Myasthenia gravis (MG) is an autoimmune antibody-mediated disorder of neuromuscular synaptic transmission. The clinical hallmark of MG consists of fluctuating fatigability and weakness affecting ocular, bulbar and (proximal) limb skeletal muscle groups. MG may either occur as an autoimmune disease with distinct immunogenetic characteristics or as a paraneoplastic syndrome associated with tumors of the thymus. Impairment of central thymic and peripheral self-tolerance mechanisms in both cases is thought to favor an autoimmune CD4+ T cell-mediated B cell activation and synthesis of pathogenic high-affinity autoantibodies of either the IgG1 and 3 or IgG4 subclass. These autoantibodies bind to the nicotinic acetylcholine receptor (AchR) itself, or muscle-specific tyrosine-kinase (MuSK), lipoprotein receptor-related protein 4 (LRP4) and agrin involved in clustering of AchRs within the postsynaptic membrane and structural maintenance of the neuromuscular synapse. This results in disturbance of neuromuscular transmission and thus clinical manifestation of the disease. Emphasizing evidence from clinical trials, we provide an updated overview on immunopathogenesis, and derived current and future treatment strategies for MG divided into: (a) symptomatic treatments facilitating neuromuscular transmission, (b) antibody-depleting treatments, and (c) immunotherapeutic treatment strategies.

GABA(B)R and AMPAR abs are well associated with LE. GABA(B)R abs lead to severe clinical, neuroradiological and EEG abnormalities with poorer outcome.

Excitatory amino acid transporters (EAATs) mediate two distinct transport processes, a stoichiometrically coupled transport of glutamate, Na ؉ , K ؉ , and H ؉ , and a pore-mediated anion conductance. We studied the anion conductance associated with two mammalian EAAT isoforms, hEAAT2 and rEAAT4, using whole-cell patch clamp recording on transfected mammalian cells. Both isoforms exhibited constitutively active, multiply occupied anion pores that were functionally modified by various steps of the Glu/Na ؉ /H ؉ /K ؉ transport cycle. Permeability and conductivity ratios were distinct for cells dialyzed with Na ؉ -or K ؉ -based internal solution, and application of external glutamate altered anion permeability ratios and the concentration dependence of the anion influx. EAAT4 but not EAAT2 anion channels displayed voltage-dependent gating that was modified by glutamate. These results are incompatible with the notion that glutamate only increases the open probability of the anion pore associated with glutamate transporters and demonstrate unique gating mechanisms of EAAT-associated anion channels. Excitatory amino acid transporters (EAATs)1 mediate the removal of glutamate from the synaptic cleft in the central nervous system and the uptake of glutamate in kidney and intestine (1-3). Five structurally distinct subtypes of mammalian glutamate transporters, EAAT1-EAAT5, have been identified in recent years (4 -9). Each of these isoforms exhibits two separate transport processes: a stoichiometrically coupled cotransport of one glutamate with three Na ϩ ions and one H ϩ , in countertransport to one K ϩ ion (10, 11); and an anion conductance that appears to be pore-mediated. The EAAT-associated anion channel is currently thought to function as a glutamategated channel with a tight coupling of channel opening and closing to conformational changes of the corresponding carrier domain. In this model, only certain carrier conformations are associated with conducting anion pores, and the anion channel cycles between conducting and non-conducting states during transitions through various conformational states of the glutamate carrier (8,9,(12)(13)(14)(15).We investigated anion conduction properties of two EAAT isoforms, human EAAT2 and rat EAAT4, using patch clamp recordings of transfected tsA201 cells under conditions that eliminate the Glu/Na ϩ /H ϩ /K ϩ current component. Our results demonstrated that opening and closing of the EAAT-associated anion channels as well as the interaction with the glutamate uptake process are more complex than previously assumed. External glutamate modifies intrinsic properties of EAAT2-and EAAT4-associated anion channels such as anion selectivity and the rate constants of anion permeation. Moreover, EAAT4 anion channels exhibit voltage-dependent opening and closing transitions that are modified by glutamate. These results provide novel insights into the function of neurotransmitter transporters and illustrate similarities as well as differences between transporter-associated pores and ion channe...

