Only small amounts of added interferon bind to the cell surface as a necessary prelude to the development of antiviral activity. Experiments described later have shown that while this step is necessary, it is not sufficient for the development of antiviral activity which still may be blocked by an inhibitor of cellular RNA synthesis, dactinomycin, even after binding.
Chick cells incubated with interferon at 1 C for several hours only developed antiviral activity after a subsequent incubation at 37 C following removal of interferon by repeated washings. Therefore a period of incubation at 37 C is required for development of antiviral activity, but it was possible that some interaction between interferon and the cell had occurred in the cold.1-3
In order to investigate this possibility, interferon was incubated at 1C with cells which were then washed many times and incubated at 37 C. The cells were found to develop