Early B cell tolerance defects in neuromyelitis optica favour anti-AQP4 autoantibody production

Brain. 2019 Jun 1;142(6):1598-1615. doi: 10.1093/brain/awz106.


Neuromyelitis optica spectrum disorders (NMOSD) constitute rare autoimmune disorders of the CNS that are primarily characterized by severe inflammation of the spinal cord and optic nerve. Approximately 75% of NMOSD patients harbour circulating pathogenic autoantibodies targeting the aquaporin-4 water channel (AQP4). The source of these autoantibodies remains unclear, but parallels between NMOSD and other autoantibody-mediated diseases posit compromised B cell tolerance checkpoints as common underlying and contributing factors. Using a well established assay, we assessed tolerance fidelity by creating recombinant antibodies from B cell populations directly downstream of each checkpoint and testing them for polyreactivity and autoreactivity. We examined a total of 863 recombinant antibodies. Those derived from three anti-AQP4-IgG seropositive NMOSD patients (n = 130) were compared to 733 antibodies from 15 healthy donors. We found significantly higher frequencies of poly- and autoreactive new emigrant/transitional and mature naïve B cells in NMOSD patients compared to healthy donors (P-values < 0.003), thereby identifying defects in both central and peripheral B cell tolerance checkpoints in these patients. We next explored whether pathogenic NMOSD anti-AQP4 autoantibodies can originate from the pool of poly- and autoreactive clones that populate the naïve B cell compartment of NMOSD patients. Six human anti-AQP4 autoantibodies that acquired somatic mutations were reverted back to their unmutated germline precursors, which were tested for both binding to AQP4 and poly- or autoreactivity. While the affinity of mature autoantibodies against AQP4 ranged from modest to strong (Kd 15.2-559 nM), none of the germline revertants displayed any detectable binding to AQP4, revealing that somatic hypermutation is required for the generation of anti-AQP4 autoantibodies. However, two (33.3%) germline autoantibody revertants were polyreactive and four (66.7%) were autoreactive, suggesting that pathogenic anti-AQP4 autoantibodies can originate from the pool of autoreactive naïve B cells, which develops as a consequence of impaired early B cell tolerance checkpoints in NMOSD patients.

Keywords: AQP4; B cells; autoantibodies; neuromyelitis optica spectrum disorder (NMOSD); tolerance.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aquaporin 4 / genetics*
  • Aquaporin 4 / immunology
  • Autoantibodies / immunology*
  • B-Lymphocytes / immunology*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Neuromyelitis Optica / genetics*
  • Neuromyelitis Optica / metabolism
  • Optic Nerve / immunology


  • Aquaporin 4
  • Autoantibodies