Dealing with Danger in the CNS: The Response of the Immune System to Injury

Fighting pathogens and maintaining tissue homeostasis are prerequisites for survival. Both of these functions are upheld by the immune system, though the latter is often overlooked in the context of the CNS. The mere presence of immune cells in the CNS was long considered a hallmark of pathology, but this view has been recently challenged by studies demonstrating that immunological signaling can confer pivotal neuroprotective effects on the injured CNS. In this review, we describe the temporal sequence of immunological events that follow CNS injury. Beginning with immediate changes at the injury site, including death of neural cells and release of damage-associated molecular patterns (DAMPs), and progressing through innate and adaptive immune responses, we describe the cascade of inflammatory mediators and the implications of their post-injury effects. We conclude by proposing a revised interpretation of immune privilege in the brain, which takes beneficial neuro-immune communications into account.

Promoting remyelination: utilizing a viral model of demyelination to assess cell-based therapies

Multiple sclerosis (MS) is a chronic inflammatory disease of the CNS. While a broad range of therapeutics effectively reduce the incidence of focal white matter inflammation and plaque formation for patients with relapse-remitting forms of MS, a challenge within the field is to develop therapies that allow for axonal protection and remyelination. In the last decade, growing interest has focused on utilizing neural precursor cells (NPCs) to promote remyelination. To understand how NPCs function in chronic demyelinating environments, several excellent pre-clinical mouse models have been developed. One well accepted model is infection of susceptible mice with neurotropic variants of mouse hepatitis virus (MHV) that undergo chronic demyelination exhibiting clinical and histopathologic similarities to MS patients. Combined with the possibility that an environmental agent such as a virus could trigger MS, the MHV model of demyelination presents a relevant mouse model to assess the therapeutic potential of NPCs transplanted into an environment in which inflammatory-mediated demyelination is established.

The Effect of Vitamin A Supplementation on FoxP3 and TGF-β Gene Expression in Avonex-Treated Multiple Sclerosis Patients

Multiple sclerosis (MS) is an autoinflammatory condition of the central nervous system with impaired T helper (Th)17 and regulatory T cell (Treg) balance that is involved in disease immunopathogenesis. The vitamin A active metabolite, retinoic acid, can re-establish this imbalance through the modulation of gene expression of specific nuclear receptors including Forkhead box P3 (FoxP3). At present, few data exist on the impact of vitamin A supplementation on T cell balance. This study reports the results of a clinical trial, over a 6-month period, of 36 relapsing-remitting MS (RRMS) patients that received vitamin A (25,000 IU retinyl palmitate) or placebo (one capsule of placebo per day). Peripheral blood mononuclear cells were isolated from patients, and the expression of FoxP3 and transforming growth factor (TGF)-β gene expression was measured using real-time PCR at the beginning and end of the study. The results of this study showed that vitamin A upregulated TGF-β and FoxP3 gene expression. Therefore, vitamin A supplementation can be considered as a new approach in MS prevention and treatment.

MS in South Asians in England: early disease onset and novel pattern of myelin autoimmunity

BACKGROUND

Epidemiological studies describe a latitude gradient for increased MS prevalence and a preponderance of disease in Caucasian individuals. However, individuals from other ethnic backgrounds and low-risk regions can acquire a raised risk through migration. Nearly a fifth of the London population is of Asian/Asian-British origin and a significant proportion of referrals are from this group.

METHODS

We investigated whether there were differences in timing, presentation, severity, and immunology of disease (with respect to CD4 myelin epitope recognition) between individuals in London with MS who were either of S. Asian or Caucasian origin. Individuals of S. Asian origin with MS were compared with healthy S. Asian controls, individuals with MS and of Caucasian origin and Caucasian controls.

RESULTS

Age at MS onset is significantly lower in the S. Asian group, attributable to earlier onset specifically in UK-born individuals, though clinical presentation is similar. Analysis of CD4 autoimmunity to myelin antigens shows disease in S. Asian individuals to encompass recognition of novel epitopes; immunity to MBP116-130 in S. Asian individuals was highly disease-specific.

