A novel sensitive and selective bioassay for human type I interferons.

We describe a novel MxA gene-induction assay for type I interferons (IFN-alpha and IFN-beta) based on the specific induction of the MxA gene in cultured human cells. Accumulated intracellular MxA protein is determined by immunologic measurement by a rapid method using commercially available materials. IFN activity can be measured accurately over a concentration range of 0.1-30 IU/ml. In contrast, type II IFN and other cytokines are not significantly detected. The MxA-induction assay has advantages in terms of specificity, reliability, and sensitivity over other methods for assaying type I IFN. It has also been adapted and validated for measuring the titers of anti-IFN-beta neutralizing antibodies in human sera.