Direct impact of T cells on neurons revealed by two-photon microscopy in living brain tissue

Inflammatory processes in the prefrontal cortex induced by systemic immune challenge: Focusing on neurons

Peripheral immune challenge induces neurobiological alterations in the brain and related neuropsychiatric symptoms both in humans and other mammals. One of the best known physiological effects of systemic inflammation is sickness behavior. However, in addition to this depression-like state, there are other cognitive outcomes of peripherally induced neuroinflammation that can be linked to the dysfunction of higher-order cortical areas, such as the prefrontal cortex (PFC). As the physiological activity of the PFC is largely based on the balanced interplay of excitatory pyramidal cells and inhibitory interneurons, it may be hypothesized that neuroinflammatory processes result in a shift of excitatory/inhibitory balance, which is a common hallmark of several neuropsychiatric conditions. Indeed, many data suggest that peripherally induced neuroinflammation is strongly associated with molecular and functional changes in PFC neurons leading to disturbances in their synaptic networks. Different experimental approaches may cause some incongruence in the reviewed data. However, it is commonly agreed that acute systemic inflammation leads to changes in the excitatory/inhibitory balance in the PFC by proinflammatory signaling at the brain borders and in the brain parenchyma. These cellular changes result in altered local and brain-wide network activity inducing disturbances in the top-down control of goal-directed behavior and cognition regulated by the PFC. Lipopolysaccharide (LPS)-treated rodents are the most widely used experimental models of peripherally induced neuroinflammation, so the majority of the reviewed data come from studies utilizing the LPS model. This may limit their general interpretation regarding the neuronal effects of peripheral immune activation. In addition, several biological variables (e.g., sex, age) can influence the PFC effects of systemic immune challenge, not only the nature and severity of immune activation. Therefore, it would be desirable to investigate inflammation-related neuronal changes in the PFC using other models of systemic inflammation as well, and to focus on the targeted fine-tuning of the affected cell types via common molecular mechanisms of the immune and nervous systems.

Immune response following traumatic spinal cord injury: Pathophysiology and therapies

Traumatic spinal cord injury (SCI) is a devastating condition that is often associated with significant loss of function and/or permanent disability. The pathophysiology of SCI is complex and occurs in two phases. First, the mechanical damage from the trauma causes immediate acute cell dysfunction and cell death. Then, secondary mechanisms of injury further propagate the cell dysfunction and cell death over the course of days, weeks, or even months. Among the secondary injury mechanisms, inflammation has been shown to be a key determinant of the secondary injury severity and significantly worsens cell death and functional outcomes. Thus, in addition to surgical management of SCI, selectively targeting the immune response following SCI could substantially decrease the progression of secondary injury and improve patient outcomes. In order to develop such therapies, a detailed molecular understanding of the timing of the immune response following SCI is necessary. Recently, several studies have mapped the cytokine/chemokine and cell proliferation patterns following SCI. In this review, we examine the immune response underlying the pathophysiology of SCI and assess both current and future therapies including pharmaceutical therapies, stem cell therapy, and the exciting potential of extracellular vesicle therapy.

A new form of axonal pathology in a spinal model of neuromyelitis optica

Neuromyelitis optica is a chronic neuroinflammatory disease, which primarily targets astrocytes and often results in severe axon injury of unknown mechanism. Neuromyelitis optica patients harbour autoantibodies against the astrocytic water channel protein, aquaporin-4 (AQP4-IgG), which induce complement-mediated astrocyte lysis and subsequent axon damage. Using spinal in vivo imaging in a mouse model of such astrocytopathic lesions, we explored the mechanism underlying neuromyelitis optica-related axon injury. Many axons showed a swift and morphologically distinct 'pearls-on-string' transformation also readily detectable in human neuromyelitis optica lesions, which especially affected small calibre axons independently of myelination. Functional imaging revealed that calcium homeostasis was initially preserved in this 'acute axonal beading' state, ruling out disruption of the axonal membrane, which sets this form of axon injury apart from previously described forms of traumatic and inflammatory axon damage. Morphological, pharmacological and genetic analyses showed that AQP4-IgG-induced axon injury involved osmotic stress and ionic overload, but does not appear to use canonical pathways of Wallerian-like degeneration. Subcellular analysis demonstrated remodelling of the axonal cytoskeleton in beaded axons, especially local loss of microtubules. Treatment with the microtubule stabilizer epothilone, a putative therapy approach for traumatic and degenerative axonopathies, prevented axonal beading, while destabilizing microtubules sensitized axons for beading. Our results reveal a distinct form of immune-mediated axon pathology in neuromyelitis optica that mechanistically differs from known cascades of post-traumatic and inflammatory axon loss, and suggest a new strategy for neuroprotection in neuromyelitis optica and related diseases.

Therapeutical Significance of Serpina3n Subsequent Cerebral Ischemia via Cytotoxic Granzyme B Inactivation

Ischemic stroke is a devastating CNS insult with few clinical cures. Poor understanding of underlying mechanistic network is the primary limitation to develop novel curative therapies. Extracellular accumulation of granzyme B subsequent ischemia promotes neurodegeneration. Inhibition of granzyme B can be one of the potent strategies to mitigate neuronal damage. In present study, we investigated the effect of murine Serpina3n and human (homolog) SERPINA3 against cerebral ischemia through granzyme B inactivation. Recombinant Serpina3n/SERPINA3 were expressed by transfected 293 T cells, and eluted proteins were examined for postischemic influence both in vitro and in vivo. During in vitro test, Serpina3n was found effective enough to inhibit granzyme B, while SERPINA3 was ineffectual to counter cytotoxic protease. Treatment of hypoxic culture with recombinant Serpina3n/SERPINA3 significantly increased cell viability in dosage-dependent manner, recorded maximum at the highest concentration (4 mM). Infarct volume analysis confirmed that 50 mg/kg dosage of exogenous Serpina3n was adequate to reduce disease severity, while SERPINA3 lacked behind in analeptic effect. Immunohistochemical test, western blot analysis, and protease activity assay’s results illustrated successful diffusion of applied protein to the ischemic lesion and reactivity with the target protease. Taken together, our findings demonstrate therapeutic potential of Serpina3n by interfering granzyme B-mediated neuronal death subsequent cerebral ischemia.

Teriflunomide Preserves Neuronal Activity and Protects Mitochondria in Brain Slices Exposed to Oxidative Stress

Teriflunomide (TFN) limits relapses in relapsing–remitting multiple sclerosis (RRMS) by reducing lymphocytic proliferation through the inhibition of the mitochondrial enzyme dihydroorotate dehydrogenase (DHODH) and the subsequent modulation of de novo pyrimidine synthesis. Alterations of mitochondrial function as a consequence of oxidative stress have been reported during neuroinflammation. Previously, we showed that TFN prevents alterations of mitochondrial motility caused by oxidative stress in peripheral axons. Here, we aimed to validate TFN effects on mitochondria and neuronal activity in hippocampal brain slices, in which cellular distribution and synaptic circuits are largely preserved. TFN effects on metabolism and neuronal activity were investigated by assessing oxygen partial pressure and local field potential in acute slices. Additionally, we imaged mitochondria in brain slices from the transgenic Thy1-CFP/COX8A)S2Lich/J (mitoCFP) mice using two-photon microscopy. Although TFN could not prevent oxidative stress-related depletion of ATP, it preserved oxygen consumption and neuronal activity in CNS tissue during oxidative stress. Furthermore, TFN prevented mitochondrial shortening and fragmentation of puncta-shaped and network mitochondria during oxidative stress. Regarding motility, TFN accentuated the decrease in mitochondrial displacement and increase in speed observed during oxidative stress. Importantly, these effects were not associated with neuronal viability and did not lead to axonal damage. In conclusion, during conditions of oxidative stress, TFN preserves the functionality of neurons and prevents morphological and motility alterations of mitochondria.

