CD8 T cells stimulated with a suboptimal dose of anti-CD3 antibodies (100 pg/ml) in the presence of IL-15 retain a naïve phenotype with expression of CD45RA, CD28, CD27 and CCR7 but acquire new functions and differentiate into immunosuppressive T cells. CD8+CCR7+ Tregs express FOXP3 and prevent CD4 T cells from responding to T-cell receptor stimulation and entering the cell cycle. Naïve CD4 T cells are more susceptible to inhibition than memory cells. The suppressive activity of CD8+CCR7+ Tregs is not mediated by IL-10, TGF-β, CTLA-4, CCL4 or adenosine and relies on interference with very early steps of the TCR signaling cascade. Specifically, CD8+CCR7+ Tregs prevent TCR-induced phosphorylation of ZAP70 and dampen the rise of intracellular calcium in CD4 T cells. The inducibility of CD8+CCR7+ Tregs is correlated to the age of the individual with peripheral blood lymphocytes of donors older than 60 years yielding low numbers of FOXP3low CD8 Treg cells. Loss of CD8+CCR7+ Tregs in the elderly host may be of relevance in the aging immune system as immunosenescence is associated with a state of chronic smoldering inflammation.
In rheumatoid arthritis (RA), hematopoietic progenitor cells (HPC) have age-inappropriate telomeric shortening suggesting premature senescence and possible restriction of proliferative capacity. In response to hematopoietic growth factors RA-derived CD34+ HPC expanded significantly less than age-matched controls. Cell surface receptors for stem cell factor (SCF), Flt 3-Ligand, IL-3 and IL-6 were intact in RA HPC but the cells had lower transcript levels of cell cycle genes, compatible with insufficient signal strength in the ERK pathway. Cytokine-induced phosphorylation of ERK1/2 was diminished in RA HPC whereas phosphorylated STAT3 and STAT5 molecules accumulated to a similar extent as in controls. Confocal microscopy demonstrated that the membrane-proximal colocalization of K-Ras and B-Raf were less efficient in RA-derived CD34+ cells. Thus, hyporesponsiveness of RA HPC to growth factors results from dampening of the ERK signaling pathways; with a defect localized in the very early steps of the ERK signaling cascade.
rheumatoid arthritis; hematopoietic progenitor cells; CD34; ERK signaling; STAT signaling
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.
Aging; signaling; T cell receptor; JAK STAT pathway; dual-specific phosphatase
Purpose of review
Granuloma formation in giant cell arteritis (GCA) emphasizes the role of the adaptive immunity and highlights the role of antigen-specific T cells. Recent data demonstrate that at least two separate lineages of CD4 T-cells participate in vascular inflammation, providing an important clue that multiple disease instigators may initiate pathogenic immunity.
IFN-γ-producing Th1 cells and IL-17-producing Th17 cells have been implicated in GCA. Patients with biopsy-positive GCA underwent two consecutive temporal artery biopsies, one prior to therapy and one while on corticosteroids. In untreated patients, Th1 and Th17 cells co-existed in the vascular lesions. Following therapy, Th17 cells were essentially lost, whereas Th1 cells persisted almost unaffected. In the peripheral blood of untreated patients Th17 frequencies were increased eightfold, but normalized with therapy. Blood Th1 cells were doubled in frequency, independent of therapy. Corticosteroids functioned by selectively suppressing IL-1β, IL-6 and IL-23-releasing antigen-presenting cells (APC), disrupting induction of Th17 cells.
At least two distinct CD4 T-cell subsets promote vascular inflammation in GCA. In early disease, APCs promote differentiation of Th17 as well as Th1 cells. Chronic disease is characterized by persistent Th1-inducing signals, independent of IL-17-mediated inflammation. More than one disease instigator may trigger APCs to induce multiple T cell lineages. Cocktails of therapies will be needed for appropriate disease control.
