Elevated interferon gamma expression in the central nervous system of tumour necrosis factor receptor 1-deficient mice with experimental autoimmune encephalomyelitis

Inflammatory disease status and response to TNF blockade are associated with mechanisms of endotoxin tolerance

The mechanisms of endotoxin tolerance (ET), which down-regulate inflammation, are well described in response to exogenous toll-like receptor ligands, but few studies have focused on ET-associated mechanisms in inflammatory disease. As blocking TNF can attenuate the development of ET, the effect of anti-TNF on the expression of key ET-associated molecules in inflammatory auto-immune disease was measured; changes in inflammatory gene expression were confirmed using an ET bioassay. The expression of immunomodulatory molecules was measured in a murine model of arthritis treated with anti-TNF and the expression of ET-associated molecules was measured in whole blood in rheumatoid arthritis (RA) and ankylosing spondylitis (AS) patients, before and after therapy. The expression of ET-associated genes was also measured in RA patient monocytes before and after therapy, in anti-TNF responders and non-responders. Tnfaip3, Ptpn6 and Irak3 were differentially expressed in affected paws, spleens, lymph nodes and circulating leucocytes in experimental murine arthritis treated with anti-TNF. Prior to therapy, the expression of TNFAIP3, INPP5D, PTPN6, CD38 and SIGIRR in whole blood differed between human healthy controls and RA or AS patients. In blood monocytes from RA patients, the expression of TNFAIP3 was significantly reduced by anti-TNF therapy in non-responders. Prior to therapy, anti-TNF non-responders had higher expression of TNFAIP3 and SLPI, compared to responders. Although the expression of TNFAIP3 was significantly higher in RA non-responders prior to treatment, the post-treatment reduction to a level similar to responders did not coincide with a clinical response to therapy.

Assessment of Mitochondrial Dysfunction in Experimental Autoimmune Encephalomyelitis (EAE) Models of Multiple Sclerosis

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) that involves the autoreactive T-cell attack on axonal myelin sheath. Lesions or plaques formed as a result of repeated damage and repair mechanisms lead to impaired relay of electrical impulses along the nerve, manifesting as clinical symptoms of MS. Evidence from studies in experimental autoimmune encephalomyelitis (EAE) models of MS strongly suggests that mitochondrial dysfunction presents at the onset of disease and throughout the disease course. The aim of this study was to determine if mitochondrial dysfunction occurs before clinical symptoms arise, and whether this is confined to the CNS. EAE was induced in C57B/L6 mice, and citrate synthase and mitochondrial respiratory chain (MRC) complex I–IV activities were assayed at presymptomatic (3 or 10 days post first immunisation (3 or 10 DPI)) and asymptomatic (17 days post first immunisation (17 DPI) time-points in central nervous system (CNS; spinal cord) and peripheral (liver and jaw muscle) tissues. Samples from animals immunised with myelin oligodendrocyte glycoprotein (MOG) as EAE models were compared with control animals immunised with adjuvant (ADJ) only. Significant changes in MOG compared to control ADJ animals in MRC complex I activity occurred only at presymptomatic stages, with an increase in the spinal cord at 10 DPI (87.9%), an increase at 3 DPI (25.6%) and decrease at 10 DPI (22.3%) in the jaw muscle, and an increase in the liver at 10 DPI (71.5%). MRC complex II/III activity changes occurred at presymptomatic and the asymptomatic stages of the disease, with a decrease occurring in the spinal cord at 3 DPI (87.6%) and an increase at 17 DPI (36.7%), increase in the jaw muscle at 10 DPI (25.4%), and an increase at 3 DPI (75.2%) and decrease at 17 DPI (95.7%) in the liver. Citrate synthase activity was also significantly decreased at 10 DPI (27.3%) in the liver. No significant changes were observed in complex IV across all three tissues assayed. Our findings reveal evidence that mitochondrial dysfunction is present at the asymptomatic stages in the EAE model of MS, and that the changes in MRC enzyme activities are tissue-specific and are not confined to the CNS.

