Put to sleep by immune cells

The immunopathogenesis of narcolepsy type 1

Narcolepsy type 1 (NT1) is a chronic sleep disorder resulting from the loss of a small population of hypothalamic neurons that produce wake-promoting hypocretin (HCRT; also known as orexin) peptides. An immune-mediated pathology for NT1 has long been suspected given its exceptionally tight association with the MHC class II allele HLA-DQB1*06:02, as well as recent genetic evidence showing associations with polymorphisms of T cell receptor genes and other immune-relevant loci and the increased incidence of NT1 that has been observed after vaccination with the influenza vaccine Pandemrix. The search for both self-antigens and foreign antigens recognized by the pathogenic T cell response in NT1 is ongoing. Increased T cell reactivity against HCRT has been consistently reported in patients with NT1, but data demonstrating a primary role for T cells in neuronal destruction are currently lacking. Animal models are providing clues regarding the roles of autoreactive CD4+ and CD8+ T cells in the disease. Elucidation of the pathogenesis of NT1 will allow for the development of targeted immunotherapies at disease onset and could serve as a model for other immune-mediated neurological diseases.

Cerebrospinal fluid proteomics in recent-onset Narcolepsy type 1 reveals activation of the complement system

Introduction

Narcolepsy type 1 (NT1) is a rare, chronic and disabling neurological disease causing excessive daytime sleepiness and cataplexy. NT1 is characterized pathologically by an almost complete loss of neurons producing the orexin neuropeptides in the lateral hypothalamus. Genetic and environmental factors strongly suggest the involvement of the immune system in the loss of orexin neurons. The cerebrospinal fluid (CSF), secreted locally and surrounding the central nervous system (CNS), represents an accessible window into CNS pathological processes.

Methods

To gain insight into the biological and molecular changes in NT1 patients, we performed a comparative proteomics analysis of the CSF from 21 recent-onset NT1 patients and from two control groups: group 1 with somatoform disorders, and group 2 patients with hypersomnia other than NT1, to control for any potential effect of sleep disturbances on CSF composition. To achieve an optimal proteomic coverage analysis, the twelve most abundant CSF proteins were depleted, and samples were analyzed by nano-flow liquid chromatography tandem mass spectrometry (nano-LC-MS/MS) using the latest generation of hybrid Orbitrap mass spectrometer.

Results and discussion

Our study allowed the identification and quantification of up to 1943 proteins, providing a remarkably deep analysis of the CSF proteome. Interestingly, gene set enrichment analysis indicated that the complement and coagulation systems were enriched and significantly activated in NT1 patients in both cohorts analyzed. Notably, the lectin and alternative complement pathway as well as the downstream lytic membrane attack complex were congruently increased in NT1. Our data suggest that the complement dysregulation in NT1 patients can contribute to immunopathology either by directly promoting tissue damage or as part of local inflammatory responses. We therefore reveal an altered composition of the CSF proteome in NT1 patients, which points to an ongoing inflammatory process contributed, at least in part, by the complement system.

Narcolepsy and H1N1 influenza immunology a decade later: What have we learned?