Insights into T-cell dysfunction in Alzheimer's disease

T cells, the critical immune cells of the adaptive immune system, are often dysfunctional in Alzheimer's disease (AD) and are involved in AD pathology. Reports highlight neuroinflammation as a crucial modulator of AD pathogenesis, and aberrant T cells indirectly contribute to neuroinflammation by secreting proinflammatory mediators via direct crosstalk with glial cells infiltrating the brain. However, the mechanisms underlying T‐cell abnormalities in AD appear multifactorial. Risk factors for AD and pathological hallmarks of AD have been tightly linked with immune responses, implying the potential regulatory effects of these factors on T cells. In this review, we discuss how the risk factors for AD, particularly Apolipoprotein E (ApoE), Aβ, α‐secretase, β‐secretase, γ‐secretase, Tau, and neuroinflammation, modulate T‐cell activation and the association between T cells and pathological AD hallmarks. Understanding these associations is critical to provide a comprehensive view of appropriate therapeutic strategies for AD.

The Single-Cell Transcriptomic Analysis of Prefrontal Pyramidal Cells and Interneurons Reveals the Neuronal Expression of Genes Encoding Antimicrobial Peptides and Immune Proteins

The investigation of the molecular background of direct communication of neurons and immune cells in the brain is an important issue for understanding physiological and pathological processes in the nervous system. Direct contacts between brain-infiltrating immune cells and neurons, and the neuromodulatory effect of immune cell-derived regulatory peptides are well established. Several aspects of the role of immune and glial cells in the direct neuro-immune communication are also well known; however, there remain many questions regarding the molecular details of signaling from neurons to immune cells. Thus, we report here on the neuronal expression of genes encoding antimicrobial and immunomodulatory peptides, as well as proteins of immune cell-specific activation and communication mechanisms. In the present study, we analyzed the single-cell sequencing data of our previous transcriptomic work, obtained from electrophysiologically identified pyramidal cells and interneurons of the murine prefrontal cortex. We filtered out the genes that may be associated with the direct communication between immune cells and neurons and examined their expression pattern in the neuronal transcriptome. The expression of some of these genes by cortical neurons has not yet been reported. The vast majority of antimicrobial (~53%) and immune cell protein (~94%) transcripts was identified in the transcriptome of the 84 cells, owing to the high sensitivity of ultra-deep sequencing. Several of the antimicrobial and immune process-related protein transcripts showed cell type-specific or enriched expression. Individual neurons transcribed only a fraction of the investigated genes with low copy numbers probably due to the bursting kinetics of gene expression; however, the comparison of our data with available transcriptomic datasets from immune cells and neurons suggests the functional relevance of the reported findings. Accordingly, we propose further experimental and in silico studies on the neuronal expression of immune system-related genes and the potential role of the encoded proteins in neuroimmunological processes.

Transduction of inflammation from peripheral immune cells to the hippocampus induces neuronal hyperexcitability mediated by Caspase-1 activation

BACKGROUND

Recent studies report infiltration of peripheral blood mononuclear cells (PBMCs) into the central nervous system (CNS) in epileptic disorders, suggestive of a potential contribution of PBMC extravasation to the generation of seizures. Nevertheless, the underlying mechanisms involved in PBMC infiltrates promoting neuronal predisposition to ictogenesis remain unclear. Therefore, we developed an in vitro model mimicking infiltration of activated PBMCs into the brain in order to investigate potential transduction of inflammatory signals from PBMCs to the CNS.

METHODS

To establish our model, we first extracted PBMCs from rat spleen, then, immunologically primed PBMCs with lipopolysaccharide (LPS), followed by further activation with nigericin. Thereafter, we co-cultured these activated PBMCs with organotypic cortico-hippocampal brain slice cultures (OCHSCs) derived from the same rat, and compared PBMC-OCHSC co-cultures to OCHSCs exposed to PBMCs in the culture media. We further targeted a potential molecular pathway underlying transduction of peripheral inflammation to OCHSCs by incubating OCHSCs with the Caspase-1 inhibitor VX-765 prior to co-culturing PBMCs with OCHSCs. After 24 h, we analyzed inflammation markers in the cortex and the hippocampus using semiquantitative immunofluorescence. In addition, we analyzed neuronal activity by whole-cell patch-clamp recordings in cortical layer II/III and hippocampal CA1 pyramidal neurons.

RESULTS

In the cortex, co-culturing immunoreactive PBMCs treated with LPS + nigericin on top of OCHSCs upregulated inflammatory markers and enhanced neuronal excitation. In contrast, no excitability changes were detected after adding primed PBMCs (i.e. treated with LPS only), to OCHSCs. Strikingly, in the hippocampus, both immunoreactive and primed PBMCs elicited similar pro-inflammatory and pro-excitatory effects. However, when immunoreactive and primed PBMCs were cultured in the media separately from OCHSCs, only immunoreactive PBMCs gave rise to neuroinflammation and hyperexcitability in the hippocampus, whereas primed PBMCs failed to produce any significant changes. Finally, VX-765 application to OCHSCs, co-cultured with either immunoreactive or primed PBMCs, prevented neuroinflammation and hippocampal hyperexcitability in OCHSCs.

CONCLUSIONS

Our study shows a higher susceptibility of the hippocampus to peripheral inflammation as compared to the cortex, mediated via Caspase-1-dependent signaling pathways. Thus, our findings suggest that Caspase-1 inhibition may potentially provide therapeutic benefits during hippocampal neuroinflammation and hyperexcitability secondary to peripheral innate immunity.

What Guides Peripheral Immune Cells into the Central Nervous System?

Multiple sclerosis (MS), an immune-mediated demyelinating disease of the central nervous system (CNS), initially presents with a relapsing-remitting disease course. During this early stage of the disease, leukocytes cross the blood–brain barrier to drive the formation of focal demyelinating plaques. Disease-modifying agents that modulate or suppress the peripheral immune system provide a therapeutic benefit during relapsing-remitting MS (RRMS). The majority of individuals with RRMS ultimately enter a secondary progressive disease stage with a progressive accumulation of neurologic deficits. The cellular and molecular basis for this transition is unclear and the role of inflammation during the secondary progressive disease stage is a subject of intense and controversial debate. In this review article, we discuss the following main hypothesis: during both disease stages, peripheral immune cells are triggered by CNS-intrinsic stimuli to invade the brain parenchyma. Furthermore, we outline the different neuroanatomical routes by which peripheral immune cells might migrate from the periphery into the CNS.

Modeling Immunity In Vitro: Slices, Chips, and Engineered Tissues

Modeling immunity in vitro has the potential to be a powerful tool for investigating fundamental biological questions, informing therapeutics and vaccines, and providing new insight into disease progression. There are two major elements to immunity that are necessary to model: primary immune tissues and peripheral tissues with immune components. Here, we systematically review progress made along three strategies to modeling immunity: ex vivo cultures, which preserve native tissue structure; microfluidic devices, which constitute a versatile approach to providing physiologically relevant fluid flow and environmental control; and engineered tissues, which provide precise control of the 3D microenvironment and biophysical cues. While many models focus on disease modeling, more primary immune tissue models are necessary to advance the field. Moving forward, we anticipate that the expansion of patient-specific models may inform why immunity varies from patient to patient and allow for the rapid comprehension and treatment of emerging diseases, such as coronavirus disease 2019.

