Paralysis of CD4(+)CD25(+) regulatory T cell response in chronic autoimmune encephalomyelitis

Adenosine A2A Receptor Signaling in the Immunopathogenesis of Experimental Autoimmune Encephalomyelitis

Our increasing appreciation of adenosine as an endogenous signaling molecule that terminates inflammation has generated excitement regarding the potential to target adenosine receptors (ARs) in the treatment of multiple sclerosis (MS), a disease of chronic neuroinflammation. Of the four G protein-coupled ARs, A2ARs are the principal mediator of adenosine’s anti-inflammatory effects and accordingly, there is a growing body of evidence surrounding the role of A2ARs in experimental autoimmune encephalomyelitis (EAE), the dominant animal model of MS. Such evidence points to a complex, often paradoxical role for A2ARs in the immunopathogenesis of EAE, where they have the ability to both exacerbate and alleviate disease severity. This review seeks to interpret these paradoxical findings and evaluate the therapeutic promise of A2ARs. In essence, the complexities of A2AR signaling arise from two properties. Firstly, A2AR signaling downregulates the inflammatory potential of TH lymphocytes whilst simultaneously facilitating the recruitment of these cells into the CNS. Secondly, A2AR expression by myeloid cells – infiltrating macrophages and CNS-resident microglia – has the capacity to promote both tissue injury and repair in chronic neuroinflammation. Consequently, the therapeutic potential of targeting A2ARs is greatly undermined by the risk of collateral tissue damage in the periphery and/or CNS.

Mechanism of experimental autoimmune encephalomyelitis in Lewis rats: recent insights from macrophages

Experimental autoimmune encephalomyelitis (EAE) in Lewis rats is an acute monophasic paralytic central nervous system disease, in which most rats spontaneously recover from paralysis. EAE in Lewis rats is induced by encephalitogenic antigens, including myelin basic protein. EAE is mediated by CD4⁺ Th1 cells, which secrete pro-inflammatory mediators, and spontaneous recovery is mediated by regulatory T cells. Recently, it was established that classically activated macrophages (M1 phenotype) play an important role in the initiation of EAE, while alternatively activated macrophages (M2 phenotype) contribute to spontaneous recovery from rat EAE. This review will summarize the neuroimmunological aspects of active monophasic EAE, which manifests as neuroinflammation followed by neuroimmunomodulation and/or neuroprotection, with a focus on the role of alternatively activated macrophages.

Recent progress of elucidating the mechanisms of drug hypersensitivity

Recent technical approaches to investigating drug hypersensitivity have provided a great deal of information to solve the mechanisms that remain poorly understood. First, immunological investigations and in silico analysis have revealed that a novel interaction between T cells and antigen-presenting cells, namely the pharmacological interaction concept, is involved in drug recognition and the hapten theory. Second, progress in immunology has provided a new concept of CD4+ T cell subsets. Th17 cells have proven to be a critical player in acute generalized exanthematous pustulosis. Our recent findings suggest that this subset might contribute to the pathogenesis of Stevens-Johnson syndrome/toxic epidermal necrolysis. Third, alarmins, molecules associated with innate immunity, are also associated with exaggeration and the persistence of severe drug hypersensitivity. The latest innovative techniques are providing a new landscape to examine drug hypersensitivity.

Trauma equals danger--damage control by the immune system

Traumatic injuries induce a complex host response that disrupts immune system homeostasis and predisposes patients to opportunistic infections and inflammatory complications. The response to injuries varies considerably by type and severity, as well as by individual variables, such as age, sex, and genetics. These variables make studying the impact of trauma on the immune system challenging. Nevertheless, advances have been made in understanding how injuries influence immune system function as well as the immune cells and pathways involved in regulating the response to injuries. This review provides an overview of current knowledge about how traumatic injuries affect immune system phenotype and function. We discuss the current ideas that traumatic injuries induce a unique type of a response that may be triggered by a combination of endogenous danger signals, including alarmins, DAMPs, self-antigens, and cytokines. Additionally, we review and propose strategies for redirecting injury responses to help restore immune system homeostasis.

