The role of complement in myasthenia gravis: serological evidence of complement consumption in vivo.
BACKGROUND
Antibodies to the acetylcholine receptor (AChR) titin and the ryanodine receptor (RyR) occur in myasthenia gravis (MG). These antibodies are capable of complement activation in vitro. The involvement of the complement system should cause consumption of complement components such as C3 and C4 in vivo.


METHODS
Complement components C3 and C4 were assayed in sera from 78 AChR antibody-positive MG patients and 52 healthy controls. Forty-eight of the patient sera contained titin antibodies as well, and 20 were also RyR antibody-positive.


RESULTS
MG patients with AChR antibody concentrations above the median (11.2 nmol/l) had significantly lower mean C3 and C4 concentrations in serum compared to those with AChR antibody concentrations below the median. Titin antibody-positive MG patients, titin antibody-negative early-onset MG patients, titin antibody-negative late-onset MG patients, and controls had similar C3 and C4 concentrations. Nor did mean C3 and C4 concentrations differ in MG patients with RyR antibodies. Patients with severe MG (grades 4 and 5) had similar C3 and similar C4 levels compared to those with mild MG (grades 1 and 2).


CONCLUSIONS
An increased in vivo complement consumption was detected in MG patients with high AChR antibody concentrations, unrelated to MG severity and non-AChR muscle antibodies.
Romi
Fredrik
F
Department of Neurology, Haukeland University Hospital, Bergen N-5021, Norway. fredrik.romi@haukeland.no
Kristoffersen
Einar K
EK
Aarli
Johan A
JA
Gilhus
Nils Erik
NE
D000906:Antibodies / Q000378:metabolism; D015932:Complement C3c / Q000502:physiology*; D015935:Complement C4b / Q000502:physiology*; D064211:Connectin; D004185:Disability Evaluation; D005260:Female; D049690:History, Ancient; D006801:Humans; D008297:Male; D009124:Muscle Proteins / Q000276:immunology; D009157:Myasthenia Gravis / Q000145:classification / Q000276:immunology* / Q000378:metabolism; D010446:Peptide Fragments; D011494:Protein Kinases / Q000276:immunology; D011950:Receptors, Cholinergic / Q000276:immunology; D019837:Ryanodine Receptor Calcium Release Channel / Q000276:immunology
D000906:Antibodies; D064211:Connectin; D009124:Muscle Proteins; D010446:Peptide Fragments; D011950:Receptors, Cholinergic; D019837:Ryanodine Receptor Calcium Release Channel; C577285:TTN protein, human; C033860:complement C4c; D015932:Complement C3c; D015935:Complement C4b; D011494:Protein Kinases