CD8+ T Cell-Mediated Mechanisms Contribute to the Progression of Neurocognitive Impairment in Both Multiple Sclerosis and Alzheimer's Disease?

Neurocognitive impairment (NCI) is one of the most relevant clinical manifestations of multiple sclerosis (MS). The profile of NCI and the structural and functional changes in the brain structures relevant for cognition in MS share some similarities to those in Alzheimer's disease (AD), the most common cause of neurocognitive disorders. Additionally, despite clear etiopathological differences between MS and AD, an accumulation of effector/memory CD8+ T cells and CD8+ tissue-resident memory T (Trm) cells in cognitively relevant brain structures of MS/AD patients, and higher frequency of effector/memory CD8+ T cells re-expressing CD45RA (TEMRA) with high capacity to secrete cytotoxic molecules and proinflammatory cytokines in their blood, were found. Thus, an active pathogenetic role of CD8+ T cells in the progression of MS and AD may be assumed. In this mini-review, findings supporting the putative role of CD8+ T cells in the pathogenesis of MS and AD are displayed, and putative mechanisms underlying their pathogenetic action are discussed. A special effort was made to identify the gaps in the current knowledge about the role of CD8+ T cells in the development of NCI to "catalyze" translational research leading to new feasible therapeutic interventions.

The LFA-1 antagonist BIRT377 reverses neuropathic pain in prenatal alcohol-exposed female rats via actions on peripheral and central neuroimmune function in discrete pain-relevant tissue regions

Previous reports show that moderate prenatal alcohol exposure (PAE) poses a risk factor for developing neuropathic pain following adult-onset peripheral nerve injury in male rats. Recently, evidence suggests that immune-related mechanisms underlying neuropathic pain in females are different compared to males despite the fact that both sexes develop neuropathy of similar magnitude and duration following chronic constriction injury (CCI) of the sciatic nerve. Data suggest that the actions of peripheral T cells play a greater role in mediating neuropathy in females. The goal of the current study is to identify specificity of immune cell and cytokine changes between PAE and non-PAE neuropathic females by utilizing a well-characterized rodent model of sciatic nerve damage, in an effort to unmask unique signatures of immune-related factors underlying the risk of neuropathy from PAE. Cytokines typically associated with myeloid cell actions such as interleukin (IL)-1β, tumor necrosis factor (TNF), IL-6, IL-4 and IL-10 as well as the neutrophil chemoattractant CXCL1, are examined. In addition, transcription factors and cytokines associated with various differentiated T cell subtypes are examined (anti-inflammatory FOXP3, proinflammatory IL-17A, IL-21, ROR-γt, interferon (IFN)-γ and T-bet). Lymphocyte function associated antigen 1 (LFA-1) is an adhesion molecule expressed on peripheral immune cells including T cells, and regulates T cell activation and extravasation into inflamed tissue regions. A potential therapeutic approach was explored with the goal of controlling proinflammatory responses in neuroanatomical regions critical for CCI-induced allodynia by blocking LFA-1 actions using BIRT377. The data show profound development of hindpaw allodynia in adult non-PAE control females following standard CCI, but not following minor CCI, while minor CCI generated allodynia in PAE females. The data also show substantial increases in T cell-associated proinflammatory cytokine mRNA and proteins, along with evidence of augmented myeloid/glial activation (mRNA) and induction of myeloid/glial-related proinflammatory cytokines, CCL2, IL-1β and TNF in discrete regions along the pain pathway (damaged sciatic nerve, dorsal root ganglia; DRG, and spinal cord). Interestingly, the characteristic anti-inflammatory IL-10 protein response to nerve damage is blunted in neuropathic PAE females. Moreover, T cell profiles are predominantly proinflammatory in neuropathic Sac and PAE females, augmented levels of Th17-specific proinflammatory cytokines IL-17A and IL-21, as well as the Th1-specific factor, T-bet, are observed. Similarly, the expression of RORγt, a critical transcription factor for Th17 cells, is detected in the spinal cord of neuropathic females. Blocking peripheral LFA-1 actions with intravenous (i.v.) BIRT377 reverses allodynia in Sac and PAE rats, dampens myeloid (IL-1β, TNF, CXCL1)- and T cell-associated proinflammatory factors (IL-17A and RORγt) and spinal glial activation. Moreover, i.v. BIRT377 treatment reverses the blunted IL-10 response to CCI observed only in neuropathic PAE rats and elevates FOXP3 in pain-reversed Sac rats. Unexpectedly, intrathecal BIRT377 treatment is unable to alter allodynia in either Sac or PAE neuropathic females. Together, these data provide evidence that: 1) fully differentiated proinflammatory Th17 cells recruited at the sciatic nerve, DRGs and lumbar spinal cord may interact with the local environment to shape the immune responses underlying neuropathy in female rats, and, 2) PAE primes peripheral and spinal immune responses in adult females. PAE is a risk factor in females for developing peripheral neuropathy after minor nerve injury.

Targeting CD52 does not affect murine neuron and microglia function

The humanized anti-CD52 antibody alemtuzumab is successfully used in the treatment of multiple sclerosis (MS) and is thought to exert most of its therapeutic action by depletion and repopulation of mainly B and T lymphocytes. Although neuroprotective effects of alemtuzumab have been suggested, direct effects of anti-CD52 treatment on glial cells and neurons within the CNS itself have not been investigated so far. Here, we show CD52 expression in murine neurons, astrocytes and microglia, both in vitro and in vivo. As expected, anti CD52-treatment caused profound lymphopenia and improved disease symptoms in mice subjected to experimental autoimmune encephalomyelitis (EAE). CD52 blockade also had a significant effect on microglial morphology in organotypic hippocampal slice cultures but did not affect microglial functions. Furthermore, anti-CD52 neither changed baseline neuronal calcium, nor did it act neuroprotective in excitotoxicity models. Altogether, our findings argue against a functionally significant role of CD52 blockade on CNS neurons and microglia. The beneficial effects of alemtuzumab in MS may be exclusively mediated by peripheral immune mechanisms.

A Confocal Reflection Super-Resolution Technique to Image Golgi-Cox Stained Neurons