IL-17; IFN-γ; T cell; Antigen-presenting cell
In the autoimmune syndrome rheumatoid arthritis (RA), T-cells and T-cell precursors have age-inappropriate shortening of telomeres and accumulate DNA double strand breaks. Whether damaged DNA elicits DNA repair activity and how this affects T-cell function and survival is unknown. Here, we report that naïve and resting T cells from RA patients are susceptible to undergo apoptosis. In such T cells, unrepaired DNA stimulates a p53-ATM-independent pathway involving the nonhomologous-end-joining protein DNA-PKcs. Upregulation of DNA-PKcs transcription, protein expression and phosphorylation in RA T cells co-occurs with diminished expression of the Ku70/80 heterodimer, limiting DNA repair capacity. Inhibition of DNA-PKcs kinase activity or gene silencing of DNA-PKcs protects RA T-cells from apoptosis. DNA-PKcs induces T-cell death by activating the JNK pathway and upregulating the apoptogenic BH3-only proteins Bim and Bmf. In essence, in rheumatoid arthritis, the DNA-PKcs-JNK-Bim/Bmf axis transmits genotoxic stress into shortened survival of naïve resting T cells, imposing chronic proliferative turnover of the immune system and premature immunosenescence. Therapeutic blockade of the DNA-PK-dependent cell-death machinery may rejuvenate the immune system in RA.
Apoptosis; DNA damage; DNA-PKcs; Rheumatoid Arthritis; T cell
A defining feature of the eukaryotic genome is the presence of linear chromosomes. This arrangement, however, poses several challenges with regard to chromosomal replication and maintenance. To prevent the loss of coding sequences and to suppress gross chromosomal rearrangements, linear chromosomes are capped by repetitive nucleoprotein structures, called telomeres. Each cell division results in a progressive shortening of telomeres that, below a certain threshold, promotes genome instability, senescence, and apoptosis. Telomeric erosion, maintenance, and repair take center stage in determining cell fate. Cells of the immune system are under enormous proliferative demand, stressing telomeric intactness. Lymphocytes are capable of upregulating telomerase, an enzyme that can elongate telomeric sequences and, thus, prolong cellular lifespan. Therefore, telomere dynamics are critical in preserving immune function and have become a focus for studies of immunosenescence and autoimmunity. In this review, we describe the role of telomeric nucleoproteins in shaping telomere architecture and in suppressing DNA damage responses. We summarize new insights into the regulation of telomerase activity, hereditary disorders associated with telomere dysfunction, the role of telomere loss in immune aging, and the impact of telomere dysfunction in chronic inflammatory disease.
Telomeres; Aging; Immunosenescence
The aged immune system, typically hyporesponsive to infection and vaccination, can be hyperresponsive in the context of inflammatory pathology. Here we review current work examining the mechanisms behind the amplified inflammatory profile of aged adaptive immunity, and the reciprocal relationship between chronic inflammation and immune aging. Aged hematopoietic stem cells are driven to differentiate following accumulated DNA damage, thus depleting the stem cell pool and increasing the number of damaged effector cells in the circulation. Chronic DNA damage responses in lymphocytes as well as senescent cells of other lineages initiate the production of inflammatory mediators. In addition, aged lymphocytes become less reliant on specific antigen for stimulation and more prone to activation through innate receptors. When these lymphocytes are exposed to inflammatory signals produced by senescent tissues, the bias toward inflammation exacerbates destruction without necessarily improving immunity.
Large vessel vasculitides, such as Takayasu arteritis and giant cell arteritis (GCA), affect vital arteries and cause clinical complications by either luminal occlusion or vessel wall destruction. Inflammatory infiltrates, often with granulomatous arrangements, are distributed as a panarteritis throughout all of the artery’s wall layers or cluster in the adventitia as a perivasculitis. Factors determining the architecture and compartmentalization of vasculitis are unknown. Human macrovessels are populated by indigenous dendritic cells (DC) positioned in the adventitia. Herein, we report that these vascular DC sense bacterial pathogens and regulate the patterning of the emerging arteritis. In human temporal artery-SCID chimeras, lipopolysaccharides stimulating Toll-like receptor (TLR) 4 and flagellin stimulating TLR5 trigger vascular DC and induce T-cell recruitment and activation. However, the architecture of the evolving inflammation is ligand specific; TLR4 ligands cause transmural panarteritis and TLR5 ligands promote adventitial perivasculitis. Underlying mechanisms involve selective recruitment of functional T cell subsets. Specifically, TLR4-mediated DC stimulation markedly enhances production of the chemokine CCL20, biasing recruitment towards CCL20-responsive CCR6+ T cells. In adoptive transfer experiments,CCR6+ T cells produce an arteritis pattern with media-invasive T cells damaging vascular smooth muscle cells. Also, CCR6+ T cells dominate the vasculitic infiltrates in patients with panarteritic GCA. Thus, depending on the original danger signal, vascular DC edit the emerging immune response by differentially recruiting specialized T effector cells and direct the disease process toward distinct types of vasculitis.
