T cell rewiring in differentiation and disease

CBLs downregulation foretells T cell ubiquitination leading to autoimmunity

In a study published in the July issue of Immunity, Li et al.1 demonstrate that expression of the E3 ubiquitin ligases CBL and CBL-B is downregulated in Tfh cells in SLE with Tfh cell expansion and autoimmunity. This leads to reduced ubiquitination of the T cell costimulator ICOS which regulates proteostasis of the Tfh cell transcription factor BCL6 via chaperone-mediated autophagy.

T Cells, Interleukin-2 and Systemic Lupus Erythematosus—From Pathophysiology to Therapy

The phenotypic and functional complexities of T cells engender complicated and often confusing concepts as to how T cells ignite, accelerate and brake the inflammatory processes involved in systemic lupus erythematosus (SLE), let alone the plasticity of T cells that takes place under different immunological contexts. Nevertheless, being one of the prime survival factors of T cells, interleukin (IL)-2 plays a potentially critical role in many immunological scenarios during the pathophysiological process of SLE. Here, the pathophysiology of lupus T cells and current, as well as ongoing, therapeutic approaches of SLE that involve low-dose IL-2 administration will be highlighted. The mechanisms of IL-2 deficiency in SLE pathophysiology, the effects of low-dose IL-2 on T cells and restoration of lupus manifestations in murine SLE models, as well as the efficacy and safety of clinical trials that evaluated low-dose IL-2-containing regimens in patients with SLE will be discussed.

Oxidative Stress in SLE T Cells, Is NRF2 Really the Target to Treat?

Oxidative stress is a major component of cellular damage in T cells from patients with systemic lupus erythematosus (SLE) resulting amongst others in the generation of pathogenic Th17 cells. The NRF2/Keap1 pathway is the most important antioxidant system protecting cells from damage due to oxidative stress. Activation of NRF2 therefore seems to represent a putative therapeutic target in SLE, which is nevertheless challenged by several findings suggesting tissue and cell specific differences in the effect of NRF2 expression. This review focusses on the current understanding of oxidative stress in SLE T cells and its pathophysiologic and therapeutic implications.

Variant to Gene Mapping to Discover New Targets for Immune Tolerance

The breakdown of immunological tolerance leads to autoimmune disease, and the mechanisms that maintain self-tolerance, especially in humans, are not fully understood. Genome-wide association studies (GWAS) have identified hundreds of human genetic loci statistically linked to autoimmune disease risk, and epigenetic modifications of DNA and chromatin at these loci have been associated with autoimmune disease risk. Because the vast majority of these signals are located far from genes, identifying causal variants, and their functional consequences on the correct effector genes, has been challenging. These limitations have hampered the translation of GWAS findings into novel drug targets and clinical interventions, but recent advances in understanding the spatial organization of the genome in the nucleus have offered mechanistic insights into gene regulation and answers to questions left open by GWAS. Here we discuss the potential for 'variant-to-gene mapping' approaches that integrate GWAS with 3D functional genomic data to identify human genes involved in the maintenance of tolerance.

T cell Metabolism in Lupus

Abnormal T cell responses are central to the development of autoimmunity and organ damage in systemic lupus erythematosus. Following stimulation, naïve T cells undergo rapid proliferation, differentiation and cytokine production. Since the initial report, approximately two decades ago, that engagement of CD28 enhances glycolysis but PD-1 and CTLA-4 decrease it, significant information has been generated which has linked metabolic reprogramming with the fate of differentiating T cell in health and autoimmunity. Herein we summarize how defects in mitochondrial dysfunction, oxidative stress, glycolysis, glutaminolysis and lipid metabolism contribute to pro-inflammatory T cell responses in systemic lupus erythematosus and discuss how metabolic defects can be exploited therapeutically.

T cell metabolism: new insights in systemic lupus erythematosus pathogenesis and therapy

T cell subsets are critically involved in the development of systemic autoimmunity and organ inflammation in systemic lupus erythematosus (SLE). Each T cell subset function (such as effector, helper, memory or regulatory function) is dictated by distinct metabolic pathways requiring the availability of specific nutrients and intracellular enzymes. The activity of these enzymes or nutrient transporters influences the differentiation and function of T cells in autoimmune responses. Data are increasingly emerging on how metabolic processes control the function of various T cell subsets and how these metabolic processes are altered in SLE. Specifically, aberrant glycolysis, glutaminolysis, fatty acid and glycosphingolipid metabolism, mitochondrial hyperpolarization, oxidative stress and mTOR signalling underwrite the known function of T cell subsets in patients with SLE. A number of medications that are used in the care of patients with SLE affect cell metabolism, and the development of novel therapeutic approaches to control the activity of metabolic enzymes in T cell subsets represents a promising endeavour in the search for effective treatment of systemic autoimmune diseases.

Calcium/Calmodulin Kinase IV Controls the Function of Both T Cells and Kidney Resident Cells

Calcium calmodulin kinase IV (CaMK4) regulates multiple processes that significantly contribute to the lupus-related pathology by controlling the production of IL-2 and IL-17 by T cells, the proliferation of mesangial cells, and the function and structure of podocytes. CaMK4 is also upregulated in podocytes from patients with focal segmental glomerulosclerosis (FSGS). In both immune and non-immune podocytopathies, CaMK4 disrupts the structure and function of podocytes. In lupus-prone mice, targeted delivery of a CaMK4 inhibitor to CD4⁺ T cells suppresses both autoimmunity and the development of nephritis. Targeted delivery though to podocytes averts the deposition of immune complexes without affecting autoimmunity in lupus-prone mice and averts pathology induced by adriamycin in normal mice. Therefore, targeted delivery of a CaMK4 inhibitor to podocytes holds high therapeutic promise for both immune (lupus nephritis) and non-immune (FSGS) podocytopathies.

