Abstract
The interferon system has been investigated in primary cell cultures established from Chinese hamster embryos and new born pups. Interferon synthesis was induced with Sindbis virus, ultraviolet irradiated Newcastle disease virus (u.v.-NDV) and with polyriboinosinic acid-polyribocytidylic acid complex [poly (rI). poly (rC)]. Only u.v.-NDV induced significant production of interferon, maximum amounts being produced in aged cells. Its apparent mol. wt. was 25000. CHO-K1 cells, an established line of Chinese hamster cells, did not synthesize interferon in response to viruses, but were sensitive to its action.