in this setting. We compared the effector function of total circulating and intrahepatic CD8 T cells in CHB patients and healthy donors. We demonstrated that CD8 T cells from CHB patients, regardless of their antigen specificity, were impaired in their ability to produce interleukin-2 and proliferate upon TCR-dependent stimulation. In contrast, these CD8 T cells had preserved production of the proinflammatory cytokines interferon-γ and tumor necrosis factor-α. This aberrant functional profile was partially attributable to down-regulation of the proximal T cell receptor signaling molecule CD3ζ, and could be corrected in vitro by transfection of CD3ζ or replenishment of the amino acid arginine required for its expression. We provide evidence for depletion of arginine in the inflamed hepatic microenvironment as a potential mechanism for these defects in global CD8 T cell signaling and function. These data imply that polarized CD8 T cells within the HBV-infected liver may impede proliferative antiviral effector function, while contributing to the proinflammatory cytokine environment.

Active systemic lupus erythematosus is associated with failure of antigen-presenting cells to express programmed death ligand-1

OBJECTIVE

Antigen-presenting cells (APC) play critical roles in establishing and maintaining peripheral tolerance. This is accomplished in part via expression of negative co-stimulatory molecules such as programmed death ligand-1 (PD-L1) on tolerogenic APC, such as immature myeloid dendritic cells (mDC). Several studies have strongly linked dysfunction of APC, including mDC, to the pathogenesis of SLE. The objective of this study was to determine whether APC expressed PD-L1 protein at normal levels during active lupus.

METHODS

Peripheral blood mononuclear cells (PBMC) were isolated from 19 paediatric patients with SLE and from 17 healthy age-matched controls. PBMC from both cohorts were cultured in the absence of exogenously added stimuli, and leucocyte PD-L1 expression was measured by flow cytometry.

RESULTS

Immature mDC and monocytes (Mo) from healthy children expressed little PD-L1 at initial isolation, but spontaneously up-regulated PD-L1 by 24 h. In contrast, both mDC and Mo from patients with active SLE failed to up-regulate PD-L1 over a 5 day time course, expressing this protein only during disease remissions.

CONCLUSIONS

These data are the first to link active lupus with reversibly decreased PD-L1 expression on professional APC, suggesting a novel mechanism for loss of peripheral tolerance in SLE.

The RNA-stabilizing protein HuR regulates the expression of zeta chain of the human T cell receptor-associated CD3 complex

T cell dysfunction is crucial to the pathogenesis of systemic lupus erythematosus (SLE); however, the molecular mechanisms involved in the deficient expression of the T cell receptor-associated CD3zeta chain in SLE are not clear. SLE T cells express abnormally increased levels of an alternatively spliced isoform of CD3zeta that lacks a 562-bp region in its 3'-untranslated region (UTR). We showed previously that two adenosine/uridine-rich elements (ARE) in this splice-deleted region of CD3zeta transcript are critical for the mRNA stability and protein expression of CD3zeta. In this study we show for the first time that the mRNA-stabilizing protein HuR binds to these two ARE bearing regions of CD3zeta 3'-UTR. Knockdown of HuR resulted in decreased expression of the CD3zeta chain, whereas overexpression led to the increase of CD3zeta chain levels. Additionally, overexpression of HuR in human T cells resulted in increased mRNA stability of CD3zeta. Our results identify the 3'-UTR of CD3zeta as a novel target for the mRNA-stabilizing protein HuR. Thus, the absence of two critical AREs in the alternatively spliced CD3zeta 3'-UTR found in SLE T cells may result in decreased HuR binding, representing a possible molecular mechanism contributing to the reduced stability and expression of CD3zeta in SLE.

Agrin signalling contributes to cell activation and is overexpressed in T lymphocytes from lupus patients

It is shown in this study that the heparan sulfate proteoglycan agrin is overexpressed in T cells isolated from patients with the autoimmune disease systemic lupus erythematosus (SLE). Freshly isolated CD4(+) and CD8(+) subpopulations both exhibited higher expression over healthy controls, which however, gradually declined when cells were cultured in vitro. Agrin expression was induced following in vitro activation of cells via their Ag receptor, or after treatment with IFN-alpha, a cytokine shown to be pathogenic in lupus. Furthermore, serum from SLE patients with active disease was able to induce agrin expression when added to T cells from healthy donors, an increase that was partially blocked by neutralizing anti-IFN-alpha Abs. Cross-linking agrin with mAbs resulted in rapid reorganization of the actin cytoskeleton, activation of the ERK MAPK cascade, and augmentation of anti-CD3-induced proliferation and IL-10 production, indicating that agrin is a functional receptor in T cells. These results demonstrate that agrin expression in human T cells is regulated by cell activation and IFN-alpha, and may have an important function during cell activation with potential implications for autoimmunity.

How signaling and gene transcription aberrations dictate the systemic lupus erythematosus T cell phenotype

T cells from patients with systemic lupus erythematosus (SLE) exhibit several discrete and specific defects that alter signaling pathways and, thus, the gene expression pattern and behavior upon stimulation. Rewiring of the CD3 complex and aggregation of surface-membrane lipid rafts grant SLE T cells a lower activation threshold and distort the ensuing signaling events. Additionally, increased expression of adhesion molecules within aggregated lipid rafts guides them to target organs. Aberrant cell signaling causes altered transcription factor expression and abnormal DNA-methylation patterns that lead to skewed gene expression. The result is an abnormally functioning T cell that exhibits several molecular alterations that can be exploited as therapeutic or diagnostic markers.