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.

TCR+CD4-CD8- T cells in antigen-specific MHC class I-restricted T-cell responses after allogeneic hematopoietic stem cell transplantation

Human TCRαβ(+) CD4(-)CD8(-) double-negative (DN) T cells represent a minor subset in peripheral blood, yet are important in infectious diseases and autoimmune responses. We examined the frequency of DN T cells in 17 patients after allogeneic hematopoietic stem cell transplantation (aHSCT) at 1, 2, 3, 6, and 12 months post-aHSCT and show that these cells increase early after aHSCT and decrease with time after aHSCT. DN T cells reside in the terminally differentiated effector (CD45RA(+)CCR7(-)) T-cell population and are polyclonal, determined by T-cell receptor Vβ CDR3 analysis. Gene expression analysis of ex vivo sorted DN T cells showed a distinct set of gene expression, including interleukin-8, as compared with CD4(+) or CD8(+) T cells. DN T cells contributed to MHC class I-restricted EBV-directed immune responses, defined by antigen-specific cytokine production and by detection of HLA-A*02:01-restricted EBV BMLF-1 (GLCTLVAML), LMP-2A (CLGGLLTMV), and HLA-A*24:02-restricted EBV BRLF-1 (DYCNVLNKEF) and EBNA3 (RYSIFFDY)-specific T cells. We created retroviral-transfected Jurkat cell lines with a Melan-A/MART-1-specific TCR(+) and the CD8α chain to study TCR(+) DN T cells in response to their nominal MHC class I/peptide ligand. We show that DN T cells exhibit increased TCRζ chain phosphorylation as compared with the TCR(+)CD8(+) transgenic T-cell line. DN T cells contribute to antigen-specific T-cell responses and represent an effector T-cell population that may be explored in immunotherapeutic approaches against viral infections or transformed cells.

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.

Critical role of histone demethylase Jmjd3 in the regulation of CD4+ T-cell differentiation

Epigenetic factors have been implicated in the regulation of CD4⁺ T cell differentiation. Jmjd3 plays a role in many biological processes, but its in vivo function in T cell differentiation remains unknown. Here, we report that Jmjd3 ablation promotes CD4⁺ T cell differentiation into Th2 and Th17 cells in the small intestine and colon, and inhibits T cell differentiation into Th1 cells under different cytokine-polarizing conditions and in a Th1-dependent colitis model. Jmjd3 deficiency also restrains the plasticity of the conversion of Th2, Th17 or Treg cells to Th1 cells. The skewing of T cell differentiation is concomitant with changes in the expression of key transcription factors and cytokines. H3K27me3 and H3K4me3 levels in Jmjd3-deficient cells are correlated with altered gene expression through interactions with specific transcription factors. Our results identify Jmjd3 as an epigenetic factor in T cell differentiation via changes in histone methylation and target gene expression.

Transcription factor Ikaros represses protein phosphatase 2A (PP2A) expression through an intronic binding site

Protein phosphatase 2A (PP2A) is a highly conserved and ubiquitous serine/threonine phosphatase. We have shown previously that PP2A expression is increased in T cells of systemic lupus erythematosus patients and that this increased expression and activity of PP2A plays a central role in the molecular pathogenesis of systemic lupus erythematosus. Although the control of PP2A expression has been the focus of many studies, many aspects of its regulation still remain poorly understood. In this study, we describe a novel mechanism of PP2A regulation. We propose that the transcription factor Ikaros binds to a variant site in the first intron of PP2A and modulates its expression. Exogenous expression of Ikaros leads to reduced levels of PP2Ac message as well as protein. Conversely, siRNA-enabled silencing of Ikaros enhances the expression of PP2A, suggesting that Ikaros acts as a suppressor of PP2A expression. A ChIP analysis further proved that Ikaros is recruited to this site in T cells. We also attempted to delineate the mechanism of Ikaros-mediated PP2Ac gene suppression. We show that Ikaros-mediated suppression of PP2A expression is at least partially dependent on the recruitment of the histone deacetylase HDAC1 to this intronic site. We conclude that the transcription factor Ikaros can regulate the expression of PP2A by binding to a site in the first intron and modulating chromatin modifications at this site via recruitment of HDAC1.

Metabolic regulation of organelle homeostasis in lupus T cells

Abnormal T-cell signaling and activation are characteristic features in systemic lupus erythematosus (SLE). Lupus T cells are shifted toward an over-activated state, important signaling pathways are rewired, and signaling molecules are replaced. Disturbances in metabolic and organelle homeostasis, importantly within the mitochondrial, endosomal, and autophagosomal compartments, underlie the changes in signal transduction. Mitochondrial hyperpolarization, enhanced endosomal recycling, and dysregulated autophagy are hallmarks of pathologic organelle homeostasis in SLE. This review is focused on the metabolic checkpoints of endosomal traffic that control immunological synapse formation and mitophagy and may thus serve as targets for treatment in SLE.