T cell; Toll-like receptor; inflammation; vascular inflammation
In rheumatoid arthritis (RA), telomeres of lymphoid and myeloid cells are age-inappropriately shortened, suggesting excessive turnover of hematopoietic precursor cells (HPC). We have examined functional competence (proliferative capacity, maintenance of telomeric reserve) of CD34+ HPC in RA.
Frequencies of peripheral blood CD34+CD45+ HPC of 63 rheumatoid factor positive RA patients and 48 matched controls were measured by flow cytometry. Proliferative burst, cell cycle dynamics, and induction of lineage-restricted receptors were tested in purified CD34+ HPC after stimulating with early hematopoietins. Telomeric sequences were quantified by real-time PCR. HPC functions were correlated with disease duration, activity, severity, and treatment.
In healthy donors, CD34+ HPC accounted for 0.05% of nucleated cells; their numbers were strictly age-dependent and declined at a rate of 1.3%/year. In RA patients, CD34+ HPC frequencies were age-independently reduced to 0.03%. Upon growth factor stimulation, control HPC passed through 5 replication cycles over 4 days. In contrast, RA-derived HPC completed only 3 generations. Telomeres of RA CD34+ HPC were age-inappropriately shortened by 1,600 bp. All HPC defects were independent from disease duration, disease activity, and smoking status; and were present to the same degree in untreated patients.
In RA, circulating bone marrow-derived progenitor cells are diminished, with concentrations stagnated at levels typical for old control individuals. HPC from RA patients display growth factor non-responsiveness and sluggish cell cycle progression; marked telomere shortening indicates proliferative stress-induced senescence. Defective HPC function independent from disease activity markers suggests bone marrow failure as a potential pathogenic factor in RA.
In rheumatoid arthritis (RA), dysfunctional T cells sustain chronic inflammatory immune responses in the synovium. Even unprimed T cells are under excessive replication pressure, suggesting an intrinsic defect in T cell regeneration. In naive CD4 CD45RA+ T cells from RA patients, DNA damage load and apoptosis rates were markedly higher than in controls; repair of radiation-induced DNA breaks was blunted and delayed. DNA damage was highest in newly diagnosed untreated patients. RA T cells failed to produce sufficient transcripts and protein of the DNA repair kinase ataxia telangiectasia (AT) mutated (ATM). NBS1, RAD50, MRE11, and p53 were also repressed. ATM knockdown mimicked the biological effects characteristic for RA T cells. Conversely, ATM overexpression reconstituted DNA repair capabilities, response patterns to genotoxic stress, and production of MRE11 complex components and rescued RA T cells from apoptotic death. In conclusion, ATM deficiency in RA disrupts DNA repair and renders T cells sensitive to apoptosis. Apoptotic attrition of naive T cells imposes lymphopenia-induced proliferation, leading to premature immunosenescence and an autoimmune-biased T cell repertoire. Restoration of DNA repair mechanisms emerges as an important therapeutic target in RA.
Inflammatory vasculopathies, ranging from the vasculitides (Takayasu arteritis, giant cell arteritis, and polyarteritis nodosa) to atherosclerosis display remarkable target tissue tropisms for selected vascular beds. Molecular mechanisms directing wall inflammation to restricted anatomical sites within the vascular tree are not understood. We have examined the ability of 6 different human macrovessels (aorta, subclavian, carotid, mesenteric, iliac, temporal arteries) to initiate innate and adaptive immune responses by comparing pathogen-sensing and T-cell stimulatory capacities.
Methods and Results
Gene expression analysis for pathogen-sensing Toll-like receptors (TLR) 1-9 showed vessel-specific profiles with TLR2 and 4 ubiquitously present, TLR7 and 9 absent, and TLR1, 3, 5, 6 and 8 expressed in selective patterns. Experiments with vessel walls stripped of the intimal or adventitial layer identified dendritic cells (DC) at the media-adventitia junction as the dominant pathogen sensors. In human artery-SCID mouse chimeras, adoptively transferred human T cells initiated vessel wall inflammation if wall-embedded DC were conditioned with TLR ligands. Wall-infiltrating T cells displayed vessel-specific activation profiles with differential production of CD40L, lymphotoxin-α, and interferon-γ. Vascular bed-specific TLR fingerprints were functionally relevant as exemplified by differential responsiveness of iliac and subclavian vessels to TLR5 but not TLR4 ligands.
