T cell receptor zeta reconstitution fails to restore responses of T cells rendered hyporesponsive by tumor necrosis factor alpha

T Cell Interactions in Mycobacterial Granulomas: Non-Specific T Cells Regulate Mycobacteria-Specific T Cells in Granulomatous Lesions

Infections with pathogenic mycobacteria are controlled by the formation of a unique structure known as a granuloma. The granuloma represents a host–pathogen interface where bacteria are killed and confined by the host response, but also where bacteria persist. Previous work has demonstrated that the T cell repertoire is heterogenous even at the single granuloma level. However, further work using pigeon cytochrome C (PCC) epitope-tagged BCG (PCC-BCG) and PCC-specific 5CC7 RAG−/− TCR transgenic (Tg) mice has demonstrated that a monoclonal T cell population is able to control infection. At the chronic stage of infection, granuloma-infiltrating T cells remain highly activated in wild-type mice, while T cells in the monoclonal T cell mice are anergic. We hypothesized that addition of an acutely activated non-specific T cell to the monoclonal T cell system could recapitulate the wild-type phenotype. Here we report that activated non-specific T cells have access to the granuloma and deliver a set of cytokines and chemokines to the lesions. Strikingly, non-specific T cells rescue BCG-specific T cells from anergy and enhance the function of BCG-specific T cells in the granuloma in the chronic phase of infection when bacterial antigen load is low. In addition, we find that these same non-specific T cells have an inhibitory effect on systemic BCG-specific T cells. Taken together, these data suggest that T cells non-specific for granuloma-inducing agents can alter the function of granuloma-specific T cells and have important roles in mycobacterial immunity and other granulomatous disorders.

The serum protein profile of early parity which induces protection against breast cancer

Early parity reduces the risk of breast cancer in women while nulliparity and late parity increase the risk of breast cancer. In order to translate this protection to women where early pregnancy is not feasible, much work has focused on understanding how parity confers protection against breast cancer, the molecular mechanisms by which this occurs is still not well understood. Healthy parous and nulliparous women were recruited for this study. We assessed serum protein profiles of early parous, late parous, and nulliparous women using the Phospho Explorer antibody array. Significantly altered proteins identified were validated by Western blot analysis. In silico analysis was performed with the data obtained. Our findings indicate increased phosphorylation levels of CDK1, AKT1 and Epo-R increased cell cycle and cell proliferation in late/nulliparous women. Increased levels of LIMK1, paxillin, caveolin-1, and tyrosine hydroxylase in late/nulliparous women demonstrate enhanced cell stress while decreased activity of p-p53 and pRAD51 in late/nulliparous women indicates decreased apoptosis and increased genomic instability. Further, increased levels of pFAK, pCD3zeta, pSTAT5B, MAP3K8 in early parous women favor enhanced innate/adaptive immunity. Overall, we have identified a unique protein signature that is responsible for the decreased risk of breast cancer and these proteins can also serve as biomarkers to predict the risk of breast cancer.

Signaling pathways in aged T cells - a reflection of T cell differentiation, cell senescence and host environment

With increasing age, the ability of the immune system to protect against new antigenic challenges or to control chronic infections erodes. Decline in thymic function and cumulating antigenic experiences of acute and chronic infections threaten T cell homeostasis, but insufficiently explain the failing immune competence and the increased susceptibility for autoimmunity. Alterations in signaling pathways in the aging T cells account for many of the age-related defects. Signaling threshold calibrations seen with aging frequently built on mechanisms that are operational in T cell development and T cell differentiation or are adaptations to the changing environment in the aging host. Age-related changes in transcription of receptors and signaling molecules shift the balance towards inhibitory pathways, most dominantly seen in CD8 T cells and to a lesser degree in CD4 T cells. Prominent examples are the expression of negative regulatory receptors of the CD28 and the TNF receptor superfamilies as well the expression of various cytoplasmic and nuclear dual-specific phosphatases.