The Interaction between Viral and Environmental Risk Factors in the Pathogenesis of Multiple Sclerosis

Multiple sclerosis (MS) is a chronic debilitating inflammatory disease of unknown ethology targeting the central nervous system (CNS). MS has a polysymptomatic onset and is usually first diagnosed between the ages of 20–40 years. The pathology of the disease is characterized by immune mediated demyelination in the CNS. Although there is no clinical finding unique to MS, characteristic symptoms include sensory symptoms visual and motor impairment. No definitive trigger for the development of MS has been identified but large-scale population studies have described several epidemiological risk factors for the disease. This list is a confusing one including latitude, vitamin D (vitD) levels, genetics, infection with Epstein Barr Virus (EBV) and endogenous retrovirus (ERV) reactivation. This review will look at the evidence for each of these and the potential links between these disparate risk factors and the known molecular disease pathogenesis to describe potential hypotheses for the triggering of MS pathology.

Cytokine Signaling in Multiple Sclerosis and Its Therapeutic Applications

Multiple sclerosis (MS) is one of the most common neurological disorders in young adults. The etiology of MS is not known but it is widely accepted that it is autoimmune in nature. Disease onset is believed to be initiated by the activation of CD4+ T cells that target autoantigens of the central nervous system (CNS) and their infiltration into the CNS, followed by the expansion of local and infiltrated peripheral effector myeloid cells that create an inflammatory milieu within the CNS, which ultimately lead to tissue damage and demyelination. Clinical studies have shown that progression of MS correlates with the abnormal expression of certain cytokines. The use of experimental autoimmune encephalomyelitis (EAE) model further delineates the role of these cytokines in neuroinflammation and the therapeutic potential of manipulating their biological activity in vivo. In this review, we will first present an overview on cytokines that may contribute to the pathogenesis of MS or EAE, and provide successful examples and roadblock of translating data obtained from EAE to MS. We will then focus in depth on recent findings that demonstrate the pathological role of granulocyte-macrophage colony-stimulating factor (GM-CSF) in MS and EAE, and briefly discuss the potential of targeting effector myeloid cells as a treatment strategy for MS.

T Lymphocytes and Inflammatory Mediators in the Interplay between Brain and Blood in Alzheimer's Disease: Potential Pools of New Biomarkers

Alzheimer's disease (AD) is a chronic neurodegenerative disorder and the main cause of dementia. The disease is among the leading medical concerns of the modern world, because only symptomatic therapies are available, and no reliable, easily accessible biomarkers exist for AD detection and monitoring. Therefore extensive research is conducted to elucidate the mechanisms of AD pathogenesis, which seems to be heterogeneous and multifactorial. Recently much attention has been given to the neuroinflammation and activation of glial cells in the AD brain. Reports also highlighted the proinflammatory role of T lymphocytes infiltrating the AD brain. However, in AD molecular and cellular alterations involving T cells and immune mediators occur not only in the brain, but also in the blood and the cerebrospinal fluid (CSF). Here we review alterations concerning T lymphocytes and related immune mediators in the AD brain, CSF, and blood and the mechanisms by which peripheral T cells cross the blood brain barrier and the blood-CSF barrier. This knowledge is relevant for better AD therapies and for identification of novel biomarkers for improved AD diagnostics in the blood and the CSF. The data will be reviewed with the special emphasis on possibilities for development of AD biomarkers.

Stage-Specific Role of Interferon-Gamma in Experimental Autoimmune Encephalomyelitis and Multiple Sclerosis

The role of interferon (IFN)-γ in multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), has remained as an enigmatic paradox for more than 30 years. Several studies attribute this cytokine a prominent proinflammatory and pathogenic function in these pathologies. However, accumulating evidence shows that IFN-γ also plays a protective role inducing regulatory cell activity and modulating the effector T cell response. Several innate and adaptive immune cells also develop opposite functions strongly associated with the production of IFN-γ in EAE. Even the suppressive activity of different types of regulatory cells is dependent on IFN-γ. Interestingly, recent data supports a stage-specific participation of IFN-γ in EAE providing a plausible explanation for previous conflicting results. In this review, we will summarize and discuss such literature, emphasizing the protective role of IFN-γ on immune cells. These findings are fundamental to understand the complex role of IFN-γ in the pathogenesis of these diseases and can provide basis for potential stage-specific therapy for MS targeting IFN-γ-signaling or IFN-γ-producing immune cells.

