Multiple Sclerosis, 1 February 2003, vol. 9, no. 1, pp. 32-35(4)
Kob M.; Harvey J.; Schautzer F.; Kascha S.; Bibl D.; Egg R.; Reindl M.; Berger T.; Deisenhammer F.
 Department of Neurology, University of Innsbruck, Innsbruck, Austria  Bayer Diagnostics, Emeryville, CA, USA  Department of Neurology, County Hospital, Villach, Austria  Department of Neurology, County Hospital, Rankweil, Austria  Department of Neurology, General Hospital, Linz, Austria
There is evidence that neutralizing antibodies (NAB) have a negative influence on the clinical and magnetic resonance imaging effects of interferon-beta (IFNb) in multiple sclerosis (MS) patients.
The current methods for NAB detection are restricted to specialized laboratories because they require a cell culture and sometimes a viral culture.
Results are typically obtained after several weeks.
Therefore, the development of a simple and rapid assay for the detection of NAB was sought.
Whole blood samples from 28 NAB-positive patients and 110 NAB-negative patients (52 with IFNb and 58 without IFNb therapy) were incubated with IFNb 976 IU/mL for 24 hours.
MxA protein levels – a specific marker of class 1 IFNb bioactivity were measured – in paired samples with and without IFNb incubation and the difference in MxA levels was calculated.
The mean increase of MxA levels after stimulation with IFNb in the NAB-positive group was 8 ng/mL (range 0–44 ng/mL) and in the NAB-negative group was 84 ng/mL (range 0–302 ng/mL).
Using an increase of 22.5 ng/mL as cut-off, the specificity of the MxA stimulation assay was 81.2% and the sensitivity was 96.4%.
The whole blood MxA stimulation assay is virtually as sensitive as the conventional NAB assay but somewhat less specific.
However, this is outweighed by the procedural advantage of the assay, which is simpler, quicker and much less expensive.