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A Sensitive Interferon Assay for Many Species of Cells: Encephalomyocarditis Virus Hemagglutinin Yield Reduction 1

Summary A new, highly sensitive assay for human interferon was developed in which the reduction in HA yield of a single-cycle infection with EMC virus is measured. The sensitivity and precision of the assay are comparable to or better than the other assays tested, depending most of all upon the cells used in the test. This simple method requires no sophisticated instrumentation, can be used on a microtiter scale, provides objective numerical results, and is readily applicable to testing large numbers of samples. The assay can be used in human lines arid diploid cell strains as well as in monkey, rabbit, cat, mouse, pig, cow, dog, and hamster-mouse hybrid cells. We are grateful to C. K. Schoenherr for her excellent technical assistance. We thank Dr. M. Essex for making it possible for one of the authors (P.J.) to work with the feline cell system in his laboratory. We appreciate the gifts of interferon from Dr. K. Cantell and Dr. J. Valenta, and of cells from Drs. G. G. Jackson, S. Baron, and E. Kilbourne.