Assay of human interferon in Vero cells by several methods

Four methods for the assay of human interferon in Vero cells were compared based on the inhibition of viral cytopathic effect (CPE) in tubes, the inhibition of CPE in microplates, the reduction of plaques, and the inhibition of quantitative hemadsorption. For inhibition of CPE, Sindbis virus, vesicular stomatitis virus, poliovirus type 2, and vaccinia virus were used for challenge. In the plaque reduction method, Sindbis virus, vesicular stomatitis virus, and poliovirus were employed, and Newcastle disease virus was used in the quantitative hemadsorption assay. Sindbis virus was most susceptible to interferon in those tests measuring inhibition of CPE, but vesicular stomatitis virus was as sensitive in the plaque reduction method. Highest titers of interferon were recorded in microplates, especially with Sindbis virus as the challenge agent, followed by the quantitative inhibition assay. The CPE inhibition method was the simplest, and the quantitative hemadsorption assay was the most rapid to perform. Reproducibilities, as shown by the coefficient of variation, were 15, 39, and 59% for plaque reduction, CPE inhibition in tubes, and CPE inhibition in microplates, respectively.