Populated by indigenous DC, medium and large human arteries have immune sensing and T-cell stimulatory functions. Each vessel in the macrovascular tree utilizes a distinct TLR profile and supports selective T-cell responses imposing vessel-specific risk for inflammatory vasculopathies.
arteries; immune system; inflammation
Dendritic cells (DCs) shape T-cell response patterns and determine early, intermediate, and late outcomes of immune recognition events. They either facilitate immunostimulation or induce tolerance, possibly determined by initial DC activation signals, such as binding Toll-like receptor (TLR) ligands. Here we report that DC stimulation through the TLR3 ligand dsRNA [poly(I:C)] limits CD4 T-cell proliferation, curtailing adaptive immune responses. CD4+ T cells instructed by either LPS or poly(I:C)-conditioned DCs promptly upregulated the activation marker CD69. Whereas LPS-pretreated DCs subsequently sustained T-cell clonal expansion, proliferation of CD4+ T cells exposed to poly(I:C)-pretreated DCs was markedly suppressed. This proliferative defect required DC-T cell contact, was independent of IFN-α, and was overcome by exogenous IL-2, indicating T-cell anergy. Coinciding with the downregulation, CD4+ T cells expressed the inhibitory receptor PD-1. Antibodies blocking the PD-1 ligand PD-L1 restored proliferation. dsRNA-stimulated DCs preferentially induced PD-L1, whereas poly(I:C) and LPS both upregulated the costimulatory molecule CD86 to a comparable extent. Poly(dA-dT), a ligand targeting the cytoplasmic RNA helicase pattern-recognition pathway, failed to selectively induce PD-L1 upregulation, assigning this effect to the TLR3 pathway. Poly(I:C)-conditioned DCs promoted accumulation of phosphorylated SHP-2, the intracellular phosphatase mediating PD-1 inhibitory effects. The ability of dsRNA to bias DC differentiation toward providing inhibitory signals to interacting CD4+ T cells may be instrumental in viral immune evasion. Conversely, TLR3 ligands may have therapeutic value in silencing pathogenic immune responses.
dendritic cell; T cell; Toll-like receptor 3; PD-L1
Giant cell arteritis (GCA) is a granulomatous vasculitis of the aorta and its branches that causes blindness, stroke and aortic aneurysm. CD4 T-cells are key pathogenic regulators, instructed by vessel wall dendritic cells (DC) to differentiate into vasculitic T cells. The unique pathways driving this DC-T-cell interaction are incompletely understood but may provide novel therapeutic targets for a disease in which the only established therapy is chronic treatment with high doses of corticosteroids.
Methods and Results
Immunohistochemical and gene expression analysis of GCA-affected temporal arteries revealed abundant expression of the NOTCH receptor and its ligands Jagged1 and Delta1. Cleavage of the NOTCH intracellular domain (NICD) in wall-infiltrating T cells indicated ongoing NOTCH pathway activation in large vessel vasculitis. NOTCH activation did not occur in small vessel vasculitis affecting branches of the vasa vasorum tree. We devised two strategies to block NOTCH pathway activation; γ-secretase inhibitor treatment, preventing nuclear translocation of the NICD, and competing for receptor-ligand interactions through excess soluble ligand, Jagged1-Fc. In humanized mice carrying human arteries NOTCH pathway disruption had strong immunosuppressive effects, inhibiting T-cell activation in the early and established phase of vascular inflammation. NOTCH inhibition was particularly effective in downregulating Th17 responses, but also markedly suppressed Th1 responses.
Blocking NOTCH signaling depleted T cells from the vascular infiltrates, implicating NOTCH-NOTCH ligand interactions in regulating T-cell retention and survival in vessel wall inflammation. Modulating the NOTCH signaling cascade emerges as a promising new strategy for immunosuppressive therapy of large vessel vasculitis.
