Autoaggressive effector T cells in the course of experimental autoimmune encephalomyelitis visualized in the light of two-photon microscopy

The C-C Chemokines CCL17 and CCL22 and Their Receptor CCR4 in CNS Autoimmunity

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS). It affects more than two million people worldwide, mainly young adults, and may lead to progressive neurological disability. Chemokines and their receptors have been shown to play critical roles in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), a murine disease model induced by active immunization with myelin proteins or transfer of encephalitogenic CD4⁺ T cells that recapitulates clinical and neuropathological features of MS. Chemokine ligand-receptor interactions orchestrate leukocyte trafficking and influence multiple pathophysiological cellular processes, including antigen presentation and cytokine production by dendritic cells (DCs). The C-C class chemokines 17 (CCL17) and 22 (CCL22) and their C-C chemokine receptor 4 (CCR4) have been shown to play an important role in homeostasis and inflammatory responses. Here, we provide an overview of the involvement of CCR4 and its ligands in CNS autoimmunity. We review key clinical studies of MS together with experimental studies in animals that have demonstrated functional roles of CCR4, CCL17, and CCL22 in EAE pathogenesis. Finally, we discuss the therapeutic potential of newly developed CCR4 antagonists and a humanized anti-CCR4 antibody for treatment of MS.

Focal transient CNS vessel leak provides a tissue niche for sequential immune cell accumulation during the asymptomatic phase of EAE induction

Peripheral immune cells are critical to the pathogenesis of neurodegenerative diseases including multiple sclerosis (MS) (Hendriks et al., 2005; Kasper and Shoemaker, 2010). However, the precise sequence of tissue events during the early asymptomatic induction phase of experimental autoimmune encephalomyelitis (EAE) pathogenesis remains poorly defined. Due to the spatial-temporal constrains of traditional methods used to study this disease, most studies had been performed in the spine during peak clinical disease; thus the debate continues as to whether tissue changes such as vessel disruption represent a cause or a byproduct of EAE pathophysiology in the cortex. Here, we provide dynamic, high-resolution information on the evolving structural and cellular processes within the gray matter of the mouse cortex during the first 12 asymptomatic days of EAE induction. We observed that transient focal vessel disruptions precede microglia activation, followed by infiltration of and directed interaction between circulating dendritic cells and T cells. Histamine antagonist minimizes but not completely ameliorates blood vessel leaks. Histamine H1 receptor blockade prevents early microglia function, resulting in subsequent reduction in immune cell accumulation, disease incidence and clinical severity.

Autoimmune disease in the brain--how to spot the culprits and how to keep them in check

Current concepts attribute an early and central role for auto-aggressive, myelin-specific T-lymphocytes in the pathogenesis of multiple sclerosis. This view emerged from immunological and pathological findings in experimental autoimmune encephalitis, an animal model characterised by pathological lesions closely resembling the ones found in multiple sclerosis. Furthermore, therapeutic strategies targeting the functions of these encephalitogenic T cells which attenuate their pathogenicity such as glatiramer acetate or anti-VLA4 antibody treatments represent proven approaches in multiple sclerosis. Nonetheless, all therapies evaluated to date either insufficiently dampen down inflammation or completely block immune processes. For this reason, there is a need to identify new therapeutic targets. We have employed live intravital two-photon microscopy to learn more about the behaviour of T cells during the preclinical phase of EAE, when T cells acquire the properties required to invade their target organ. Furthermore, we were able to identify an unexpected locomotive behaviour of T cells at the blood-brain barrier, which occurs immediately before diapedesis and the induction of paralytic disease. Such studies might open new avenues for the treatment of CNS autoimmune diseases. Multiple sclerosis is considered to be an autoimmune disease in which self-reactive T cells enter the central nervous system (CNS) and create an inflammatory milieu that destroys myelin and neurons. Immunomodulatory strategies for the treatment of multiple sclerosis target this process by attempting to inactivate these auto-aggressive T cells. However, so far, these strategies have failed to extinguish disease activity completely. For this reason, there is a need to understand in more detail the mechanisms by which T cells become encephalitogenic, how they enter the nervous system, and what the signals are that guide them along this path. If these processes could be better understood, it may be possible to design more effective and specific therapies for multiple sclerosis. This article will give a brief overview about our recent findings obtained using intravital imaging of autoaggressive effector T cells in an experimental model of multiple sclerosis. This new technological approach might help to fill some gaps in the understanding of autoimmune pathogenesis of multiple sclerosis.

