title: A sensitive non-isotopic assay for acetylcholine receptor autoantibodies.
abstract: 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.
authors.affiliation: FIRS Laboratories, RSR Ltd., Parc Ty Glas, Llanishen, Cardiff, CF14 5DU, UK.
authors.forename: Rachel
authors.initials: R
authors.lastname: Hewer
authors.forename: Ian
authors.initials: I
authors.lastname: Matthews
authors.forename: Shu
authors.initials: S
authors.lastname: Chen
authors.forename: Vivienne
authors.initials: V
authors.lastname: McGrath
authors.forename: Michele
authors.initials: M
authors.lastname: Evans
authors.forename: Emma
authors.initials: E
authors.lastname: Roberts
authors.forename: Sarah
authors.initials: S
authors.lastname: Nute
authors.forename: Jane
authors.initials: J
authors.lastname: Sanders
authors.forename: Jadwiga
authors.initials: J
authors.lastname: Furmaniak
authors.forename: Bernard Rees
authors.initials: BR
authors.lastname: Smith
mesh_terms: 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
chemical_list: D000911:Antibodies, Monoclonal; D001323:Autoantibodies; D011950:Receptors, Cholinergic