Metal-based Golgi-Cox (GC) staining is an established method used to visualise neurons with great morphological detail. Although GC stained samples are imaged routinely under transmitted light microscopy, this method is unable to yield information on the three-dimensional structure of dendrites and neurons and thus help reveal the connective properties of the central nervous system. Although a few studies have attempted simultaneous visualisation of GC staining and antigen-specific fluorescent labelling under a confocal reflection technique, the resolution of both confocal reflection and fluorescence modalities used to acquire GC reflection and fluorescently stained antibody signals are still limited by the diffraction limit of light at about 220 nm. Here, we report a confocal reflection super-resolution technique (CRSR) to break this diffraction barrier, which is achieved by minimising the pinhole size from 1 airy unit (AU) to 0.1 AU. This is achieved by minimising or closing the confocal pinhole size and is possible in this reflection modality, unlike fluorescence, because it is not a photon limited technique. Utilising the lowest wavelength of light available in the system (405 nm), the CRSR technique results in ∼30% lateral and axial resolution improvement. We also show that the CRSR technique can be used in conjunction to visualise both GC and immunofluorescence targets to create precise and improved three-dimensional visualisation and analysis. In addition, using these superresolution confocal reflection data sets from GC in CRSR mode significantly reduced the data overestimation, improving the accuracy of statistical analysis of dendritic spine density and average spine dimensions. Combining the 0.1 AU setting with deconvolution routines, the signal-to-noise ratio and resolution could further be improved an additional ∼20-25%, yielding CRSR images with resolutions up to 2-fold over the diffraction limit both laterally and axially. The improved precision of both visualisation and quantification of subdiffraction limited dendritic spines using the CRSR technique may prove to be critical in investigations that concern changes in detailed neuron morphology under central nervous system disease conditions such as multiple sclerosis and Alzheimer's disease. LAY DESCRIPTION: For over a century, Golgi-Cox (GC) has been a leading staining technique in the field of neuroscience, used to visualise neurons with great morphological detail. GC stained brain or spinal cord samples are conventionally visualised under transmitted light techniques. This limits the view of Golgi-staining to a two-dimensional image. A recent report showed that Golgi staining can be visualised in three-dimensions using the reflection modality of the confocal microscope. This visualisation also allows for the simultaneous acquisition of immunofluorescence signals. However, the reported resolution of Golgi staining confocal reflection is limited by the diffraction limit of light, which is around 220 nm. Here, we report a superresolution confocal reflection technique (CRSR) that achieves superresolution by minimising the pinhole size used in confocal microscopy. The CRSR technique results in ∼30% lateral and axial resolution improvement. Adding a deconvolution step in the final processing could improve the SNR and resolution even further up to 2-fold improvement in resolution over the diffraction limit both laterally and axially. We hope that this improved visualisation will help in investigations that concern changes in detailed neuron morphology under central nervous system disease conditions such as multiple sclerosis and Alzheimer's disease.

Low-Dose Maraviroc, an Antiretroviral Drug, Attenuates the Infiltration of T Cells into the Central Nervous System and Protects the Nigrostriatum in Hemiparkinsonian Monkeys

Parkinson's disease (PD) is the most common neurodegenerative movement disorder in humans. Despite intense investigation, no effective therapy is available to stop the progression of this disease. It is becoming clear that both innate and adaptive immune responses are active in PD. Accordingly, we have reported a marked increase in RANTES and eotaxin, chemokines that are involved in T cell trafficking, in vivo in the substantia nigra (SN) and the serum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-intoxicated hemiparkinsonian monkeys. Because RANTES and eotaxin share a common receptor, CCR5, we examined the efficacy of maraviroc, an inhibitor of CCR5 and a Food and Drug Administration-approved drug against HIV infection, in hemiparkinsonian rhesus monkeys. First, we found glial limitans injury, loss of GFAP immunostaining, and infiltration of T cells across the endothelial monolayer in SN of hemiparkinsonian monkeys. However, oral administration of a low dose of maraviroc protected glia limitans partially, maintained the integrity of endothelial monolayer, reduced the infiltration of T cells, attenuated neuroinflammation, and decreased α-synucleinopathy in the SN. Accordingly, maraviroc treatment also protected both the nigrostriatal axis and neurotransmitters and improved motor functions in hemiparkinsonian monkeys. These results suggest that low-dose maraviroc and other CCR5 antagonists may be helpful for PD patients.

Emerging targets for reprograming the immune response to promote repair and recovery of function after spinal cord injury

PURPOSE OF REVIEW

In adult mammals, a traumatic spinal cord injury (SCI) elicits a chronic unregulated neuroinflammatory response accompanied by seemingly paradoxical suppression of systemic immunity. These SCI-induced changes in immune function contribute to poor neurological outcomes and enhanced morbidity or mortality. Nonspecific anti-inflammatory or proinflammatory therapies are ineffective and can even worsen outcomes. Therefore, recent experimental SCI research has advanced the understanding of how neuroimmune cross-talk contributes to spinal cord and systemic pathology.

RECENT FINDINGS

It is now appreciated that the immune response caused by injury to the brain or spinal cord encompasses heterogeneous elements that can drive events on the spectrum between exacerbating pathology and promoting tissue repair, within the spinal cord and throughout the body. Recent novel discoveries regarding the role and regulation of soluble factors, monocytes/macrophages, microRNAs, lymphocytes and systemic immune function are highlighted in this review.

SUMMARY

A more nuanced understanding of how the immune system responds and reacts to nervous system injury will present an array of novel therapeutic opportunities for clinical SCI and other forms of neurotrauma.

The spleen as a neuroimmune interface after spinal cord injury

Traumatic spinal cord injury (SCI) causes widespread damage to neurons, glia and endothelia located throughout the spinal parenchyma. In response to the injury, resident and blood-derived leukocytes orchestrate an intraspinal inflammatory response that propagates secondary neuropathology and also promotes tissue repair. SCI also negatively affects autonomic control over peripheral immune organs, notably the spleen. The spleen is the largest secondary lymphoid organ in mammals, with major roles in blood filtration and host defense. Splenic function is carefully regulated by neuroendocrine mechanisms that ensure that the immune responses to infection or injury are proportionate to the initiating stimulus, and can be terminated when the stimulus is cleared. After SCI, control over the viscera, including endocrine and lymphoid tissues is lost due to damage to spinal autonomic (sympathetic) circuitry. This review begins by examining the normal structure and function of the spleen including patterns of innervation and the role played by the nervous system in regulating spleen function. We then describe how after SCI, loss of proper neural control over splenic function leads to systems-wide neuropathology, immune suppression and autoimmunity. We conclude by discussing opportunities for targeting the spleen to restore immune homeostasis, reduce morbidity and mortality, and improve functional recovery after SCI.

Optic neuritis as a phase 2 paradigm for neuroprotection therapies of multiple sclerosis: update on current trials and perspectives

PURPOSE OF REVIEW

In multiple sclerosis as the most common inflammatory demyelinating disease in Western countries, major therapeutic success has been achieved with regard to strategies targeting immunological master switches. These approaches effectively reduce inflammatory disease activity but fail to address ongoing neurodegeneration or disturbed regeneration. However, intense research efforts investigating molecular mechanisms of disease have identified 'druggable' targets for prevention of inflammatory neurodegeneration and disturbed regeneration. This review covers recent developments in clinical trials using optic neuritis as a model for screening such neuroprotective and neuroregenerative therapeutic approaches.

RECENT FINDINGS

Optic neuritis has been used in a series of recent pilot studies investigating the effects of erythropoietin, simvastatin, autologous mesenchymal stem cells, phenytoin, as well as blockade of LINGO-1 (opicinumab). Of note, these studies applied novel outcome measures related to function and structure of the visual pathway, including optical coherence tomography, full-field visual-evoked potentials, multifocal visual-evoked potential, high as well as low-contrast visual acuity. Comparison of these different approaches reveals novel insights into short-term evolution of neurobiological effects during optic neuritis and the window of opportunity for therapeutic interventions.

SUMMARY

Translation of neuroprotective and neuroregenerative approaches to clinical reality represents a huge challenge. Optic neuritis as a prototypic autoimmune demyelinating disease offers an option for testing new therapies targeting key deleterious processes in multiple sclerosis.

