Aberrant reactive oxygen and nitrogen species generation in rheumatoid arthritis (RA): causes and consequences for immune function, cell survival, and therapeutic intervention

Does metabolic reprogramming underpin age-associated changes in T cell phenotype and function?

T cells are required for an effective adaptive immune response. The principal function of T cells is to promote efficient removal of foreign material by identifying and mounting a specific response to nonself. A decline in T cell function in aging is thought to contribute to reduced response to infection and vaccination and an increase in autoimmunity. This may in part be due to the age-related decrease in naïve CD4(+) T cells and increase in antigen-experienced CD4(+) T cells, loss of redox homeostasis, and impaired metabolic switching. Switching between subsets is triggered by the integration of extracellular signals sensed through surface receptors and the activation of discrete intracellular metabolic pathways. This article explores how metabolic programming and loss of redox homeostasis during aging may contribute to age-associated changes in T cell phenotype and function.

Molecular hydrogen: new antioxidant and anti-inflammatory therapy for rheumatoid arthritis and related diseases

Rheumatoid arthritis (RA) is a chronic inflammatory disease in which the progressive destruction of joint causes morbidity. It is also associated with an increased risk of atherosclerosis, which can result in cardiovascular disease and mortality. The therapeutic goal is to control the systemic inflammation to obtain not only the remission of symptoms, but also improve general state of health. Although recent biologic immunosuppressive therapies targeting pro-inflammatory cytokines have spawned a paradigm shift regarding the prognosis of RA, these therapies possess inherent side effects. Also, early diagnosis of the disease remains confounded by uncertainty. While the mechanisms responsible for the onset of RA remain unclear, reactive oxygen species (ROS) play a significant role in the pathogenesis of RA. ROS play a central role both upstream and downstream of NF-κB and TNFα pathways, which are located at the center of the inflammatory response. Among the ROS, the hydroxyl radical is the most harmful, and molecular hydrogen (H2) is a selective scavenger for this species. Recently, it has been shown that H2 is useful when administered along with the conventional therapy in RA as it acts to reduce oxidative stress in the patients. Especially in the early stage, H2 showed significant therapeutic potential, which also seemed to assist diagnosis and treatment decisions of RA. The possible expectations regarding the potential benefits of H2 by reducing the oxidative stress, resulting from inflammatory factors, are raised and discussed here. They include prevention of RA and related atherosclerosis, as well as therapeutic validity for RA

Healthy ageing and depletion of intracellular glutathione influences T cell membrane thioredoxin-1 levels and cytokine secretion

BACKGROUND

During ageing an altered redox balance has been observed in both intracellular and extracellular compartments, primarily due to glutathione depletion and metabolic stress. Maintaining redox homeostasis is important for controlling proliferation and apoptosis in response to specific stimuli for a variety of cells. For T cells, the ability to generate specific response to antigen is dependent on the oxidation state of cell surface and cytoplasmic protein-thiols. Intracellular thiols are maintained in their reduced state by a network of redox regulating peptides, proteins and enzymes such as glutathione, thioredoxins and thioredoxin reductase. Here we have investigated whether any relationship exists between age and secreted or cell surface thioredoxin-1, intracellular glutathione concentration and T cell surface thioredoxin 1 (Trx-1) and how this is related to interleukin (IL)-2 production.

RESULTS

Healthy older adults have reduced lymphocyte surface expression and lower circulating plasma Trx-1 concentrations. Using buthionine sulfoximine to deplete intracellular glutathione in Jurkat T cells we show that cell surface Trx-1 is lowered, secretion of Trx-1 is decreased and the response to the lectin phytohaemagglutinin measured as IL-2 production is also affected. These effects are recapitulated by another glutathione depleting agent, diethylmaleate.

CONCLUSION

Together these data suggest that a relationship exists between the intracellular redox compartment and Trx-1 proteins. Loss of lymphocyte surface Trx-1 may be a useful biomarker of healthy ageing.

