Influence of the rate of cell growth and cell density on interferon action in chick embryo cells

Comparative production of interferon by human fetal, neonatal, and maternal cells

Production of interferon was studied in fibroblasts cultured from human fetal, neonatal, and maternal tissue. Human fetal and maternal cells were paired to diminish genetic variability. Fetal cells displayed an increased response to two inducers of interferon, virus and synthetic double-stranded ribopolynucleotide. Fetal cells released 300-fold more interferon than maternal cells on exposure to poly rI:rC. This enhanced capacity for interferon production was consistent in cultures developed from fetal skin obtained between the 10th and 20th gestational week. The response was relatively stable, persisting in cells cultured for 18 generations (about 14 weeks). On infection with Newcastle disease virus, fetal cells produced, on the average, 4 to 6.5 times more interferon than maternal or neonatal cells. The virus was adsorbed with equal efficiency by each type of cell. Increased production is apparently independent of the rates of overall protein synthesis, since fetal and maternal cells have very similar rates of total protein synthesis.

Expression of authentic vaccinia virus-specific and inserted viral and cellular genes under control of an early vaccinia virus promoter is regulated post-transcriptionally in interferon-treated chick embryo fibroblasts

The interferon sensitivity of the expression of an influenza-virus hemagglutinin (HA) gene cloned into the thymidine kinase (TK) gene of vaccinia virus was studied in chick embryo fibroblasts (CEF) and Madin-Darby bovine kidney (MDBK) cells. In CEF, the expression of the HA gene is inhibited by pretreatment of cells with homologous interferon. In MDBK cells, on the other hand, expression of the HA is not impaired by pretreatment with human interferon-alpha, and the synthesis of early vaccinia virus enzymes was also unaffected. These results indicate that the interferon sensitivity of HA gene expression is at least in part controlled by flanking regions of vaccinia virus DNA. In this report, we also address the question whether the expression of an influenza virus HA gene and the human histone H1 zero gene under control of a vaccinia virus immediate early promoter is affected in interferon-treated CEF by a post-transcriptional mechanism in the same way as the expression of the viral TK gene. In interferon-treated cells mRNA synthesis specific for all these genes was enhanced. Steady state mRNA levels 6 hr p.i. were, however, lower than the amounts expected from the rate of mRNA synthesis during the first 6 hr p.i., suggesting that part of the viral RNA was degraded. Degradation resistant mRNA accumulated in the interferon-treated cells in an amount comparable to that found in infected CEF. This RNA could be translated into viral protein in a cell-free system. Therefore the degradation of viral mRNA cannot solely be responsible for the inhibition of viral protein synthesis in interferon-treated cells.

Evidence for the identity of murine gamma interferon and macrophage activating factor

Macrophages activating factor (MAF) in mouse lymphokine preparations was quantitated using a tumor cell cytotoxicity assay. MAF activity was compared with gamma interferon (IFN-gamma) activity, and the lymphokine mixture subjected to a variety of protein fractionation procedures. No significant difference in the ratio of MAF activity to IFN activity was observed following any of the fractionation steps, even after MAF had been purified to a specific activity of 1 X 10(6) u/mg protein. Gel permeation using high pressure liquid chromatography showed a coincident peak of MAF and IFN activity at approximately 55 kD. Both activities were reduced at similar rates following heating at 56 degrees C or incubation at 4 degrees C in pH 2 buffer. Finally, induction of lymphokines using different inducers (mitogens or antigens) or cell populations always resulted in similar ratios of MAF activity to IFN activity. These results support the hypothesis that MAF and IFN-gamma are identical proteins.

Role of G0-G1 arrest in the inhibition of tumor cell growth by interferon

We report here that human leukocyte interferon preparations are capable of influencing the transition of human melanoma cells from the "A" state to the "B" phase. Human melanoma cells that enter a quiescent stage at high cell density are more sensitive to the cytostatic action of interferon than those that continue to proliferate under similar conditions. Cell cycle perturbations caused by interferon in these cells include a decreased transition rate out of G0-G1 ("A" state) into S ("B" phase) and a prolongation of S. These findings support the idea that some metabolic event is required for progress through the G0-G1 phase of the cell cycle and is susceptible to interferon action.

Noncycling tumor cells are sensitive targets for the antiproliferative activity of human interferon

Resting Burkitt's lymphoma cells (Daudi) in culture are more sensitive targets for the antiproliferative activity of purified human fibroblast interferon than cells that are rapidly multiplying. Thus, interferon may be of significant clinical value in neoplasms involving stem cells and, after chemotherapy, in suppressing the reemergence of tumors.

Cellular interactions determine the rate and degree of interferon action

The rate and degree of interferon action on mouse embryo (ME), mouse L, and human amnion (WISH) cells were found to be dependent on the cell density. The most precipitous drop in interferon action occurred just below cell confluency. This effect was shown with both vesicular stomatitis virus and Sindbis virus and at both constant and variable input multiplicities of infection. At both "high" and "low" cell densities, cells attached to a surface develop viral resistance faster than suspended cells. These data indicate that either cell contact or close cell proximity is required for maximal interferon activity. These results are discussed in relation to interferon-induced transfer of viral resistance.

Vesicular stomatitis virus plaque production in monolayer cultures with liquid overlay medium: description and adaptation to a one-day, human interferon-plaque

Vesicular stomatitis virus forms discrete, microscopic plaques in stationary cultures of the WISH amnion cell line. Microplaque formation is rapid, reproducible, and easily quantitated, occurs at temperatures ranging from 33 to 40 degrees C, and does not require a semisolid overlay. WISH cells, however, are less sensitive to vesicular stomatitis virus than are chicken embryo, 3T6, or Vero cells. WISH amnion cells also are highly sensitive to the antiviral effects of human interferon, and a quantitative human interferon assay, based on vesicular stomatitis virus plaque reduction in WISH cells, is described. This interferon assay can be performed within 1 day, uses a liquid overlay medium, does not require a vital stain, is as sensitive as other methods that use diploid cell strains, and is performed in a microtiter system.

Viral infection and interferon in cell cultures aged in vitro

Cells from leucosis-free chick embryos (skin and muscles), grown in vitro 1 and 7 days with no medium change, are used as a model for young dividing and stationary in vitro aged cells, respectively. Aged cultures are advantageous for IF induction by cytopathic and noncytopathic viruses. Decreased virus production in them is ascribed to a back effect of the early formed IF onto the inducing virus. A factor which stimulates viral IF interferon induction also in young cultures, is released from aged cells into the medium. This factor could belong -- according to its properties and action -- into the class of chalones.