Blocking of Interferon Production by Chromatographically Purified

Exposure of cell cultures to interferon can modify their response to interferon inducers in two ways: Interferon may be liberated earlier or in larger amounts than in the ab-sence of pretreatment (1-4), or the quantity of interferon produced is greatly diminished if not entirely blocked (1, 2, 5-7). Studies conducted in the Newcastle disease virus-l cell system disclosed that the block-ing property of interferon preparations was closely allied with their protective effect (7, 8), but preliminary experiments also sug-gested that interferon and blocker might be separate entities (9). Recent developments in purification meth-ods of L cell interferon (10) prompted a re-investigation of the nature of a possible fac-tor capable of blocking interferon production. The present experiments dwelt on the time of appearance, sensitivity to actinomycin D as well as attempts a t chromatographic separa-tion of blocking and interferon activities. In additional studies, chromatographically puri-fied interferon was used for pretreatment of cultures to clarify some quantitative aspects of the blocking phenomenon as it pertains to live or irradiated viral and nonviral inducers. Materials and Methods. Cell cultures. Sus-pended L cells were propagated as described earlier ( 11) with the following modification: The cells were grown in minimum essential medium (MEM) for suspension cultures, con