Enhanced Production of Interferon by Temperature Shift-Down from 37 C to 25 C in Rabbit Cell Cultures Stimulated with Newcastle Disease Virus

Abstract

Preincubation of Newcastle disease virus (NDV)-infected RK13 cells at 37 C considerably en-hanced subsequent interferon (IF) production at 25 C. The optimal length of this preincubation was about 7 to 9 hr. It was postulated that the intracellular events leading to IF production in NDV-in-duced cells might proceed in two distinct phases, early and late; the early phase to prepare the cells for IF synthesis proceeds only at 37 C whereas the late phase in which IF is readily synthesized occurs both at 37 C and at 25 C. Similar events seemed to occur in cultures of cells from in vivo induced rabbits. This concept was substantiated by experiments using actinomycin D and cycloheximide, which sug-gested that protein synthesis at 37 C during the first 7 hr was essential for subsequent IF production at 25 C. A prolonged preincubation at 37 C resulted in decreased IF production, suggesting that a puta-tive regulatory protein might be synthesized at 37 C which could not be readily synthesized at 25 C.