Arteries; Inflammation; T-cell; NOTCH; Costimulation; IFN-γ; IL-17
Acute coronary syndromes (ACS) are precipitated by a rupture of the atherosclerotic plaque, often at the site of T cell and macrophage infiltration. Here, we show that plaque-infiltrating CD4 T cells effectively kill vascular smooth muscle cells (VSMC). VSMCs sensitive to T cell–mediated killing express the death receptor DR5 (TNF-related apoptosis-inducing ligand [TRAIL] receptor 2), and anti-TRAIL and anti-DR5 antibodies block T cell–mediated apoptosis. CD4 T cells that express TRAIL upon stimulation are expanded in patients with ACS and more effectively induce VSMC apoptosis. Adoptive transfer of plaque-derived CD4 T cells into immunodeficient mice that are engrafted with human atherosclerotic plaque results in apoptosis of VSMCs, which was prevented by coadministration of anti-TRAIL antibody. These data identify that the death pathway is triggered by TRAIL-producing CD4 T cells as a direct mechanism of VSMC apoptosis, a process which may lead to plaque destabilization.
RA is a quintessential autoimmune disease with a growing number of cells, mediators, and pathways implicated in this tissue-injurious inflammation. Now Kuhn and colleagues have provided convincing evidence that autoantibodies reacting with citrullinated proteins, known for their sensitivity and specificity as biomarkers in RA, enhance tissue damage in collagen-induced arthritis (see the related article beginning on page 961). This study adds yet another soldier to the growing army of autoaggressive mechanisms that underlie RA. With great success researchers have dismantled the pathogenic subunits of RA, adding gene to gene, molecule to molecule, and pathway to pathway in an ever more complex scheme of dysfunction. The complexity of the emerging disease model leaves us speechless. It seems that with this wealth of data available, we need to develop a new theory for this disease. We may want to seek guidance from our colleagues in physics and mathematics who have successfully integrated their knowledge of elementary particles and the complexity of their interacting forces by formulating the string theory.
The cytokines B lymphocyte stimulator (BLyS) and a proliferation-inducing ligand (APRIL) enhance autoimmune disease by sustaining B cell activation. In RA, B cells contribute to the formation of 3 functionally distinct types of lymphoid microarchitectures in the inflamed synovium: ectopic GCs; T cell–B cell aggregates lacking GC reactions; and unorganized, diffuse infiltrates. We examined 72 tissues representing the 3 types of synovitis for BLyS and APRIL production and for expression of APRIL/BLyS receptors. Biologic effects of BLyS and APRIL were explored by treating human synovium–SCID mouse chimeras with the APRIL and BLyS decoy receptor transmembrane activator and CAML interactor:Fc (TACI:Fc). GC+ synovitis had the highest levels of APRIL, produced exclusively by CD83+ DCs. BLyS was present in similar levels in all tissue types and derived exclusively from CD68+ macrophages. In GC+ synovitis, treatment with TACI:Fc resulted in GC destruction and marked inhibition of IFN-γ and Ig transcription. In contrast, inhibition of APRIL and BLyS in aggregate and diffuse synovitis left Ig levels unaffected and enhanced IFN-γ production. These differential immunomodulatory effects correlated with the presence of TACI+ T cells in aggregate and diffuse synovitis and their absence in GC+ synovitis. We propose that BLyS and APRIL regulate B cell as well as T cell function and have pro- and antiinflammatory activities in RA.
The ability of the human immune system to respond to vaccination declines with age. We identified an age-associated defect in T cell receptor (TCR)-induced ERK phosphorylation in naïve CD4+ T cells (P<0.0001) while other signals, such as ZAP70 and PLC-γ1 phosphorylation were not impaired. The defective ERK signaling was caused by the dual specific phosphatase (DUSP) 6 whose protein levels increased with age (r = 0.68, P < 0.0001) due to a decline in repression by miR-181a (r = −0.59, P < 0.0001). Reconstitution of miR-181a lowered DUSP6 levels in naïve CD4+ T cells in elderly individuals. DUSP6 repression with miR-181a or specific siRNA, and DUSP6 inhibition with the allosteric inhibitor (E)-2-benzylidene-3-(cyclohexylamino)-2,3-dihydro-1H-inden-1-one improved CD4+ T cell responses as seen by increased expression of activation markers, improved proliferation and supported preferential TH1 differentiation. DUSP6 is a potential intervention target for restoring T cell responses in the elderly, which may augment the effectiveness of vaccination.