Regulatory T cell-mediated control of autoantibody-induced inflammation

Autoimmune inflammation including autoantibody-induced inflammation is responsible for the lethal organ damage. Autoantibody-induced inflammation can be separated in two components, autoantibody production, and local inflammatory responses. Accumulating evidence has suggested that regulatory T cells (Treg) control both antibody production and the numbers and functions of effector cells such as innate cells and T helper cells. Autoantibodies are produced by both the follicular and extrafollicular pathways. Recently, follicular regulatory T cells (T(FR)) and Qa-1 restricted CD8(+) Treg were identified as populations that are capable of suppressing follicular T helper cell (T(FH))-mediated antibody production. In local inflammation, CD4(+)CD25(+)Foxp3(+) Treg have the capacity to control inflammation by suppressing cytokine production in T helper cells. Although complement proteins contribute to autoantibody-induced local inflammation by activating innate cells, Treg including CD4(+)CD25(+)Foxp3(+) Treg are able to suppress innate cells, chiefly via IL-10 production. IL-10-secreting T cells such as T regulatory type I (Tr1) and Tr1-like cells might also play roles in the control of Th17 and innate cells. Therefore, several kinds of Tregs have the potential to control autoimmune inflammation by suppressing both autoantibody production and the local inflammatory responses induced by autoantibodies.

Dynamic interplay of T helpercell subsets in experimental autoimmune encephalomyelitis

AIM: To investigate the temporal onset and dynamic interplay of CD4⁺ T helper cell subsets in experimental autoimmune encephalomyelitis (EAE).

METHODS: EAE was induced in C57BL/6 mice by immunization with myelin oligodendrocyte glycoprotein peptide p35-55. The clinical signs were scored and the tissue samples and immune cells isolated for analysis at different phases of EAE. The expression levels of inflammatory cytokines and related transcription factors were detected by quantitative reverse transcription polymerase chain reaction (PCR) and enzyme linked immunosorbant assay (ELISA). The percentages of Th1, Th17, Th2, Treg and memory T cell subsets in EAE were analyzed by immunostaining and flow cytometry. The data were analyzed by statistical techniques.

RESULTS: Quantitative real-time PCR analysis showed that EAE mice express elevated levels of Th1 [interferon gamma (IFNγ), interleukin (IL)-12p40], Th17 [IL-17, related orphan receptor gamma (RORγ), IL-12p40] and Treg [Foxp3, Epstein-Barr virus induced gene 3 (EBI3), IL-10] genes in the central nervous system at the peak of the disease. Whereas, the expression of Th1 (IFNγ, T-bet, IL-12p35, IL-12p40), Th17 (RORγ, IL-12p40), Th2 (IL-4) and Treg (Foxp3, EBI3) response genes was reduced in the spleen during pre-disease but gradually recovered at the later phases of EAE. ELISA and flow cytometry analyses showed an increase in Th17 response in the periphery, while Th1 response remained unchanged at the peak of disease. The mRNA levels of IFNγ, IL-17 and IL-12p40 in the brain were increased by 23 (P < 0.001), 9 (P < 0.05) and 14 (P < 0.01) fold, respectively, on day 21 of EAE. Conversely, the mRNA expression of IL-10 was increased by 2 fold (P < 0.05) in the spleen on day 21. CD4⁺CD25⁺Foxp3⁺Treg response was reduced at pre-disease but recovered to naïve levels by disease onset. The percentage of CD25⁺Foxp3⁺ regulatory T cells decreased from 7.7% in the naïve to 3.2% (P < 0.05) on day 7 of EAE, which then increased to 8.4% by day 28. Moreover, the CD4⁺CD127⁺CD44^high memory T cell response was increased during the onset and recovery phases of EAE. The memory and effector cells showed an inverse relationship in EAE, where the memory T cells increased from 12.3% in naïve to 20% by day 21, and the effector cells decreased from 32% in naïve to 21% (P < 0.01) by day 21. The wild type C57BL/6 mice with EAE showed elevated levels of effector-memory T cells (T_EM) with concomitant reduction in central-memory T cells (T_CM), but the EAE-resistant IL-7R deficient mice showed elevated T_CM with no effect on T_EM cells in EAE.

CONCLUSION: Our findings highlight the temporal onset and dynamic interplay of effector, memory and regulatory CD4⁺ T cell subsets and its significance to clinical outcome in EAE and other autoimmune diseases.

Immunohistochemical studies on disabled-2 protein in the spinal cords of rats with experimental autoimmune encephalomyelitis

