Rapid, quantitative, semiautomated assay for virus-induced and immune human interferons.

An improved human interferon (IF) assay is described. This procedure is based on the ability of encephalomyocarditis virus to replicate in WISH cell microcultures with the production of discrete plaques in the presence of a liquid tissue culture medium. Performance of 50% plaque reduction endpoint assays in micro-culture required only 0.1 ml of specimen for determinations using duplicate dilutions beginning at 1:3. Semiautomated equipment facilitated simultaneous in situ dilution and distribution of multiple IF samples in cultures containing preformed WISH cell monolayers. An incubation period of 5 to 6 h was adequate for development of maximal antiviral activity by both virus- and immune-induced IF. Sensitivity of the encephalomyocarditis microplaque reduction assay was comparable to that of other commonly used techniques. The method is rapid, can be completed within 30 h from the beginning of the IF assay, and is able to accommodate as many as 40 to 50 samples at a single time. Encephalomyocarditis microplaque reduction is suitable for the quantitation of IF as an antiviral agent or a lymphokine.