A sensitive non-isotopic assay for acetylcholine receptor autoantibodies.
BACKGROUND
Detection and measurement of serum acetylcholine receptor autoantibodies (AChRAb) are useful in the diagnosis and management of myasthenia gravis (MG). An immunoprecipitation assay (IPA) based on AChR labelled with 125I-alpha bungarotoxin is widely used for measurement of AChRAb, but a non-isotopic assay of sensitivity and specificity comparable to IPA is not available as yet.


METHODS
A new AChRAb ELISA, which is based on the ability of AChRAb to compete with 3 different AChR monoclonal antibodies (MAbs 1-3) for binding sites on affinity purified fetal and adult-type AChR preparations, is described. The sensitivity and specificity of the ELISA were assessed by comparing assay results with a conventional IPA.


RESULTS
There was good agreement between the IPA and the ELISA for measurement of AChRAb (r = 0.85; n = 83; p <0.001). 76/83 MG sera were positive in the ELISA, whilst 72/83 were positive by IPA. Eight sera were positive in the ELISA (inhibition range 18%-46%) but negative by IPA (0.33-0.47 nmol/L toxin bound) and 4 sera were negative in the ELISA (inhibition range -1% to15%) whilst positive by IPA (0.56-2.9 nmol/L toxin bound). Overall 80/83 (96%) of the MG sera were AChRAb positive in one or both assays. In addition, all 191 control serum samples which were negative for AChRAb by IPA were below or equal to 16% of inhibition in our ELISA. The AChRAb ELISA also showed good inter-assay and intra-assay precision.


CONCLUSIONS
The AChRAb ELISA we have described has sensitivity and specificity at least as high as our current radioactive IPA. It has good precision and good handling characteristics making it suitable for routine use.
Hewer
Rachel
R
FIRS Laboratories, RSR Ltd., Parc Ty Glas, Llanishen, Cardiff, CF14 5DU, UK.
Matthews
Ian
I
Chen
Shu
S
McGrath
Vivienne
V
Evans
Michele
M
Roberts
Emma
E
Nute
Sarah
S
Sanders
Jane
J
Furmaniak
Jadwiga
J
Smith
Bernard Rees
BR
D000328:Adult; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D000918:Antibody Specificity / Q000276:immunology; D001323:Autoantibodies / Q000097:blood*; D001327:Autoimmune Diseases / Q000097:blood / Q000175:diagnosis; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D005260:Female; D005333:Fetus; D006801:Humans; D051379:Mice; D008815:Mice, Inbred Strains; D009157:Myasthenia Gravis / Q000097:blood* / Q000175:diagnosis; D011485:Protein Binding / Q000276:immunology; D011817:Rabbits; D011950:Receptors, Cholinergic / Q000276:immunology*; D012680:Sensitivity and Specificity
D000911:Antibodies, Monoclonal; D001323:Autoantibodies; D011950:Receptors, Cholinergic