Disabled-2 (Dab-2), an adaptor protein of transforming growth factor beta (TGF-β) signaling, was studied in the spinal cords of rats with experimental autoimmune encephalomyelitis (EAE) to evaluate the possible involvement of Dab-2 in the pathogenesis of EAE using Western blot and immunohistochemical analyses. Western blot analysis showed that two isoforms (p96 kDa and p67 kDa) of Dab-2 were detected in the spinal cords of rats used as controls. Both isoforms of Dab-2 were significantly elevated in the EAE spinal cord at the peak stage of EAE (P<0.05) and declined at the recovery stage. However, only the p96 kDa isoform was markedly phosphorylated in the EAE spinal cord. Immunohistochemistry showed that Dab-2 and p-Dab-2 were detected in some vascular endothelial cells, glial cells, and some neurons in the rat spinal cords of normal and immunized CFA-alone controls. In EAE lesions, Dab-2 and p-Dab-2 were immunodetected in some inflammatory cells (mainly in ED1-positive macrophages and R73-positive T cells), while the enhanced immunoreactivity of Dab-2 in spinal cord cells suggested constitutive expression. Additionally, TGF-β1 immunoreactivity showed a similar expression pattern of Dab-2 in EAE lesions. These findings suggest that Dab-2 is transiently upregulated and phosphorylated (particularly the p96 kDa isoform) in EAE, a CNS autoimmune disease, and may be involved in TGF-β signaling.

Tissue concentration changes of amino acids and biogenic amines in the central nervous system of mice with experimental autoimmune encephalomyelitis (EAE)

We have characterized the changes in tissue concentrations of amino acids and biogenic amines in the central nervous system (CNS) of mice with MOG(35-55)-induced experimental autoimmune encephalomyelitis (EAE), an animal model commonly used to study multiple sclerosis (MS). High performance liquid chromatography was used to analyse tissue samples from five regions of the CNS at the onset, peak and chronic phase of MOG(35-55) EAE. Our analysis includes the evaluation of several newly examined amino acids including d-serine, and the inter-relations between the intraspinal concentration changes of different amino acids and biogenic amines during EAE. Our results confirm many of the findings from similar studies using different variants of the EAE model as well as those examining changes in amino acid and biogenic amine levels in the cerebrospinal fluid (CSF) of MS patients. However, several notable differences were observed between mice with MOG(35-55)-induced EAE with findings from human studies and other EAE models. In addition, our analysis has identified strong correlations between different amino acids and biogenic amines that appear to change in two distinct groups during EAE. Group I analyte concentrations are increased at EAE onset and peak but then decrease in the chronic phase with a large degree of variability. Group II is composed of amino acids and biogenic amines that change in a progressive manner during EAE. The altered levels of these amino acids and biogenic amines in the disease may represent a critical pathway leading to neurodegenerative processes that are now recognized to occur in EAE and MS.

Characterization of relapsing-remitting and chronic forms of experimental autoimmune encephalomyelitis in C57BL/6 mice

Multiple sclerosis (MS) is an autoimmune, demyelinating disease of the central nervous system (CNS). Like MS, the animal model experimental autoimmune encephalomyelitis (EAE) is characterized by CNS inflammation and demyelination and can follow a relapsing-remitting (RR) or chronic (CH) disease course. The molecular and pathological differences that underlie these different forms of EAE are not fully understood. We have compared the differences in RR- and CH-EAE generated in the same mouse strain (C57BL/6) using the same antigen. At the peak of disease when mice in both groups have similar clinical scores, CH-EAE is associated with increased lesion burden, myelin loss, axonal damage, and chemokine/cytokine expression when compared with RR-EAE. We further showed that inflammation and myelin loss continue to worsen in later stages of CH-EAE, whereas these features are largely resolved at the equivalent stage in RR-EAE. Additionally, axonal loss at these later stages is more severe in CH-EAE than in RR-EAE. We also demonstrated that CH-EAE is associated with a greater predominance of CD8(+) T cells in the CNS that exhibit MOG(35-55) antigen specificity. These studies therefore showed that, as early as the peak stage of disease, RR- and CH-EAE differ remarkably in their immune cell profile, chemokine/cytokine responses, and histopathological features. These data also indicated that this model of CH-EAE exhibits pathological features of a chronic-progressive disease profile and suggested that the sustained chronic phenotype is due to a combination of axonal loss, myelin loss, and continuing inflammation.

CCR6 regulates EAE pathogenesis by controlling regulatory CD4+ T-cell recruitment to target tissues

The T-cell subsets, characterized by their cytokine production profiles and immune regulatory functions, depend on correct in vivo location to interact with accessory or target cells for effective immune responses. Differentiation of naive CD4(+) T cells into effectors is accompanied by sequentially regulated expression of the chemokine receptors responsible for cell recruitment to specific tissues. We studied CCR6 function in EAE, a CD4(+) T-cell-mediated CNS disease characterized by mononuclear infiltration and demyelination. CCR6(-/-) mice showed an altered time course of EAE development, with delayed onset, a higher clinical score, and more persistent symptoms than in controls. An imbalanced cytokine profile and reduced Foxp3(+) cell frequency characterized CNS tissues from CCR6(-/-) compared with CCR6(+/+) mice during the disease effector phase. Transfer of CCR6(+/+) Treg to CCR6(-/-) mice the day before EAE induction reduced the clinical score associated with an increased in infiltrating Foxp3(+) cells and recovery of the cytokine balance in CCR6(-/-) mouse CNS. Competitive assays between CCR6(+/+) and CCR6(-/-) Treg adoptively transferred to CCR6(-/-) mice showed impaired ability of CCR6(-/-) Treg to infiltrate CNS tissues in EAE-affected mice. Our data indicate a CCR6 requirement by CD4(+) Treg to downregulate the CNS inflammatory process and neurological signs associated with EAE.

