Aquaporin-4 water channel expression by thymoma of patients with and without myasthenia gravis.
BACKGROUND
Neuromyelitis optica (NMO) is a serious idiopathic inflammatory demyelinating disorder characterized by acute transverse myelitis and optic neuritis. A significant proportion of NMO patients are seropositive for NMO-IgG, an autoantibody targeting aquaporin-4 (AQP4) water channel. Paraneoplastic NMO associated various tumors were recently reported.


OBJECTIVE
We studied the expression of AQP4 by thymoma from patients with and without myasthenia gravis (MG).


METHODS
Thymoma obtained from thymomectomy in patients with and without MG were studied by immunohistochemistry and western blot.


RESULTS
Ten thymoma patients (9 with MG) and two control patients without thymoma or MG were studied. Immunohistochemistry revealed AQP4 immunoreactivity in cell membrane of thymoma cells from all ten thymoma specimens whereas thymic tissues from patients without thymoma or MG were negative for AQP4 immunoreactivity. Western blot revealed that lysates of nine of the ten thymoma specimens reacted with anti-human AQP4 antibody with a band of ~30 kDa compatible with the molecular weight of AQP4. Interestingly, immunofluorescence revealed that IgG isolated from 2 NMO patients seropositive for NMO-IgG bound to cell membrane of thymoma cells from all ten thymoma specimens while IgG from healthy control subject did not.


CONCLUSIONS
Thymoma cells of patients with and without MG express AQP4. AQP4 autoantibodies from serum of NMO patients bound to AQP4 expressed on thymoma cell membrane.
Chan
K H
KH
University Department of Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong. koonho@hkucc.hku.hk
Kwan
J S C
JS
Ho
P W L
PW
Ho
S L
SL
Chui
W H
WH
Chu
A C Y
AC
Ho
J W M
JW
Zhang
W Y
WY
Kung
M H W
MH
D000328:Adult; D000368:Aged; D051401:Aquaporin 4 / Q000096:biosynthesis* / Q000235:genetics; D005260:Female; D005786:Gene Expression Regulation / Q000276:immunology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D013945:Thymoma / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D013953:Thymus Neoplasms / Q000276:immunology / Q000378:metabolism* / Q000473:pathology
C496030:AQP4 protein, human; D051401:Aquaporin 4