Sulforaphane restores cellular glutathione levels and reduces chronic periodontitis neutrophil hyperactivity in vitro

The production of high levels of reactive oxygen species by neutrophils is associated with the local and systemic destructive phenotype found in the chronic inflammatory disease periodontitis. In the present study, we investigated the ability of sulforaphane (SFN) to restore cellular glutathione levels and reduce the hyperactivity of circulating neutrophils associated with chronic periodontitis. Using differentiated HL60 cells as a neutrophil model, here we show that generation of extracellular O2 (. -) by the nicotinamide adenine dinucleotide (NADPH) oxidase complex is increased by intracellular glutathione depletion. This may be attributed to the upregulation of thiol regulated acid sphingomyelinase driven lipid raft formation. Intracellular glutathione was also lower in primary neutrophils from periodontitis patients and, consistent with our previous findings, patients neutrophils were hyper-reactive to stimuli. The activity of nuclear factor erythroid-2-related factor 2 (Nrf2), a master regulator of the antioxidant response, is impaired in circulating neutrophils from chronic periodontitis patients. Although patients' neutrophils exhibit a low reduced glutathione (GSH)/oxidised glutathione (GSSG) ratio and a higher total Nrf2 level, the DNA-binding activity of nuclear Nrf2 remained unchanged relative to healthy controls and had reduced expression of glutamate cysteine ligase catalytic (GCLC), and modifier (GCLM) subunit mRNAs, compared to periodontally healthy subjects neutrophils. Pre-treatment with SFN increased expression of GCLC and GCM, improved intracellular GSH/GSSG ratios and reduced agonist-activated extracellular O2 (. -) production in both dHL60 and primary neutrophils from patients with periodontitis and controls. These findings suggest that a deficiency in Nrf2-dependent pathways may underpin susceptibility to hyper-reactivity in circulating primary neutrophils during chronic periodontitis.

Resolution of inflammation: mechanisms and opportunity for drug development

Inflammation is a beneficial host reaction to tissue damage and has the essential primary purpose of restoring tissue homeostasis. Inflammation plays a major role in containing and resolving infection and may also occur under sterile conditions. The cardinal signs of inflammation dolor, calor, tumor and rubor are intrinsically associated with events including vasodilatation, edema and leukocyte trafficking into the site of inflammation. If uncontrolled or unresolved, inflammation itself can lead to further tissue damage and give rise to chronic inflammatory diseases and autoimmunity with eventual loss of organ function. It is now evident that the resolution of inflammation is an active continuous process that occurs during an acute inflammatory episode. Successful resolution requires activation of endogenous programs with switch from production of pro-inflammatory towards pro-resolving molecules, such as specific lipid mediators and annexin A1, and the non-phlogistic elimination of granulocytes by apoptosis with subsequent removal by surrounding macrophages. These processes ensure rapid restoration of tissue homeostasis. Here, we review recent advances in the understanding of resolution of inflammation, highlighting the pharmacological strategies that may interfere with the molecular pathways which control leukocyte survival and clearance. Such strategies have proved beneficial in several pre-clinical models of inflammatory diseases, suggesting that pharmacological modulation of the resolution process may be useful for the treatment of chronic inflammatory diseases in humans.

Apoptosis of rheumatoid arthritis fibroblast-like synoviocytes: possible roles of nitric oxide and the thioredoxin 1

Rheumatoid arthritis is a chronic inflammatory disease characterized by synovial hyperplasia and progressive joint destruction. The impaired apoptosis of rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS) is pivotal in this process. However, the molecular mechanisms responsible for the reduced apoptosis are not fully understood. Both nitric oxide and thioredoxin 1 as two important mediators are widely investigated in the pathogenesis of rheumatoid arthritis. Interestingly, studies have showed that thioredoxin 1 may serve as a master regulator of S-nitrosylation of caspase-3 to fine-tune apoptosis in vivo. Thus, it is anticipated that further investigations on the role of thioredoxin 1 in the S-nitrosylation and denitrosylation of caspase-3 in RA-FLS will likely provide a novel understanding of mechanisms implicated in the impaired apoptosis of RA-FLS. In this paper, we will provide an overview on pathways involved in the reduced apoptosis of RA-FLS and then discuss specially the possible roles of nitric oxide and the thioredoxin 1 redox system associated with apoptosis of RA-FLS.

