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Antibodies Against Glutamic Acid Decarboxylase 65 Are Locally Produced in the CSF and Arise During Affinity
Michelle Biljecki1, Katharina Eisenhut1, Eduardo Beltrán1
1From the Institute of Clinical Neuroimmunology (M.B., K.E., E.B., S.W., S.M., A.T., A.F.-H., T.K., M.K., E.M., F.S.T.), University Hospital, Ludwig-Maximilians-Universität Munich; Biomedical Center (BMC) (M.B., K.E., E.B., S.W., S.M., A.T., A.F.-H., T.K., M.K., E.M., F.S.T.), Medical Faculty, Ludwig-Maximilians-Universität Munich, Martinsried; Graduate School of Systemic Neurosciences Ludwig-Maximilians-Universität Munich (M.B., K.E.); Munich Cluster for Systems Neurology (SyNergy) (E.B., M.K., F.S.T.); Innate Immunity Unit (A.T.), Institut Pasteur, Inserm U1223, Paris, France; Université de Paris (A.T.), Sorbonne Paris Cité, France; Institute of Laboratory Medicine (P.E.), University Hospital, LMU Munich; Institute of Clinical and Molecular Virology (P.S.), University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg; and Department of Neurology (J.L.), University Hospital Ulm, Germany.
Background And Objectives:
Antibodies (Abs) against the cytoplasmic protein glutamic acid decarboxylase 65 (GAD65) are detected in patients with neurologic syndromes together referred to as GAD65-Ab spectrum disorders. The response of some of these patients to plasma exchange or immunoglobulins indicates that GAD65-Abs could contribute to disease pathogenesis at least at some stages of disease. However, the involvement of GAD65-reactive B cells in the CNS is incompletely understood.
Methods:
We studied 7 patients with high levels of GAD65-Abs and generated monoclonal Abs (mAbs) derived from single cells in the CSF. Sequence characteristics, reactivity to GAD65, and the role of somatic hypermutations of the mAbs were analyzed.
Results:
Twelve CSF-derived mAbs were generated originating from 3 patients with short disease duration, and 7/12 of these mAbs (58%) were GAD65 reactive in at least 1 detection assay. Four of 12 (33%) were definitely positive in all 3 detection assays. The intrathecal anti-GAD65 response was polyclonal. GAD65-Abs were mostly of the IgG1 subtype and had undergone affinity maturation. Reversion of 2 GAD65-reactive mAbs to their corresponding germline-encoded unmutated common ancestors abolished GAD65 reactivity.
Discussion:
GAD65-specific B cells are present in the CNS and represent a sizable fraction of CSF B cells early in the disease course. The anti-GAD65 response in the CSF is polyclonal and shows evidence of antigen-driven affinity maturation required for GAD65 recognition. Our data support the hypothesis that the accumulation of GAD65-specific B cells and plasma cells in the CSF is an important feature of early disease stages.
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