Purification of mouse L cell interferon. Essentially pure preparations with associated cell growth inhibitory activity.

Mouse L cell interferon induced by Newcastle disease virus was purified by a combination of salt precipitation, ion exchange chromatography, gel filtration, and affinity chromatography using anti-interferon anti-body. The preparation was labeled with 125I at a later step of purification, which served as an index of protein concentration. Two main species of interferon molecules differing in molecular weight were separated from each other, and the final preparations obtained were shown to be essentially pure by polyacrylamide gel electrophoresis in the absence as well as in the presence of sodium dodecyl sulfate. The highest specific activities obtained were 2.6 X 10(9) and 7.3 X 10(8) international units/mg of protein (determined by 125I radioactivity) for the 40,000- and 24,000-dalton species, respectively. The preparations at different steps of purification, including those of the highest purity, were tested for the anti-cell growth activity. Their activities were found to be indistinguishable from each other when compared at the same antiviral doses, indicating that the anti-cell growth activity is carried by the interferon molecules themselves.