CD4 T cells in immunity and immunotherapy of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, with prevalence progressively increasing with aging. Pathological hallmarks of the disease include accumulation of amyloid β-protein (Aβ) peptides and neurofibrillary tangles in the brain associated with glial activation and synaptotoxicity. In addition, AD involves peripheral and brain endogenous inflammatory processes that appear to enhance disease progression. More than a decade ago a new therapeutic paradigm emerged for AD, namely the activation of the adaptive immune system directly against the self-peptide Aβ, aimed at lowering its accumulation in the brain. This was the first time that a brain peptide was used to vaccinate human subjects in a manner similar to classic viral or bacterial vaccines. The vaccination approach has taken several forms, from initially active to passive and then back to modified active vaccines. As the first two approaches to date failed to show sufficient efficacy, the last is presently being evaluated in ongoing clinical trials. The present review summarizes the immunogenic characteristics of Aβ in humans and mice and discusses past, present and future Aβ-based immunotherapeutic approaches for AD. We emphasize potential pathogenic and beneficial roles of CD4 T cells in light of the pathogenesis and the general decline in T-cell responsiveness evident in the disease.

T cells specifically targeted to amyloid plaques enhance plaque clearance in a mouse model of Alzheimer's disease

Patients with Alzheimer's disease (AD) exhibit substantial accumulation of amyloid-β (Aβ) plaques in the brain. Here, we examine whether Aβ vaccination can facilitate the migration of T lymphocytes to specifically target Aβ plaques and consequently enhance their removal. Using a new mouse model of AD, we show that immunization with Aβ, but not with the encephalitogenic proteolipid protein (PLP), results in the accumulation of T cells at Aβ plaques in the brain. Although both Aβ-reactive and PLP-reactive T cells have a similar phenotype of Th1 cells secreting primarily IFN-γ, the encephalitogenic T cells penetrated the spinal cord and caused experimental autoimmune encephalomyelitis (EAE), whereas Aβ T cells accumulated primarily at Aβ plaques in the brain but not the spinal cord and induced almost complete clearance of Aβ. Furthermore, while a single vaccination with Aβ resulted in upregulation of the phagocytic markers triggering receptors expressed on myeloid cells-2 (TREM2) and signal regulatory protein-β1 (SIRPβ1) in the brain, it caused downregulation of the proinflammatory cytokines TNF-α and IL-6. We thus suggest that Aβ deposits in the hippocampus area prioritize the targeting of Aβ-reactive but not PLP-reactive T cells upon vaccination. The stimulation of Aβ-reactive T cells at sites of Aβ plaques resulted in IFN-γ-induced chemotaxis of leukocytes and therapeutic clearance of Aβ.

GM-CSF-facilitated dendritic cell recruitment and survival govern the intestinal mucosal response to a mouse enteric bacterial pathogen

Granulocyte-macrophage colony-stimulating factor (GM-CSF) promotes dendritic cell (DC) differentiation and survival in vitro. However, its role in host defense at the intestinal mucosa is unknown. We report that infection with the mouse enteric pathogen, Citrobacter rodentium, increased colonic GM-CSF production and CD11c(+) DC recruitment. After infection, GM-CSF(-/-) mice had fewer mucosal CD11c(+) DCs, greater bacterial burden, increased mucosal inflammation and systemic spread of infection, decreased antibody responses, and delayed pathogen clearance. This defective mucosal response was rescued by GM-CSF administration to GM-CSF(-/-) mice and mimicked by CD11c(+) DC depletion in wild-type animals. Diminished mucosal DC numbers in infected GM-CSF(-/-) mice reflected decreased DC recruitment and survival, with the recruitment defect being related to a failure to upregulate epithelial cell production of the DC chemoattractant, CCL22. Thus, GM-CSF produced in the intestinal mucosa acts to enhance host protection against an enteric bacterial pathogen through regulating recruitment and survival of DCs.