Detection and isolation of human serum autoantibodies that recognize oxidatively modified autoantigens

The breakdown of human immune tolerance to self-proteins occurs by a number of mechanisms, including posttranslational modifications of host molecules by reactive oxygen, nitrogen, or chlorine species. This has led to great interest in detecting serum autoantibodies raised against small quantities of oxidatively modified host proteins in patients with autoimmune inflammatory diseases, such as rheumatoid arthritis. Here, we provide protocols for the preparation and chemical characterization of oxidatively modified protein antigens and procedures for their use in immunoblotting and ELISAs that detect autoantibodies against these antigens in clinical samples. These gel electrophoresis- and plate reader-based immunochemical methods sometimes suffer from low analytical specificity and/or sensitivity when used for serum autoantibody detection. This is often because a single solid-phase protein (antigen) is exposed to a complex mixture of serum proteins that undergo nonspecific binding. Therefore more sensitive/specific techniques are required to detect autoantibodies specifically directed against oxidatively modified proteins. To address this, we describe novel affinity chromatography protocols by which purified autoantibodies are isolated from small volumes (<1 ml) of serum. We have also developed strategies to conjugate submilligram amounts of isolated immunoglobulins and other proteins to fluorophores. This set of methods will help facilitate the discovery of novel diagnostic autoantibodies in patients.

Carvedilol alleviates adjuvant-induced arthritis and subcutaneous air pouch edema: modulation of oxidative stress and inflammatory mediators

Rheumatoid arthritis (RA) is a systemic inflammatory disease with cardiovascular complications as the leading cause of morbidity. Carvedilol is an adrenergic antagonist which has been safely used in treatment of several cardiovascular disorders. Given that carvedilol has powerful antioxidant/anti-inflammatory properties, we aimed to investigate its protective potential against arthritis that may add further benefits for its clinical usefulness especially in RA patients with concomitant cardiovascular disorders. Two models were studied in the same rat; adjuvant arthritis and subcutaneous air pouch edema. Carvedilol (10mg/kg/day p.o. for 21days) effectively suppressed inflammation in both models with comparable efficacy to the standard anti-inflammatory diclofenac (5mg/kg/day p.o.). Notably, carvedilol inhibited paw edema and abrogated the leukocyte invasion to air pouch exudates. The latter observation was confirmed by the histopathological assessment of the pouch lining that revealed mitigation of immuno-inflammatory cell influx. Carvedilol reduced/normalized oxidative stress markers (lipid peroxides, nitric oxide and protein thiols) and lowered the release of inflammatory cytokines (TNF-α & IL-6), and eicosanoids (PGE2 & LTB4) in sera and exudates of arthritic rats. Interestingly, carvedilol, per se, didn't present any effect on assessed biochemical parameters in normal rats. Together, the current study highlights evidences for the promising anti-arthritic effects of carvedilol that could be mediated through attenuation of leukocyte migration, alleviation of oxidative stress and suppression of proinflammatory cytokines and eicosanoids.

Silicon, a Possible Link between Environmental Exposure and Autoimmune Diseases: The Case of Rheumatoid Arthritis

Silicon is one of the most common chemicals on earth. Several compounds such as silica, asbestos, silicone or, nanoparticles are built from tetrahedral units with silicon as the central atom. Despite these, structural similarities, they have rarely been analyzed as a group. These compounds generate significant biological alterations that include immune hyperactivation, production of the reactive species of oxygen and tissue injury. These pathological processes may trigger autoimmune responses and lead to the development of rheumatoid arthritis. Populations at risk include those that constantly work in industrial process, mining, and agriculture as well as those that undergo silicone implants. Herein a review on the main features of these compounds and how they may induce autoimmune responses is presented.

