SUMMARYThe anticellular and antiviral effects of human leukocyte interferons were studied in vitro in the transformed human embryonic cell lines, RSa and RSb. The growth of these cells was inhibited and they began to deteriorate about 48 h after treatment with 5oo units]ml of interferon. When interferon was washed out within 48 h, their growth recovered gradually. The effects of interferon on cell growth depended on the amount of interferon added per cell. A subline, named IF r, was isolated which grows in the presence of 2ooo units/ml of interferon, whereas growth of vesicular stomatitis virus in these cells is suppressed by IO units/ml of interferon, just as in the parent cells. The anticellular and antiviral effects of interferon on IF r cells are discussed in relation to cell surface receptors.

Interferon induces two double-stranded RNA-dependent enzymatic activities: an oligoisoadenylate synthetase that converts ATP to ppp(A2'p).5'A, and a protein phosphokinase. We have explored the level and inducibility of these two enzymes in a human cell line (HEC-1) totally insensitive to both the antiviral and the anticellular actions of interferon. The activities of both enzymes are high in untreated cells and only minor changes occur after treatment with interferon, even at high concentrations. Interferon-treated HEC-1 cells do not contain an inhibitor of the oligoisoadenylate synthetase activity. The products of this HEC-1 oligoisoadenylate synthetase consist mainly of dimers, trimers, and tetramers as found in other cell lines after interferon treatment. The synthetase level is unaffected by treating the cells with anti-interferon antiserum, indicating that the results cannot be explained by a spontaneous low production of interferon by these cells. Furthermore, virus multiplication is not inhibited, even after treatment with interferon. These observations suggest that either the two enzymatic activities do not suffice for the establishment of an antiviral state in vivo or that a regulatory control mechanism, lost in these cells and common for both enzymes, is required for the expression of the antiviral action of interferon. This might explain both the constitutivity of the two enzymes and the interferon resistance observed.

Human enbryo cells were successively transformed by the Schmidt-Ruppin strain of Rous sarcoma virus (SR-RSV) and simian virus 40 (SV40) in vitro, and the double transformant HuE 13 RS was established. From this cell line the two clonal cell lines RSa and RSb were isolated. In both, presence of SV40 T antigens was demonstrated by the fluorescent antibody technique, and the presence of RSV genomes was verified in one RSb clone by focus formation after fusion with chick embryo cells. Growth of these cells was affected by dibutyryl cAMP without marked morphologic changes. Cells were extremely sensitive to the anticellular action of human leukocyte interferon.

The effects of human a and fJ interferons (IFN) on the production of HBsAg by PLCjPRF/5 cells, an HBsAg-producing human hepatoma cell line, were studied in the exponential and stationary phases of cell growth. When exponential phase cells were treated with 100 or 1,000 U of IFN per ml for 48 hr, the amount of HBsAg in the culture medium decreased. The number of cells and the synthesis of DNA and proteins were also reduced by the IFN treatment. These results suggested that IFN did not affect the production of HBsAg specifically in exponential phase cells. When cells in the stationary phase were similarly treated with IFN, HBsAg production was not inhibited nor did the number of cells decrease.To examine the antiviral state induced by IFN in PLCjPRF/5, induction of 2'5'-0Iigo(A) synthetase and susceptibility to two kinds of viruses were examined. The 2'5'-0Iigo(A) synthetase activity was increased in an IFN-dose dependent manner. Susceptibility to vesicular stomatitis virus (VSV) and encephalomyocarditis virus (EMCV) was decreased by treatment with 10 and 100 U of IFN per ml for 20 hr. It was concluded that IFN-a and IFN-fJ induce 2'5'-0Iigo(A) synthetase and the antiviral state, but do not inhibit HBsAg production by PLC/ PRF/5 cells.Interferon (IFN) is known for its therapeutic effect in several human viral infections. Recently, a number of reports have suggested certain effects of IFN in the treatment of chronic hepatitis B virus infection (9,12,13,18). IFN treatment reduces hepatitis B virus-specific DNA-polymerase activity and other viral markers in the serum of patients with chronic hepatitis (22). Several viral markers also disappear or decrease in hepatic tissue (21). Other workers, however, observed no effect of IFN treatment except for a transient decrease in DNA-polymerase activity (26). These conflicting results may be attributed to the differences in the amount and duration of IFN treatment given or in the immunological state of the Abbreviations: IFN, interferon; VSV, vesicular stomatitis virus; EMCV, encephalomyocarditis virus; TCIDso, 50% tissue culture infectious dose; MEM, Eagle's minimal essential medium. 705

No abstract