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The cytotoxic activity of peripheral blood natural killers (NK) against target cells (TC) J-96 and L-929 with high sensitivity to interferon (IFN) action, J-41 and MCB resistant to IFN action and line K-562 labelled by H3-uridine was studied in 14 hrs cytotoxic test. It has been shown that human TC J-96 didn't differ from the J-41 in their sensitivity to NK cytotoxicity and they are strongly resistant to NK than TC K-562. The murine TC L-929 as the human TC didn't differ from the MCB in their sensitivity to NK lysis and had also the same sensitivity to NK as the K-562 cells.

The R-method of differential chromosome staining by length was applied to comparative karyological studies on the culture of J 96 human cells susceptible to enteroviruses, and on the J 41 cell line derived from this culture and possessing high specific resistance to Coxsackie B viruses. Karyotype of the J 41 cell line was shown to be deprived of chromosome G21 (P less than 0.0001). The number of other chromosomes varied from cell to cell, but they are constantly present in the majority of cells of both the J 96 and J 41 cell lines. A conclusion is drawn that chromosome G21 incorporates gene(s) which controls the human cells susceptibility to Coxsackie B viruses.

The antiproliferative (AP) action of human leukocytic interferon (HLI) of varying degrees of purification was studied and compared in cultures of human cells differing in interferon sensitivity. The concentrated and purified preparations of HLI suppressed the incorporation of 3H-thymidine and mitotic activities of the cultures sensitive to HLI of the cells, affecting, but insignificantly, the proliferation of the resistant cell culture. Poorly purified HLI suppressed the proliferation of both cell types. This indicates that native HLI contains impurities that have an AP action and exerts no antiviral activity.

Preparations of human leukocyte interferon obtained by multi-stage purification procedure exhibited ribonuclease activity with the optimum at pH 7.0--7.5. The enzyme possessed the endonuclease action mechanism. Most substances studied for their effect on the RNA-ase activity in human interferon preparations showed many of them to act on the enzyme in the same way as on other ribonucleases. However, dithioerythritie, a reducing agent for disulfide bounds, activated the ribonuclease in the interferon preparation, as distinct from the pancreatic ribonuclease, which was inhibited by this preparation. Patterns of protein and RNA-ase distribution were obtained by electrophoresis in polyacrylamide gel.