Heme oxygenase 1 attenuates interleukin-1β-induced cytosolic phospholipase A2 expression via a decrease in NADPH oxidase/reactive oxygen species/activator protein 1 activation in rheumatoid arthritis synovial fibroblasts

OBJECTIVE

Reactive oxygen species (ROS) produced by cytokines induce the expression of inflammatory mediators in rheumatoid arthritis (RA). Heme oxygenase 1 (HO-1) exerts an antiinflammatory effect. The aim of this study was to examine the mechanisms underlying interleukin-1β (IL-1β)-induced cytosolic phospholipase A2 (cPLA2) expression through ROS generation as modulated by HO-1 in RA synovial fibroblasts (RASFs).

METHODS

IL-1β-induced ROS generation was determined by flow cytometry. The involvement of MAPKs and NADPH oxidase (NOX)/ROS in IL-1β-induced cPLA2 expression was investigated using pharmacologic inhibitors and transfection with small interfering RNAs (siRNAs) and was analyzed by Western blotting and promoter assay. Overexpression of HO-1 was performed by transfection of RASFs with a recombinant adenovirus containing human HO-1 plasmid. SCID mice with inflammation caused by IL-1β were infected with adenovirus containing HO-1. Histologic characterization of joint inflammation and local expression of cPLA2 were evaluated after treatment.

RESULTS

IL-1β-induced cPLA2 expression was mediated through NOX activation/ROS production, which was attenuated by N-acetylcysteine (NAC; a scavenger of ROS), the inhibitors of NOX (diphenyleneiodonium chloride and apocynin), MEK-1/2 (U0126), and JNK-1/2 (SP600125), transfection with the respective siRNAs, and the overexpression of HO-1 in RASFs. IL-1β-induced cPLA2 expression was mediated through recruitment of activator protein 1 (AP-1) to the cPLA2 promoter region, which was attenuated by NAC and overexpression of HO-1. Furthermore, HO-1 overexpression inhibited IL-1β-mediated cPLA2 expression in SCID mice.

CONCLUSION

In RASFs, IL-1β induced cPLA2 expression via activation of p42/p44 MAPK and JNK-1/2, leading to p47phox phosphorylation, ROS production, and AP-1 activation. The induction of HO-1 exerted protective effects on the pathogenesis of RA.

Cocoa intake attenuates oxidative stress associated with rat adjuvant arthritis

Cocoa contains flavonoids with antioxidant properties. The aim of this study was to ascertain the effect of cocoa intake on oxidative stress associated with a model of chronic inflammation such as adjuvant arthritis. Female Wistar rats were fed with a 5% or 10% cocoa-enriched diet or were given p.o. a quercetin suspension every other day for 10 days. Arthritis was induced by a heat-killed Mycobacterium butyricum suspension. Reactive oxygen species (ROS) produced by macrophages, and splenic superoxide dismutase (total, cytoplasmic and mitochondrial) and catalase activities were determined. Clinically, joint swelling in arthritic rats was not reduced by antioxidants; however, the 5% cocoa diet and quercetin administration reduced ROS production. Moreover, the 5% cocoa diet normalized the activities of superoxide dismutase and catalase. In conclusion, a cocoa diet reduces the oxidative stress associated with a chronic inflammatory pathology, although it was not enough to attenuate joint swelling.

