SUMMARY

Cultures of primary mouse kidney cells and those of L cells produced interferon in response to Newcastle disease virus and polyinosinic-polycytidylic acid. The interferon produced by L cells was made between 8 and ~8 hr post-inoculation irrespective of the inducer. The interferon produced by mouse kidney cell cultures in response to Newcastle disease virus was made between 8 and I8 hr while that produced in response to polyinosinic-polycytidylic acid was made between 2 and i2 hr. Pre-treatment of L cells with interferon i hibited interferon production by both inducers, but pre-treatment of mouse kidney cell cultures inhibited only the 8 to 18 hr interferon stimulated by Newcastle disease virus. Thus the induction process stimulated by polyinosinic-polycytidylic acid was probably different in L cells from that in mouse kidney cells. On the basis of the time required toinduce inter-feron production and the sensitivity of the induction process to the inhibitory effects of interferon pre-treatment, the induction process stimulated by polyinosinic-polycytidylic acid must be regulated ifferently in L cells and mouse kidney cells. The ability to stimulate interferon production repeatedly in mouse kidney cells by polyinosinic-polycytidylic acid indicated an induction process dependent only on the presence of an effective inducer. Primary cultures of mouse kidney cells which produced good yields of interferon with polyinosinic-polycytidylic acid lost their ability to respond to this inducer after a single passage. S condary cultures till responded toNewcastle disease virus, however. We suggest that primary cultures of mouse kidney cells contain two types of cells each of which responds uniquely to one type of inducer and each perhaps with its own distinct induction process