Glycine Receptor ß-Targeting Autoantibodies Contribute to the Pathology of Autoimmune Diseases.

BACKGROUND AND OBJECTIVES: Stiff-person syndrome (SPS) and progressive encephalomyelitis with rigidity and myoclonus (PERM) are rare neurologic disorders of the CNS. Until now, exclusive GlyRα subunit-binding autoantibodies with subsequent changes in function and surface numbers were reported. GlyR autoantibodies have also been described in patients with focal epilepsy. Autoimmune reactivity against the GlyRß subunits has not yet been shown. Autoantibodies against GlyRα1 target the large extracellular N-terminal domain. This domain shares a high degree of sequence homology with GlyRß making it not unlikely that GlyRß-specific autoantibody (aAb) exist and contribute to the disease pathology. METHODS: In this study, we investigated serum samples from 58 patients for aAb specifically detecting GlyRß. Studies in microarray format, cell-based assays, and primary spinal cord neurons and spinal cord tissue immunohistochemistry were performed to determine specific GlyRß binding and define aAb binding to distinct protein regions. Preadsorption approaches of aAbs using living cells and the purified extracellular receptor domain were further used. Finally, functional consequences for inhibitory neurotransmission upon GlyRß aAb binding were resolved by whole-cell patch-clamp recordings. RESULTS: Among 58 samples investigated, cell-based assays, tissue analysis, and preadsorption approaches revealed 2 patients with high specificity for GlyRß aAb. Quantitative protein cluster analysis demonstrated aAb binding to synaptic GlyRß colocalized with the scaffold protein gephyrin independent of the presence of GlyRα1. At the functional level, binding of GlyRß aAb from both patients to its target impair glycine efficacy. DISCUSSION: Our study establishes GlyRß as novel target of aAb in patients with SPS/PERM. In contrast to exclusively GlyRα1-positive sera, which alter glycine potency, aAbs against GlyRß impair receptor efficacy for the neurotransmitter glycine. Imaging and functional analyses showed that GlyRß aAbs antagonize inhibitory neurotransmission by affecting receptor function rather than localization.

Different Patterns of Autoantibody Secretion by Peripheral Blood Mononuclear Cells in Autoimmune Nodopathies.

BACKGROUND AND OBJECTIVES: Autoimmune nodopathies with antibodies against the paranodal proteins show a distinct phenotype of a severe sensorimotor neuropathy. In some patients, complete remission can be achieved after treatment with rituximab whereas others show a chronic course. For optimal planning of treatment, predicting the course of disease and therapeutic response is crucial. METHODS: We stimulated peripheral blood mononuclear cells in vitro to find out whether secretion of specific autoantibodies may be a predictor of the course of disease and response to rituximab. RESULTS: Three patterns could be identified: In most patients with anti-Neurofascin-155-, anti-Contactin-1-, and anti-Caspr1-IgG4 autoantibodies, in vitro production of autoantibodies was detected, indicating autoantigen-specific memory B cells and short-lived plasma cells/plasmablasts as the major source of autoantibodies. These patients generally showed a good response to rituximab. In a subgroup of patients with anti-Neurofascin-155-IgG4 autoantibodies and insufficient response to rituximab, no in vitro autoantibody production was found despite high serum titers, indicating autoantibody secretion by long-lived plasma cells outside the peripheral blood. In the patients with anti-pan-Neurofascin autoantibodies-all with a monophasic course of disease-no in vitro autoantibody production could be measured, suggesting a lack of autoantigen-specific memory B cells. In some of them, autoantibody production by unstimulated cells was detectable, presumably corresponding to high amounts of autoantigen-specific plasmablasts-well in line with a severe but monophasic course of disease. DISCUSSION: Our data suggest that different B-cell responses may occur in autoimmune nodopathies and may serve as markers of courses of disease and response to rituximab.