Molecular basis for T cell response induced by altered peptide ligand of type II collagen

Mounting evidence from animal models has demonstrated that alterations in peptide-MHC interactions with the T cell receptor (TCR) can lead to dramatically different T cell outcomes. We have developed an altered peptide ligand of type II collagen, referred to as A9, which differentially regulates TCR signaling in murine T cells leading to suppression of arthritis in the experimental model of collagen-induced arthritis. This study delineates the T cell signaling pathway used by T cells stimulated by the A9·I-A(q) complex. We have found that T cells activated by A9 bypass the requirement for Zap-70 and CD3-ζ and signal via FcRγ and Syk. Using collagen-specific T cell hybridomas engineered to overexpress either Syk, Zap-70, TCR-FcRγ, or CD3-ζ, we demonstrate that A9·I-A(q) preferentially activates FcRγ/Syk but not CD3-ζ/Zap-70. Moreover, a genetic absence of Syk or FcRγ significantly reduces the altered peptide ligand induction of the nuclear factor GATA3. By dissecting the molecular mechanism of A9-induced T cell signaling we have defined a new alternate pathway that is dependent upon FcRγ and Syk to secrete immunoregulatory cytokines. Given the interest in using Syk inhibitors to treat patients with rheumatoid arthritis, understanding this pathway may be critical for the proper application of this therapy.

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.

T cells stimulated with an analog peptide of type II collagen require the Fc receptor γ-chain to secrete interleukin-4 and suppress autoimmune arthritis in mice

OBJECTIVE

To explore the characteristics of the T cell population that responds to an analog peptide (A9) of type II collagen and regulates autoimmunity, using the collagen-induced arthritis (CIA) model.

METHODS

Analog peptide A9 is a 26-amino acid peptide analogous to the sequence of a segment of type II collagen (CII245-270) but with substitutions at amino acid positions 260 (alanine for isoleucine), 261 (hydroxyproline for alanine), and 263 (asparagine for phenylalanine). We previously showed that A9 profoundly suppressed CIA and immune responses to type II collagen. In order to determine the mechanism of suppression, we used transgenic mice whose T cells express a type II collagen-specific receptor (T cell receptor) and performed passive cell transfer experiments.

RESULTS

The results demonstrated that suppression of CIA by A9 is dependent on T cells. Using multiparameter flow cytometry, we determined that the cells responsible for suppression were CD4+ and expressed high levels of Fcε receptor Iγ chain (FcRγ). To establish the significance of this finding, we obtained mice genetically deficient in FcRγ in order to perform passive transfer experiments. The resulting FcRγ-/- CD4+ T cells, when primed by culture with A9, could not transfer the suppression of arthritis or secrete cytokines in response to A9.

CONCLUSION

Taken together, the results of this study suggest that the suppression of arthritis and the Th2 cytokine profile elicited by A9 is dependent on the presence of FcRγ in T cells. These findings are novel and may have therapeutic potential for patients with autoimmune arthritis.

Novel therapeutic approaches to lupus glomerulonephritis: translating animal models to clinical practice

Systemic lupus erythematosus is a chronic autoimmune disease frequently affecting the kidney. Renal involvement is characterized by glomerular immune complex deposits and proliferative glomerulonephritis progressing to glomerulosclerosis and kidney failure. The development of systemic lupus erythematosus is regulated genetically, and lupus susceptibility genes have been linked to immune hyper-responsiveness and loss of immune regulation. In addition to the systemic immune defects, recent studies in animal models show that susceptibility to lupus nephritis is influenced by intrinsic renal factors. Thus, renal cell responses to immune-mediated glomerular injury determine disease outcome. This supports the idea that future treatments for lupus nephritis need to focus on regulating end-organ responses. The feasibility of this approach has been shown in animal models of kidney disease. For more than 50 years, the emphasis in management of lupus nephritis has been suppression of autoimmune responses and systemic control of inflammation. This review describes recently developed targeted drug delivery technologies and potential targets that can regulate glomerular cell responses, offering a novel therapeutic approach for lupus nephritis.

Alternative splicing factor/splicing factor 2 regulates the expression of the zeta subunit of the human T cell receptor-associated CD3 complex

T cells from patients with systemic lupus erythematosus express decreased levels of the T cell receptor-associated CD3 zeta chain, a feature directly linked to their aberrant function. The decrease in CD3zeta protein expression is in part due to decreased levels of functional wild type isoform of the 3'-untranslated region (UTR) of CD3zeta mRNA with concomitant increased levels of an unstable alternatively spliced isoform. In order to identify factors involved in the post-transcriptional regulation of CD3zeta, we performed mass spectrometric analysis of Jurkat T cell nuclear proteins "pulled down" by a CD3zeta 3'-UTR oligonucleotide, which identified the splicing protein alternative splicing factor/splicing factor 2 (ASF/SF2). We show for the first time that ASF/SF2 binds specifically to the 3'-UTR of CD3zeta and regulates expression of CD3zeta protein by limiting the production of the alternatively spliced isoform. During activation of human T cells, an increase in the wild type CD3zeta mRNA is associated with increased expression of ASF/SF2. Finally, we show a significant correlation between ASF/SF2 and CD3zeta protein levels in T cells from systemic lupus erythematosus patients. Thus, our results identify ASF/SF2 as a novel factor in the regulation of alternative splicing of the 3'-UTR of CD3zeta and protein expression in human T cells.

