Interaction of interferon with chick embryo cells

Effect of interferon on cyclic adenosine monophosphate levels in cells

Treatment of murine and human cells with homologous interferon (IFN) resulted in an elevation of the cellular cyclic adenosine monophosphate (cAMP) levels in a time- and dose-dependent manner. A similar elevation of cAMP levels could be produced by treatment of cells with isoproterenol, prostaglandin or methylxanthine. However, these agents did not produce an antiviral state. Pretreatment with an inhibitor of adenyl cyclase, N-ethylmaleimide, prevented the effect of IFN on cAMP levels, but did not influence tis antiviral activity.

Antagonism in action between mouse or human interferon and platelet growth factor

Human leukocyte and mouse fibroblast interferons abolished the mitogenic effect of human or bovine platelet growth factor (PGF) on human or mouse cells. Conversely, the antiviral and anticellular activity of both forms of interferon was inhibited by PGF in the homologous and in certain heterologous cell systems.

Effect of serum on the antiviral and anticellular activities of mouse interferon

Fetal bovine serum markedly decreased the ability of mouse L-929 interferon preparations to inhibit the formation of L-929 clones, but did not affect their ability to inhibit vesicular stomatitis virus (VSV) plaque formation in these cells. This dissociation of effects by interferon preparations indicates that: 1. the mechanism of action of interferon for its anticlonal antiviral activities is different; or 2. the molecule responsible for the anticlonal activity is a separate growth inhibitory factor.

Recovery of cell-bound interferon

Interferon could be recovered from homologous cells to which it was applied but could not be recovered from heterologous cells. The amount of interferon that could be recovered from cells corresponded to the sensitivity of the cells to the antiviral activity of the interferon: mouse embryo fibroblasts, which were 5 to 10 times as sensitive as L-929 cells to interferon, bound 5 to 10 times more interferon than the latter, whereas Lpa cells, which were only one-third as sensitive as L-929 cells to interferon, bound only one-third as much as the latter. The concentration of cell-bound interferon was as much as 150 times the extracellular concentration of interferon applied to the cells. Interferon bound to cells at 4 C with the same efficiency as it did to cells at 37 C, and actinomycin D-treated cells bound interferon as well as normal cells. Even though the total amount of interferon bound to cells was as much as 30% of the amount of interferon applied to them, no loss of antiviral activity was detectable from the medium.

Dye uptake assay: an efficient and sensitive method for human interferon titration

Currently, human interferon (IF) assays are generally performed by plaque reduction or visual cytopathic effect methods. Both are time-consuming, subjective in interpretation, and, in the case of the latter, relatively insensitive. An adaption of the dye uptake method for human IF titration which uses foreskin-derived fibroblasts and vesicular stomatitis virus is described. This assay is reproducible and sensitive (1 unit = 3 international units). By direct comparison, however, it is somewhat less sensitive than the plaque reduction assay (1 unit = 1.1 international units). This assay is especially recommended for use in needed clinical investigations of human IF because of its technical simplicity, allowing efficient handling of large numbers of specimens.

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

Chick embryo cells became more sensitive to the action of interferon the longer they remained in culture. This phenomenon was found even before confluency had been reached. The relative insensitivity of newly seeded cells was not due to a loss of receptors. Cells synthesizing deoxyribonucleic acid (DNA) at a high rate were less sensitive to interferon action than cells synthesizing DNA at a low rate, but the inhibition of DNA synthesis had no effect on interferon action. An increase in the number of cells used for seeding resulted in an earlier appearance of increased sensitivity to interferon action. These results are discussed in relation to the induction process in animal cells.