Quantitative Determination of Infectious Units of Measles Virus by Counts of Immunofluorescent Foci.

Abstract

Monolayers of human carcinoma cells (H.Ep.-2) infected with measles virus were maintained under methyl cellulose. The cell sheets were stained by the Coons indirect fluorescent antibody technic. Discrete fluorescent foci could be counted where virus antigen was present in infected cells. An assay of infectious virus was based on this technic. The number of fluorescent foci was proportional to the amount of virus added, and virus assays agreed with infectivity titrations in tubes. The method should be useful with other cell-virus systems, particularly those in which virus antigen is produced in the absence of cell destruction.