CONCLUSIONS

These findings emphasize the need to define disease profiles across ethnicities and identify environmental triggers conferring acquired risk. Such findings must inform choices for immunotherapeutic interventions suitable for all, across ethnicities.

Critical role for prokineticin 2 in CNS autoimmunity

Objective:

To investigate the potential role of prokineticin 2 (PK2), a bioactive peptide involved in multiple biological functions including immune modulation, in CNS autoimmune demyelinating disease.

Methods:

We investigated the expression of PK2 in mice with experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS), and in patients with relapsing-remitting MS. We evaluated the biological effects of PK2 on expression of EAE and on development of T-cell response against myelin by blocking PK2 in vivo with PK2 receptor antagonists. We treated with PK2 immune cells activated against myelin antigen to explore the immune-modulating effects of this peptide in vitro.

Results:

Pk2 messenger RNA was upregulated in spinal cord and lymph node cells (LNCs) of mice with EAE. PK2 protein was expressed in EAE inflammatory infiltrates and was increased in sera during EAE. In patients with relapsing-remitting MS, transcripts for PK2 were significantly increased in peripheral blood mononuclear cells compared with healthy controls, and PK2 serum concentrations were significantly higher. A PK2 receptor antagonist prevented or attenuated established EAE in chronic and relapsing-remitting models, reduced CNS inflammation and demyelination, and decreased the production of interferon (IFN)-γ and interleukin (IL)-17A cytokines in LNCs while increasing IL-10. PK2 in vitro increased IFN-γ and IL-17A and reduced IL-10 in splenocytes activated against myelin antigen.

Conclusion:

These data suggest that PK2 is a critical immune regulator in CNS autoimmune demyelination and may represent a new target for therapy.

No quiet surrender: molecular guardians in multiple sclerosis brain

The brain under immunological attack does not surrender quietly. Investigation of brain lesions in multiple sclerosis (MS) reveals a coordinated molecular response involving various proteins and small molecules ranging from heat shock proteins to small lipids, neurotransmitters, and even gases, which provide protection and foster repair. Reduction of inflammation serves as a necessary prerequisite for effective recovery and regeneration. Remarkably, many lesion-resident molecules activate pathways leading to both suppression of inflammation and promotion of repair mechanisms. These guardian molecules and their corresponding physiologic pathways could potentially be exploited to silence inflammation and repair the injured and degenerating brain and spinal cord in both relapsing-remitting and progressive forms of MS and may be beneficial in other neurologic and psychiatric conditions.

Protein phosphorylation detection using dual-mode field-effect devices and nanoplasmonic sensors

Phosphorylation by kinases is an important post-translational modification of proteins. It is a critical control for the regulation of vital cellular activities, and its dysregulation is implicated in several diseases. A common drug discovery approach involves, therefore, time-consuming screenings of large libraries of candidate compounds to identify novel inhibitors of protein kinases. In this work, we propose a novel method that combines localized surface plasmon resonance (LSPR) and electrolyte insulator semiconductor (EIS)-based proton detection for the rapid identification of novel protein kinase inhibitors. In particular, the selective detection of thiophosphorylated proteins by LSPR is achieved by changing their resonance properties via a pre-binding with gold nanoparticles. In parallel, the EIS field-effect structure allows the real-time electrochemical monitoring of the protein phosphorylation by detecting the release of protons associated with the kinases activity. This innovative combination of both field-effect and nanoplasmonic sensing makes the detection of protein phosphorylation more reliable and effective. As a result, the screening of protein kinase inhibitors becomes more rapid, sensitive, robust and cost-effective.

Regulation of Treg-associated CD39 in multiple sclerosis and effects of corticotherapy during relapse

Background:

Accumulating data highlight proinflammatory processes leading to MS relapses. Whether anti-inflammatory mechanisms are concomitantly activated is unclear. The ectonucleotidase CD39 has been described as a novel T regulatory cell (Treg) marker. The purpose of this study was to explore whether regulatory mechanisms are activated during MS relapses and reinforced by intravenous methylprednisolone (ivMP).

