DLD Muscle Specific Tyrosine Kinase (MuSK) Autoantibody RIA Elisa

ASSAY PRINCIPLE 
In RSR’s MuSK Ab radioimmunoassay (RIA), MuSK Ab in patient sera and controls are allowed to interact with 125I-labelled MuSK protein (125I-MuSK). After incubation at room temperature overnight, the resulting antigen-antibody complexes are immunoprecipitated by the addition of anti-human IgG. After a second incubation of 2 hours, precipitation enhancer and wash solution are added and the samples centrifuged. Unbound 125I-MuSK is removed from the tubes by aspiration of the supernatant. The level of radioactivity remaining in the tube is proportional to the antibody level in the test sample.

STORAGE AND PREPARATION OF SERUM SAMPLES 
Sera to be analysed should be assayed soon after separation or stored, preferably in aliquots, at or below –20oC. 15 L is sufficient for one assay (duplicate determinations). Repeated freeze thawing or increases in storage temperature must be avoided. Do not use lipaemic or haemolysed serum samples. Do not use plasma in the assay. When required, bring test sera to room temperature and mix gently to ensure homogeneity. Centrifuge serum prior to assay (preferably for 5 min at about 10,000rpm i.e. about 10,000g in a microfuge) to remove any particulate matter. Please do not omit this centrifugation step if sera are cloudy or contain particulates.

CLINICAL EVALUATION 
Clinical Specificity 
Sera from 50 individual healthy blood donors were assayed in the MuSK Ab RIA. 50 (100%) were identified as being negative for MuSK Ab. 
Clinical Sensitivity 
Serum samples from 18 patients with clinical symptoms of MG but negative for AChR Ab were assayed in the MuSK Ab RIA. 18 (100%) were positive for MuSK Ab. 
Lower DetectionLimit 
The negative control was assayed 20 times and the mean and standard deviation calculated. The lower detection limit at 2 standard deviations was 0.0023 nmol/L.