Usefulness of Intravital Multiphoton Microscopy in Visualizing Study of Mouse Cochlea and Volume Changes in the Scala Media

Conventional microscopy has limitations in viewing the cochlear microstructures due to three-dimensional spiral structure and the overlying bone. But these issues can be overcome by imaging the cochlea in vitro with intravital multiphoton microscopy (MPM). By using near-infrared lasers for multiphoton excitation, intravital MPM can detect endogenous fluorescence and second harmonic generation of tissues. In this study, we used intravital MPM to visualize various cochlear microstructures without any staining and non-invasively analyze the volume changes of the scala media (SM) without removing the overlying cochlear bone. The intravital MPM images revealed various tissue types, ranging from thin membranes to dense bone, as well as the spiral ganglion beneath the cochlear bone. The two-dimensional, cross-sectional, and serial z-stack intravital MPM images also revealed the spatial dilation of the SM in the temporal bone of pendrin-deficient mice. These findings suggest that intravital MPM might serve as a new method for obtaining microanatomical information regarding the cochlea, similar to standard histopathological analyses in the animal study for the cochlea. Given the capability of intravital MPM for detecting an increase in the volume of the SM in pendrin-deficient mice, it might be a promising new tool for assessing the pathophysiology of hearing loss in the future.

Induction of Adaptive Immunity Leads to Nigrostriatal Disease Progression in MPTP Mouse Model of Parkinson's Disease

Although the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model is the most widely used animal model for Parkinson's disease (PD), it is known that nigrostriatal pathologies do not persist in the acute MPTP mouse model. This study highlights the importance of adaptive immunity in driving persistent and progressive disease in acute MPTP-intoxicated mice. Although marked infiltration of T cells into the nigra was found on 1 d of MPTP insult, T cell infiltration decreased afterward, becoming normal on 30 d of insult. Interestingly, twice-weekly supplementation of RANTES and eotaxin, chemokines that are involved in T cell trafficking, drove continuous T cell infiltration to the nigra and incessant glial inflammation. Supplementation of RANTES and eotaxin was also associated with the induction of nigral α-synuclein pathology, persistent loss of dopaminergic neurons and striatal neurotransmitters, and continuous impairment of motor functions in MPTP-intoxicated mice. In contrast, supplementation of TNF-α and IL-1β, widely studied proinflammatory cytokines, did not induce persistent disease in MPTP-insulted mice. Our results suggest that induction of adaptive immunity by RANTES and eotaxin could hold the key for driving persistent nigrostriatal pathologies in the MPTP mouse model, and that targeting these factors may halt disease progression in PD patients.

The contribution of oligodendrocytes and oligodendrocyte progenitor cells to central nervous system repair in multiple sclerosis: perspectives for remyelination therapeutic strategies

Oligodencrocytes (OLs) are the main glial cells of the central nervous system involved in myelination of axons. In multiple sclerosis (MS), there is an imbalance between demyelination and remyelination processes, the last one performed by oligodendrocyte progenitor cells (OPCs) and OLs, resulting into a permanent demyelination, axonal damage and neuronal loss. In MS lesions, astrocytes and microglias play an important part in permeabilization of blood-brain barrier and initiation of OPCs proliferation. Migration and differentiation of OPCs are influenced by various factors and the process is finalized by insufficient acummulation of OLs into the MS lesion. In relation to all these processes, the author will discuss the potential targets for remyelination strategies.

Role of Oligodendrocyte Dysfunction in Demyelination, Remyelination and Neurodegeneration in Multiple Sclerosis

Oligodendrocytes (OLs) are the myelinating cells of the central nervous system (CNS) during development and throughout adulthood. They result from a complex and well controlled process of activation, proliferation, migration and differentiation of oligodendrocyte progenitor cells (OPCs) from the germinative niches of the CNS. In multiple sclerosis (MS), the complex pathological process produces dysfunction and apoptosis of OLs leading to demyelination and neurodegeneration. This review attempts to describe the patterns of demyelination in MS, the steps involved in oligodendrogenesis and myelination in healthy CNS, the different pathways leading to OLs and myelin loss in MS, as well as principles involved in restoration of myelin sheaths. Environmental factors and their impact on OLs and pathological mechanisms of MS are also discussed. Finally, we will present evidence about the potential therapeutic targets in re-myelination processes that can be accessed in order to develop regenerative therapies for MS.

B-Cell Depletion with CD20 Antibodies as New Approach in the Treatment of Inflammatory and Immunological Events Associated with Spinal Cord Injury

Spinal cord injury (SCI) is a highly debilitating pathology that has irreversible impacts and results in functional loss. We evaluated the anti-inflammatory and immunologic role of antibody-mediated depletion of B cells through the glycoengineered anti-muCD20 antibody (18B12) in an experimental model of spinal cord compression, in vivo and ex vivo. Intraperitoneal 18B12 was administered at a dose of 30 mg/kg, 1 h and 6 h after SCI, and mice were sacrificed 24 h after trauma. We demonstrated, in vivo, that 18B12 slowed severe hindlimb motor dysfunction (Basso Mouse Scale score) and neuronal death by histological evaluation in SCI mice, as well as decreased expression of nuclear factor-kB, inducible nitric oxide synthase, cytokines, and glial fibrillary acidic protein. Also, 18B12 reduced expression of microglia, just as it lowered the expression of B and T lymphocytes. Moreover, in spinal cord organotypic cultures, pretreatment with 18B12 significantly reduced nitric oxide expression and protected cells from cell death [3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay]. In this study, we showed that 18B12 treatment reduces the development of inflammation and tissue injury by alteration of the immune system associated with SCI. This study increases the current knowledge that B-cell depletion is able to exert immunomodulating actions in damaged spinal cords.

Live Imaging of Influenza Infection of the Trachea Reveals Dynamic Regulation of CD8+ T Cell Motility by Antigen

During a primary influenza infection, cytotoxic CD8+ T cells need to infiltrate the infected airways and engage virus-infected epithelial cells. The factors that regulate T cell motility in the infected airway tissue are not well known. To more precisely study T cell infiltration of the airways, we developed an experimental model system using the trachea as a site where live imaging can be performed. CD8+ T cell motility was dynamic with marked changes in motility on different days of the infection. In particular, significant changes in average cell velocity and confinement were evident on days 8–10 during which the T cells abruptly but transiently increase velocity on day 9. Experiments to distinguish whether infection itself or antigen affect motility revealed that it is antigen, not active infection per se that likely affects these changes as blockade of peptide/MHC resulted in increased velocity. These observations demonstrate that influenza tracheitis provides a robust experimental foundation to study molecular regulation of T cell motility during acute virus infection.

Influenza virus infects the cells that line the trachea and lung airways. Virus-specific cytotoxic (cell killing) T cells are the first line of adaptive immunity responsible for elimination of infected cells. We studied the cell movement, or motility, of these T cells responding to infection in the mouse trachea. Multiphoton live imaging was used to observe the cells in real time in intact tissue and measure their movement both quantitatively and qualitatively. The behavior of the CD8+ T cells responding to influenza infection was highly variable depending on the day after infection the imaging was performed. The most dramatic changes occurred after infectious virus was eliminated from the tissue, triggering a substantial shift in cell motility between days 8 and 9. Blocking peptide/MHC complexes with antibodies reversed cell arrest, increased velocities, and reduced confinement, similar to the changes observed from days 8 to 9. This suggested antigen-presentation persists after virus clearance with continued T cell engagement, and that T cell motility in the infected tissue is dynamically regulated by the infection and the presence of antigen-bearing cells in particular. In addition, these studies establish the trachea as a suitable site for live imaging of immune responses to virus infection.