Methods:

Blood samples were collected from stable and relapsing MS patients and healthy controls. We used FOXP3 methylation-specific qPCR and CD4+CD25highFOXP3+ analysis to quantify Tregs. Cytokine mRNA expression levels were measured in peripheral blood mononuclear cells (PBMCs) and in CD4+ T cells. CD39 expression was determined by flow cytometry in monocytes, NK, T and B cells. CD39 enzymatic activity was assessed by ATP luminometry.

Results:

The proportion of Tregs was similar in relapsing MS patients and healthy controls. CD39 mRNA level was higher in PBMCs of relapsing MS patients than in controls. The proportion of CD39-expressing Tregs was higher in MS patients. IvMP decreased the overall proportion of Tregs while it increased CD39 mRNA levels, the proportions of CD39-expressing Tregs and monocytes as well as CD39 ectonucleotidase activity.

Conclusions:

Our data suggest that immunoregulatory mechanisms are ongoing in MS patients, particularly during relapses, and strengthened by ivMP.

Development of therapies for autoimmune disease at Stanford: a tale of multiple shots and one goal

The title of this contribution on Immunology at Stanford is purposely ambiguous. One goal is the development of safe and effective therapy for autoimmune diseases. Another definition of goal is to score, and this would ultimately mean the development of an approved drug. Indeed, the efforts in my four decades at Stanford, have included the discovery and subsequent development of a monoclonal antibody to block homing to the inflamed brain, leading to natalizumab, an approved therapeutic for two autoimmune diseases: relapsing-remitting MS and for inflammatory bowel disease. Multiple attempts to develop new therapies for autoimmune disease are described here: The trimolecular complex and the immune synapse serve as one major set of targets, with attempts to inhibit particular major histocompatibility molecules, the variable regions of the T cell receptor, and CD4. Other approaches focusing on antigen-specific tolerance include ongoing attempts with tolerizing DNA vaccines in type 1 diabetes. Finally, the repurposing of popular drugs approved for other indications, including statins and inhibitors of angiotensin converting enzyme is under development and showing promise in the clinic, particularly for secondary progressive multiple sclerosis. The milieu within Stanford Immunology has helped to nurture these efforts to translate discoveries in immunology and to take them from bench to bedside.

Control of lymphocyte egress from lymph nodes through β2-adrenergic receptors

Using pharmacological activation and genetic ablation of β₂-adrenergic receptors (β₂ARs) in mice, Nakai et al. show that β₂ARs expressed on lymphocytes can regulate egress of these cells from lymph nodes, while altering the responsiveness of chemokine receptors CCR7 and CXCR4. They identify that β₂ARs can physically interact with these chemokine receptors. And, in mouse models of T cell–mediated inflammation, β₂AR-mediated signals are shown to inhibit trafficking of antigen-primed T cells, reducing their numbers in inflamed peripheral tissues.

Lymphocyte recirculation through secondary lymphoid organs is essential for immunosurveillance and lymphocyte effector functions. Here, we show that signals through β₂-adrenergic receptors (β₂ARs) expressed on lymphocytes are involved in the control of lymphocyte dynamics by altering the responsiveness of chemoattractant receptors. Agonist stimulation of lymphocyte β₂ARs inhibited egress of lymphocytes from lymph nodes (LNs) and rapidly produced lymphopenia in mice. Physiological inputs from adrenergic nerves contributed to retention of lymphocytes within LNs and homeostasis of their distribution among lymphoid tissues. β₂ARs physically interacted with CCR7 and CXCR4, chemokine receptors promoting lymphocyte retention in LNs. Activation of β₂ARs enhanced retention-promoting signals through CCR7 and CXCR4, and consequently inhibited lymphocyte egress from LNs. In models of T cell–mediated inflammatory diseases, β₂AR-mediated signals inhibited LN egress of antigen-primed T cells and reduced their recruitment into peripheral tissues. Thus, this study reveals a novel mechanism for controlling lymphocyte trafficking and provides additional insights into immune regulation by the nervous system.