In the wake of the A/California/7/2009 H1N1 influenza pandemic vaccination campaigns in 2009-2010, an increased incidence of the chronic sleep-wake disorder narcolepsy was detected in children and adolescents in several European countries. Over the last decade, in-depth epidemiological and immunological studies have been conducted to investigate this association, which have advanced our understanding of the events underpinning the observed risk. Narcolepsy with cataplexy (defined as type-1 narcolepsy, NT1) is characterized by an irreversible and chronic deficiency of hypocretin peptides in the hypothalamus. The multifactorial etiology is thought to include genetic predisposition, head trauma, environmental triggers, and/or infections (including influenza virus infections), and an increased risk was observed following administration of the A/California/7/2009 H1N1 vaccine Pandemrix (GSK). An autoimmune origin of NT1 is broadly assumed. This is based on its strong association with a predisposing allele (the human leucocyte antigen DQB1*0602) carried by the large majority of NT1 patients, and on links with other immune-related genetic markers affecting the risk of NT1. Presently, hypotheses on the underlying potential immunological mechanisms center on molecular mimicry between hypocretin and peptides within the A/California/7/2009 H1N1 virus antigen. This molecular mimicry may instigate a cross-reactive autoimmune response targeting hypocretin-producing neurons. Local CD4⁺ T-cell responses recognizing peptides from hypocretin are thought to play a central role in the response. In this model, cross-reactive DQB1*0602-restricted T cells from the periphery would be activated to cross the blood-brain barrier by rare, and possibly pathogen-instigated, inflammatory processes in the brain. Current hypotheses suggest that activation and expansion of cross-reactive T-cells by H1N1/09 influenza infection could have been amplified following the administration of the adjuvanted vaccine, giving rise to a “two-hit” hypothesis. The collective in silico, in vitro, and preclinical in vivo data from recent and ongoing research have progressively refined the hypothetical model of sequential immunological events, and filled multiple knowledge gaps. Though no definitive conclusions can be drawn, the mechanistical model plausibly explains the increased risk of NT1 observed following the 2009-2010 H1N1 pandemic and subsequent vaccination campaign, as outlined in this review.

Fundamental mechanistic insights from rare but paradigmatic neuroimmunological diseases

The pathophysiology of complex neuroimmunological diseases, such as multiple sclerosis and autoimmune encephalitis, remains puzzling - various mechanisms that are difficult to dissect seem to contribute, hampering the understanding of the processes involved. Some rare neuroimmunological diseases are easier to study because their presentation and pathogenesis are more homogeneous. The investigation of these diseases can provide fundamental insights into neuroimmunological pathomechanisms that can in turn be applied to more complex diseases. In this Review, we summarize key mechanistic insights into three such rare but paradigmatic neuroimmunological diseases - Susac syndrome, Rasmussen encephalitis and narcolepsy type 1 - and consider the implications of these insights for the study of other neuroimmunological diseases. In these diseases, the combination of findings in humans, different modalities of investigation and animal models has enabled the triangulation of evidence to validate and consolidate the pathomechanistic features and to develop diagnostic and therapeutic strategies; this approach has provided insights that are directly relevant to other neuroimmunological diseases and applicable in other contexts. We also outline how next-generation technologies and refined animal models can further improve our understanding of pathomechanisms, including cell-specific and antigen-specific CNS immune responses, thereby paving the way for the development of targeted therapeutic approaches.

Reviewing the Clinical Implications of Treating Narcolepsy as an Autoimmune Disorder

Narcolepsy type 1 (NT1) is a lifelong sleep disorder, primarily characterized clinically by excessive daytime sleepiness and cataplexy and pathologically by the loss of hypocretinergic neurons in the lateral hypothalamus. Despite being a rare disorder, the NT1-related burden for patients and society is relevant due to the early onset and chronic nature of this condition. Although the etiology of narcolepsy is still unknown, mounting evidence supports a central role of autoimmunity. To date, no cure is available for this disorder and current treatment is symptomatic. Based on the hypothesis of the autoimmune etiology of this disease, immunotherapy could possibly represent a valid therapeutic option. However, contrasting and limited results have been provided so far. This review discusses the evidence supporting the use of immunotherapy in narcolepsy, the outcomes obtained so far, current issues and future directions.

An association between air pollution and daily most frequently visits of eighteen outpatient diseases in an industrial city

Toxic effects of air pollutants were individually identified in various organs of the body. However, the concurrent occurrences and the connection of diseases in multiple organs arise from air pollution has not been concurrently studied before. Here we hypothesize that there exist connected health effects arise from air pollution when diseases in various organs were considered together. We used medical data from hospital outpatient visits for various organs in the body with a disease-air pollution model that represents each of the diseases as a function of the environmental factors. Our results show that elevated air pollution risks (above 40%) concurrently occurred in diseases of spondylosis, cerebrovascular, pneumonia, accidents, chronic obstructive pulmonary disease (COPD), influenza, osteoarthritis (OA), asthma, peptic ulcer disease (PUD), cancer, heart, hypertensive, diabetes, kidney, and rheumatism. Air pollutants that were associated with elevated health risks are particular matters with diameters equal or less than 2.5 μm (PM_2.5), nitrogen dioxide (NO₂), ozone (O₃), particular matters with diameters equal or less than 10 μm (PM₁₀), carbon monoxide (CO), and nitrogen oxide (NO). Concurrent occurrences of diseases in various organs indicate that the immune system tries to connectively defend the body from persistent and rising air pollution.