In vivo imaging in autoimmune diseases in the central nervous system

Intravital imaging is becoming more popular and is being used to visualize cellular motility and functions. In contrast to in vitro analysis, which resembles in vivo analysis, intravital imaging can be used to observe and analyze cells directly in vivo. In this review, I will summarize recent imaging studies of autoreactive T cell infiltration into the central nervous system (CNS) and provide technical background. During their in vivo journey, autoreactive T cells interact with many different cells. At first, autoreactive T cells interact with endothelial cells in the airways of the lung or with splenocytes, where they acquire a migratory phenotype to infiltrate into the CNS. After arriving at the CNS, they interact with endothelial cells of the leptomeningeal vessels or the choroid plexus before passing through the blood-brain barrier. CNS-infiltrating T cells become activated by recognizing endogenous autoantigens presented by local antigen-presenting cells (APCs). This activation was visualized in vivo by using protein-based sensors. One such sensor detects changes in intracellular calcium concentration as an early marker of T cell activation. Another sensor detects translocation of Nuclear factor of activated T-cells (NFAT) from cytosol to nucleus as a definitive sign of T cell activation. Importantly, intravital imaging is not just used to visualize cellular behavior. Together with precise analysis, intravital imaging deepens our knowledge of cellular functions in living organs and also provides a platform for developing therapeutic treatments.

Death Ligands and Autoimmune Demyelination

Death ligands induce apoptosis, which is a cell suicide program leading mainly to selective elimination of an organism's useless cells. Importantly, the dying cell is an active participant in its own demise (“cellular suicide”). Under physiological conditions, apoptosis is most often found during normal cell turnover and tissue homeostasis, embryogenesis, induction and maintenance of immune tolerance, development of the nervous system, and endocrine-dependent tissue atrophy. However, apoptotic processes have also been suggested to contribute to the pathology of the autoimmune demyelinating disease multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis. Here, apoptosis plays a double role. On one hand, impaired apoptosis may result in increased numbers or persistence of activated myelinspecific T cells. On the other hand, local tissue damage involves apoptosis of oligodendrocytes and neurons, leading to the clinical symptoms. In this article, an overview is given of the current knowledge of the roles of apoptosis-mediating and immune regulatory death ligands of the tumor necrosis factor (TNF) family (TNF, lymphotoxin-beta, OX40L [CD134L], CD154 [CD40L], CD95L, CD70 [CD27L], CD153 [CD30L], 4-1BBL [CD137L], TRAIL, TWEAK, BAFF, GITRL) in the pathogenesis of MS and of their implications for related therapeutic strategies.

Tanshinone IIA attenuates experimental autoimmune encephalomyelitis in rats

Multiple sclerosis (MS) is an inflammatory autoimmune neurodegenerative disease, which features focal demyelination and inflammatory cell infiltration of the brain and the spinal cord. Tanshinone IIA (TSIIA), one of the major fat‑soluble components of Salvia miltiorrhiza (Danshen), has anti‑inflammatory, immunoregulatory and neuroprotective activity; however, its efficacy in MS remains unknown. The current study was designed to investigate the potential therapeutic function of TSIIA on MS in the experimental autoimmune encephalomyelitis (EAE) rat model. In comparison to the vehicle control group, the TSIIA‑treated groups showed notably improved clinical symptoms and pathological changes, including central nervous system inflammatory cell infiltration and demyelination. Following administration of TSIIA, the quantity of CD4+ T cells, CD8+ T cells and macrophages/microglia in the spinal cord were reduced to different extents. Furthermore, TSIIA was also shown to downregulate interleukin (IL)‑17 and IL‑23 levels in the brain and serum of EAE rats. The results collectively provide evidence that TSIIA alleviates EAE and support its utility as a novel therapy for MS.

Imaging Axonal Degeneration and Repair in Preclinical Animal Models of Multiple Sclerosis

Multiple sclerosis (MS) is a central nervous system (CNS) disease characterized by chronic neuroinflammation, demyelination, and axonal damage. Infiltration of activated lymphocytes and myeloid cells are thought to be primarily responsible for white matter damage and axonopathy. Over time, this neurologic damage manifests clinically as debilitating motor and cognitive symptoms. Existing MS therapies focus on symptom relief and delay of disease progression through reduction of neuroinflammation. However, long-term strategies to remyelinate, protect, or regenerate axons have remained elusive, posing a challenge to treating progressive forms of MS. Preclinical mouse models and techniques, such as immunohistochemistry, flow cytometry, and genomic and proteomic analysis have provided advances in our understanding of discrete time-points of pathology following disease induction. More recently, in vivo and in situ two-photon (2P) microscopy has made it possible to visualize continuous real-time cellular behavior and structural changes occurring within the CNS during neuropathology. Research utilizing 2P imaging to study axonopathy in neuroinflammatory demyelinating disease has focused on five areas: (1) axonal morphologic changes, (2) organelle transport and health, (3) relationship to inflammation, (4) neuronal excitotoxicity, and (5) regenerative therapies. 2P imaging may also be used to identify novel therapeutic targets via identification and clarification of dynamic cellular and molecular mechanisms of axonal regeneration and remyelination. Here, we review tools that have made 2P accessible for imaging neuropathologies and advances in our understanding of axonal degeneration and repair in preclinical models of demyelinating diseases.

Neutralization of RANTES and Eotaxin Prevents the Loss of Dopaminergic Neurons in a Mouse Model of Parkinson Disease

Parkinson disease (PD) is second only to Alzheimer disease as the most common human neurodegenerative disorder. Despite intense investigation, no interdictive therapy is available for PD. Recent studies indicate that both innate and adaptive immune processes are active in PD. Accordingly, we found a rapid increase in RANTES (regulated on activation normal T cell expressed and secreted) and eotaxin, chemokines that are involved in T cell trafficking, in vivo in the substantia nigra pars compacta and the serum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice. RANTES and eotaxin were also up-regulated in the substantia nigra pars compacta of post-mortem PD brains as compared with age-matched controls. Therefore, we investigated whether neutralization of RANTES and eotaxin could protect against nigrostriatal degeneration in MPTP-intoxicated mice. Interestingly, after peripheral administration, functional blocking antibodies against RANTES and eotaxin reduced the infiltration of CD4(+) and CD8(+) T cells into the nigra, attenuated nigral expression of proinflammatory molecules, and suppressed nigral activation of glial cells. These findings paralleled dopaminergic neuronal protection, normalized striatal neurotransmitters, and improved motor functions in MPTP-intoxicated mice. Therefore, we conclude that attenuation of the chemokine-dependent adaptive immune response may be of therapeutic benefit for PD patients.

Axonal degeneration in multiple sclerosis: defining therapeutic targets by identifying the causes of pathology

Current therapeutics in multiple sclerosis (MS) target the putative inflammation and immune attack on CNS myelin. Despite their effectiveness in blunting the relapse rate in MS patients, such therapeutics do not prevent MS disease progression. Importantly, specific clinical dilemma arises through inability to predict MS progression and thereby therapeutically target axonal injury during MS, limiting permanent disability. The current review identifies immune and neurobiological principles that govern the sequelae of axonal degeneration during MS disease progression. Defining the specific disease arbiters, inflammatory and autoimmune, oligodendrocyte dystrophy and degenerative myelin, we discuss a basis for a molecular mechanism in axons that may be targeted therapeutically, in spatial and temporal manner to limit axonal degeneration and thereby halt progression of MS.