Inhibitor of kappa B epsilon (IκBε) is a non-redundant regulator of c-Rel-dependent gene expression in murine T and B cells

Inhibitors of kappa B (IκBs) -α, -β and -ε effect selective regulation of specific nuclear factor of kappa B (NF-κB) dimers according to cell lineage, differentiation state or stimulus, in a manner that is not yet precisely defined. Lymphocyte antigen receptor ligation leads to degradation of all three IκBs but activation only of subsets of NF-κB-dependent genes, including those regulated by c-Rel, such as anti-apoptotic CD40 and BAFF-R on B cells, and interleukin-2 (IL-2) in T cells. We report that pre-culture of a mouse T cell line with tumour necrosis factor-α (TNF) inhibits IL-2 gene expression at the level of transcription through suppressive effects on NF-κB, AP-1 and NFAT transcription factor expression and function. Selective upregulation of IκBε and suppressed nuclear translocation of c-Rel were very marked in TNF-treated, compared to control cells, whether activated via T cell receptor (TCR) pathway or TNF receptor. IκBε associated with newly synthesised c-Rel in activated cells and, in contrast to IκBα and -β, showed enhanced association with p65/c-Rel in TNF-treated cells relative to controls. Studies in IκBε-deficient mice revealed that basal nuclear expression and nuclear translocation of c-Rel at early time-points of receptor ligation were higher in IκBε-/- T and B cells, compared to wild-type. IκBε-/- mice exhibited increased lymph node cellularity and enhanced basal thymidine incorporation by lymphoid cells ex vivo. IκBε-/- T cell blasts were primed for IL-2 expression, relative to wild-type. IκBε-/- splenic B cells showed enhanced survival ex vivo, compared to wild-type, and survival correlated with basal expression of CD40 and induced expression of CD40 and BAFF-R. Enhanced basal nuclear translocation of c-Rel, and upregulation of BAFF-R and CD40 occurred despite increased IκBα expression in IκBε-/- B cells. The data imply that regulation of these c-Rel-dependent lymphoid responses is a non-redundant function of IκBε.

Central role of nitric oxide in the pathogenesis of rheumatoid arthritis and systemic lupus erythematosus

Nitric oxide (NO) has been shown to regulate T cell functions under physiological conditions, but overproduction of NO may contribute to T lymphocyte dysfunction. NO-dependent tissue injury has been implicated in a variety of rheumatic diseases, including systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Several studies reported increased endogenous NO synthesis in both SLE and RA, and recent evidence suggests that NO contributes to T cell dysfunction in both autoimmune diseases. The depletion of intracellular glutathione may be a key factor predisposing patients with SLE to mitochondrial dysfunction, characterized by mitochondrial hyperpolarization, ATP depletion and predisposition to death by necrosis. Thus, changes in glutathione metabolism may influence the effect of increased NO production in the pathogenesis of autoimmunity.

TNFRI is a positive T-cell costimulatory molecule important for the timing of cytokine responses

Tumor necrosis factor (TNF)- and TNF receptor I (TNFRI)-deficient mice are resistant to initiation and show delayed resolution of disease in paradigms of autoimmune disease, but the contribution of TNF/TNFRI signaling to T-cell activation and effector responses has not been determined. In this study, we investigated the role of TNFRI in T-cell receptor (TCR)-mediated T-cell activation in vitro and in vivo using CD3(+)-enriched primary T cells and mice deficient in TNFRI. Following TCR engagement, TNFRI knockout (KO) T cells showed significantly delayed proliferation, cell division, upregulation of interleukin 2 (IL-2) and IL-2 receptor alpha chain (CD25) mRNA and cell-surface expression of CD25 compared with wild-type (WT) cells. Thus, WT and TNFRI KO cells showed equivalent proliferation peaks at 48 and 72 h, respectively. TNFRI KO mice also developed a defective primary T-cell response to ovalbumin and an acute contact hypersensitivity response to oxazolone (4-ethoxymethylene-2-phenyl-2-oxazolin-5-one). However, TNFRI KO splenocytes that were stimulated by TCR engagement in vitro for 96 h produced significantly higher intracellular levels of interferon-gamma (IFN-gamma), IL-2 and TNF-alpha, but not IL-17, compared with WT cells, in correlation with their relatively higher proliferation rate at this time point. Further, TCR-stimulated CD3(+)-enriched TNFRI KO T cells showed similarly higher production and secretion of IFN-gamma and IL-2 compared with WT, suggesting that TNFRI-mediated cytokine regulation might involve a T-cell autonomous effect. Our results show a novel role for TNFRI as a positive T-cell costimulatory molecule that is important for timely T-cell activation and effector cytokine production and the development of primary immune responses in mice.

