Neuroimmunology update

1. NEUROIMMUNOLOGY: The Newer Frontiers in Autoimmunity…Recent Advances DR RAJESH V BENDRE MD(PATH), DNB(PATH), DPB Chief Pathologist, Head Laboratory & Blood Bank Services Jaslok Hospital & Research Center

2. INTRODUCTION The Central Nervous System - Immunological Privileged Site- Facts – Favouring CNS as immnunological privileged site- • Blood brain barrier (BBB)- Anatomic • No MHC molecules on nerve cells, • No classical dendritic cells & lymphatics in CNS However, Recent Evidences- Intrathecal immune response - The Central Nervous System- Immunological Privileged Site? • BBB- Functional- Passage of memory T and B cells through BBB, which can generate immunological response • APC- Microglia can process & present antigens Friend of Neurons - Phagocytose apoptotic neurons, Secrete neuroprotective factors & IL10 Foe of Neurons - Secrete neurotoxic molecules - TNF ,IL1 & free radical species , induce apoptosis, interact with astrocytes -eliciting gliosis

3. Neuroimmunology-Evolving & Emerging Field Immune response to diseases of the nervous system • Intra thecalhumoral specific response to various antigens as diagnostic tool in - Demyelinating diseases (Central-MS, NMO, Peripheral -GBS), - Infections- viral. • Autoimmune Encephalitides associated with antibodies to neuronal cell surface antigens (GAD, NMDA, VGKC) • Paraneoplastic Syndromes -AetiologyAntineuronal antibodies to intracellular antigens (Hu, Ri, Ma, Tr, CV2, amphiphysin). • Neuromuscular disorders- Aetiology for Myaesthenia Gravis (Achrab, MUSK ab), Eaton- Lambert Syndrome(VGCC Ab) • Importantly, these immune mediated CNS disorders are often treatable with immunotherapy.

4. Multiple SclerosisAn Immunogenetic Disease Environmental Factors Microbial Agents- EBV, HHV6 Vitamin D • Genetic Predisposition • HLA-DR2 (DRß1*1501)(Antigen presentation) • MS cluster/community • Regulatory T cells • Memory B cells Data supported by the Multiple Sclerosis International Federation World MS Atlas, which projects a prevalence of 3/100,000 in India, which is nearly triple the estimate of previous reports. In a prospective and longitudinal study of CNS demyelinating disorders which included 51 patients, Pandit et al 2008. found 47% of their MS cases have clinical attacks confined to the optic nerve and spinal cord Immune Dysregulation- Autoimmunity MS

5. Multiple Sclerosis-Lab Diagnosis • IntrathecalIgG Synthesis- • This indicates expansion of B cells in the CNS • and is a characteristic feature of MS. • In the McDonald criteria, a positive CSF study is defined as one showing either oligoclonalIgG bands or a high IgG index, which are two different indicators of intrathecalIgG synthesis. These indicators differ in sensitivity and specificity, and there are also differences in the techniques of CSF analysis. • The sensitivity(90%) for detecting oligoclonalIgG banding with Isoelectric focusing is high. • Approximately 79%-90% of all patients with multiple sclerosis have permanently observable oligoclonal bands. However also varies with the type of MS- ( 90%) in relapsing-remitting MS, it seems to be substantially lower in primary-progressive MS.

6. MS – CSF OCB Isoelectric focusing of CSF. Lane 4 (CSF) and 4’ (serum). is positive for oligoclonal bands. The IgG index was 0.7 (ref. interval 0.3–0.8). The serum/CSF albumin ratio was <9 indicating normal permeability of the blood brain barrier. Other patients are negative for oligoclonal banding shown in lanes 2(mirror image), 3, and 5.

