Abstract
Vitamin A (retinoic acid) suppressed interferon production by L cells infected with Newcastle disease virus (NDV). This suppression was maximal when cells were treated with retinoic acid for 2 h after NDV adsorption, indicating that the inhibitory step was an early event. It was not due to inhibition of total RNA synthesis. Retinoic acid treatment caused both a delay in appearance of interferon and a reduced rate of synthesis thereafter.