ObjectiveAutoimmune encephalitis is most frequently associated with anti‐NMDAR autoantibodies. Their pathogenic relevance has been suggested by passive transfer of patients' cerebrospinal fluid (CSF) in mice in vivo. We aimed to analyze the intrathecal plasma cell repertoire, identify autoantibody‐producing clones, and characterize their antibody signatures in recombinant form.MethodsPatients with recent onset typical anti‐NMDAR encephalitis were subjected to flow cytometry analysis of the peripheral and intrathecal immune response before, during, and after immunotherapy. Recombinant human monoclonal antibodies (rhuMab) were cloned and expressed from matching immunoglobulin heavy‐ (IgH) and light‐chain (IgL) amplicons of clonally expanded intrathecal plasma cells (cePc) and tested for their pathogenic relevance.ResultsIntrathecal accumulation of B and plasma cells corresponded to the clinical course. The presence of cePc with hypermutated antigen receptors indicated an antigen‐driven intrathecal immune response. Consistently, a single recombinant human GluN1‐specific monoclonal antibody, rebuilt from intrathecal cePc, was sufficient to reproduce NMDAR epitope specificity in vitro. After intraventricular infusion in mice, it accumulated in the hippocampus, decreased synaptic NMDAR density, and caused severe reversible memory impairment, a key pathogenic feature of the human disease, in vivo.InterpretationA CNS‐specific humoral immune response is present in anti‐NMDAR encephalitis specifically targeting the GluN1 subunit of the NMDAR. Using reverse genetics, we recovered the typical intrathecal antibody signature in recombinant form, and proved its pathogenic relevance by passive transfer of disease symptoms from man to mouse, providing the critical link between intrathecal immune response and the pathogenesis of anti‐NMDAR encephalitis as a humorally mediated autoimmune disease.

The enzymes gelatinase A/matrix metalloproteinase-2 (MMP-2) and gelatinase B/MMP-9 are essential for induction of neuroinflammatory symptoms in experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis (MS); in the absence of these enzymes, the disease does not develop. We therefore investigated the cellular sources and relative contributions of MMP-2 and MMP-9 to disease at early stages of EAE induction. We demonstrated that MMP-9 from an immune cell source is required in EAE for initial infiltration of leukocytes into the central nervous system and that MMP-9 activity is a reliable marker of leukocyte penetration of the blood-brain barrier. We then developed a molecular imaging method to visualize MMP activity in the brain using fluorescent- and radioactive-labeled MMP inhibitors (MMPis) in EAE animals and used the radioactive MMP ligand for positron emission tomography (PET) imaging of MMP activity in patients with MS. In contrast to traditional T1-gadolinium contrast-enhanced MRI, MMPi-PET enabled tracking of MMP activity as a unique feature of early lesions and ongoing leukocyte infiltration. MMPi-PET therefore allows monitoring of the early steps of MS development and provides a sensitive, noninvasive means of following lesion formation and resolution in murine EAE and human MS.

Cytotoxic CD8ϩ T cells are considered important effector cells contributing to neuronal damage in inflammatory and degenerative CNS disorders. Using time-lapse video microscopy and two-photon imaging in combination with whole-cell patch-clamp recordings, we here show that major histocompatibility class I (MHC I)-restricted neuronal antigen presentation and T cell receptor specificity determine CD8 ϩ T-cell locomotion and neuronal damage in culture and hippocampal brain slices. Two separate functional consequences result from a direct cell-cell contact between antigen-presenting neurons and antigen-specific CD8 ϩ T cells. (1) An immediate impairment of electrical signaling in single neurons and neuronal networks occurs as a result of massive shunting of the membrane capacitance after insertion of channel-forming perforin (and probably activation of other transmembrane conductances), which is paralleled by an increase of intracellular Ca 2ϩ levels (within Ͻ10 min). (2) Antigen-dependent neuronal apoptosis may occur independently of perforin and members of the granzyme B cluster (within ϳ1 h), suggesting that extracellular effects can substitute for intracellular delivery of granzymes by perforin. Thus, electrical silencing is an immediate consequence of MHC I-restricted interaction of CD8 ϩ T cells with neurons. This mechanism is clearly perforin-dependent and precedes, but is not causally linked, to neuronal cell death.

Rasmussen encephalitis (RE) is a rare paediatric epilepsy with uni-hemispheric inflammation and progressive neurological deficits. To elucidate RE immunopathology, we applied T-cell receptor (TCR) sequencing to blood (n=23), cerebrospinal fluid (n=2) and brain biopsies (n=5) of RE patients, and paediatric controls. RE patients present with peripheral CD8+ T-cell expansion and its strength correlates with disease severity. In addition, RE is the only paediatric epilepsy with prominent T-cell expansions in the CNS. Consistently, common clones are shared between RE patients, who also share MHC-I alleles. Public RE clones share Vβ genes and length of the CDR3. Rituximab/natalizumab/basiliximab treatment does not change TCR diversity, stem cell transplantation replaces the TCR repertoire with minimal overlap between donor and recipient, as observed in individual cases. Our study supports the hypothesis of an antigen-specific attack of peripherally expanded CD8+ lymphocytes against CNS structures in RE, which might be ameliorated by restricting access to the CNS.

Only higher CASPR2 serum antibody titres indicate anti-CASPR2 encephalitis, and diagnostic accuracy increases if MRI findings are considered. Anti-CASPR2 encephalitis has characteristic features and a favourable outcome with immunotherapy.