Age dependent course of EAE in Aire-/- mice

This study explores the consequences of deficiency in the autoimmune regulator (Aire) on the susceptibility to experimental autoimmune encephalomyelitis (EAE). Increased susceptibility to EAE was found in Aire knockout (KO) compared to wild type (WT) in 6month old mice. In contrast, 2month old Aire KO mice were less susceptible to EAE than WT mice, and this age-related resistance correlated with elevated proportions of T regulatory (Treg) cells in their spleen and brain. Combined with our previous findings in experimental autoimmune myasthenia gravis, we suggest an age-related association between Aire and Treg cells in the susceptibility to autoimmunity.

Functional immunoimaging: the revolution continues

Ten years ago, in 2002, the introduction of dynamic in vivo imaging to immunologists set a new standard for studying immune responses. In particular, two-photon imaging has provided tremendous insights into immune cell dynamics in various contexts, including infection, cancer, transplantation and autoimmunity. Whereas initial studies were restricted to the migration of and interactions between immune cells, recent advances are bringing intravital imaging to a new level in which cell dynamics and function can be investigated simultaneously. These exciting developments further broaden the applications of immunoimaging and provide unprecedented opportunities to probe and decode immune cell communication in situ.

Increased accumulation of regulatory granulocytic myeloid cells in mannose receptor C type 1-deficient mice correlates with protection in a mouse model of neurocysticercosis

Neurocysticercosis (NCC) is a central nervous system (CNS) infection caused by the metacestode stage of the parasite Taenia solium. During NCC, the parasites release immunodominant glycan antigens in the CNS environment, invoking immune responses. The majority of the associated pathogenesis is attributed to the immune response against the parasites. Glycans from a number of pathogens, including helminths, act as pathogen-associated molecular pattern molecules (PAMPs), which are recognized by pattern recognition receptors (PRRs) known as C-type lectin receptors (CLRs). Using a mouse model of NCC by infection with the related parasite Mesocestoides corti, we have investigated the role of mannose receptor C type 1 (MRC1), a CLR which recognizes high-mannose-containing glycan antigens. Here we show that MRC1(-/-) mice exhibit increased survival times after infection compared with their wild-type (WT) counterparts. The decreased disease severity correlates with reduced levels of expression of markers implicated in NCC pathology, such as interleukin-1β (IL-1β), IL-6, CCL5, and matrix metalloproteinase 9 (MMP9), in addition to induction of an important repair marker, fibroblast growth factor 2 (FGF2). Furthermore, the immune cell subsets that infiltrate the brain of MRC1(-/-) mice are dramatically altered and characterized by reduced numbers of T cells and the accumulation of granulocytic cells with an immune phenotype resembling granulocytic myeloid-dependent suppressor cells (gMDSCs). The results suggest that MRC1 plays a critical role in myeloid plasticity, which in turn affects the adaptive immune response and immunopathogenesis during murine NCC.

Dynamic development of glucocorticoid resistance during autoimmune neuroinflammation

CONTEXT

Glucocorticoids (GC) are powerful endogenous and therapeutic modulators of inflammation and play a critical role for controlling autoimmunity. GC resistance can be seen in patients with cell-mediated autoimmune disorders, but it is unknown whether this represents a stable trait or a state.

OBJECTIVE

The objective of the study was to determine whether GC resistance of T cell responses is dynamically regulated in experimental autoimmune encephalomyelitis (EAE) and multiple sclerosis (MS).

DESIGN

This was a translational observational study. PATIENTS AND ANIMALS: EAE was induced in C57BL/6 mice. A cross-sectional sample of 25 patients with relapsing-remitting MS was included as well as four MS patients during pregnancy and postpartum.

MAIN OUTCOME MEASURES

Outcome measures included GC sensitivity of T cell proliferation and GC-mediated apoptosis.

RESULTS

GC resistance was seen in both autoantigen-specific and nonspecific responses of T cells obtained from mice with EAE. GC resistance preceded clinical symptoms and central nervous system infiltration of immune cells. T cells obtained during EAE were resistant to GC-induced apoptosis, and this was linked to down-regulation of GC receptor-α expression. GC resistance in T cells was also seen in MS patients with radiological evidence for ongoing inflammation. GC resistance was absent in the MS patients during pregnancy, when relapse risk is decreased, but recurred postpartum, a time of increased relapse risk.

CONCLUSIONS

These data demonstrate that GC resistance during autoimmune neuroinflammation is dynamically regulated. This has implications for the timing of steroid treatments and provides a putative pathway to explain the observed association between psychological stress and exacerbation of autoimmune diseases.

