Cellular alteration by interferon: a virus-free system for assaying interferon.

A system is described for assaying mouse interferon without using a viral "challenge" agent. Interferon-treated L cells were destroyed by exposure to polyriboinosinic.polyribocytidylic acid [poly(I).poly(C)], and the amount of destruction was dependent on both the concentration of interferon to which the cells were exposed and the amount of poly(I).poly(C) used as the "challenge" material. If the amount of poly(I).poly(C) was constant, the concentration of interferon could be determined by quantitating cell destruction 6 hr after addition of the double-stranded ribonucleic acid. In addition to eliminating the necessity for employing infectious virus for interferon assays, this system has the advantages of being quicker, easier, and more sensitive than other interferon assays. The sensitivity of the assay is related directly to the amount of poly(I).poly(C) applied to the cells, with each fivefold increase of poly(I).poly(C) giving about a fivefold increase of sensitivity.