Cross-recognition of a myelin peptide by CD8+ T cells in the CNS is not sufficient to promote neuronal damage

Multiple sclerosis (MS) is an inflammatory disease of the CNS thought to be driven by CNS-specific T lymphocytes. Although CD8(+) T cells are frequently found in multiple sclerosis lesions, their distinct role remains controversial because direct signs of cytotoxicity have not been confirmed in vivo. In the present work, we determined that murine ovalbumin-transgenic (OT-1) CD8(+) T cells recognize the myelin peptide myelin oligodendrocyte glycoprotein 40-54 (MOG40-54) both in vitro and in vivo. The aim of this study was to investigate whether such cross-recognizing CD8(+) T cells are capable of inducing CNS damage in vivo. Using intravital two-photon microscopy in the mouse model of multiple sclerosis, we detected antigen recognition motility of the OT-1 CD8(+) T cells within the CNS leading to a selective enrichment in inflammatory lesions. However, this cross-reactivity of OT-1 CD8(+) T cells with MOG peptide in the CNS did not result in clinically or subclinically significant damage, which is different from myelin-specific CD4(+) Th17-mediated autoimmune pathology. Therefore, intravital imaging demonstrates that local myelin recognition by autoreactive CD8(+) T cells in inflammatory CNS lesions alone is not sufficient to induce disability or increase axonal injury.

Systemic inflammation and the brain: novel roles of genetic, molecular, and environmental cues as drivers of neurodegeneration

The nervous and immune systems have evolved in parallel from the early bilaterians, in which innate immunity and a central nervous system (CNS) coexisted for the first time, to jawed vertebrates and the appearance of adaptive immunity. The CNS feeds from, and integrates efferent signals in response to, somatic and autonomic sensory information. The CNS receives input also from the periphery about inflammation and infection. Cytokines, chemokines, and damage-associated soluble mediators of systemic inflammation can also gain access to the CNS via blood flow. In response to systemic inflammation, those soluble mediators can access directly through the circumventricular organs, as well as open the blood–brain barrier. The resulting translocation of inflammatory mediators can interfere with neuronal and glial well-being, leading to a break of balance in brain homeostasis. This in turn results in cognitive and behavioral manifestations commonly present during acute infections – including anorexia, malaise, depression, and decreased physical activity – collectively known as the sickness behavior (SB). While SB manifestations are transient and self-limited, under states of persistent systemic inflammatory response the cognitive and behavioral changes can become permanent. For example, cognitive decline is almost universal in sepsis survivors, and a common finding in patients with systemic lupus erythematosus. Here, we review recent genetic evidence suggesting an association between neurodegenerative disorders and persistent immune activation; clinical and experimental evidence indicating previously unidentified immune-mediated pathways of neurodegeneration; and novel immunomodulatory targets and their potential relevance for neurodegenerative disorders.

Dual destructive and protective roles of adaptive immunity in neurodegenerative disorders

Inappropriate T cell responses in the central nervous system (CNS) affect the pathogenesis of a broad range of neuroinflammatory and neurodegenerative disorders that include, but are not limited to, multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer’s disease and Parkinson’s disease. On the one hand immune responses can exacerbate neurotoxic responses; while on the other hand, they can lead to neuroprotective outcomes. The temporal and spatial mechanisms by which these immune responses occur and are regulated in the setting of active disease have gained significant recent attention. Spatially, immune responses that affect neurodegeneration may occur within or outside the CNS. Migration of antigen-specific CD4+ T cells from the periphery to the CNS and consequent immune cell interactions with resident glial cells affect neuroinflammation and neuronal survival. The destructive or protective mechanisms of these interactions are linked to the relative numerical and functional dominance of effector or regulatory T cells. Temporally, immune responses at disease onset or during progression may exhibit a differential balance of immune responses in the periphery and within the CNS. Immune responses with predominate T cell subtypes may differentially manifest migratory, regulatory and effector functions when triggered by endogenous misfolded and aggregated proteins and cell-specific stimuli. The final result is altered glial and neuronal behaviors that influence the disease course. Thus, discovery of neurodestructive and neuroprotective immune mechanisms will permit potential new therapeutic pathways that affect neuronal survival and slow disease progression.

Pathology of multiple sclerosis and related inflammatory demyelinating diseases

This article provides a comprehensive overview of the pathology of multiple sclerosis (MS), including recent insights into its molecular neuropathology and immunology. It shows that all clinical manifestations of relapsing and progressive MS display the same basic features of pathology, such as chronic inflammation, demyelination in the white and gray matter, and diffuse neurodegeneration within the entire central nervous system. However, the individual components of the pathological spectrum vary quantitatively between early relapsing and late progressive MS. Widespread confluent and plaque-like demyelination with oligodendrocyte destruction is the unique pathological hallmark of the disease, but axonal injury and neurodegeneration are additionally present and in part extensive. Remyelination of existing lesions may occur in MS brains; it is extensive in a subset of patients, while it fails in others. Active tissue injury in MS is always associated with inflammation, consistent with T-cell and macrophage infiltration and microglia activation. Recent data suggest that oxidative injury and subsequent mitochondrial damage play a major pathogenetic role in neurodegeneration. Finally we discuss similarities and differences of the pathology between classical MS and other inflammatory demyelinating diseases, such as neuromyelitis optica, concentric sclerosis, or acute disseminated encephalomyelitis.

Lymphocytes and autoimmunity after spinal cord injury

Over the past 15 years an immense amount of data has accumulated regarding the infiltration and activation of lymphocytes in the traumatized spinal cord. Although the impact of the intraspinal accumulation of lymphocytes is still unclear, modulation of the adaptive immune response via active and passive vaccination is being evaluated for its preclinical efficacy in improving the outcome for spinal-injured individuals. The complexity of the interaction between the nervous and the immune systems is highlighted in the contradictions that appear in response to these modulations. Current evidence regarding augmentation and inhibition of the adaptive immune response to spinal cord injury is reviewed with an aim toward reconciling conflicting data and providing consensus issues that may be exploited in future therapies. Opportunities such an approach may provide are highlighted as well as the obstacles that must be overcome before such approaches can be translated into clinical trials.

Axonal pathology and demyelination in viral models of multiple sclerosis

Multiple sclerosis (MS) is an immune-mediated inflammatory demyelinating disease of the central nervous system (CNS). Monozygotic twin studies suggest that while there is a genetic contribution, genetics alone cannot be the sole determining factor in the development of MS. As the rates of MS are increasing, particularly among women, environmental factors such as viral infections are coming to the foreground as potential agents in triggering disease in genetically susceptible individuals. This review highlights pathological aspects related to two pre-clinical viral models for MS; data are consistent between these two models as experimental infection of susceptible mice can induce axonal degeneration associated with demyelination. These data are consistent with observations in MS that axonal damage or Wallerian degeneration is occurring within the CNS contributing to the disability and disease severity. Such early damage, where axonal damage is primary to secondary demyelination, could set the stage for more extensive immune mediated demyelination arising later.

Two-photon imaging of remyelination of spinal cord axons by engrafted neural precursor cells in a viral model of multiple sclerosis

Neural precursor cells (NPCs) offer a promising approach for treating demyelinating diseases. However, the cellular dynamics that underlie transplanted NPC-mediated remyelination have not been described. Using two-photon imaging of a newly developed ventral spinal cord preparation and a viral model of demyelination, we describe the motility and intercellular interactions of transplanted mouse NPCs expressing green fluorescent protein (GFP) with damaged axons expressing yellow fluorescent protein (YFP). Our findings reveal focal axonal degeneration that occurs in the ventral side of the spinal cord within 1 wk following intracranial instillation with the neurotropic JHM strain of mouse hepatitis virus (JHMV). Axonal damage precedes extensive demyelination and is characterized by swelling along the length of the axon, loss of YFP signal, and transected appearance. NPCs engrafted into spinal cords of JHMV-infected mice exhibited diminished migration velocities and increased proliferation compared with transplanted cells in noninfected mice. NPCs preferentially accumulated within areas of axonal damage, initiated direct contact with axons, and subsequently expressed the myelin proteolipid protein gene, initiating remyelination. These findings indicate that NPCs transplanted into an inflammatory demyelinating microenvironment participate directly in therapeutic outcome through the wrapping of myelin around damaged neurons.

