Interferon induction by viruses. XIII. Detection and assay of interferon induction-suppressing particles.

An assay is described for detecting and measuring the capacity of a single virus particle to suppress completely the yield of interferon from a cell otherwise competent to product interferon. The assay defines virus populations in terms of a newly quantifiable attribute--interferon induction-suppressing particles (ISP). The antagonistic actions of interferon-inducing particles and interferon induction-suppressing particles are thought to determine the interferon-inducing capacity intrinsic to a virus population.