Measurement and meaning of markers of reactive species of oxygen, nitrogen and sulfur in healthy human subjects and patients with inflammatory joint disease

Reactive species of oxygen, nitrogen and sulfur play cell signalling roles in human health, e.g. recent studies have shown that increased dietary nitrate, which is a source of RNS (reactive nitrogen species), lowers resting blood pressure and the oxygen cost of exercise. In such studies, plasma nitrite and nitrate are readily determined by chemiluminescence. At sites of inflammation, such as the joints of RA (rheumatoid arthritis) patients, the generation of ROS (reactive oxygen species) and RNS overwhelms antioxidant defences and one consequence is oxidative/nitrative damage to proteins. For example, in the inflamed joint, increased RNS-mediated protein damage has been detected in the form of a biomarker, 3-nitrotyrosine, by immunohistochemistry, Western blotting, ELISAs and MS. In addition to NO•, another cell-signalling gas produced in the inflamed joint is H2S (hydrogen sulfide), an RSS (reactive sulfur species). This gas is generated by inflammatory induction of H2S-synthesizing enzymes. Using zinc-trap spectrophotometry, we detected high (micromolar) concentrations of H2S in RA synovial fluid and levels correlated with clinical scores of inflammation and disease activity. What might be the consequences of the inflammatory generation of reactive species? Effects on inflammatory cell-signalling pathways certainly appear to be crucial, but in the current review we highlight the concept that ROS/RNS-mediated protein damage creates neoepitopes, resulting in autoantibody formation against proteins, e.g. type-II collagen and the complement component, C1q. These autoantibodies have been detected in inflammatory autoimmune diseases.

Cyclo(His-Pro) exerts anti-inflammatory effects by modulating NF-κB and Nrf2 signalling

Cyclo(His-Pro) is an endogenous cyclic dipeptide that exerts oxidative damage protection by selectively activating the transcription factor Nrf2 signalling pathway. Given the existence of a tight interplay of the Nrf2/NF-κB systems and that the pro-inflammatory response is governed by transcription factor NF-κB, here we sought to investigate whether and how cyclo(His-Pro) interferes with the cross-talk between the antioxidant Nrf2/heme oxygenase-1 and the pro-inflammatory NF-κB pathways. By knocking down the Nrf2 gene, we confirmed that cyclo(His-Pro) inhibits NF-κB nuclear accumulation induced by paraquat in rat pheochromocytoma PC12 cells via the Nrf2/heme oxygenase-1 pathway. The protection required functional heme oxygenase-1 activity, since zinc protoporphyrin IX, a heme oxygenase-1 inhibitor, prevented NF-κB inhibition, and the presence of exogenous carbon monoxide and bilirubin afforded cytoprotection against paraquat-induced toxicity by preventing NF-κB activation. Cyclooxygenase-2 and matrix metalloproteinase 3, two gene products governed by NF-κB, were down-regulated by cyclo(His-Pro) and up-regulated in heme oxygenase-1 knock-down cells. We validated the general mechanism underlying the anti-inflammatory effects by treating PC12 and murine microglial BV2 cells with different pro-inflammatory agents. Finally, cyclo(His-Pro) reduced 12-otetradecanoylphorbol-13-acetate-induced oedema in mouse ear inflammation model. Results, by showing that cyclo(His-pro) suppresses the pro-inflammatory NF-κB signalling via the Nrf2-mediated heme oxygenase-1 activation, contribute to the understanding of essential cellular pathways and allow the proposal of cyclo(His-Pro) as an in vivo anti-inflammatory compound.

NOX2 complex-derived ROS as immune regulators

Reactive oxygen species (ROS) are a heterogeneous group of highly reactive molecules that oxidize targets in a biologic system. During steady-state conditions, ROS are constantly produced in the electron-transport chain during cellular respiration and by various constitutively active oxidases. ROS production can also be induced by activation of the phagocyte NADPH oxidase 2 (NOX2) complex in a process generally referred to as an oxidative burst. The induced ROS have long been considered proinflammatory, causing cell and tissue destruction. Recent findings have challenged this inflammatory role of ROS, and today, ROS are also known to regulate immune responses and cell proliferation and to determine T-cell autoreactivity. NOX2-derived ROS have been shown to suppress antigen-dependent T-cell reactivity and remarkably to reduce the severity of experimental arthritis in both rats and mice. In this review, we discuss the role of ROS and the NOX2 complex as suppressors of autoimmunity, inflammation, and arthritis.