ERK-dependent T cell receptor threshold calibration in rheumatoid arthritis

Immune responses to citrullinated neoantigens and clinical efficacy of costimulation blockade indicate a general defect in maintaining T cell tolerance in rheumatoid arthritis (RA). To examine whether TCR threshold calibration contributes to disease pathogenesis, signaling in RA T cells was quantified. RA patients had a selective increase in ERK phosphorylation compared with demographically matched controls due to a mechanism distal of Ras activation. Increased ERK responses included naive and memory CD4 and CD8 T cells and did not correlate with disease activity. The augmented ERK activity delayed SHP-1 recruitment to the TCR synapse and sustained TCR-induced Zap70 and NF-kappaB signaling, facilitating responses to suboptimal stimulation. Increased responsiveness of the ERK pathway was also a characteristic finding in the SKG mouse model of RA where it preceded clinical symptoms. Treatment with subtherapeutic doses of a MEK-1/2 inhibitor delayed arthritis onset and reduced severity, suggesting that increased ERK phosphorylation predisposes for autoimmunity and can be targeted to prevent disease.

T cell abnormalities in systemic lupus erythematosus

Because of the consensus that T cells play a central role in the pathogenesis of systemic lupus erythematosus (SLE), we explored the molecular basis of the defective function of SLE T cells for expression of signal transduction molecules, as well as surface structures such as adhesion molecules, by extensively testing peripheral blood T cells from SLE patients. Upregulated expression and function of adhesion molecules was observed in T cells from patients with active SLE who had specific clinical manifestations such as vasculitis, epithelitis and arthritis, but proximal signal transduction was defective. Comprehensive analysis to identify the molecules responsible for the defects showed the expression of the TCR zeta chain was attenuated, or absent in more than half of SLE patients. Moreover, the aberrant transcripts of the TCR zeta chain, including spliced variants lacking exon 7 and with a short 3' UTR, were detected in SLE T cells. Although attenuated expression of the TCR zeta chain is also observed in patients with cancers, infections and other autoimmune diseases, sustained attenuation of TCR zeta expression and aberrant transcripts are only observed in SLE. In this review we discuss the unique features of the TCR zeta defects in SLE.

Genomic expression profiling of TNF-alpha-treated BDC2.5 diabetogenic CD4+ T cells

TNF-alpha plays an important role in immune regulation, inflammation, and autoimmunity. Chronic TNF exposure has been shown to down-modulate T cell responses. In a mouse T cell hybridoma model, TNF attenuated T cell receptor (TCR) signaling. We have confirmed that chronic TNF and anti-TNF exposure suppressed and increased T cell responses, respectively. In adult TCR (BDC2.5) transgenic nonobese diabetic mice, DNA microarray analysis of global gene expression in BDC2.5 CD4(+) T cells in response to chronic TNF or anti-TNF exposure showed that genes involved in functional categories including T cell signaling, cell cycle, proliferation, ubiquitination, cytokine synthesis, calcium signaling, and apoptosis were modulated. Genes such as ubiquitin family genes, cytokine inducible Src homology 2-containing genes, cyclin-dependent kinase inhibitors p21, p57, calmodulin family genes (calmodulin-1, -2, and -3) and calcium channel voltage-dependent, N type alpha1B subunit (CaV2.2) were induced by TNF, whereas Vav2, Rho GTPase-activating protein, calcium channel voltage-dependent, L type alpha1C subunit (CaV1.2), IL-1 receptor-associated kinase-1 and -2, and IL enhancer binding factor 3 were reduced by TNF. Genes such as CaV1.2 and proliferating cell nuclear antigen, repressed by TNF, were induced by anti-TNF treatment. Further, we showed that chronic TNF exposure impaired NF-kappaB and adaptor protein 1 transactivation activity, leading to T cell unresponsiveness. Thus, our results present a detailed picture of transcriptional programs affected by chronic TNF exposure and provide candidate target genes that may function to mediate TNF-induced T cell unresponsiveness.

