The mode of production of endotoxin-induced interferon in rabbit tissue cells. I. Development of priming by pretreatment with interferon.

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 x 10(4) - 1.0 x 10(5) 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.