49] Virus plaque-reduction assay for interferon: Microplaque and regular macroplaque reduction assays

Abstract

Publisher Summary This chapter describes procedures to perform microplaque and regular (macroplaque) plaque reduction Interferon (IF) assays. The plaque reduction IF assay is precise, sensitive, and reproducible, which can be used to assay all known types of IF. For optimum precision and reproducibility, the reduction in plaque numbers must be proportional to the IF dilution. Thus, it is important to prevent secondary plaque formation, which will result in an inaccurate end point determination. Various culture techniques and overlay media containing agar, agarose, methyl cellulose, carboxymethyl cellulose, starch, gelatin, and homologous antibody have been used for this purpose. Variations in IF titers with the plaque reduction assay are primarily dependent upon changes in sensitivity of the cells to IF and the virus. An internal reference standard should be established and titrated with each set of IF assays to monitor reproducibility and normalize IF titers. Some disadvantages associated with the plaque reduction assay are (a) the length of time required to develop and count plaques, (b) day-to- day variation in plaque numbers resulting from changes in cell sensitivity to IF and virus, and (c) subjective determination of what constitutes a plaque when certain viruses are used.