Novel molecular targets in the treatment of systemic lupus erythematosus

T cells from patients with systemic lupus erythematosus (SLE) display a number of biochemical abnormalities which include altered expression of key signaling molecules, heightened calcium responses, and skewed expression of transcription factors. These defects are involved in the altered behavior of SLE T cells and are probably central in the disease pathogenesis. The aim of this communication is to review the defects that have been consistently documented in SLE T cells, highlighting molecules and pathways that represent therapeutic targets.

Systemic lupus erythematosus: new molecular targets

T cells from patients with systemic lupus erythematosus exhibit a notable array of defects that probably contribute to the origin and development of the disease. Such abnormalities include an abnormal response to stimulation, aberrant expression of molecules that play key roles in intracellular signalling pathways, altered transcription factor activation and binding, and skewed gene expression. The combination of these alterations leads the cell to the expression of a particular phenotype that intense research has gradually uncovered over the last years. The aim of this article is to review the findings that have allowed us to better understand the behaviour of the lupus T cell and highlight the molecules that represent potential therapeutic targets.

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.

Nitric oxide, mitochondrial hyperpolarization, and T cell activation

T lymphocyte activation is associated with nitric oxide (NO) production, which plays an essential role in multiple T cell functions. NO acts as a messenger, activating soluble guanyl cyclase and participating in the transduction signaling pathways involving cyclic GMP. NO modulates mitochondrial events that are involved in apoptosis and regulates mitochondrial membrane potential and mitochondrial biogenesis in many cell types, including lymphocytes. Mitochondrial hyperpolarization (MHP), an early and reversible event during both activation and apoptosis of Tlymphocytes, is regulated by NO. Here, we discuss recent evidence that NO-induced MHP represents a molecular switch in multiple T cell signaling pathways. Overproduction of NO in systemic lupus erythematosus induces mitochondrial biogenesis and alters Ca(2+) signaling. Thus, whereas NO plays a physiological role in lymphocyte cell signaling, its overproduction may disturb normal T cell function, contributing to the pathogenesis of autoimmunity.

Lipid rafts in health and disease

Lipid rafts are sphingolipid- and cholesterol-rich domains of the plasma membrane which contain a variety of signalling and transport proteins. Different subtypes of lipid rafts can be distinguished according to their protein and lipid composition. Caveolae are types of rafts that are rich in proteins of the caveolin family (caveolin-1, -2 and -3) which present a distinct signalling platform. The importance of lipid raft signalling in the pathogenesis of a variety of conditions, such as Alzheimer's, Parkinson's, cardiovascular and prion diseases, systemic lupus erythematosus and HIV, has been elucidated over recent years and makes these specific membrane domains an interesting target for pharmacological approaches in the cure and prevention of these diseases. This Review analyses the importance of lipid raft proteins and lipids in health and disease, with a focus on the current state of knowledge.

Stability and translation of TCR zeta mRNA are regulated by the adenosine-uridine-rich elements in splice-deleted 3' untranslated region of zeta-chain

Systemic lupus erythematosus (SLE) T cells display reduced expression of TCR zeta protein. Recently, we reported that in SLE T cells, the residual TCR zeta protein is predominantly derived from an alternatively spliced form that undergoes splice deletion of 562 nt (from 672 to 1233 bases) within the 3' untranslated region (UTR) of TCR zeta mRNA. The stability and translation of the alternatively spliced form of TCR zeta mRNA are low compared with that of the wild-type TCR zeta mRNA. We report that two adenosine-uridine-rich sequence elements (AREs), defined by the splice-deleted 3' UTR region, but not an ARE located upstream are responsible for securing TCR zeta mRNA stability and translation. The stabilizing effect of the splice-deleted region-defined AREs extended to the luciferase mRNA and was not cell type-specific. The findings demonstrate distinct sequences within the splice-deleted region 672 to 1233 of the 3' UTR, which regulate the transcription, mRNA stability, and translation of TCR zeta mRNA. The absence of these sequences represents a molecular mechanism that contributes to altered TCR zeta-chain expression in lupus.

FcR gamma presence in TCR complex of double-negative T cells is critical for their regulatory function

TCRalphabeta+CD4-CD8- double-negative (DN) T regulatory (Treg) cells have recently been shown to suppress Ag-specific immune responses mediated by CD8+ and CD4+ T cells in humans and mice. Our previous study using cDNA microarray analysis of global gene expression showed that FcRgamma was the most highly overexpressed gene in functional DN Treg cell clones compared with nonfunctional mutant clones. In this study, we demonstrate that FcRgamma-deficient DN T cells display markedly reduced suppressive activity in vitro. In addition, unlike FcRgamma-sufficient DN T cells, FcRgamma-deficient DN T cells were unable to prolong donor-specific allograft survival when adoptively transferred to recipient mice. Protein analyses indicate that in addition to FcRgamma, DN Treg cell clones also express higher levels of TCRbeta, while mutant clones expressed higher levels of Zap70 and Lck. Within DN Treg cells, we found that FcRgamma associates with the TCR complex and that both FcRgamma and Syk are phosphorylated in response to TCR cross-linking. Inhibition of Syk signaling and FcRgamma expression were both found to reduce the suppressive function of DN Treg cells in vitro. These results indicate that FcRgamma deficiency significantly impairs the ability of DN Treg cells to down-regulate allogeneic immune responses both in vitro and in vivo, and that FcRgamma plays a role in mediating TCR signaling in DN Treg cells.