Determination of human leukocytic interferon by a microfluorometric immunological method

The possibility of quantitative determination of human leukocytic interferon by means of anti-interferon antibodies labeled with fluorescein isothiocyanate (FITC) was studied. As a result of prolonged immunization of a donkey with a preparation of human leukocytic interferon and subsequent fractionation and immunosorption, a donkey antiinterferon immunoglobulin with high specific activity was obtained. This immunoglobulin was labeled with FITC and used for quantitative determination of human leukocytic interferon in direct and indirect immunologic inhibition of fluorescence tests. The titers of the various preparations of human leukocytic interferon in the inhibition of fluorescence test were comparable with the titers of these same preparations in the test of inhibition of virus cytopathic action by interferon.