Perforin level in CD4+ T cells from patients with systemic lupus erythematosus

CD4(+) T cells from patients with systemic lupus erythematosus (SLE) exhibit increased expression of various proteins contributing to defective function of CD4(+) T cells. We evaluated the transcript and protein levels of perforin (PRF1) in CD4(+) T cells from SLE patients (n = 41) and healthy individuals (n = 34). The CD4(+) T cells were obtained by a positive biomagnetic separation system. The amounts of mRNA were determined by reverse transcription and real-time quantitative PCR. The protein levels in the CD4(+) T cells were evaluated by Western blotting analysis. We observed significantly higher levels of PRF1 protein (p = 0.013) in SLE CD4(+) T cells than in controls. There was no significant increase in PRF1 transcript levels (p = 0.908) in CD4(+) T cells from SLE patients as compared to healthy individuals. Moreover, we did not observe a correlation between PRF1 transcript and protein levels in SLE CD4(+) T cells and disease activity expressed by the SLEDAI scale. We confirmed previous observations that demonstrated higher levels of PRF1 protein in CD4(+) T cells from SLE patients. However, we did not find a correlation between PRF1 transcripts and proteins in CD4(+) T cells and SLE disease activity.

Fyn and CD70 expression in CD4+ T cells from patients with systemic lupus erythematosus

OBJECTIVE

CD4+ T cells from patients with systemic lupus erythematosus (SLE) display defective function that contributes to abnormal activation of B cells and autoantibody production.

METHODS

We compared the transcript and protein levels of Fyn and CD70 in CD4+ T cells from patients with SLE (n = 41) and healthy individuals (n = 34). The CD4+ T cells were isolated by positive biomagnetic separation technique. The quantitative analysis of messenger RNA was performed by reverse transcription and real-time quantitative PCR. The protein contents in the CD4+ T cells were determined by Western blotting analysis.

RESULTS

We observed significantly higher levels of Fyn (p = 0.03) and CD70 (p = 0.029) transcripts in SLE CD4+ T cells than in controls. There was a significant increase in CD70 protein levels (p < 0.0001), but not Fyn protein levels (p = 0.081) in CD4+ T cells from patients with SLE compared to healthy individuals. In the group with high disease activity [SLE Disease Activity Index (SLEDAI) >/= 9], we observed a significantly higher Fyn protein content than in controls (p = 0.030). There was no correlation between Fyn and CD70 protein levels in SLE CD4+ T cells and disease activity as expressed in the SLEDAI scale.

CONCLUSION

We confirmed previous observations of higher expression of CD70 in CD4+ T cells from patients with SLE. Our findings suggest that increased Fyn protein content in CD4+ T cells can be associated with high SLE disease activity.

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.

Localization of Kv1.3 channels in the immunological synapse modulates the calcium response to antigen stimulation in T lymphocytes

The immunological synapse (IS), a highly organized structure that forms at the point of contact between a T cell and an APC, is essential for the proper development of signaling events, including the Ca(2+) response. Kv1.3 channels control Ca(2+) homeostasis in human T cells and move into the IS upon Ag presentation. However, the process involved in channel accumulation in the IS and the functional implications of this localization are not yet known. Here we define the movement of Kv1.3 into the IS and study whether Kv1.3 localization into the IS influences Ca(2+) signaling in Jurkat T cells. Crosslinking of the channel protein with an extracellular Ab limits Kv1.3 mobility and accumulation at the IS. Moreover, Kv1.3 recruitment to the IS does not involve the transport of newly synthesized channels and it does not occur through recycling of membrane channels. Kv1.3 localization in the IS modulates the Ca(2+) response. Blockade of Kv1.3 movement into the IS by crosslinking significantly increases the amplitude of the Ca(2+) response triggered by anti-CD3/anti-CD28-coated beads, which induce the formation of the IS. On the contrary, the Ca(2+) response induced by TCR stimulation without the formation of the IS with soluble anti-CD3/anti-CD28 Abs is unaltered. The results presented herein indicate that, upon Ag presentation, membrane-incorporated Kv1.3 channels move along the plasma membrane to localize in the IS. This localization is important to control the amplitude of the Ca(2+) response, and disruption of this process can account for alterations of downstream Ca(2+)-dependent signaling events.

T cell receptor signaling induced by an analog peptide of type II collagen requires activation of Syk

We have previously described an analog peptide of type II collagen (CII) that can suppress collagen-induced arthritis (CIA). This analog peptide represents CII(245-270), the immunodominant epitope of CII, but with substitutions at 260, 261, and 263 - CII(245-270) (A(260), B(261), and N(263)) (A9). To elucidate the mechanisms responsible for suppression, we used mice transgenic for a collagen-specific T cell receptor (TCR). When we found that APCs pulsed with A9 failed to induce T cell phosphorylation of TCR-zeta and ZAP-70, we explored alternative signaling pathways. We determined that A9 instead induced phosphorylation of spleen tyrosine kinase (Syk). The importance of Syk was confirmed by the use of chemical Syk inhibitors, which blocked both cytokine secretion and activation of GATA-3 mediated by peptide A9. In summary, T cells use an alternative pathway in response to A9 that involves Syk. This novel T cell pathway may represent an important means for altering T cell phenotypes.

The Sts proteins target tyrosine phosphorylated, ubiquitinated proteins within TCR signaling pathways

The T cell receptor (TCR) detects the presence of infectious pathogens and activates numerous intracellular signaling pathways. Protein tyrosine phosphorylation and ubiquitination serve as key regulatory mechanisms downstream of the TCR. Negative regulation of TCR signaling pathways is important in controlling the immune response, and the Suppressor of TCR Signaling proteins (Sts-1 and Sts-2) have been shown to function as critical negative regulators of TCR signaling. Although their mechanism of action has yet to be fully uncovered, it is known that the Sts proteins possess intrinsic phosphatase activity. Here, we demonstrate that Sts-1 and Sts-2 are instrumental in down-modulating proteins that are dually modified by both protein tyrosine phosphorylation and ubiquitination. Specifically, both naïve and activated T cells derived from genetically engineered mice that lack the Sts proteins display strikingly elevated levels of tyrosine phosphorylated, ubiquitinated proteins following TCR stimulation. The accumulation of the dually modified proteins is transient, and in activated T cells but not naïve T cells is significantly enhanced by co-receptor engagement. Our observations hint at a novel regulatory mechanism downstream of the T cell receptor.