Neuronal and astrocytic interactions modulate brain endothelial properties during metabolic stresses of in vitro cerebral ischemia

Neurovascular and gliovascular interactions significantly affect endothelial phenotype. Physiologically, brain endothelium attains several of its properties by its intimate association with neurons and astrocytes. However, during cerebrovascular pathologies such as cerebral ischemia, the uncoupling of neurovascular and gliovascular units can result in several phenotypical changes in brain endothelium. The role of neurovascular and gliovascular uncoupling in modulating brain endothelial properties during cerebral ischemia is not clear. Specifically, the roles of metabolic stresses involved in cerebral ischemia, including aglycemia, hypoxia and combined aglycemia and hypoxia (oxygen glucose deprivation and re-oxygenation, OGDR) in modulating neurovascular and gliovascular interactions are not known. The complex intimate interactions in neurovascular and gliovascular units are highly difficult to recapitulate in vitro. However, in the present study, we used a 3D co-culture model of brain endothelium with neurons and astrocytes in vitro reflecting an intimate neurovascular and gliovascular interactions in vivo. While the cellular signaling interactions in neurovascular and gliovascular units in vivo are much more complex than the 3D co-culture models in vitro, we were still able to observe several important phenotypical changes in brain endothelial properties by metabolically stressed neurons and astrocytes including changes in barrier, lymphocyte adhesive properties, endothelial cell adhesion molecule expression and in vitro angiogenic potential.

Immune regulation of multiple sclerosis

Multiple sclerosis (MS) is considered a prototype inflammatory autoimmune disorder of the central nervous system (CNS). The etiology of this disease remains unknown, but an interplay between as yet unidentified environmental factors and susceptibility genes appears most likely. In consequence, these factors trigger a cascade, involving an inflammatory response within the CNS that results in demyelination, oligodendrocyte death, axonal damage, gliosis, and neurodegeneration. How these complex traits translate into the clinical presentation of the disease is a focus of ongoing research. The central hypothesis is that T lymphocytes with receptors for CNS myelin components are driving the disease. The initial activation of autoreactive lymphocytes is thought to take place in the systemic lymphoid organs, most likely through molecular mimickry or nonspecifically through bystander activation. These autoreactive lymphocytes can migrate to the CNS where they become reactivated upon encountering their target antigen, initiating an autoimmune inflammatory attack. This ultimately leads to demyelination and axonal damage. This chapter focuses on the role of T and B lymphocytes in the immunopathogenesis of MS.

Multiple sclerosis: molecular mechanisms and therapeutic opportunities

The pathophysiology of multiple sclerosis (MS) involves several components: redox, inflammatory/autoimmune, vascular, and neurodegenerative. All of them are supported by the intertwined lines of evidence, and none of them should be written off. However, the exact mechanisms of MS initiation, its development, and progression are still elusive, despite the impressive pace by which the data on MS are accumulating. In this review, we will try to integrate the current facts and concepts, focusing on the role of redox changes and various reactive species in MS. Knowing the schedule of initial changes in pathogenic factors and the key turning points, as well as understanding the redox processes involved in MS pathogenesis is the way to enable MS prevention, early treatment, and the development of therapies that target specific pathophysiological components of the heterogeneous mechanisms of MS, which could alleviate the symptoms and hopefully stop MS. Pertinent to this, we will outline (i) redox processes involved in MS initiation; (ii) the role of reactive species in inflammation; (iii) prooxidative changes responsible for neurodegeneration; and (iv) the potential of antioxidative therapy.

Intravital imaging of autoreactive T cells in living animals

Developing technologies now allow observing cellular motility and functions in the living animal. Here, we introduce the method of intravital imaging by using two-photon microscopy. To acquire images with good quality, a highly stablilized tissue is required. Additionally, physiological parameters of the animal need to be controlled during the entire period of intravital imaging. We image rat autoreactive T cells within the spinal cord leptomeninges. Those autoantigen specific T cells were labeled in vitro by using fluorescent protein coding retroviral vectors. Adoptively transferred T cells migrate into the spinal cord with highly reproducible time kinetic. Intravital imaging was performed within the deeply anesthetized animals. Although two-photon microscopy is a powerful tool, the penetration depth in certain tissues, like the spinal cord parenchyma, is still limited. To overcome this issue, imaging of explanted acute spinal cord slices was performed under nearly physiological conditions. Results obtained from intravital imaging will strengthen the "snap shots" analysis such as FACS and quantitative PCR, and can provide new insight into cellular mechanisms in vivo.

Peripheral tolerance and autoimmunity: lessons from in vivo imaging

Multi-photon microscopy has taken hold as a widely used technique in immunology, allowing for imaging of the kinetics of immune cell motility and cell-cell interactions, but what have we learned from this technique about the processes involved in peripheral tolerance and autoimmunity? Various studies have now looked at the dynamics of several mechanisms of peripheral T cell tolerance and efforts to examine the dynamics of the autoimmune response at the disease site are also under way. Here, we will discuss the findings of studies that use multi-photon microscopy to examine the dynamics of T cell tolerance in the lymph nodes and of the autoimmune processes involved in models of type 1 diabetes and multiple sclerosis. An emerging theme from these studies is that short T cell-antigen presenting cell interactions can lead to tolerance, and that autoreactive T cell restimulation at the disease site can play an important role in autoimmune disease exacerbation.

Two-photon imaging of immune cells in neural tissue

To develop new therapeutic strategies for many central nervous system (CNS) diseases, it is essential to observe the motility and function of immune cells within neural tissue. Two-photon laser-scanning microscopy is an outstanding technique for imaging these phenomena under in vivo-like conditions. To gain deeper insight into the pathological phenomena that occur during chronic neuroinflammation of the CNS, we use it to view acute murine hippocampal slices cocultured with different subpopulations of immune cells and to view in vivo the brain stem of anesthetized transgenic mice affected by experimental autoimmune encephalomyelitis (EAE), a murine model of multiple sclerosis. This protocol describes the preparation of cocultures of acute hippocampal slices with antigen-specific T helper 17 (Th17) cells migrating into the parenchyma, and the preparation of anesthetized mice for imaging the brain stem. We also discuss technical aspects of dual-color, two-photon laser-scanning microscopy that is used to image these samples and that allows for greater flexibility in the choice of fluorophores.

Neurodegeneration in multiple sclerosis: novel treatment strategies

In recent years it has become clear that the neuronal compartment already plays an important role early in the pathology of multiple sclerosis (MS). Neuronal injury in the course of chronic neuroinflammation is a key factor in determining long-term disability in patients. Viewing MS as both inflammatory and neurodegenerative has major implications for therapy, with CNS protection and repair needed in addition to controlling inflammation. Here, the authors' review recently elucidated molecular insights into inflammatory neuronal/axonal pathology in MS and discuss the resulting options regarding neuroprotective and regenerative treatment strategies.