Elevated ATG5 expression in autoimmune demyelination and multiple sclerosis

Multiple sclerosis (MS) is an inflammatory central nervous system (CNS) disorder characterized by T cell-mediated demyelination. In MS, prolonged T cell survival and increased T cell proliferation have been linked to disease relapse and progression. Recently, the autophagy-related gene 5 (Atg5) has been shown to modulate T cell survival. In this study, we examined the expression of Atg5 using both a mouse model of autoimmune demyelination as well as blood and brain tissues from MS cases. Quantitative real-time PCR analysis of RNA isolated from blood samples of experimental autoimmune encephalomyelitis (EAE) mice revealed a strong correlation between Atg5 expression and clinical disability.Analysis of protein extracted from these cells confirmed both upregulation and post-translational modification of Atg5, the latter of which was positively correlated with EAE severity. Analysis of RNA extracted from T cells isolated by negative selection indicated that Atg5 expression was significantly elevated in individuals with active relapsing-remitting MS compared to non-diseased controls. Brain tissue sections from relapsing-remitting MS cases examined by immunofluorescent histochemistry suggested that encephalitogenic T cells are a source of Atg5 expression in MS brain samples. Together these data suggest that increased T cell expression of Atg5 may contribute to inflammatory demyelination in MS.

Blockade of tumor necrosis factor in collagen-induced arthritis reveals a novel immunoregulatory pathway for Th1 and Th17 cells

IL-17 is implicated in the pathogenesis of rheumatoid arthritis (RA) and has previously been shown to be induced by tumor necrosis factor (TNF) in vitro. The aim of this study was to assess the impact of TNF inhibition on IL-17 production in collagen-induced arthritis, a model of RA. TNF blockade using TNFR-Fc fusion protein or anti-TNF monoclonal antibody reduced arthritis severity but, unexpectedly, expanded populations of Th1 and Th17 cells, which were shown by adoptive transfer to be pathogenic. Th1 and Th17 cell populations were also expanded in collagen-immunized TNFR p55^−/− but not p75^−/− mice. The expression of IL-12/IL-23 p40 was up-regulated in lymph nodes (LN) from p55^−/− mice, and the expansion of Th1/Th17 cells was abrogated by blockade of p40. Treatment of macrophages with rTNF also inhibited p40 production in vitro. These findings indicate that at least one of the ways in which TNF regulates Th1/Th17 responses in arthritis is by down-regulating the expression of p40. Finally, although TNF blockade increased numbers of Th1 and Th17 cells in LN, it inhibited their accumulation in the joint, thereby providing an explanation for the paradox that anti-TNF therapy ameliorates arthritis despite increasing numbers of pathogenic T cells.

The integrated stress response prevents demyelination by protecting oligodendrocytes against immune-mediated damage

In response to ER stress, the pancreatic endoplasmic reticulum kinase (PERK) coordinates an adaptive program known as the integrated stress response (ISR) by phosphorylating the alpha subunit of eukaryotic translation initiation factor 2 (eIF2alpha). IFN-gamma, which activates the ER stress response in oligodendrocytes, is believed to play a critical role in the immune-mediated CNS disorder multiple sclerosis (MS) and its mouse model, experimental autoimmune encephalomyelitis (EAE). Here we report that CNS delivery of IFN-gamma before EAE onset ameliorated the disease course and prevented demyelination, axonal damage, and oligodendrocyte loss. The beneficial effects of IFN-gamma were accompanied by PERK activation in oligodendrocytes and were abrogated in PERK-deficient animals. Our results indicate that IFN-gamma activation of PERK in mature oligodendrocytes attenuates EAE severity and suggest that therapeutic approaches to activate the ISR could prove beneficial in MS.