Differential expression and molecular associations of Syk in systemic lupus erythematosus T cells

Diminished expression of TCR zeta and reciprocal up-regulation and association of FcRgamma with the TCR/CD3 complex is a hallmark of systemic lupus erythematosus (SLE) T cells. In this study we explored whether differential molecular associations of the spleen tyrosine kinase Syk that preferentially binds to FcRgamma contribute to pathological amplification of signals downstream of this "rewired TCR" in SLE. We detected higher amounts of Syk expression and activity in SLE compared with normal T cells. Selective inhibition of the activity of Syk reduced the strength of TCR-induced calcium responses and slowed the rapid kinetics of actin polymerization exclusively in SLE T cells. Syk and ZAP-70 also associated differently with key molecules involved in cytoskeletal and calcium signaling in SLE T cells. Thus, while Vav-1 and LAT preferentially bound to Syk, phospholipase C-gamma1 bound to both Syk and ZAP-70. Our results show that differential associations of Syk family kinases contribute to the enhanced TCR-induced signaling responses in SLE T cells. Thus, we propose molecular targeting of Syk as a measure to control abnormal T cell responses in SLE.

Genetic variation in the interleukin-10 gene promoter in Polish patients with systemic lupus erythematosus

Identification of susceptibility genes in systemic lupus erythematosus (SLE) has recently become a topic of interest. The IL-10 promoter contains three single base-pair substitutions at -627C > A, -854C > T and -1117G > A. These single base-pair substitutions produce three different haplotypes, GCC, ACC and ATA, which affect IL-10 expression. We examined the distribution of -627C > A, -854C > T and -1117G > A IL-10 promoter polymorphisms in patients with SLE (n = 103, women only) and matched controls (n = 300). Despite the higher prevalence of the GCC/GCC, GCC/ATA and ATA/ATA genotypes in SLE patients than in controls, we observed that only GCC/GCC genotype frequency distribution was significant between these groups. We observed that women with the GCC/GCC genotype displayed an approximately twofold increased risk of SLE OR = 2.245 (95% CI = 1.354-3.721, P = 0.0022). We did not find any associations between various genotypes of IL-10 promoter haplotypes and clinical manifestations or autoantibody production in patients with SLE. Our observations indicate that the GCC/GCC promoter genotype may contribute to SLE incidence in Polish patients.

Spleen tyrosine kinase: a novel target for therapeutic intervention of rheumatoid arthritis

BACKGROUND

In the last few years, significant progress has been made in understanding the pathogenic mechanisms and in defining the role of relevant cells and molecules in the pathophysiology of rheumatoid arthritis (RA). Various therapies, both biological (anti-TNF, anti-interleukins [e.g., IL-1]) and small molecule inhibitors have been explored for the treatment of RA.

OBJECTIVE

To date, no single signaling pathway inhibitor as wide acting as the corticosteroids, is known. However, treatment with corticosteroids is also associated with allied side effects. Despite a lot of efforts in the category of small molecule inhibitors, no inhibitor is available to deal with RA at both fronts (inflammation and tissue damage), without causing immense side effects.

METHOD

This present review explores the role of spleen tyrosine kinase (Syk) in the pathogenesis of RA and also discusses how it may meet the present day therapeutic requirements for the treatment of RA. This review gives an in-depth discussion on the role of Syk signaling in RA, the possibilities of using Syk as a target and also discusses the possible side effects that could be associated with its inhibition.

CONCLUSION

We propose Syk inhibition as a potential therapeutic approach for the treatment of RA.

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.

Proximal signaling control of human effector CD4 T cell function

The functional coupling of T cell receptor (TCR)-mediated signaling events in primary human T cells remains undefined. We demonstrate here that alterations in the expression of proximal TCR-coupled signaling subunits are associated with distinct effector capacities in differentiated human CD4 T cells. Analysis of proximal signaling profiles using biochemical and single cell approaches reveals decreased CD3zeta and ZAP-70 expression correlating with functional anergy, with increased CD3zeta/ ZAP-70 expression and phosphorylation connoting acquisition of effector capacity. By contrast, the FcRgamma signaling subunit known to be expressed in human effector cells and in T cells from the autoimmune disease SLE is up-regulated upon activation, yet does not correlate with functional capacity in effector cells, and does not alter signaling or function in primary FcRgamma transfectants. Our results have implications for targeting signaling molecules in immunotherapy and evaluating the functional consequence of signaling alterations associated with autoimmunity and chronic diseases.

