Striational autoantibodies in myasthenia gravis patients recognize I-band titin epitopes.
Myasthenia gravis (MG) patients develop autoantibodies primarily against the acetylcholine receptor in the motor endplate, but also against intracellular striated muscle proteins, notably titin, the giant elastic protein of the myofibrillar cytoskeleton. Titin antibodies have previously been shown to be directed against a single epitope on the molecule, located at the A-band/I-band junction and referred to as the main immunogenic region (MIR) of titin. By using immunofluorescence microscopy on stretched single myofibrils, we now report that approximately 40% of the sera from 18 MG/thymoma patients and 8 late-onset MG patients with thymus atrophy contain antibodies that bind to a more central I-band titin region. This region consists of homologous immunoglobulin domains and is known to be differentially spliced dependent on muscle type. All patients with I-band titin antibodies also had antibodies against the MIR. Although a statistically significant correlation between the occurrence of I-band titin antibodies and MG severity was not apparent, the results could hint at an initial immunoreactivity to titin's MIR, followed by reactivity along the titin molecule in the course of the disease.
Lübke
E
E
Institute of Physiology II, University of Heidelberg, Germany.
Freiburg
A
A
Skeie
G O
GO
Kolmerer
B
B
Labeit
S
S
Aarli
J A
JA
Gilhus
N E
NE
Wollmann
R
R
Wussling
M
M
Rüegg
J C
JC
Linke
W A
WA
D000328:Adult; D000368:Aged; D001323:Autoantibodies / Q000276:immunology*; D001327:Autoimmune Diseases / Q000209:etiology / Q000276:immunology*; D064211:Connectin; D003598:Cytoskeletal Proteins / Q000276:immunology*; D000939:Epitopes / Q000276:immunology*; D005260:Female; D006801:Humans; D008297:Male; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D008875:Middle Aged; D009124:Muscle Proteins / Q000276:immunology*; D009157:Myasthenia Gravis / Q000209:etiology / Q000276:immunology*; D016133:Polymerase Chain Reaction; D011494:Protein Kinases / Q000276:immunology*; D011950:Receptors, Cholinergic / Q000276:immunology; D012720:Severity of Illness Index; D013945:Thymoma / Q000150:complications / Q000276:immunology; D013950:Thymus Gland / Q000473:pathology; D013953:Thymus Neoplasms / Q000150:complications / Q000276:immunology
D001323:Autoantibodies; D064211:Connectin; D003598:Cytoskeletal Proteins; D000939:Epitopes; D009124:Muscle Proteins; D011950:Receptors, Cholinergic; C577285:TTN protein, human; D011494:Protein Kinases