Antiproliferative assay of human leucocyte interferon.

An in vitro microtitration system of the antiproliferative effect of human leucocyte interferon (IFN-alpha(Le)) was investigated. The preliminary experiments suggested that the antiproliferative effect of IFN-alpha(Le) was increased by prolonging the incubation period, by reducing the target cell concentration, and might be prescribed by the total IFN amounts in the challenge medium. By employing a system consisted of 1.5 X 10(4) Daudi cells in 0.2 ml of medium containing IFN dilutions and an incubation period of 3 days at 37 degrees C, the antiproliferative effects of twenty-one lots of partially purified IFN-alpha(Le) (PIF-alpha(Le)) preparations were titrated. The interassay variations in the antiproliferative titers of three PIF-alpha(Le) established in the present system were found to be in the same range as those in the antiviral titers estimated by a standard macroplaque reduction assay. The each titration curve was parallel, and the antiproliferative titers, assessed by the reciprocals of the IFN dilutions which suppress the cell growth in 50%, were significantly (p less than 0.01) correlated to the antiviral international units of them.