Altered dynamics of Kv1.3 channel compartmentalization in the immunological synapse in systemic lupus erythematosus

Aberrant T cell responses during T cell activation and immunological synapse (IS) formation have been described in systemic lupus erythematosus (SLE). Kv1.3 potassium channels are expressed in T cells where they compartmentalize at the IS and play a key role in T cell activation by modulating Ca(2+) influx. Although Kv1.3 channels have such an important role in T cell function, their potential involvement in the etiology and progression of SLE remains unknown. This study compares the K channel phenotype and the dynamics of Kv1.3 compartmentalization in the IS of normal and SLE human T cells. IS formation was induced by 1-30 min exposure to either anti-CD3/CD28 Ab-coated beads or EBV-infected B cells. We found that although the level of Kv1.3 channel expression and their activity in SLE T cells is similar to normal resting T cells, the kinetics of Kv1.3 compartmentalization in the IS are markedly different. In healthy resting T cells, Kv1.3 channels are progressively recruited and maintained in the IS for at least 30 min from synapse formation. In contrast, SLE, but not rheumatoid arthritis, T cells show faster kinetics with maximum Kv1.3 recruitment at 1 min and movement out of the IS by 15 min after activation. These kinetics resemble preactivated healthy T cells, but the K channel phenotype of SLE T cells is identical to resting T cells, where Kv1.3 constitutes the dominant K conductance. The defective temporal and spatial Kv1.3 distribution that we observed may contribute to the abnormal functions of SLE T cells.

Prevalence of ZAP-70, LAT, SLP-76, and DNA methyltransferase 1 expression in CD4+ T cells of patients with systemic lupus erythematosus

T cells from systemic lupus erythematosus (SLE) patients exhibit defective function of CD4(+) T cells that can be responsible for improper activation of B cells and antibody biosynthesis against host antigens. We compared the level of ZAP-70, LAT, and SLP-76, transcripts and proteins in CD4(+) T cells from SLE patients (n = 22) and healthy individuals (n = 15). We also determined DNA methyltransferase 1 (DNMT1) protein content in CD4(+) T cells of SLE patients. The CD4(+) T cells were isolated by positive biomagnetic separation technique. The quantitative analysis of messenger RNA (mRNA) was performed by reverse transcription and real-time quantitative polymerase chain reaction (RQ-PCR) SYBR Green I system. The protein level in the CD4(+) T cells was determined by Western blotting analysis. We found that the LAT protein level was significantly higher in SLE CD4(+) T cells than in controls (P = 0.006). Western blot analysis revealed that ZAP-70 protein content in SLE CD4(+) T cells may be reciprocally correlated with disease activity expressed in SLEDAI scale (R = -0.623, P = 0.002) or number of affected organ systems (R = -0.549, P = 0.008). We also observed reciprocal correlation between DNMT1 protein content in CD4(+) T cells and disease activity scored with SLEDAI scale (R = -0.779, P = 0.001) or number of affected organ systems (R = -0.617, P = 0.019), respectively. Our findings might indicate that LAT, ZAP-70, and DNMT1 protein levels in CD4(+) T cells can be associated with SLE disease.

The cytotoxic T cell response to peptide analogs of the HLA-A*0201-restricted MUC1 signal sequence epitope, M1.2

The mucin MUC1 molecule is overexpressed on a variety of adenocarcinomas and is thus, a potential target for immunotherapy. Of the MUC1 peptides that bind to HLA-A*0201(A2), M1.2 (LLLLTVLTV) from the signal sequence appears to be the most immunogenic in humans. Here we have shown that large numbers (10(9)) of tetramer-binding M1.2-specific cytotoxic T lymphocytes (CTL) can be generated ex vivo from circulating precursors, derived from healthy adults. However, there was significant interpersonal variation in the level of co-stimulatory signal required. Tetramer-binding cells also required maturation in culture to become proficient killers of the HLA-A2(+) MUC1(+) MCF7 cell line, known to express a low number of endogenously processed M1.2. The functional avidity of M1.2-specific CTL, however, was low as compared to CTL specific for an HIV-1 epitope. Despite the low avidity, M1.2-specific CTL were polyfunctional, secreting multiple cytokines upon degranulation with antigen recognition. To identify potential agonist peptides that may be superior immunogens, an M1.2-specific CTL culture was used to scan a large nonameric combinatorial peptide library. Of 54 predicted peptides, 4 were "consensus" agonists because they were recognized by CTL from two other donors. Two agonists, p29 (LLPWTVLTV) and p15 (VLLWTVLTV), were equally stimulatory when loaded onto C1R target cells transfected with wild-type HLA-A2. Both agonists induced IL-2, TNF-alpha, IFN-gamma, and degranulation with M1.2-specific CTL. In contrast, production of these cytokines, which are tightly regulated by specific activation through the T cell receptor, was restricted when the CTL were stimulated with peptides loaded onto C1R cells that were transfected with an HLA-A2 molecule bearing a mutation that abrogates binding to the CD8 co-receptor. Thus, activation by both M1.2 and its agonists was dependent upon CD8, showing that compensation by the co-receptor was necessary for the human T cell response to M1.2.

Cell-specific expression and pathway analyses reveal alterations in trauma-related human T cell and monocyte pathways

Monitoring genome-wide, cell-specific responses to human disease, although challenging, holds great promise for the future of medicine. Patients with injuries severe enough to develop multiple organ dysfunction syndrome have multiple immune derangements, including T cell apoptosis and anergy combined with depressed monocyte antigen presentation. Genome-wide expression analysis of highly enriched circulating leukocyte subpopulations, combined with cell-specific pathway analyses, offers an opportunity to discover leukocyte regulatory networks in critically injured patients. Severe injury induced significant changes in T cell (5,693 genes), monocyte (2,801 genes), and total leukocyte (3,437 genes) transcriptomes, with only 911 of these genes common to all three cell populations (12%). T cell-specific pathway analyses identified increased gene expression of several inhibitory receptors (PD-1, CD152, NRP-1, and Lag3) and concomitant decreases in stimulatory receptors (CD28, CD4, and IL-2Ralpha). Functional analysis of T cells and monocytes confirmed reduced T cell proliferation and increased cell surface expression of negative signaling receptors paired with decreased monocyte costimulation ligands. Thus, genome-wide expression from highly enriched cell populations combined with knowledge-based pathway analyses leads to the identification of regulatory networks differentially expressed in injured patients. Importantly, application of cell separation, genome-wide expression, and cell-specific pathway analyses can be used to discover pathway alterations in human disease.

