A simplified and standardized neutralization enzyme immunoassay for the quantification of measles neutralizing antibody

A simplified and standardized neutralization enzyme immunoassay (Nt-EIA) wa s developed to detect measles Virus growth in Vero cells and to quantify me asles neutralizing antibody. Heat-inactivated sera were diluted serially 4- fold and tested in duplicate. The 50% reduction point (50%RP) of virus grow th was calculated using the Reed-Muench formula and the neutralizing antibo dy titre of test sera was converted into mIU/ml by comparing their 50%RP wi th that of the international standard serum. The optimal virus input and in cubation time were found to be 50-100 plaque forming unit (PFU)/well and 64 -72 h, respectively. The simplified Nt-EIA had a good reproducibility with only 3.7-4.2% of duplicate tests having a ratio >4 in an evaluation of intr a assay Variation and the coefficients of variance were 2-9% in an evaluati on of inter assay variation. In addition, the simplified Nt-EIA had a high sensitivity (98.6%). specificity (100%) and agreement (98.8%) in qualitativ e comparison with plaque reduction neutralization test (PRNT). In quantitat ive comparison, the correlation coefficient between Nt-EIA and PRNT was 0.8 3 without log transformation or 0.77 after log transformation and 90% of 61 positive sera had a ratio <4 between antibody titre tested by the two meth ods. The simplified Nt-EIA is thus a suitable alternative to the PRNT for t he quantification of measles neutralizing antibody. (C) 1999 Elsevier Scien ce B.V. All rights reserved.