Conditions required for induction of interferon by rotaviruses and for their sensitivity to its action.

Our investigations of interferon induction by rotaviruses showed that only when cells were pretreated with interferon, i.e., primed, could infectious rotaviruses induce significant quantities of interferon. As little as 0.5 U of interferon provided sufficient priming for this induction. UV-irradiated rotaviruses induced significant levels of interferon, and priming only marginally enhanced the yields. Neither heat-inactivated virus nor serum-neutralized virus was able to induce interferon, even when cells were primed. When cells were treated with purified virus double-stranded RNA in the presence of DEAE-dextran to facilitate uptake, interferon was induced, although priming did not enhance yields. These results strongly implicate the viral double-stranded RNA as the effector for interferon induction. The insensitivity of rotaviruses to interferon in vitro was also studied. Results suggested that this lack of sensitivity was not due to any inherent resistance of the virus to the antiviral proteins, but rather to lack of activation of cellular enzymes exhibiting antiviral activity.