Pattern-specific loss of aquaporin-4 immunoreactivity distinguishes neuromyelitis optica from multiple sclerosis

• Published in: Brain (London, England : 1878) Vol. 130; no. 5; pp. 1194 - 1205
• Main Authors: Roemer, Shanu F., Parisi, Joseph E., Lennon, Vanda A., Benarroch, Eduardo E., Lassmann, Hans, Bruck, Wolfgang, Mandler, Raul N., Weinshenker, Brian G., Pittock, Sean J., Wingerchuk, Dean M., Lucchinetti, Claudia F.
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01-05-2007; Oxford Publishing Limited (England)
• Subjects: Adolescent; Adult; Aged; Aged, 80 and over; Aquaporin 4 - immunology; Astrocytes - immunology; Autoantibodies - analysis; Biological and medical sciences; Brain - immunology; Case-Control Studies; Diagnosis, Differential; Disease Progression; Female; Humans; Immunoglobulin G - immunology; Immunohistochemistry; Immunomodulators; Macrophages - immunology; Male; Medical sciences; Middle Aged; Multiple Sclerosis - immunology; Multiple sclerosis and variants. Guillain barré syndrome and other inflammatory polyneuropathies. Leukoencephalitis; Myelin Sheath - immunology; Neurology; Neuromyelitis Optica - immunology; Oligodendroglia - immunology; Optic Nerve - immunology; Pharmacology. Drug treatments; Spinal Cord - immunology; blood-brain barrier; aquaporin-4; astrocyte; multiple sclerosis; demyelination; neuromyelitis optica; Multiple sclerosis; Nervous system diseases; Optic nerve; Neuroglia; Central nervous system; Neurooptic myelitis; Astrocyte; Blood brain barrier; Encephalon; Inflammatory disease; Eye disease; Cranial nerve disease; Visual pathway; Demyelination; Central nervous system disease; Spinal cord disease; Aquaporin
• ISSN: 0006-8950; 1460-2156
• DOI: 10.1093/brain/awl371

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease that typically affects optic nerves and spinal cord. Its pathogenic relationship to multiple sclerosis (MS) is uncertain. Unlike MS, NMO lesions are characterized by deposits of IgG and IgM co-localizing with products of complement activation in a vasculocentric pattern around thickened hyalinized blood vessels, suggesting a pathogenic role for humoral immunity targeting an antigen in the perivascular space. A recently identified specific serum autoantibody biomarker, NMO-IgG, targets aquaporin-4 (AQP4), the most abundant water channel protein in the CNS, which is highly concentrated in astrocytic foot processes. We analysed and compared patterns of AQP4 immunoreactivity in CNS tissues of nine patients with NMO, 13 with MS, nine with infarcts and five normal controls. In normal brain, optic nerve and spinal cord, the distribution of AQP4 expression resembles the vasculocentric pattern of immune complex deposition observed in NMO lesions. In contrast to MS lesions, which exhibit stage-dependent loss of AQP4, all NMO lesions demonstrate a striking loss of AQP4 regardless of the stage of demyelinating activity, extent of tissue necrosis, or site of CNS involvement. We identified a novel NMO lesion in the spinal cord and medullary tegmentum extending into the area postrema, characterized by AQP4 loss in foci that were inflammatory and oedematous, but neither demyelinated nor necrotic. Foci of AQP4 loss coincided with sites of intense vasculocentric immune complex deposition. These findings strongly support a role for a complement activating AQP4-specific autoantibody as the initiator of the NMO lesion, and further distinguish NMO from MS.