Free radicals and redox signalling in T-cells during chronic inflammation and ageing

During chronic inflammation and ageing, the increase in oxidative stress in both intracellular and extracellular compartments is likely to influence local cell functions. Redox changes alter the T-cell proteome in a quantitative and qualitative manner, and post-translational modifications to surface and cytoplasmic proteins by increased reactive species can influence T-cell function. Previously, we have shown that RA (rheumatoid arthritis) T-cells exhibit reduced ROS (reactive oxygen species) production in response to extracellular stimulation compared with age-matched controls, and basal ROS levels [measured as DCF (2′,7′-dichlorofluorescein) fluorescence] are lower in RA T-cells. In contrast, exposing T-cells in vitro to different extracellular redox environments modulates intracellular signalling and enhances cytokine secretion. Together, these data suggest that a complex relationship exists between intra- and extra-cellular redox compartments which contribute to the T-cell phenotype.

Enhancement of Allergen-induced Airway Inflammation by NOX2 Deficiency

Background

NADPH oxidase (NOX) modulates cell proliferation, differentiation and immune response through generation of reactive oxygen species. Particularly, NOX2 is recently reported to be important for regulating Treg cell differentiation of CD4+ T cells.

Methods

We employed ovalbumin-induced airway inflammation in wild-type and NOX2-deficient mice and analyzed tissue histopathology and cytokine profiles.

Results

We investigated whether NOX2-deficiency affects T cell-mediated airway inflammation. Ovalbumin injection which activates T cell-mediated allergic response increased airway inflammation in wild-type mice, as evidenced by increased immune cell infiltration, allergic cytokine expression, and goblet cell hyperplasia in the lung. Interestingly, NOX2 knockout (KO) mice were more susceptible to allergen-induced lung inflammation compared to wild-type mice. Immune cells including neutrophils, lymphocytes, macrophages, and eosinophils were drastically infiltrated into the lung of NOX2 KO mice and mucus secretion was substantially increased in deficiency of NOX2. Furthermore, inflammatory allergic cytokines and eotaxin were significantly elevated in NOX2 KO mice, in accordance with enhanced generation of inflammatory cytokines interleukin-17 and interferon-γ by CD4+ T cells.

Conclusion

These results indicate that NOX2 deficiency favorably produces inflammatory cytokines by T cells and thus increases the susceptibility to severe airway inflammation.

Spontaneous and aging-dependent development of arthritis in NADPH oxidase 2 deficiency through altered differentiation of CD11b+ and Th/Treg cells

Emerging evidence indicates that NADPH oxidase (NOX) and its reactive oxygen species (ROS) products modulate a variety of cellular events, including proliferation, differentiation, and apoptosis. In this study, we investigated the functions of NOX2 and ROS in immune modulation using NOX2 knockout (KO) mice. Interestingly, NOX2 KO mice spontaneously developed arthritis with onset at 6-7 wk of age and high incidence (60%) at 15-18 wk of age. Arthritis severity in NOX2 KO mice was proportionally increased with age and higher in females than in males. Bone destruction was confirmed by microcomputed tomography scanning and histological analyses of joints. Inflammatory factors, including TNF-α, IL-1β, and RANKL, and serum level of anti-type II collagen IgG were significantly increased in NOX2 KO mice. In addition, NOX2 deficiency perturbed the immune system upon aging. NOX2 KO mice demonstrated preferred development of CD11b+Gr-1+ myeloid cells with profound production of proinflammatory cytokines and augmented expression of IL-17 through the activation of STAT3 and RORγt in vivo. NOX2 deficiency increased differentiation of effector Th cells in vitro and decreased CD25+FoxP3+ Treg cells both in vitro and in vivo. Furthermore, adoptive transfer of NOX2-deficient CD4(+) T cells into RAG KO mice increased arthritic inflammation compared with WT cells. These results demonstrated that NOX2 deficiency affected the development of CD11b+ myeloid cells and Th17/Treg cells, and thus promoted inflammatory cytokine production and inflammatory arthritis development, strongly supporting a crucial role for ROS generation in the modulation of Th17/Treg cell development and its related inflammatory immune response upon aging.