CCR2+Ly-6Chi monocytes are crucial for the effector phase of autoimmunity in the central nervous system

The chemokine receptor CCR2 plays a vital role for the induction of autoimmunity in the central nervous system. However, it remains unclear how the pathogenic response is mediated by CCR2-bearing cells. By combining bone marrow chimerism with gene targeting we detected a mild disease-modulating role of CCR2 during experimental autoimmune encephalomyelitis, a model for central nervous system autoimmunity, on radio-resistant cells that was independent from targeted CCR2 expression on endothelia. Interestingly, absence of CCR2 on lymphocytes did not influence autoimmune demyelination. In contrast, engagement of CCR2 on accessory cells was required for experimental autoimmune encephalomyelitis induction. CCR2+Ly-6Chi monocytes were rapidly recruited to the inflamed central nervous system and were crucial for the effector phase of disease. Selective depletion of this specific monocyte subpopulation through engagement of CCR2 strongly reduced central nervous system autoimmunity. Collectively, these data indicate a disease-promoting role of CCR2+Ly-6Chi monocytes during autoimmune inflammation of the central nervous system.

Increased X-linked inhibitor of apoptosis protein (XIAP) expression exacerbates experimental autoimmune encephalomyelitis (EAE)

Dysregulated apoptotic signaling has been implicated in most forms of cancer and many autoimmune diseases, such as multiple sclerosis (MS). We have previously shown that the anti-apoptotic protein X-linked inhibitor of apoptosis (XIAP) is elevated in T cells from mice with experimental autoimmune encephalomyelitis (EAE). In MS and EAE, the failure of autoimmune cells to undergo apoptosis is thought to exacerbate clinical symptoms and contribute to disease progression and CNS tissue damage. Antisense-mediated knockdown of XIAP, in vivo, increases the susceptibility of effector T cells to apoptosis, thus attenuating CNS inflammation and thereby alleviating the clinical signs of EAE. We report for the first time, generation of transgenic mice whereby the ubiquitin promoter drives expression of XIAP (ubXIAP), resulting in increased XIAP expression in a variety of tissues, including cells comprising the immune system. Transgenic ubXIAP mice and wild-type (WT) littermates were immunized with myelin oligodendrocyte glycoprotein (MOG35-55) in complete Freund's adjuvant and monitored daily for clinical symptoms of EAE over a 21-day period. The severity of EAE was increased in ubXIAP mice relative to WT-littermates, suggesting that XIAP overexpression enhanced the resistance of T cells to apoptosis. Consistent with this finding, T cells derived from MOG35-55-immunized ubXIAP mice and cultured in the presence of antigen were more resistant to etoposide-mediated apoptosis compared to WT-littermates. This work identifies XIAP is an important apoptotic regulator in EAE and a potential pharmacological target for treating autoimmune diseases such as MS.

Frequency of Foxp3+CD4CD25+ T cells is associated with the phenotypes of allergic asthma

BACKGROUND AND OBJECTIVE

A forkhead/winged-helix family transcriptional repressor, Foxp3, is highly expressed on CD4(+)CD25(+) T regulatory cells. The role of Foxp3(+)CD4(+)CD25(+) T regulatory cells in asthma remains to be elucidated. Using mouse models and peripheral blood mononuclear cells (PBMC) from subjects with allergic asthma, we aimed to explore whether Foxp3(+)CD4(+)CD25(+) T regulatory cells associate with asthma phenotypes.

METHODS

Foxp3(+)CD4(+)CD25(+) T cells were detected by FACS and the correlation between the frequency of Foxp3(+)CD4(+)CD25(+) T cells and asthma phenotypes was assessed.

