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

Abstract

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.

• Authors: Sudhakar Reddy Kalluri, Zsolt Illes, Rajneesh Srivastava, Bruce Cree, Til Menge, Jeffrey L Bennett, Achim Berthele, Bernhard Hemmer
• Journal: Archives of neurology (Arch Neurol) Vol. 67 Issue 10 Pg. 1201-8 (Oct 2010) ISSN: 1538-3687 [Electronic] United States
• PMID: 20937947 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• AQP4 protein, human
• Aquaporin 4
• Immunoglobulin G

Topics

• Adult
• Aged
• Aquaporin 4 (blood, cerebrospinal fluid, genetics, 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, cerebrospinal fluid)
• Male
• Middle Aged
• Neuromyelitis Optica (blood, cerebrospinal fluid, immunology)
• Transfection (methods)
• Young Adult