Towards a unifying, systems biology understanding of large-scale cellular death and destruction caused by poorly liganded iron: Parkinson's, Huntington's, Alzheimer's, prions, bactericides, chemical toxicology and others as examples

Exposure to a variety of toxins and/or infectious agents leads to disease, degeneration and death, often characterised by circumstances in which cells or tissues do not merely die and cease to function but may be more or less entirely obliterated. It is then legitimate to ask the question as to whether, despite the many kinds of agent involved, there may be at least some unifying mechanisms of such cell death and destruction. I summarise the evidence that in a great many cases, one underlying mechanism, providing major stresses of this type, entails continuing and autocatalytic production (based on positive feedback mechanisms) of hydroxyl radicals via Fenton chemistry involving poorly liganded iron, leading to cell death via apoptosis (probably including via pathways induced by changes in the NF-κB system). While every pathway is in some sense connected to every other one, I highlight the literature evidence suggesting that the degenerative effects of many diseases and toxicological insults converge on iron dysregulation. This highlights specifically the role of iron metabolism, and the detailed speciation of iron, in chemical and other toxicology, and has significant implications for the use of iron chelating substances (probably in partnership with appropriate anti-oxidants) as nutritional or therapeutic agents in inhibiting both the progression of these mainly degenerative diseases and the sequelae of both chronic and acute toxin exposure. The complexity of biochemical networks, especially those involving autocatalytic behaviour and positive feedbacks, means that multiple interventions (e.g. of iron chelators plus antioxidants) are likely to prove most effective. A variety of systems biology approaches, that I summarise, can predict both the mechanisms involved in these cell death pathways and the optimal sites of action for nutritional or pharmacological interventions.

The effect of ageing on macrophage Toll-like receptor-mediated responses in the fight against pathogens

The cellular changes during ageing are incompletely understood yet immune system dysfunction is implicated in the age-related decline in health. The acquired immune system shows a functional decline in ability to respond to new pathogens whereas serum levels of cytokines are elevated with age. Despite these age-associated increases in circulating cytokines, the function of aged macrophages is decreased. Pathogen-associated molecular pattern receptors such as Toll-like receptors (TLRs) are vital in the response of macrophages to pathological stimuli. Here we review the evidence for defective TLR signalling in normal ageing. Gene transcription, protein expression and cell surface expression of members of the TLR family of receptors and co-effector molecules do not show a consistent age-dependent change across model systems. However, there is evidence for impaired downstream signalling events, including inhibition of positive and activation of negative modulators of TLR induced signalling events. In this paper we hypothesize that despite a poor inflammatory response via TLR activation, the ineffective clearance of pathogens by macrophages increases the duration of their activation and contributes to perpetuation of inflammatory responses and ageing.

The discovery of novel experimental therapies for inflammatory arthritis

Conventional and biologic disease-modifying antirheumatic drugs have revolutionized the medical therapy of inflammatory arthritis. However, it remains unclear as to what can be done to treat immune-mediated chronic inflammation after patients become refractory to these therapies or develop serious side-effects and/or infections forcing drug withdrawal. Because of these concerns it is imperative that novel targets be continuously identified and experimental strategies designed to test potential arthritis interventions in vitro, but more importantly, in well-validated animal models of inflammatory arthritis. Over the past few years, sphingosine-1-phosphate, interleukin-7 receptor, spleen tyrosine kinase, extracellular signal-regulated kinase, mitogen-activated protein kinase 5/p38 kinase regulated/activated protein kinase, micro-RNAs, tumor necrosis factor-related apoptosis inducing ligand and the polyubiquitin-proteasome pathway were identified as promising novel targets for potential antiarthritis drug development. Indeed several experimental compounds alter the biological activity of these targets and have shown clinical efficacy in animal models of arthritis. A few of them have even entered the first phase of human clinical trials.