Variation in ability of measles virus plaque progeny to induce interferon.

Plaque progeny of three interferon (IF)-inducing strains of measles virus (Edmonston, Schwarz, and CC) were examined for ability to induce IF in BSC-1 cells. Only after passage in Vero cells did any of the Edmonston progeny induce IF. The vast majority of plaque progeny selected from the Schwarz strain induced IF, even though this virus was originally derived from the Edmonston strain. This property was retained even after serial plaque purification of the progeny. However, the Schwarz-derived CC strain consisted of a population generally unable to induce IF. Stocks grown from both Edmonston and CC plaques demonstrating the IF+ phenotype maintained this characteristic as a whole, but it was not a property that was inherited by all progeny in the stocks. Levels of IF induced were approximately the same for all strains, even though the proportion of inducing progeny varied markedly among them. These noninducing variants appeared to be normal, fully infectious measles virions. The results suggest that induction of IF by measles virus is at least partially under the genetic control of the virus.