Abstract
An antimalarial drug chloroquine produced a potent and specific inhibition on the interferon synthesis by primary chick embryonic cells (PCE) inoculated with UV-irradiated Newcastle disease virus (NDV) . This inhibition was not mediated by the induction of a substance antagonistic to interferon both in vitro and in vivo. Within the concentration range where chloroquine blocked interferon synthesis almost completely (20 to 30μg/ml), the growth of live NDV was not suppressed. Moreover, no alteration in the cellular incorporation capacities of leucine or uridine into acid insoluble fraction were observed. PCE cells once inoculated with UV-irradiated NDV and treated with a sufficient concentration of chloroquine to stop interferon synthesis, acquired a tolerant state to subsequent induction of interferon. This interferon producing system was most sensitive to chloroquine for about four hr from the addition of the inducer.
