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The results of the study of the antiproliferative effect of swine leukocyte interferon and of an inhibitor of interferon effect in experimental mice with transplanted Krebs-2 ascitic carcinoma cells are presented. The interferon inhibitor exerted antiproliferative effect similar to that of native swine interferon. Combined use of swine interferon and interferon inhibitor did not lead to summation of the antiproliferative effect of these preparations.

Studies on the antagonists of interferon effect ("stimulon", "TAI", "blocker", "antiinterferon") formed under the influence of viruses and mitogens as well as those found in noninfected tissues deal largely with their blocking effect on the antiviral activity of interferon. Previously we had found an inhibitor of antiviral effect in preparations of human cadaverous and swine leukocyte interferons. This paper presents the results of studies on some physico-chemical properties of an inhibitor of the effect of swine leukocyte interferon and its antiproliferative activity. The inhibitor is resistant to the effect of nucleases and lyophilization, manifests limited heterospecificity towards interferons and cell cultures, has marked antiproliferative activity in different cell cultures including those of tumor origin.

A comparative study of different methods for concentration of porcine leukocyte interferon active in human cells was carried out. Ultrafiltration in an apparatus TCF-10 was found to be the most effective method of concentration by which preparations of porcine interferon showing antiviral activity up to 1 X 10(6) IU/ml were obtained. The total antiviral activity of concentrated interferon was twice as high as that of the native preparation. This increase of the total initial activity is due to the removal in the process of concentration of an inhibitor of antiviral activity which was isolated and concentrated. The concentrated preparation of porcine leukocyte interferon is now undergoing trials in veterinary and medicine.

A simple method for increasing the activity of human leukocyte interferon is described. It is based on the removal from the native preparation of a presumed inhibitor of antiviral effect followed by condensation of the resulting fractions by thin-canal cells TCF-10 of an Amicon apparatus. With this method of concentration there was no loss of the general initial antiviral activity. Depending on the titer of the initial interferon and the condensation degree, the native interferon was concentrated 32--350-fold. The resulting concentrated interferon preparation is nontoxic, areactogenic, safe in animal trials and may be recommended for trials as a therapeutic-prophylactic means in various viral diseases.