Interferon Induction by Viruses. XIV. Development of Interferon Inducibility and Its Inhibition in Chick Embryo Cells "Aged"In Vitro

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Abstract
Studies with a number of viruses revealed a time-dependent acquisition of interferon (IFN) inducibility in primary chick embryo cells as they "aged" in vitro for 2-12 days at a confluent cell density without a medium change. The time-course for the development of IFN inducibility was established by generating and analyzing a family of dose (multiplicity)-response (IFN yield) curves, using Newcastle disease virus (NDV, strain LaSota) as the inducer. Cells produced little or no IFN for the first 4-5 days. Between 5 and 6 days the cells gradually developed the capacity to respond to NDV (and other viruses). Maximal yields of IFN were inducible by day 10. This time-dependent development of IFN inducibility was abrogated almost completely when "aging" was carried out in the presence of drugs that inhibited the synthesis of cyclic derivatives of C20 oxygenated unsaturated fatty acids, i.e., inhibitors of prostaglandin/leukotriene synthesis and the arachidonic acid cascade. Of the prostaglandin synthesis inhibitors, indomethacin was particularly effective. Cells treated on day 0 with 10 micrograms/ml of indomethacin produced 100- to 1000-fold less IFN than controls when induced on day 8. To prevent maximally the development of IFN inducibility, indomethacin must be added within the first 2 days of seeding. After about 2 days, the cells begin to escape the action of the drug. Indomethacin added at the time of induction had no effect on the yield of IFN. IFN inducibility was partially restored when indomethacin was removed during the aging process. "Aging" chick cells in low concentrations of cycloheximide (0.5 micrograms/ml) produced results comparable to incubation with indomethacin. Neither reagent had any marked effect on the rate of total protein or RNA synthesis, nor did their action prevent the induction of stress (heat shock) proteins. Cells "aged" in indomethacin were threefold less efficient in responding to the action of IFN, whereas aging in cycloheximide had no effect on IFN's action. Plaque formation on drug-treated cells was normal for viruses that were poor inducers of IFN. However, both the plaquing efficiency and plaque size of Sindbis virus (an excellent IFN inducer) were enhanced markedly on cells treated with indomethacin or low concentrations of cycloheximide during the aging process. These data implicate a family of fatty acid derivatives of arachadonic acid, including prostaglandins and leukotrienes, in the development of IFN inducibility in primary chick embryo cells "aged" in vitro.