Transcriptome analysis of the ependymal barrier during murine neurocysticercosis

BACKGROUND

Central nervous system (CNS) barriers play a pivotal role in the protection and homeostasis of the CNS by enabling the exchange of metabolites while restricting the entry of xenobiotics, blood cells and blood-borne macromolecules. While the blood-brain barrier and blood-cerebrospinal fluid barrier (CSF) control the interface between the blood and CNS, the ependyma acts as a barrier between the CSF and parenchyma, and regulates hydrocephalic pressure and metabolic toxicity. Neurocysticercosis (NCC) is an infection of the CNS caused by the metacestode (larva) of Taenia solium and a major cause of acquired epilepsy worldwide. The common clinical manifestations of NCC are seizures, hydrocephalus and symptoms due to increased intracranial pressure. The majority of the associated pathogenesis is attributed to the immune response against the parasite. The properties of the CNS barriers, including the ependyma, are affected during infection, resulting in disrupted homeostasis and infiltration of leukocytes, which correlates with the pathology and disease symptoms of NCC patients.

RESULTS

In order to characterize the role of the ependymal barrier in the immunopathogenesis of NCC, we isolated ependymal cells using laser capture microdissection from mice infected or mock-infected with the closely related parasite Mesocestoides corti, and analyzed the genes that were differentially expressed using microarray analysis. The expression of 382 genes was altered. Immune response-related genes were verified by real-time RT-PCR. Ingenuity Pathway Analysis (IPA) software was used to analyze the biological significance of the differentially expressed genes, and revealed that genes known to participate in innate immune responses, antigen presentation and leukocyte infiltration were affected along with the genes involved in carbohydrate, lipid and small molecule biochemistry. Further, MHC class II molecules and chemokines, including CCL12, were found to be upregulated at the protein level using immunofluorescence microscopy. This is important, because these molecules are members of the most significant pathways by IPA analyses.

CONCLUSION

Thus, our study indicates that ependymal cells actively express immune mediators and likely contribute to the observed immunopathogenesis during infection. Of particular interest is the major upregulation of antigen presentation pathway-related genes and chemokines/cytokines. This could explain how the ependyma is a prominent source of leukocyte infiltration into ventricles through the disrupted ependymal lining by way of pial vessels present in the internal leptomeninges in murine NCC.

Mechanisms of dendritic cell trafficking across the blood-brain barrier

Although the central nervous system (CNS) is considered to be an immunoprivileged site, it is susceptible to a host of autoimmune as well as neuroinflammatory disorders owing to recruitment of immune cells across the blood-brain barrier into perivascular and parenchymal spaces. Dendritic cells (DCs), which are involved in both primary and secondary immune responses, are the most potent immune cells in terms of antigen uptake and processing as well as presentation to T cells. In light of the emerging importance of DC traficking into the CNS, these cells represent good candidates for targeted immunotherapy against various neuroinflammatory diseases. This review focuses on potential physiological events and receptor interactions between DCs and the microvascular endothelial cells of the brain as they transmigrate into the CNS during degeneration and injury. A clear understanding of the underlying mechanisms involved in DC migration may advance the development of new therapies that manipulate these mechanistic properties via pharmacologic intervention. Furthermore, therapeutic validation should be in concurrence with the molecular imaging techniques that can detect migration of these cells in vivo. Since the use of noninvasive methods to image migration of DCs into CNS has barely been explored, we highlighted potential molecular imaging techniques to achieve this goal. Overall, information provided will bring this important leukocyte population to the forefront as key players in the immune cascade in the light of the emerging contribution of DCs to CNS health and disease.

Pathophysiology of multiple sclerosis and the place of teriflunomide

Significant progress in multiple sclerosis (MS) treatment has been made over the last two decades, including the emergence of disease-modifying therapy (DMT). However, substantial unmet medical need persists and has stimulated the search for new therapeutics. Teriflunomide, one of the several oral DMTs under investigation, is a selective inhibitor of de novo pyrimidine synthesis which exerts a cytostatic effect on proliferating T- and B lymphocytes in the periphery and thus has both antiproliferative and anti-inflammatory properties. Anti-inflammatory effects have been demonstrated in rodent MS models, with reductions in macrophage and B- and T-cell infiltration in the central nervous system and preservation of myelin and oligodendrocytes. Delays in disease onset, reductions in disease relapses and improvements in clinical symptoms were also observed. A proof-of-concept clinical trial in patients with relapsing MS demonstrated that teriflunomide significantly reduced magnetic resonance imaging (MRI) activity and improved clinical endpoints, with both effects maintained with longer-term treatment. Additional studies have shown that teriflunomide can be safely added to beta interferon or glatiramer acetate therapy, with some evidence of additional improvements in MRI disease burden and clinical signs. Teriflunomide has an acceptable and manageable safety and tolerability profile. A large clinical programme is underway to further elucidate the role of teriflunomide in the treatment of MS.