Therapeutic uses of anti-α4-integrin (anti-VLA-4) antibodies in multiple sclerosis

Multiple sclerosis (MS) is a disorder of putative autoimmune origin, where immune cells invade the central nervous system and cause damage by attacking the myelin sheath of nerve cells. The blockade of the integrin very late antigen-4 (VLA-4) with the monoclonal antibody natalizumab has become the most effective therapy against MS since its approval in 2004. It is assumed that the inhibition of VLA-4-mediated immune cell adhesion to the endothelium of the blood-brain barrier (BBB) alleviates pathogenic processes of MS and, therefore, reduces disease severity and burden. Not all approaches to treat additional immune-mediated disorders (e.g. Rasmussen encephalitis and neuromyelitis optica) with natalizumab have been successful, but allowed researchers to gain additional insight into mechanisms of specific immune cell subsets' migration through the BBB in the human system. While the long-term efficacy and general tolerability of natalizumab in MS are clear, the over 400 cases of natalizumab-associated progressive multifocal leukoencephalopathy (PML) have been of great concern and methods of risk stratification in patients have become a major area of research. Modern risk stratification includes established factors such as treatment duration, previous immune-suppressive therapy, and anti-John Cunningham virus (JCV) antibody seropositivity, but also experimental factors such as anti-JCV antibody titers and levels of L-selectin. Today, anti-VLA-4 therapy is reserved for patients with highly active relapsing-remitting MS and patients are monitored closely for early signs of potential PML.

Human Wharton's Jelly-Derived Stem Cells Display Immunomodulatory Properties and Transiently Improve Rat Experimental Autoimmune Encephalomyelitis

Umbilical cord matrix or Wharton's jelly-derived stromal cells (WJ-MSCs) are an easily accessible source of mesenchymal-like stem cells. Recent studies describe a hypoimmunogenic phenotype, multipotent differentiation potential, and trophic support function for WJ-MSCs, with variable clinical benefit in degenerative disease models such as stroke, myocardial infarction, and Parkinson's disease. It remains unclear whether WJ-MSCs have therapeutic value for multiple sclerosis (MS), where autoimmune-mediated demyelination and neurodegeneration need to be halted. In this study, we investigated whether WJ-MSCs possess the required properties to effectively and durably reverse these pathological hallmarks and whether they survive in an inflammatory environment after transplantation. WJ-MSCs displayed a lowly immunogenic phenotype and showed intrinsic expression of neurotrophic factors and a variety of anti-inflammatory molecules. Furthermore, they dose-dependently suppressed proliferation of activated T cells using contact-dependent and paracrine mechanisms. Indoleamine 2,3-dioxygenase 1 was identified as one of the main effector molecules responsible for the observed T-cell suppression. The immune-modulatory phenotype of WJ-MSCs was further enhanced after proinflammatory cytokine treatment in vitro (licensing). In addition to their effect on adaptive immunity, WJ-MSCs interfered with dendritic cell differentiation and maturation, thus directly affecting antigen presentation and therefore T-cell priming. Systemically infused WJ-MSCs potently but transiently ameliorated experimental autoimmune encephalomyelitis (EAE), an animal model for MS, when injected at onset or during chronic disease. This protective effect was paralleled with a reduction in autoantigen-induced T-cell proliferation, confirming their immunomodulatory activity in vivo. Surprisingly, in vitro licensed WJ-MSCs did not ameliorate EAE, indicative of a fast rejection as a result of enhanced immunogenicity. Collectively, we show that WJ-MSCs have trophic support properties and effectively modulate immune cell functioning both in vitro and in the EAE model, suggesting WJ-MSC may hold promise for MS therapy. Future research is needed to optimize survival of stem cells and enhance clinical durability.

