Induction and cross-species activity of rat fibroblast-derived interferon

Interferon derived from rat fibroblasts (RFA-1) was pH 2 stable and heat labile. Denaturants such as SDS and urea inactivated this interferon but beta-mercaptoethanol alone did not. IFN yield after Newcastle disease virus was multiplicity of infection (moi) dependent. Optimal induction was obtained with an moi of 10. RFA-1 cells produced small amounts of IFN (less than or equal to 10(1.5) U/ml) when exposed to varying amounts of poly(rI): poly(rC). Addition of DEAE-dextran and/or pretreatment with IFN did not change this response. Pretreatment resulted in increased interferon production, priming, but on the average it was only about a 2-fold increase. However, the kinetics of interferon production were altered by pretreatment with IFN whether there was an increase in production or not. Both IFN synthesis and production peaks were detected 2-4 h earlier in IFN-pretreated RFA-1 cells. Rat IFN exhibited a great deal of cross-species activity. It is 100-300% cross-reactive on mouse (L929B and 3T3) cells, and 5-10% active on guinea pig fibroblasts, human (GM 2767) and bovine (MDBK) cells. These cells were more sensitive to rat IFN than Jensen sarcoma cells (a rat tumour cell line). Neither chicken embryo fibroblasts nor monkey (Vero) cells developed an antiviral state when exposed to rat IFN.