Mouse interferons: production by Ehrlich ascites tumour cells infected with Newcastle disease virus and its enhancement by theophylline.

Conditions are described for the production of 0.3 to 0.7 NIH mouse reference standard units of interferon per cell from Ehrlich ascites tumour cells cultured as monolayers and induced by infection with Newcastle disease virus (NDV). Inclusion of theophylline (6 mM) in the medium increased the interferon yield three to four times. Cells infected with NDV started to lyse at about 15 p.i., but infected, theophylline-treated cells lysed only 24 p.i. Several other methylxanthines (e.g. theobromine, caffeine and isobutylmethylxanthine) when tested a concentrations similar to that of theophylline, did not boost interferon production. Dibutyryl cyclic AMP (10(-10) to 10(-2)M) did not substitute for theophylline in increasing interferon production, and, if used together with theophylline, did not cause further enhancement.