Targeting integrins and adhesion molecules to combat inflammatory bowel disease

: The etiologies of Crohn's disease and ulcerative colitis, the 2 major forms of inflammatory bowel disease in humans, remain unknown, but experimental studies suggest that inflammatory bowel disease results from interaction between environmental and genetic factors, which promotes an exaggerated and inappropriately controlled inflammatory response that is directed against normal components of the gut flora. There is also evidence that tissue damage is due to a dynamic interplay between immune and nonimmune cells, and recruitment of lymphocytes from the blood stream to the gut wall is crucial for amplifying and sustaining the ongoing mucosal inflammation. These advances have led to the development of several compounds blocking gut homing of effector lymphocytes, which have recently been used or are now ready to move into clinical practice. This article summarizes the recent data on the use of integrin-targeting and adhesion molecule-targeting therapeutics to attenuate the detrimental inflammatory response in inflammatory bowel disease.

Why are prions and amyloid structures immune suppressive and other intriguing questions facing neuroimmunologists in the future

The immune system plays a major role in certain diseases of the brain like multiple sclerosis and neuromyelitis optica, while the brain may play a major role in modulating certain immunologic diseases of the periphery like inflammatory bowel disease. The most significant developments in neuroimmunology will involve explorations of the roles for the immune system in neurodegenerative conditions often associated with the presence of amyloid deposits. Here I present my personal perspectives on four of the most intriguing challenges that we face in the future of neuroimmunology: (1) Why are the traditional hallmarks of innate and adaptive inflammation conspicuously absent from brains of individuals with prion disease and amyloid pathology? (2) What is the role of adaptive and innate immunity in progressive forms of multiple sclerosis? (3) Is molecular mimicry an adequate explanation for the initiation of neuroinflammatory disease and for exacerbations in conditions like multiple sclerosis, narcolepsy, and neuromyelitis optica? (4) Do neural pathways regulate inflammatory diseases outside the nervous system?

VLA-4 blockade promotes differential routes into human CNS involving PSGL-1 rolling of T cells and MCAM-adhesion of TH17 cells

Schneider-Hohendorf describe expression of adhesion molecules MCAM and PSGL-1 on human CD4⁺ T cells and Th17 T cells in multiple sclerosis patients under long-term natalizumab treatment. The authors identify that despite blockade of VLA-4, MCAM⁺ T cells can migrate through the blood–brain barrier to access the CNS through PSGL-1 and MCAM.

The focus of this study is the characterization of human T cell blood–brain barrier migration and corresponding molecular trafficking signatures. We examined peripheral blood and cerebrospinal fluid immune cells from patients under long-term anti–very late antigen-4 (VLA-4)/natalizumab therapy (LTNT) and from CNS specimens. LTNT patients’ cerebrospinal fluid T cells exhibited healthy central-/effector-memory ratios, but lacked CD49d and showed enhanced myeloma cell adhesion molecule (MCAM) expression. LTNT led to an increase of PSGL-1 expression on peripheral T cells. Although vascular cell adhesion molecule-1 (VLA-4 receptor) was expressed at all CNS barriers, P-selectin (PSGL-1-receptor) was mainly detected at the choroid plexus. Accordingly, in vitro experiments under physiological flow conditions using primary human endothelial cells and LTNT patients’ T cells showed increased PSGL-1–mediated rolling and residual adhesion, even under VLA-4 blockade. Adhesion of MCAM⁺/T_H17 cells was not affected by VLA-4 blocking alone, but was abrogated when both VLA-4 and MCAM were inhibited. Consistent with these data, MCAM⁺ cells were detected in white matter lesions, and in gray matter of multiple sclerosis patients. Our data indicate that lymphocyte trafficking into the CNS under VLA-4 blockade can occur by using the alternative adhesion molecules, PSGL-1 and MCAM, the latter representing an exclusive pathway for T_H17 cells to migrate over the blood–brain barrier.