Quantification and functional characterization of antibodies to native aquaporin 4 in neuromyelitis optica

Arch Neurol. 2010 Oct;67(10):1201-8. doi: 10.1001/archneurol.2010.269.


Background: Antibodies targeting membrane proteins play an important role in various autoimmune diseases of the nervous system. So far, assays allowing proper analysis of such autoantibodies are largely missing. A serum autoantibody to aquaporin 4 (AQP4) is associated with neuromyelitis optica (NMO). Although several assays are able to detect this autoantibody, they do not allow determination of the biological activity of anti-AQP4 antibodies.

Objective: To develop a bioassay for quantification and characterization of human anti-AQP4 antibodies.

Design, setting, and participants: We developed a novel bioassay for quantification and characterization of human anti-AQP4 antibodies based on high-level expression of native AQP4 (nAQP4) protein on the surface of human astroglioma cells. The test was validated in 2 independent cohorts of patients with NMO spectrum disease.

Results: We detected anti-nAQP4-IgG with a sensitivity of 57.9% and specificity of 100% in patients with NMO spectrum diseases, suggesting that our bioassay is at least as sensitive and specific as the gold-standard NMO-IgG assay. The anti-AQP4 antibodies belonged predominantly to the IgG1 isotype and bound with high affinity to the extracellular domain of nAQP4. Our data suggest that the autoantibody exerts pathological properties because nAQP4-IgG-positive sera induced cell death of nAQP4-expressing cells by antibody-dependent cellular natural killer cell cytotoxic effect and complement activation. Furthermore, nAQP4-IgG titers strongly correlated with in vitro cytotoxic effect.

Conclusions: In NMO, this assay may help to unravel the biological function of anti-nAQP4-IgG. Our findings demonstrate the potential of bioassays to characterize biologically relevant antibodies in human autoimmune diseases.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aquaporin 4 / blood*
  • Aquaporin 4 / cerebrospinal fluid
  • Aquaporin 4 / genetics
  • Aquaporin 4 / immunology*
  • Biological Assay / methods
  • Cell Line, Tumor
  • Cohort Studies
  • Cytotoxicity Tests, Immunologic / methods
  • Female
  • Flow Cytometry / methods
  • Gene Expression Regulation, Neoplastic / physiology
  • Glioma / pathology
  • Humans
  • Immunoglobulin G / blood*
  • Immunoglobulin G / cerebrospinal fluid
  • Male
  • Middle Aged
  • Neuromyelitis Optica / blood*
  • Neuromyelitis Optica / cerebrospinal fluid
  • Neuromyelitis Optica / immunology*
  • Transfection / methods
  • Young Adult


  • AQP4 protein, human
  • Aquaporin 4
  • Immunoglobulin G