Inhibition of lipopolysaccharide-induced microglia activation by calcitonin gene related peptide and adrenomedullin

Calcitonin gene related peptide (CGRP) and adrenomedullin are potent biologically active peptides that have been proposed to play an important role in vascular and inflammatory diseases. Their function in the central nervous system is still unclear since they have been proposed as either pro-inflammatory or neuroprotective factors. We investigated the effects of the two peptides on astrocytes and microglia, cells of the central nervous system that exert a strong modulatory activity in the neuroinflammatory processes. In particular, we studied the ability of CGRP and adrenomedullin to modulate microglia activation, i.e. its competence of producing and releasing pro-inflammatory cytokines/chemokines that are known to play a crucial role in neuroinflammation. In this work we show that the two neuropeptides exert a potent inhibitory effect on lipopolysaccharide-induced microglia activation in vitro, with strong inhibition of the release of pro-inflammatory mediators (such as NO, cytokines and chemokines). Both CGRP and adrenomedullin are known to promote cAMP elevation, this second messenger cannot fully account for the observed inhibitory effects, thereby suggesting that other signaling pathways are involved. Interestingly, the inhibitory effect of CGRP and adrenomedullin appears to be stimulus specific, since direct activation with pro-inflammatory cytokines was not affected. Our findings clarify aspects of microglia activation, and contribute to the comprehension of the switch from reparative to detrimental function that occurs when glia is exposed to different conditions. Moreover, they draw the attention to potential targets for novel pharmacological intervention in pathologies characterized by glia activation and neuroinflammation.

Mechanisms of T-cell migration across the BBB

Under physiological conditions, the highly specialized BBB strictly limits the entrance of immune cells into the CNS. By contrast, in the course of neuroinflammation such as that observed in multiple sclerosis, circulating T cells readily breach the BBB and initiate a cascade of events culminating in disease onset. Lymphocyte extravasation across the BBB occurs through a sequential multistep process, orchestrated by chemokines and cell adhesion molecules that precisely regulate the dynamic interaction of T cells with the endothelial cells forming the BBB. In this article, we will discuss the molecular players triggering the sophisticated process of T-cell migration across the BBB during pathological conditions.

In vivo real-time multiphoton imaging of T lymphocytes in the mouse brain after experimental stroke

BACKGROUND AND PURPOSE

To gain a better understanding of T cell behavior after stroke, we have developed real-time in vivo brain imaging of T cells by multiphoton microscopy after middle cerebral artery occlusion.

METHODS

Adult male hCD2-GFP transgenic mice that exhibit green fluorescent protein-labeled T cells underwent permanent left distal middle cerebral artery occlusion by electrocoagulation (n=6) or sham surgery (n=6) and then multiphoton laser imaging 72 hours later.

RESULTS

Extravasated T cell number significantly increased after middle cerebral artery occlusion versus sham. Two T cell populations existed after middle cerebral artery occlusion, possibly driven by 2 T cell subpopulations; 1 had significantly lower and the other significantly higher track velocity and displacement rate than sham.

CONCLUSIONS

The different motilities and behaviors of T cells observed using our imaging approach after stroke could reveal important mechanisms of immune surveillance for future therapeutic exploitations.

Trafficking of immune cells in the central nervous system

The CNS is an immune-privileged environment, yet the local control of multiple pathogens is dependent on the ability of immune cells to access and operate within this site. However, inflammation of the distinct anatomical sites (i.e., meninges, cerebrospinal fluid, and parenchyma) associated with the CNS can also be deleterious. Therefore, control of lymphocyte entry and migration within the brain is vital to regulate protective and pathological responses. In this review, several recent advances are highlighted that provide new insights into the processes that regulate leukocyte access to, and movement within, the brain.

