2-5A synthetase activity does not increase in interferon-resistant Friend leukemia cell variants treated with alpha/beta interferon despite the presence of high-affinity interferon receptor sites.

The presence of interferon (IFN) receptors on mouse Friend leukemia cells (FLC) has been investigated in binding experiments with highly purified 125I-labeled mouse alpha/beta IFN. Both IFN-resistant clones and wild-type IFN-sensitive FLC showed a specific saturable binding site for mouse IFN with a similar affinity constant. In contrast to IFN-sensitive FLC, IFN-resistant FLC variants were not inducible by IFN for double-stranded RNA-dependent 2-5A synthetase activity.