Cytokine inhibitors in rheumatoid arthritis and other autoimmune diseases

The clinical success of TNFalpha blocking biologics in a growing number of immune-mediated pathologies, including rheumatoid arthritis, Crohn's disease, ankylosing spondylitis and psoriasis, confirms the importance of TNFalpha in driving chronic inflammation and represents an important step forward in the treatment of these conditions. TNFalpha blockade, however, is a treatment, rather than a cure, and is not effective in all patients or in all autoimmune diseases and further research is needed to get closer to a cure. Recently, the identification of a novel, IL-17 producing, T helper cell subset, that plays a dominant pathogenic role in animal models of autoimmunity, is a major advance on existing knowledge, although the role of these cells in human disease remains to be established. Cytokines driving angiogenesis are also important in disease chronicity and thus might be valid therapeutic targets.

Nitric oxide, chronic inflammation and autoimmunity

Whilst many physiological functions of nitric oxide (NO) have been revealed so far, recent evidence proposes an essential role for NO in T lymphocyte activation and signal transduction. NO acts as a second messenger, activating soluble guanyl cyclase and participating in signal transduction pathways involving cyclic GMP. NO modulates mitochondrial events that are involved in apoptosis and regulates mitochondrial biogenesis in many cell types, including lymphocytes. Several studies undertaken on patients with RA and SLE have documented increased endogenous NO synthesis, although the effects of NO may be distinct. Here, we discuss recent evidence that NO contributes to T cell dysfunction in both SLE and RA by altering multiple signaling pathways in T cells. Although NO may play a physiological role in lymphocyte cell signaling, its overproduction may perturb T cell activation, differentiation and effector responses, each of which may contribute in different ways to the pathogenesis of autoimmunity.

An Essential Role for TNF in Modulating Thresholds for Survival, Activation, and Tolerance of CD8+ T Cells

TNF and its receptors p55 and p75 are known to be important in the homeostasis of the peripheral immune system. Previous studies have presented apparently contradictory evidence for an in vivo role of TNF in T cells. In this study, we analyzed TNF-deficient mice crossed with the F5 TCR-transgenic animals. We show that endogenous TNF modulates several aspects of homeostasis of peripheral F5 CD8 T cells. We found that F5/TNF(-/-)mice had reduced numbers of peripheral F5 T cells, F5/TNF(-/-) CD8 T cells exhibited reduced survival potential, and furthermore that T cell-derived TNF is required for optimum recovery of naive CD8 T cells in lymphopenic hosts, suggesting its involvement in the survival of peripheral CD8 T cells. Both peptide activation and ensuing Ag-induced apoptosis are quantitatively reduced in TNF(-/-) CD8 T cells. The latter observations can be related to decreased binding activities of NF-kappaB and NF-ATp observed in Ag-stimulated F5/TNF(-/-) T cells. Finally, in a CD8 T cell tolerance model, endogenous TNF was necessary for several parameters of CD8 T cell tolerance induction. Collectively, our results provide evidence that endogenous TNF modulates thresholds in several ligand-driven T cell responses.

CTLA-4IG suppresses reactive oxygen species by preventing synovial adherent cell-induced inactivation of rap1, a ras family GTPASE mediator of oxidative stress in rheumatoid arthritis T cells

OBJECTIVE

Oxidative stress contributes to the inflammatory properties of rheumatoid arthritis (RA) synovial T lymphocytes. This study was undertaken to investigate the mechanisms leading to production of reactive oxygen species (ROS) and oxidative stress in RA synovial T lymphocytes.