The assembly of inflammatory lesions in rheumatoid arthritis is highly regulated and typically leads to the formation of lymphoid follicles with germinal center (GC) reactions. We used microdissection of such extranodal follicles to analyze the colonizing T cells. Although the repertoire of follicular T cells was diverse, a subset of T cell receptor (TCR) sequences was detected in multiple independent follicles and not in interfollicular zones, suggesting recognition of a common antigen. Unexpectedly, the majority of shared TCR sequences were from CD8 T cells that were highly enriched in the synovium and present in low numbers in the periphery. To examine their role in extranodal GC reactions, CD8 T cells were depleted in human synovium-SCID mouse chimeras. Depletion of synovial CD8 T cells caused disintegration of the GC-containing follicles. In the absence of CD8 T cells, follicular dendritic cells disappeared, production of lymphotoxin-α1β2 markedly decreased, and immunoglobulin (Ig) secretion ceased. Immunohistochemical studies demonstrated that these CD8 T cells accumulated at the edge of the mantle zone. Besides their unique localization, they were characterized by the production of interferon (IFN)-γ, lack of the pore-forming enzyme perforin, and expression of CD40 ligand. Perifollicular IFN-γ+ CD8 T cells were rare in secondary lymphoid tissues but accounted for the majority of IFN-γ+ cells in synovial infiltrates. We propose that CD8+ T cells regulate the structural integrity and functional activity of GCs in ectopic lymphoid follicles.
lymphoid follicle; rheumatoid arthritis; lymphoid neogenesis; pathogenesis; CD40
Inflammation plays a central role in atherosclerosis. However, the detailed changes in the composition and quantity of leukocytes in the arterial wall during atherogenesis are not fully understood due in part to the lack of suitable methods and animal models.
Methods and Results
We developed a 10-fluorochrome, 13-parameter flow cytometry method to quantitate 7 major leukocyte subsets in a single digested arterial wall sample. ApoE−/− mice underwent left carotid artery (LCA) partial ligation and fed high-fat diet for 4 to 28 days. Monocyte/macrophages, dendritic cells, granulocytes, NK cells, and CD4 T-cells significantly infiltrated the LCA as early as 4d. Monocyte/macrophages and dendritic cells decreased between 7d and 14d, while T-cell numbers remained steady. Leukocyte numbers peaked at 7d, preceding atheroma formation at 14d. B-cells entered LCA by 14d. Control right carotid and sham-ligated LCAs showed no significant infiltrates. PCR and ELISA arrays showed that expression of pro-inflammatory cytokines and chemokines peaked at 7 and 14-days post-ligation, respectively.
This is the first quantitative description of leukocyte number and composition over the life span of murine atherosclerosis. These results show that disturbed flow induces rapid and dynamic leukocyte accumulation in the arterial wall during the initiation and progression of atherosclerosis.
Atherosclerosis; disturbed flow; leukocytes; flow cytometry; inflammation
Immune aging is best known for its immune defects that increase susceptibility to infections and reduce adaptive immune responses to vaccination. In parallel, the aged immune system is prone to autoimmune responses and many autoimmune diseases increase in incidence with age or are even preferentially encountered in the elderly. Why an immune system that suboptimally responds to exogenous antigen fails to maintain tolerance to self-antigens appears to be perplexing. In this review, we will discuss age-associated deviations in the immune repertoire and the regulation of signaling pathways that may shed light on this conundrum.
immunosenescence; autoimmunity; inflammation; pathogenesis; DNA damage response; T cell receptor signaling; rheumatoid arthritis; giant cell arteritis
Immune aging is associated with loss of critical immune functions, such as host protection from infection and malignancy. Unexpectedly, immunosenescence also renders the host susceptible to inflammation, which may translate into tissue-damaging disease as the senescent immune system loses its ability to maximize inflammatory protection while minimizing inflammatory injury. On the other hand, chronic inflammation associated with immune-mediated disease represents a profound stress factor for the immune system, affecting cellular turn-over, replication and exhaustion. Immune cell longevity is tightly connected to the functional integrity of telomeres which are regulated by cell multiplication, exposure to oxidative stress and DNA repair mechanisms. Lymphocytes are amongst the few cell types that can actively elongate telomeres through the action of telomerase. In patients with the autoimmune disease rheumatoid arthritis (RA), telomerase deficiency is associated with prematurity of immune aging. Patients with RA have other defects in DNA repair mechanisms, including the kinase Ataxia telangiectasia mutated (ATM), critically involved in the repair of DNA double strand breaks. ATM deficiency in RA shortens lymphocyte survival. Dynamics of telomeric length and structure are beginning to be understood and have distinct patterns in different autoimmune diseases, suggesting a multitude of molecular mechanisms defining the interface between chronic immune stimulation and progressive aging of the immune system.
