Characterization of A Novel Autoimmune Encephalitis Associated Antibody against CRMP2

ObjectiveAutoimmune encephalitis (AE) is a large category disorder urging antibody characterization. The aim was to identify a novel AE related autoantibody targeting an intracellular synaptic protein. MethodsSuspected AE patients had negative conventional antibodies screening but strong immunolabel signals on rat brain sections with the serum and cerebrospinal fluid (CSF) samples were considered burdening unkown antibody. Immunoprecipitation from the rat brain protein lysate followed by mass spectrometry analysis was used to identify the targeting antigen. Western blotting and/or cell-based assay (CBA) with antigen-overexpressing HEK293T cells were used for antibody specificity, epitope and IgG subtype determination. Patients with similar immunostaining pattern on rat brain sections were retrospectively screened for the antibody. ResultsThe antibody against collapsin response mediator protein 2 (CRMP2), a synaptic protein involved in axon guidance, was identified in a patient with suspected AE. The patient samples reactivated with HEK293T cell overexpressed CRMP2, rather than CRMP1, 3, 4, and 5. The patient samples mainly stained neuronal cytoplasm of the cortex, hippocampus and cerebellum Purkinje cells. This reactivity was eliminated by pre-immunoabsorption with CRMP2-overexpressing HEK293T cells. CRMP2 truncation experiments indicated that 536 amino acids at C-terminus was necessary for the epitope. Subtype analysis showed that anti-CRMP2 antibody was IgG4. Moreover, screening from 19 suspected AE patients led to identification of anti-CRMP2 antibody in another patient with a diagnosis of encephalomyelitis. The two patients responded to immunotherapy. ConclusionsThis study discovered a novel anti-CRMP2 antibody associated with AE. Testing of the antibody might be promising for AE diagnosis and treatment.