Rat interferons. III. Antiviral activity and effect of "priming" on interferon production in homologous and heterologous cell lines.

Studies on interferon from rat serum sensitive to pH 2-0 showed the following: 1) Its action is stronger in cultures of heterologous L cells than in rat fibroblast cultures. 2) Resistance acquired under the influence of interferon lasts longer in a heterologous than in a homologous system. 3) Actinomycin D added to cultures after 4 hours of contact with interferon inhibits its activity in L cells, and potentiates its activity in RE cells. 4) In rat embryonic cells treated with interferon, interferon production following induction with ND virus is blocked. Similar blocking was observed in cultures of L cells after 24-hour priming; after 6 hours of exposure of L cells to rat interferon, on the other hand, production of interferon was enhanced.