Immunotherapy in Narcolepsy

PURPOSE OF REVIEW

Narcolepsy type 1 (NT1) is a chronic and disabling sleep disorder due to the loss of hypocretinergic neurons in the lateral hypothalamus pathophysiologically linked to an autoimmune process. Current treatment is symptomatic, and no cure is available to date. Immunotherapy is considered a promising future therapeutic option, and this review discusses the rationale for immunotherapy in narcolepsy, current evidences of its effects, outcome measures, and future directions.

RECENT FINDINGS

A limited number of case reports and uncontrolled small case series have reported the effect of different immunotherapies in patients with NT1. These studies were mainly based on the use of intravenous immunoglobulin (IVig), followed by corticosteroids, plasmapheresis, and monoclonal antibodies. Although initial reports showed an improvement of symptoms, particularly when patients were treated close to disease onset, other observations have not confirmed these results. Inadequate timing of treatment, placebo effects, and spontaneous improvement due to the natural disease course can account for these contrasting findings. Moreover, clear endpoints and standardized outcome measures have not been used and are currently missing in the pediatric population. On the basis of the available data, there are no enough evidences to support the use of immunotherapy in NT1. Randomized, controlled studies using clear endpoints and new outcome measures are needed to achieve a definitive answer about the usefulness of these treatments in narcolepsy.

Shared T cell receptor chains in blood memory CD4+ T cells of narcolepsy type 1 patients

Convergent evidence points to the involvement of T cells in the pathogenesis of narcolepsy type 1 (NT1). Here, we hypothesized that expanded disease-specific T cell clones could be detected in the blood of NT1 patients. We compared the TCR repertoire of circulating antigen-experienced CD4⁺ and CD8⁺ T cells from 13 recently diagnosed NT1 patients and 11 age-, sex-, and HLA-DQB1*06:02-matched healthy controls. We detected a bias in the usage of TRAV3 and TRAV8 families, with public CDR3α motifs only present in CD4⁺ T cells from patients with NT1. These findings may offer a unique tool to identify disease-relevant antigens.

Neurobiological and immunogenetic aspects of narcolepsy: Implications for pharmacotherapy

Excessive daytime sleepiness (EDS) and cataplexy are common symptoms of narcolepsy, a sleep disorder associated with the loss of hypocretin/orexin (Hcrt) neurons. Although only a few drugs have received regulatory approval for narcolepsy to date, treatment involves diverse medications that affect multiple biochemical targets and neural circuits. Clinical trials have demonstrated efficacy for the following classes of drugs as narcolepsy treatments: alerting medications (amphetamine, methylphenidate, modafinil/armodafinil, solriamfetol [JZP-110]), antidepressants (tricyclic antidepressants, selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors), sodium oxybate, and the H₃-receptor inverse agonist/antagonist pitolisant. Enhanced catecholamine availability and regulation of locus coeruleus (LC) norepinephrine (NE) neuron activity is likely central to the therapeutic activity of most of these compounds. LC NE neurons are integral to sleep/wake regulation and muscle tone; reduced excitatory input to the LC due to compromise of Hcrt/orexin neurons (likely due to autoimmune factors) results in LC NE dysregulation and contributes to narcolepsy/cataplexy symptoms. Agents that increase catecholamines and/or LC activity may mitigate EDS and cataplexy by elevating NE regulation of GABAergic inputs from the amygdala. Consequently, novel medications and treatment strategies aimed at preserving and/or modulating Hcrt/orexin-LC circuit integrity are warranted in narcolepsy/cataplexy.