Encephalitogenic T-cells increase numbers of CNS T-cells regardless of antigen specificity by both increasing T-cell entry and preventing egress

This study utilized an adoptive transfer model of experimental autoimmune encephalomyelitis (EAE) induction in mice to characterize the mechanisms involved in CNS accumulation of transferred and host T-cells. Using a flow cytometric technique, we examined phenotypic characteristics of CNS T-cells following disease initiation and the role of T-cell activation in CNS invasion and retention. Host T-cell activation increased cell recruitment and EAE severity. CNS antigen specific T-cells were required to induce T-cell retention within the CNS. Once retention was initiated, CNS T-cells were retained regardless of specificity. This study characterizes mechanisms involved in CNS accumulation of T-cells during EAE pathogenesis.

Advances in imaging of new targets for pharmacological intervention in stroke: real-time tracking of T-cells in the ischaemic brain

BACKGROUND AND PURPOSE

T-cells may play a role in the evolution of ischaemic damage and repair, but the ability to image these cells in the living brain after a stroke has been limited. We aim to extend the technique of real-time in situ brain imaging of T-cells, previously shown in models of immunological diseases, to models of experimental stroke.

EXPERIMENTAL APPROACH

Male C57BL6 mice (6-8 weeks) (n= 3) received a total of 2-5 x 10(6) carboxyfluorescein diacetate succinimidyl ester (CFSE)-labelled lymphocytes from donor C57BL6 mice via i.v. injection by adoptive transfer. Twenty-four hours later, recipient mice underwent permanent left distal middle cerebral artery occlusion (MCAO) by electrocoagulation or by sham surgery under isoflurane anaesthesia. Female hCD2-green fluorescent protein (GFP) transgenic mice that exhibit GFP-labelled T-cells underwent MCAO. At 24 or 48 h post-MCAO, a sagittal brain slice (1500 microm thick) containing cortical branches of the occluded middle cerebral artery (MCA) was dissected and used for multiphoton laser scanning microscopy (MPLSM).

KEY RESULTS

Our results provide direct observations for the first time of dynamic T-cell behaviour in living brain tissue in real time and herein proved the feasibility of MPLSM for ex vivo live imaging of immune response after experimental stroke.

CONCLUSIONS AND IMPLICATIONS

It is hoped that these advances in the imaging of immune cells will provide information that can be harnessed to a therapeutic advantage.

CD8+ T cells and neuronal damage: direct and collateral mechanisms of cytotoxicity and impaired electrical excitability

Cytotoxic CD8(+) T cells are increasingly recognized as key players in various inflammatory and degenerative central nervous system (CNS) disorders. CD8(+) T cells are believed to actively contribute to neural damage in these CNS conditions. Conceptually, one can separate two possible ways that CD8(+) T cells harm neuronal function or integrity: CD8(+) T cells either directly target neurons and their neurites in an antigen- or contact-dependent fashion, or exert their action via "collateral" mechanisms of neuronal damage that might follow destruction of the myelin sheath or glial cells in both the CNS gray and white matter. After introducing clinical examples, in which the putative relevance CD8(+) T cells has been demonstrated, we summarize knowledge on the sequence of initiation and execution of CD8(+) T-cell responses in the CNS. This includes the initial antigen cross-presentation and priming of naive CD8(+) T cells, followed by the invasion, migration, and target-cell recognition of CD8(+) effector T cells in the CNS parenchyma. Moreover, we discuss mechanisms of impaired electrical signaling and cell death of neurons as direct and collateral targets of CD8(+) T cells in the CNS.

Imaging effector memory T cells in the ear after induction of adoptive DTH

Delayed type hypersensitivity (DTH) is an immune reaction in which the main players are CCR7(-) effector / memory T lymphocytes. Here, we demonstrate a method for inducing and recording the progress of a DTH reaction in the rat ear. This is followed by a demonstration of the preparation of rat ear tissue for two-photon imaging of the CCR7(-) effector / memory T cell response. An adoptive DTH is induced by the intraperitoneal injection of GFP-labeled Ova-specific CCR7(-) effector / memory T cell line (Beeton, C J. Visualized Experiments, Issue 8). Cells are then allowed to equilibrate in the rat for 48 hours before challenge by injecting one ear with saline (control ear) and the other with a 1:1 mix of Ova and Ova conjugated to Texas-Red (Ova-TR) to allow visualization of resident antigen-presenting cells. We describe a method of tissue preparation useful for imaging the motility of cells within the deep dermal layer during an immune response, in conjunction with visualization of collagen fibers by second harmonic generation. Ear tissue is cut into 5 x 5 mm squares (slightly larger is better) and mounted onto plastic cover slips using Vetbondtrade mark, which are then secured using silicone grease in an imaging chamber and superfused by oxygen-bubbled tissue culture medium at 37 degrees C.