7. NeuromyelitisOptica SPECTRUM DISORDERS (NMOSD) - In India NMO diagnosed by Winger chuck criteria 2006 – Incidence is 2.6% (Pandit et al 2014). Aquaporin 4 IgG Antibodies by Indirect Immunofluorescence – Aquaporin4 is an osmosis driven water channel protein present on astrocytes Anti Myelin Associated OligodendrocyteIgG Antibodies by Indirect Immunofluorescence

8. AUTOIMMUNE ENCEPHALITIDES- • Clinical Presentation- • The subacute onset of amnesia, disorientation, and seizures • Differential Diagnosis – • Viral Encephalitis, Hashimoto’s Encephalopathy, Wernicke’s Encephalopathy & Idiopathic Encephalopathy. • What Are the Autoimmune Encephalitides? • The Origin of Autoimmune Encephalitis – • - Limbic encephalitis in patients with a remote cancer (Brierley et al., 1960) • discovery of Antibodies which target the extracellular domain of neuronal proteins - associated with Autoimmune Encephalitis. The common targets defined so far are LGI1, CASPR-2, VGKC, NMDA, AMPA, GABA receptors. • (Vincent et al.1999, 2004 & 2006) (Dalmau & Rosenfeld, 2008). • Recent surveys have suggested that a proportion of these previously idiopathic cases are associated with autoantibodies directed against neuronal proteins (Granerod et al, 2010). • Incidence of such specific autoantibodies is shown in about 8% Encephalitides cases.

9. AUTOIMMUNE ENCEPHALITIDES- Pathophysiology • Synaptic plasticity is an essential property of neurons and is essential for memory, learning and cognition • Synaptic plasticity depends on the interactions of ion channels and synaptic receptors, including Excitatory- glutamate NMDA (N-methyl-D-aspartate) receptors, AMPA (alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid) receptors & • Inhibitory- GABA (gamma-aminobutyric acid) receptors. • Antibodies directed against these surface anigens essential in neurotransmission, & thus adversely impacting synaptic plasticity, is the pathogenetic basis for various “Autoimmune Encephalitides”

10. AUTOIMMUNE ENCEPHALITIDES- Classification Currently, such antibodies can be classified according to the location of the recognized antigen into three major groups:

11. AUTOIMMUNE ENCEPHALITIDES- Clinical Presentation

12. AUTOIMMUNE ENCEPHALITIDES- Clinical Presentation Autoimmune encephalitis: case series & comprehensive review of the literature T.Wingfield et al. Q J Med 2011; 104:921–931

13. AUTOIMMUNE ENCEPHALITIDES- Clinical Presentation Autoimmune Encephalitis -New Awareness, Challenging Questions. S Irani, Vincent et al. Discovery Medicine May,2011.

14. AUTOIMMUNE ENCEPHALITIDES- Laboratory Test

15. Anti- Neuronal Antibodies – Paraneoplastic syndromes Line Blot Assay : - For antibodies seen in Paraneoplastic syndromes

16. Anti- Neuronal Antibodies – • These antibodies can occur before the appearance of detectable tumour. • The associated tumors can be benign or malignant. • Associated ANA can interfere in interpretation & Blot assay recommended in such cases to confirm antineuronal antibodies

17. Peripheral Nervous system - Autoantibody Gangliosides are a family of glycolipids which are particularly abundant in membrane components of the nervous system. They are composed of a hydrophobic lipid part and a hydrophilic oligosaccharide part. These autoantibodies frequently react with epitopes of the carbohydrate region of cell surface glycoconjugates. Glycoconjugates include glycoproteins (e g MAG) or glycolipids (e g Gangliosides).

18. Peripheral Nervous system - Autoantibody • Line Blot Assay : • GangliosidesAb

19. Neuromuscular disorders • Post Synaptic - In myaesthenia gravis, the End Plate Potential (EPP) fails to effectively activate the muscle fiber due to an autoimmune reaction against Acetylcholine receptors (common), resulting in muscle weakness and fatigue. It has recently been realized that a second category of gravis is due to auto-antibodies against MuSK (muscle specific tyrosine kinase). • Pre Synaptic – In Lambert-Eaton myasthenic syndrome, is usually associated with presynaptic antibodies to the voltage-dependent calcium channel (VGCC). These Autoantibodies namely ACRAB, MUSK & VGCC can be tested in serum by immunoprecipitation reaction using Radioimmunoassay (RIA) technique

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