Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


Epitope Mapping of the Autoantigen Aquaporin-4 Reveals Linear Epitopes Located in the Intracellular Region of the Molecule.

Kabylafka1,  Eleni I., Routsias1,  John G., Alexopoulos1,  Haralampos, Tzioufas2,  Athanasios G.

Department of Pathophysiology, Medical School of Athens, Athens, Greece
Medical School-Univ of Athens, Athens, Greece

Background:

Autoantibodies to aquaporin-4 (AQP4), a water channel localized in astrocytic foot processes at the blood-brain barrier, have been shown to correlate with Neuromyelitis Optica (Devic's syndrome), a rare syndrome. The main symptoms of the syndrome are optic neuritis and myelitis. The latter can be found in the context of a systemic autoimmune disease, such as Systemic Lupus Erythematosus (SLE), and primary Sjögren's syndrome (pSS). Despite the fact that anti-AQP4 antibodies have an established role in the pathogenesis of Neuromyelitis Optica, their fine specificity and regulation of their production has not been clarified. The aim of the present study was to identify the B cell linear epitopes of the AQP4 protein, investigate putative similarities with other molecules and evaluate the sensitivity and specificity in detecting anti-AQP4 autoantibodies.

Methods:

Sera from 21 patients with Devic's syndrome, all positive for anti-AQP4 antibodies using indirect immunofluorescence in mouse brain tissue, were used. Sera from 23 SLE and 23 pSS patients, without neurologic involvement were utilized as disease controls. 26 healthy individuals were also used. 11 overlapping peptides, spanning the entire intracellular and extracellular domains of the AQP4 molecule, were synthesized (Bio-synthesis Inc, U.S.A.), and all sera were screened by ELISA for the presence of antibodies against the peptides. The cut-off values for each peptide assay were determined using the mean OD plus 2 SD of sera from 26 healthy controls. Specificity was evaluated by homologous inhibition assays.

Results:

Reactivity against 3 different peptides spanning the sequences aa1–22 [MSDRPTARRWGKCGPLCTRENI], aa88–113 [FGHISGGHINPAVTVAMVCTRKISIA] and aa252–275 [FCPDVEFKRRFKEAFSKAAQQTKG] was demonstrated in 33%, 24% and 24% of sera from Devic's patients, respectively, while 38% of patients' sera were reactive against at least one of the 3 peptides. All epitopes were localized in the intracellular domains of AQP4. A 73% sequence similarity was observed between the [aa252–275] peptide (amino acids 257–271), and the aa219–233 domain of the Tax-1 HTLV-1 protein, which appears to play a pathogenetic role for spastic paraparesis. None of healthy controls showed any reactivity. Homologous inhibition assays produced high inhibition rates (84.3%, 71.1% and 84% for peptides aa1–22, aa88–113 and aa252–275, respectively). SLE patients tested positive for antibodies against peptides aa1–22, aa88–113 and aa252–275 in 8.6%, 0% and 8.6%, respectively, while pSS patients recognized the above peptides in 8.6%, 4.3% and 8.6%.

Conclusions:

This is the first epitope mapping of the autoantigen AQP4. Most of antibodies to AQP4 are directed against conformational epitopes but a significant proportion targets certain linear epitopes, located in the intracellular domains of the molecule. Future studies in our laboratory are aiming to determine the pathogenic relevance of these epitopes.

To cite this abstract, please use the following information:
Kabylafka, Eleni I., Routsias, John G., Alexopoulos, Haralampos, Tzioufas, Athanasios G.; Epitope Mapping of the Autoantigen Aquaporin-4 Reveals Linear Epitopes Located in the Intracellular Region of the Molecule. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :1895
DOI: 10.1002/art.29660

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