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.

A Common Site of the Fc Receptor γ Subunit Interacts with the Unrelated Immunoreceptors FcαRI and FcϵRI

The transmembrane (TM) region of the Fc receptor-gamma (FcRgamma) chain is responsible for the association of this ubiquitous signal transduction subunit with many immunoreceptor ligand binding chains, making FcRgamma key to a number of leukocyte activities in immunity and disease. Some receptors contain a TM arginine residue that interacts with Asp-11 of the FcRgamma subunit, but otherwise the molecular basis for the FcRgamma subunit interactions is largely unknown. This study reports residues in the TM region of the FcRgamma subunit are important for association with the high affinity IgE receptor FcepsilonRI and a leukocyte receptor cluster member, the IgA receptor FcalphaRI. FcRgamma residue Leu-21 was essential for surface expression of FcepsilonRIalpha/gamma2 and Tyr-8, Leu-14, and Phe-15 contributed to expression. Likewise, detergent-stable FcRgamma association with FcalphaRI was also dependent on Leu-14 and Leu-21 and in addition required residues Tyr-17, Tyr-25, and Cys-26. Modeling the TM regions of the FcRgamma dimer indicated these residues interacting with both FcalphaRI and FcepsilonRI are near the interface between the two FcRgamma TM helices. Furthermore, the FcRgamma residues interacting with FcalphaRI form a leucine zipper-like interface with mutagenesis confirming a complementary interface comprising FcalphaRI residues Leu-217, Leu-220, and Leu-224. The dependence of these two nonhomologous receptor interactions on FcRgamma Leu-14 and Leu-21 suggests that all the associated Fc receptors and the activating leukocyte receptor cluster members interact with this one site. Taken together these data provide a molecular basis for understanding how disparate receptor families assemble with the FcRgamma subunit.

Autoimmunity in systemic lupus erythematosus: integrating genes and biology

Susceptibility to the autoimmune phenotype of systemic lupus erythematosus (SLE) is heritable. Linkage analysis and recent advances in the field of single nucleotide polymorphisms (SNPs) have resulted in the identification of several genetic loci and functional allelic variants of signaling proteins which have become the mainstay of understanding disease susceptibility and exploring the basis of autoimmunity in SLE. However, genetic heterogeneity and possible epistatic interactions among genetic elements have precluded replication of these findings in multiple population groups and thus complicated their interpretation. In this regard, the discovery that a plethora of normal signaling proteins are expressed in abnormal amounts in immune cells from patients with SLE has gained significance. Thus, the key to precise elucidation of the pathologic basis of autoimmunity in SLE lies in tying genetics and disease biology. This review highlights recent discoveries of important functional genetic variants and altered expression of normal signaling proteins that network together to disrupt peripheral tolerance and initiate the autoimmune process in SLE.

Abnormal differentiation of memory T cells in systemic lupus erythematosus

OBJECTIVE

The chemokine receptor CCR7 and the tumor necrosis factor receptor family member CD27 define 3 distinct, progressively more differentiated maturational stages of CD4 memory subpopulations in healthy individuals: the CCR7+, CD27+, the CCR7-, CD27+, and the CCR7-, CD27- populations. The goal of this study was to examine maturational disturbances in CD4 T cell differentiation in systemic lupus erythematosus (SLE), using these phenotypic markers.

METHODS

Phenotypic analysis by flow cytometry, in vitro stimulation experiments, telomere length measurement, and determination of inducible telomerase were carried out. RESULTS. In SLE patients, significant increases of CCR7-, CD27- and CCR7-, CD27+ and a reduction of CCR7+, CD27+ CD4 memory T cells were found. In vitro stimulation of SLE T cells showed a stepwise differentiation from naive to CCR7+, CD27+ to CCR7-, CD27+ to CCR7-, CD27-; telomere length and inducible telomerase decreased in these subsets in the same progressive sequence. The in vitro proliferative response of these populations progressively declined as their susceptibility to apoptosis increased. Interestingly, a significant reduction in inducible telomerase was noted in SLE naive and CCR7+, CD27+ CD4+ memory T cells. Additionally, SLE CCR7-, CD27+ and CCR7-, CD27- CD4 memory T cells proliferated poorly in response to in vitro stimulation and underwent significantly more apoptosis than their normal counterparts. Finally, expression of CXCR4 was significantly reduced in all SLE subsets compared with normal.

CONCLUSION

Together these data indicate an increased degree of in vivo T cell stimulation in SLE, resulting in the accumulation of terminally differentiated memory T cells with a decreased proliferative capacity and an increased tendency to undergo apoptosis upon stimulation.

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

T cells isolated from patients with systemic lupus erythematosus (SLE) express low levels of CD3zeta-chain, a critical molecule involved in TCR-mediated signaling, but the involved mechanisms are not fully understood. In this study we examined caspase-3 as a candidate for cleaving CD3zeta in SLE T cells. We demonstrate that SLE T cells display increased expression and activity of caspase-3. Treatment of SLE T cells with the caspase-3 inhibitor Z-Asp-Glu-Val-Asp-FMK reduced proteolysis of CD3zeta and enhanced its expression. In addition, Z-Asp-Glu-Val-Asp-FMK treatment increased the association of CD3zeta with lipid rafts and simultaneously reversed the abnormal lipid raft preclustering, heightened TCR-induced calcium responses, and reduced the expression of FcRgamma-chain exclusively in SLE T cells. We conclude that caspase-3 inhibitors can normalize SLE T cell function by limiting the excessive digestion of CD3zeta-chain and suggest that such molecules can be considered in the treatment of this disease.