METHODS

ROS production in T lymphocytes from the peripheral blood (PB) of healthy donors and from the PB and synovial fluid (SF) of RA patients was measured by ROS-dependent fluorescence of 6-carboxy-2',7'-dichlorofluorescein. Rap1 GTPase activation was assessed by activation-specific probe precipitation. Proliferation of RA PB and SF T lymphocytes was assayed by 3H-thymidine incorporation. In some experiments, RA PB T cells were preincubated with autologous SF or with PB or SF adherent cells. Experiments were performed in the absence or presence of transwell membranes or CTLA-4Ig fusion proteins. Short- and long-term stimulations of healthy donor PB T lymphocytes were performed with inflammatory cytokines, in the absence or presence of activating anti-CD28 antibodies.

RESULTS

T lymphocyte ROS production and Rap1 inactivation were mediated by cell-cell contact with RA synovial adherent cells, and this correlated with T cell mitogenic hyporesponsiveness. CTLA4-Ig blockade of synovial adherent cell signaling to CD28 T cells reversed the inhibition of Rap1 activity and prevented induction of ROS. Introduction of active RapV12 into T cells also prevented induction of ROS production. Coincubation of T cells with stimulating anti-CD28 antibodies and inflammatory cytokines synergistically increased T cell ROS production.

CONCLUSION

Cell-cell contact between T cells and RA synovial adherent cells mediates Rap1 inactivation and subsequent ROS production in T lymphocytes following exposure to inflammatory cytokines. This process can be blocked by CTLA4-Ig fusion protein.

What does tumour necrosis factor excess do to the immune system long term?

Members of the tumour necrosis factor (TNF)/TNF-receptor (TNF-R) superfamily coordinate the immune response at multiple levels. For example, TNF, LTalpha, LTbeta and RANKL provide signals required for lymphoid neogenesis, CD27, OX-40, 4-1BB and CD30 deliver costimulatory signals to augment immune responses, while pro-apoptotic members such as TNF, CD95L and TRAIL may contribute to the termination of the response. Biological identity of individual family members has been revealed through studies of gain of function or gene deficient mutants. Most notable are the development of spontaneous inflammatory polyarthritis in human TNF-globin transgenic mice, the auto-inflammatory syndromes resulting from mutations in the 55-kDa TNF-R, and, in particular, the obligatory role for the RANKL/RANK axis in osteoclastogenesis and bone remodelling. A growing appreciation of the molecular basis of signalling pathways transduced by TNF-R has provided a framework for better understanding the biology of this expanding family. For while the rapid and robust activation of NF-kappaB and MAPK pathways is typical of acute TNF-R engagement, the molecular basis of sustained receptor signalling remains a mystery, in spite of its relevance to chronic inflammatory and immune responses. Focusing on T cells, this report describes some of the molecular footprints of sustained TNF-R engagement and illustrates how these may influence immune function. A common theme arising is that prolonged TNF stimulation alters signalling thresholds over time. The authors propose that one major outcome of long term exposure to TNF is a state of localised IL-2 deficiency at sites of inflammation. The implications of this deficiency are discussed.

c-Rel-dependent priming of naive T cells by inflammatory cytokines

The intrinsic refractoriness of naive T cells for cytokine production is counteracted by cells of the innate immune system. Upon sensing danger via Toll-like receptors, these cells upregulate T cell costimulatory molecules and secrete cytokines that enhance T cell activation. We show that cytokine-mediated priming of naive T cells requires the NF-kappaB family member c-Rel. In resting naive cells c-Rel is associated primarily with IkappaBbeta, an inhibitory molecule that is not effectively degraded by TCR signals. Exposure of T cells to proinflammatory cytokines, TNF-alpha and IL-1beta, shifts c-Rel to IkappaBalpha-associated complexes that are readily targeted by the TCR. As a consequence, IL-2 and IFN-gamma mRNA are produced more quickly, and at higher levels, in cytokine-primed T cells. This mechanism does not operate in effector T cells where cytokine gene expression is c-Rel-independent. We propose that c-Rel plays a crucial role as a target of innate signals in T cells.

