Production of interferon in human fibroblast cultures: effect of temperature

To obtain several harvests of interferon from the same culture the human fibroblasts have been incubated at various temperatures after the induction with virus. Preincubation of the culture infected with Newcastle Disease virus (NDV) at 37 degrees C for 8-10 hrs before the transfer of it to 25 degrees C resulted in the optimal harvest of interferon at 24th and 48th hrs after the induction. Also the preincubation of the culture infected with NDV for 8-10 hrs at 25 degrees C before its transfer to 37 degrees C resulted in better harvests of interferon than that obtained after the constant incubation at 37 degrees C. The same preparation of NDV could be used repeatedly 10 times without substantial loss of its interferon-inducing activity.