Development of a novel efficient fluorescence-based plaque reduction microneutralization assay for measles virus immunity.

The measurement of functional measles virus-specific neutralizing antibodies is of considerable interest for vaccine-related research. In this study, we developed and standardized a simple, rapid, highly sensitive, and reproducible fluorescence-based plaque reduction microneutralization (PRMN) assay with visual and automated readout, using a recombinant measles virus engineered to express enhanced green fluorescent protein. The assay is performed in micro format, requires less time to complete (2 versus 4 to 7 days), and is less labor-intensive and less costly than the classical plaque reduction neutralization (PRN) test, widely accepted as the "gold standard" in measles serology. Two available WHO international anti-measles virus standards and one in-house reference serum were used to develop and standardize the new assay. The mean PRMN values from repeated assays were found to be similar to those reported in the literature or assigned to the WHO standards by the classical PRN assay. For validation, we used three groups of low, moderate, and high measles virus vaccine responders' sera with moderate values of correlation in antibody levels (mIU/ml) between PRMN and the Dade Behring immunoglobulin G enzyme immunoassay (EIA). The PRMN assay was more sensitive at low antibody levels and more informative in terms of protection than this commercial EIA. In conclusion, we have developed and validated a sensitive and high-throughput measles virus-specific PRMN that can be readily used in large population-based measles studies.