Viral infection and interferon in cell cultures aged in vitro

Cells from leucosis-free chick embryos (skin and muscles), grown in vitro 1 and 7 days with no medium change, are used as a model for young dividing and stationary in vitro aged cells, respectively. Aged cultures are advantageous for IF induction by cytopathic and noncytopathic viruses. Decreased virus production in them is ascribed to a back effect of the early formed IF onto the inducing virus. A factor which stimulates viral IF interferon induction also in young cultures, is released from aged cells into the medium. This factor could belong -- according to its properties and action -- into the class of chalones.