Characteristics of spontaneously produced and of virus-induced human LuKII cell interferons

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Abstract
Several human lymphoblastoid cell lines produced significant levels of interferon (IFN) activity in the absence of any IFN inducees. We have partially purified spontaneous IFN (SpIFN) from LuKII cells and compared it with the IFN activity produced by the same cells following Sendai virus induction. Virus-induced LuKII IFN reached maximum titers of 1000–6000 reference units/ml at 12 to 15 houts post-induction and produced a heterogeneous electrophoretic profile with major (18,500 dalton) and minor (23,500 dalton) species. Spontaneous LuKII IFN was produced very slowly over several days and reached maximum titers of 100–1000 reference units/ml. Crude SpIFN (25–100 ref. units/ml) was purified to 1–6×105 ref. units/ml with a 53–80 percent overall recovery, and it consistently migrated as a homogeneous 20,000 dalton band upon SDS gel electrophoresis. Although spontaneously produced and virus-induced lymphoblastoid IFNs differed in their ability to be neutralized by anti-mouse IFN antiserum (18), both types of IFN were only 1 percent cross-reactive on heterologous mouse L cells. We conclude that IFN definitely can be produced by many human lymphoblastoid cell lines in the absence of inducers, and that LuKII SpIFN has different characteristics than the IFNs produced by the same cell line following viral induction. Since it is now known that there are many IFN-α genes (3, 10), it seems likely that these cell lines may provide a system for studying the selective expression of one or more of these genes.