RESULTS

The frequency of Foxp3(+)CD4(+)CD25(+) T cells among total CD4(+)CD25(+) T cells in the lungs showed an inverse correlation with eosinophilic inflammation in BALB/c, A/J and C57BL/6 strains. In addition, the frequency of Foxp3(+)CD4(+)CD25(+) T cells was inversely correlated with BHR and allergen-specific IgE levels in the serum of A/J mice. In BALB/c mice, the frequency of Foxp3(+)CD4(+)CD25(+) T cells correlated with the level of IL-10 in BAL fluid. The inverse correlation between the frequency of Foxp3(+)CD4(+)CD25(+) T cells and eosinophilic inflammation disappeared when mice were treated with anti-IL-10 receptor mAb during allergen challenge. Interestingly, intracellular cytokine staining of lung cells revealed that IL-10 was predominantly produced by Foxp3(-)CD4(+)CD25(+) T cells. The frequency of Foxp3(+)CD4(+)CD25(+) T cells among total CD4(+)CD25(+) T cells in PBMC of asthmatics was significantly lower than that of healthy subjects, although there was no significant correlation between the frequency of Foxp3(+)CD4(+)CD25(+) T cells and asthma severity.

CONCLUSIONS

These results suggest a role for lung Foxp3(+)CD4(+)CD25(+) T cells in the regulation of asthma phenotypes, presumably through an IL-10-mediated mechanism.

Regulatory T cells in the control of inflammatory demyelinating diseases of the central nervous system

PURPOSE OF REVIEW

New concepts in fundamental immunology, in particular the identification of a lineage of CD4 T cells endowed with regulatory properties, have revolutionized the understanding of immune-mediated diseases both in experimental models and in humans.

RECENT FINDINGS

The impact of the T regulatory cells, characterized by the expression of CD25 and the foxp3 transcription factor, on the development and remission from central nervous system inflammation, and their therapeutic potential, is being aggressively studied in preclinical animal models. Recent data indicate that the CD4CD25foxp3 T regulatory cells act both at the level of secondary lymphoid organs and in the inflamed central nervous system during experimental autoimmune encephalomyelitis. They contribute to the natural protection against autoimmunity and participate in the spontaneous remission of disease. Their role in multiple sclerosis is still unclear, but convergent data indicate that circulating CD4CD25 T cells from patients with multiple sclerosis exhibit defective regulatory properties. Several disease-modifying therapies act on T regulatory cells and their beneficial effects on multiple sclerosis could, in part, result from this mode of action.

SUMMARY

A better understanding of the induction of T regulatory cells, of their mechanisms of action, and of approaches to manipulate them in vivo may offer new therapeutic opportunities for patients with multiple sclerosis.

The role of regulatory T cells in multiple sclerosis

The dysregulation of inflammatory responses and of immune self-tolerance is considered to be a key element in the autoreactive immune response in multiple sclerosis (MS). Regulatory T (T(REG)) cells have emerged as crucial players in the pathogenetic scenario of CNS autoimmune inflammation. Targeted deletion of T(REG) cells causes spontaneous autoimmune disease in mice, whereas augmentation of T(REG)-cell function can prevent the development of or alleviate variants of experimental autoimmune encephalomyelitis, the animal model of MS. Recent findings indicate that MS itself is also accompanied by dysfunction or impaired maturation of T(REG) cells. The development and function of T(REG) cells is closely linked to dendritic cells (DCs), which have a central role in the activation and reactivation of encephalitogenic cells in the CNS. DCs and T(REG) cells have an intimate bidirectional relationship, and, in combination with other factors and cell types, certain types of DCs are capable of inducing T(REG) cells. Consequently, T(REG) cells and DCs have been recognized as potential therapeutic targets in MS. This Review compiles the current knowledge on the role and function of various subsets of T(REG) cells in MS and experimental autoimmune encephalomyelitis. We also highlight the role of tolerogenic DCs and their bidirectional interaction with T(REG) cells during CNS autoimmunity.

Essential role of CD8+CD122+ regulatory T cells in the recovery from experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is one of the best-documented animal models of autoimmune disease. We examined the role of CD8+CD122+ regulatory T cells, which we previously identified as naturally occurring regulatory T cells that effectively regulate CD8+ T cells, in EAE. Depletion of CD8+CD122+ regulatory T cells by in vivo administration of anti-CD122 mAb resulted in persistent EAE symptoms. Transfer of CD8+CD122+ regulatory T cells into EAE mice at the peak EAE score clearly improved symptoms, indicating an important role of CD8+CD122+ regulatory T cells in the recovery phase of EAE. This was further confirmed by an increase and a decrease in the number of infiltrating T cells in the CNS and T cell cytokine production in mice that were depleted of or complemented with CD8+CD122+ cells. Furthermore, transfer of preactivated CD8+CD122+ regulatory T cells resulted in diminished EAE symptoms, especially in the recovery phase of EAE. These results elucidate the essential role of CD8+CD122+ regulatory T cells in the recovery phase of EAE and suggest the preventive effect of preactivated CD8+CD122+ regulatory T cells for EAE.