Abstract
The presence of a low level of interferon (IFN) activity was demonstrated in aged culture medium of primary chick embryo (CE) cells. The endogenous cytoplasmic level of 2',5'-oligoadenylate (2',5'-A) synthetase activity also increased during cell ageing. This increase was suppressed by addition of antiserum against chick IFN. In contrast, anti-chick IFN serum did not inhibit the ageing effect, i.e. the enhanced production of IFN upon induction after a prolonged preincubation of CE cells. This result indicates that the occurrence of the ageing effect is not mediated by the IFN system which had been expressed spontaneously.