Telomere; Telomere Dysfunction; Autoimmunity; Rheumatoid arthritis; Lupus; Shelterin; Telomerase; Diabetes; Sarcoidosis
Susceptibility for giant cell arteritis increases with chronological age, in parallel with age-related restructuring of the immune system and age-induced remodeling of the vascular wall. Immunosenescence results in shrinkage of the naïve T-cell pool, contraction of T-cell diversity, and impairment of innate immunity. Aging of immunocompetent cells forces the host to take alternative routes for protective immunity and confers risk for pathogenic immunity that causes chronic inflammatory tissue damage. Dwindling immunocompetence is particularly relevant as the aging host is forced to cope with an ever growing infectious load. Immunosenescence coincides with vascular aging during which the arterial wall undergoes dramatic structural changes and medium and large arteries lose their pliability and elasticity. On the molecular level, elastic fibers deteriorate and matrix proteins accumulate biochemical modifications. Thus, the aging process impacts the two major biologic systems that liaise to promote giant cell arteritis; the immune system and the vessel wall niche.
RA is the prototypic chronic inflammatory disease, characterized by progressive articular cartilage and bone destruction. The systemic nature of RA is evidenced by the increased risk of atherosclerosis and lymphoproliferative disorders. Components of both the innate and adaptive immune system are implicated in the pathophysiology of the articular and extra-articular manifestations of the disease. A fundamental process in the onset of RA is the breakdown in self-tolerance. Accelerated ageing of immune cells (immunosenescence) appears to be a major mechanism favouring the disruption of tolerance. Telomere erosion, a hallmark of immunosenescence, is present in lymphoid (naïve and memory T cells) and myeloid (granulocytes) cells in RA. The premature ageing process also involves the haematopoietic stem and progenitor cells (CD34+ HSPC), thus extending the RA immunopathogenesis to include early events in the shaping of the immune system. This review summarizes current concepts of HSPC ageing and its impact on immune regeneration, highlighting the phenotypic and functional similarities between elderly and RA HSPC.
Rheumatoid arthritis; Haematopoietic progenitor cells; Telomeres; CD34+ cells; Ageing
Statins reduce cardiovascular-related morbidity and mortality, but their effects on inflammation in atherosclerosis are not fully understood. We investigated whether statins can modulate cytotoxic functions of CD4 T cells in acute coronary syndrome (ACS).
Methods and Results
Fresh CD4 T cells were isolated from 55 patients with ACS without statin treatment on admission and from 34 age-matched controls. CD4 T cells collected from ACS patients induced endothelial cell apoptosis significantly more than control T cells. The TNF-related apoptosis-inducing ligand (TRAIL) receptor DR5 was strongly upregulated on endothelial cells, and TRAIL-specific antibodies effectively blocked CD4 T cell-mediated apoptosis, indicating that T cell-mediated endothelial death was dependent on the TRAIL pathway. Expression of both the activating antigen CD69 and TRAIL was enhanced on ACS T cells. In in-vitro assays rosuvastatin, fluvastatin, and pitavastatin directly blocked CD4 T cell-mediated endothelial cell apoptosis and reduced T cell-expression of CD69 and TRAIL through TCR-induced Extracellar signal-Regulated Kinases (ERK) activation.
Activated CD4 T cells expressing TRAIL are enriched in the blood of ACS patients and induce endothelial injury, which may contribute to the destabilization of the plaque. Early statin therapy may suppress T cell-mediated endothelial cell damage in atherosclerotic plaques and thus prevent cardiovascular events.
Zinc enhances TCR signaling in part by inhibiting Shp-1 recruitment to the TCR synapse.
Zinc is a trace element that is essential for innate and adaptive immune responses. In addition to being a structural element of many proteins, zinc also functions as a neurotransmitter and an intracellular messenger. Temporal or spatial changes in bioavailable zinc may influence the activity of several enzymes, including kinases and phosphatases. We provide evidence that zinc functions as an ionic signaling molecule after T cell activation. Cytoplasmic zinc concentrations increased within 1 min after T cell receptor (TCR) triggering, in particular in the subsynaptic compartment. The increase depended on the extracellular zinc concentrations and was inhibited by silencing zinc transporter Zip6. Increased zinc influx reduced the recruitment of SHP-1 to the TCR activation complex, augmented ZAP70 phosphorylation and sustained calcium influx. By calibrating TCR activation thresholds, increased extracellular zinc bioavailability facilitated the induction of T cell proliferative responses to suboptimal stimuli.