Study of the in vivo priming effect of interferon in mice.

Intramuscular injection of mice with 2000 IU/g partially purified murine interferon (IFN) alpha/beta 3 h before the induction of IFN by intraperitoneally administered 3 micrograms/g poly rI:rC enhanced early IFN production. The differences between the serum IFN levels of IFN-pretreated and control animals were about 10-fold during the first 2 to 3 h of in vivo IFN production. In later stages these differences tended to decrease, and from 8 h post-induction they disappeared. IFN exerted its in vivo priming activity equally after intravenous, intraperitoneal or intramuscular injection. A similar enhancement of IFN production was observed when it was induced by poly rI:rC administered either intraperitoneally or intramuscularly. The duration of IFN pretreatment influenced the establishment of the in vivo primed state. Following administration of 2000 IU/g murine IFN alpha/beta intramuscularly, maximal priming developed after 3 h, and no primed IFN response was detected when the inoculation of IFN preceded inducer administration by 12 h or more. The manifestation of in vivo priming was optimal when 1500 to 3000 IU/g pretreating doses of IFN were applied. Reduction of the amount of injected IFN below this level markedly decreased priming, indicating a time- and dose-dependent induction of priming in vivo.