Immunization against GAD induces antibody binding to GAD-independent antigens and brainstem GABAergic neuronal loss.
Stiff person syndrome (SPS) is a highly-disabling neurological disorder of the CNS characterized by progressive muscular rigidity and spasms. In approximately 60-80% of patients there are autoantibodies to glutamic acid decarboxylase (GAD), the enzyme that synthesizes gamma-amino butyric acid (GABA), the predominant inhibitory neurotransmitter of the CNS. Although GAD is intracellular, it is thought that autoimmunity to GAD65 may play a role in the development of SPS. To test this hypothesis, we immunized mice, that expressed enhanced green fluorescent protein (EGFP) under the GAD65 promoter, with either GAD65 (n = 13) or phosphate buffered saline (PBS) (n = 13). Immunization with GAD65 resulted in autoantibodies that immunoprecipitated GAD, bound to CNS tissue in a highly characteristic pattern, and surprisingly bound not only to GAD intracellularly but also to the surface of cerebellar neurons in culture. Moreover, immunization resulted in immunoglobulin diffusion into the brainstem, and a partial loss of GAD-EGFP expressing cells in the brainstem. Although immunization with GAD65 did not produce any behavioral abnormality in the mice, the induction of neuronal-surface antibodies and the trend towards loss of GABAergic neurons in the brainstem, supports a role for humoral autoimmunity in the pathogenesis of SPS and suggests that the mechanisms may involve spread to antigens expressed on the surface of these neurons.
Neuroimmunology Group, Weatherall Institute of Molecular Medicine and Nuffield Department of Clinical Neurosciences, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom ; Department of Clinical Medicine, University of Colombo, Colombo, Sri Lanka.
Thashi
T
Chang
Harry
H
Alexopoulos
Philippa
P
Pettingill
Mary
M
McMenamin
Robert
R
Deacon
Ferenc
F
Erdelyi
Gabor
G
Szabó
Camilla J
CJ
Buckley
Angela
A
Vincent
D000818:Animals; D001323:Autoantibodies / Q000096:biosynthesis* / Q000276:immunology; D015551:Autoimmunity; D002478:Cells, Cultured; D002531:Cerebellum / Q000276:immunology* / Q000473:pathology; D005260:Female; D059330:GABAergic Neurons / Q000276:immunology* / Q000473:pathology; D017930:Genes, Reporter; D005968:Glutamate Decarboxylase / Q000008:administration & dosage* / Q000235:genetics / Q000276:immunology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007114:Immunization; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D050506:Mutant Chimeric Proteins / Q000235:genetics / Q000276:immunology*; D011485:Protein Binding; D021381:Protein Transport; D016750:Stiff-Person Syndrome / Q000139:chemically induced / Q000276:immunology* / Q000473:pathology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D001323:Autoantibodies; D050506:Mutant Chimeric Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; C401141:glutamate decarboxylase 2