T cell hyperactivity in lupus as a consequence of hyperstimulatory antigen-presenting cells

Sle3 is an NZM2410-derived lupus susceptibility locus on murine chromosome 7. Congenic recombination has resulted in a novel mouse strain, B6.Sle3, associated with serum antinuclear autoantibodies (ANAs), T cell hyperactivity, and elevated CD4/CD8 ratios. An OVA-specific TCR transgene was used as a tool to demonstrate that Sle3 facilitated heightened T cell expansion in vitro, and in vivo, following antigen challenge. Indeed, continued T cell expansion was noted even in response to a tolerogenic signal. However, these phenotypes did not appear to be T cell intrinsic but were dictated by hyperstimulatory B6.Sle3 APCs. Importantly, B6.Sle3-derived DCs and macrophages appeared to be significantly more mature/activated, less apoptotic, and more proinflammatory and were better at costimulating T cells in vitro, compared with the B6 counterparts. Finally, the adoptive transfer of B6.Sle3-derived DCs into healthy B6 recipients elicited increased CD4/CD8 ratios and serum ANAs, 2 cardinal Sle3-associated phenotypes. We posit that their heightened expression of various costimulatory molecules, including CD80, CD106, I-A, and CD40, and their elevated production of various cytokines, including IL-12 and IL-1beta, may explain why Sle3-bearing DCs may be superior at breaching self tolerance. These studies provide mechanistic evidence indicating that intrinsic abnormalities in DCs and possibly other myeloid cells may dictate several of the phenotypes associated with systemic lupus, including ANA formation and T cell hyperactivity.

Signaling control of memory T cell generation and function

Memory T cells exhibit low activation thresholds and mediate rapid effector responses when recalled by antigen; contrasting the higher activation threshold, slower responses and predominant IL-2 production by naive T cells. While the sequence of intracellular events coupling the T cell-receptor (TCR) to naive T cell activation is well characterized, biochemical control of memory T cell differentiation and function remains undefined. In this review, we will discuss recent developments in T cell-receptor signal transduction as they pertain to memory T cells, and will discuss how signal dampening may drive memory generation, and more efficient spatial organization of signaling molecules may promote rapid recall responses.

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.

Alterations in lipid raft composition and dynamics contribute to abnormal T cell responses in systemic lupus erythematosus

In response to appropriate stimulation, T lymphocytes from systemic lupus erythematosus (SLE) patients exhibit increased and faster intracellular tyrosine phosphorylation and free calcium responses. We have explored whether the composition and dynamics of lipid rafts are responsible for the abnormal T cell responses in SLE. SLE T cells generate and possess higher amounts of ganglioside-containing lipid rafts and, unlike normal T cells, SLE T cell lipid rafts include FcRgamma and activated Syk kinase. IgM anti-CD3 Ab-mediated capping of TCR complexes occurs more rapidly in SLE T cells and concomitant with dramatic acceleration of actin polymerization kinetics. The significance of these findings is evident from the observation that cross-linking of lipid rafts evokes earlier and higher calcium responses in SLE T cells. Thus, we propose that alterations in the lipid raft signaling machinery represent an important mechanism that is responsible for the heightened and accelerated T cell responses in SLE.

Human T cell clones specific for heterogeneous nuclear ribonucleoprotein A2 autoantigen from connective tissue disease patients assist in autoantibody production

OBJECTIVE

To identify and characterize human T cells reactive with heterogeneous nuclear RNP A2 (hnRNP A2) antigen, and to determine the ability of hnRNP-reactive T cells to assist in the production of human autoantibodies.

METHODS

T cells from patients with high serum levels of anti-hnRNP IgG autoantibody were stimulated with an hnRNP recombinant fusion protein, and the cells were cloned by limiting dilution. The surface phenotype and cytokine profiles of the T cells were examined by flow cytometry and enzyme-linked immunosorbent assay (ELISA), respectively. T cell clones were cultured with highly purified autologous B cells, and the ability of T cells to enhance autoantibody production under a variety of conditions was measured by ELISA.

RESULTS

Human T cells reactive with hnRNP antigen were cloned from 2 patients with systemic lupus erythematosus (SLE) and 1 patient with mixed connective tissue disease (MCTD). The T cells were CD4+ and had a Th1-like functional phenotype. In coculture in vitro with autologous B cells, T cell clones augmented anti-hnRNP autoantibody production and did so without the need for direct T cell-B cell contact.

CONCLUSION

This study provides direct evidence for a role of anti-hnRNP-reactive T cells in autoantibody production in SLE and MCTD. These findings support the notion that hnRNP-reactive T cells play a role in the pathogenesis of these diseases.

Ubiquitin ligases in T cell activation and autoimmunity

Ubiquitination-mediated protein modifications are increasingly recognized as key regulatory events in many basic cell biology processes. A key class of enzymes called ubiquitin ligases, which has been shown to play a crucial role in the ubiquitination process, can positively or negatively regulate T cell responses. This review summarizes the recent advances defining the roles of several ubiquitin ligases in T cell activation and autoimmunity.