The Mode of Production of Endotoxin-Induced Interferon in Rabbit Tissue Cells

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Abstract
In vitro production of endotoxin‐induced interferon in rabbit tissue cell cultures could be enhanced by pretreatment with interferon. The enhancible state developed from the first hr of incubation at 37 C and a maximal priming effect was attained at 6 hr of incubation. Yields of interferon from unprimed cultures were usually 20–200 units/ml. In contrast, the primed cultures constantly yielded 1,000–2,500 units/ml of interferon. The pretreatment with interferon seemed to cause an earlier appearance of detectable interferon and the primed cells became more sensitive to endotoxin. It turned out that 10–30 units/ml of rabbit interferon were enough to develop the maximal priming. Even when cells were pretreated with higher doses of rabbit interferon such as 1.0 × 104–1.0 × 105 units/ml, the same level of priming effect was always observed without diminution. Various types of homologous (rabbit) and heterologous (human and mouse) interferon preparations showed similar dose‐dependent enhancement of interferon production in proportion to the antiviral titers of these preparations as tested with RK‐13 cells of rabbit origin.