Modulation of CD28 expression with anti-tumor necrosis factor alpha therapy in rheumatoid arthritis

OBJECTIVE

The immune system of patients with rheumatoid arthritis (RA) is characterized by the accumulation of CD4+ T cells deficient in CD28 expression and the up-regulation of tumor necrosis factor alpha (TNFalpha). Previous in vitro studies have shown that TNFalpha induces transcriptional silencing of the CD28 gene. Because reduced expression of CD28 in T cells compromises immunocompetence, we examined whether CD28 expression is reduced in patients with RA in vivo and whether the reduction is related to TNFalpha.

METHODS

Patients with RA and age-matched individuals were recruited. Peripheral blood mononuclear cells were stained for CD3, CD4, CD8, CD28, TNF receptor I (TNFRI), and TNFRII, and analyzed by quantitative flow cytometry. The number of CD28 and TNFR molecules was monitored in a subgroup of patients with RA undergoing treatment with anti-TNFalpha.

RESULTS

In addition to higher frequencies of CD28null T cells, patients with RA had significantly reduced numbers of CD28 and TNFRI molecules on CD4+,CD28+ T cells. Normal expression could be restored in vitro by overnight culture, suggesting that CD28 in patients was modulated by exogenous factors. In contrast, treatment with TNFalpha in vitro resulted in further down-regulation. CD28 expression was normalized in patients undergoing TNFalpha-neutralizing therapy.

CONCLUSION

Overproduction of TNFalpha in RA induces a global down-regulation of CD28 in CD4+ T cells and may cause reduced sensitivity to costimulatory signals in T cell responses.

Chronic TNF-α exposure impairs TCR-signaling via TNF-RII but not TNF-RI

Chronic exposure to TNF-alpha has been shown to impair T cell-activation in mice and in humans. In the present study, we investigated a possible role of TNF-RII in this long-term effect of TNF-alpha. Chronic TNF-alpha exposure led to suppression of subsequent TCR stimulation (e.g., TCR/CD28-induced proliferation, cytokine production (IFN-gamma, TNF-alpha)) but left TCR independent restimulation unaffected. Activation of T cells during TNF-alpha exposure was required for the inhibitory effect on TCR stimulation. In contrast to the mouse model, the inhibitory effect of long-term TNF-alpha exposure was mediated via TNF-RII but not TNF-receptor I, and surface expression of the TCR/CD3 complex remained unchanged. Chronic TNF-RII triggering downregulated T cell activation at an early level, as TCR-induced calcium flux and IL-2 mRNA expression were impaired after preculture in the presence of anti-TNF-RII mAbs. Furthermore, chronic TNF-RII-stimulation specifically downregulated store operated calcium channels, which contribute to sustained TCR-induced calcium influx.

Persistent TNF-α exposure impairs store operated calcium influx in CD4+ T lymphocytes

Persistent tumour necrosis factor alpha (TNF-alpha) exposure uncouples proximal T-cell receptor (TCR)-signalling events. Here, we demonstrate that chronic TNF-alpha exposure also attenuates signalling distal to the TCR, by specifically inhibiting Ca2+ influx evoked by thapsigargin in CD4+ T-cells. Mitogen-induced Ca2+ responses were impaired in a dose dependent manner, and TCR-induced Ca2+ responses were also significantly reduced. The impairment of Ca2+ influx strongly correlated with poor function as proliferative responses to both mitogen and anti-CD3/CD28 stimulation were suppressed. Our findings show that persistent TNF-alpha exposure of T-cells specifically inhibits store operated Ca2+ influx. This may affect gene activation and contribute to the poor T-cell function in chronic inflammatory disease.