Printed in Great Britain 149 Rapid Onset of Hyporesponsiveness to Interferon Induction on Re-exposure to Polyribonucleotide

Only doses of complexed polyriboinosinic:polyribocytidylic acids sufficient o induce interferon, stimulated hyporesponsiveness to re-induction in rabbit kidney cells. Results of experiments designed to delineate the earliest ime of appearance of hyporesponsiveness suggested the time of onset was less than I h after the end of a I h exposure to the inducer. The duration of hyporesponsiveness was about 24 h. Interferon itself did not produce hyporesponsiveness. Hence hyporesponsive-ness must be related to an event or a substance synthesized before interferon production. The best candidate is a control protein inhibiting interferon produc-tion which is rapidly synthesized following exposure to an inducer