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E A Havell

Publications and source records attributed to E A Havell.

71 records · Page 4Linked to original sources
PubMed1977

Synthesis of human interferon by Xenopus laevis oocytes: two structural genes for interferons in human cells.

Human fibroblasts and leukocytes produce interferons which may be distinguished by their antigenic and species specificity as well as by their molecular weight distributions. To elucidate the basis for these differences, we isolated mRNA from induced human fibroblasts and lymphoblastoid (Namalva) cells and studied the products of translation in Xenopus laevis oocytes. The mRNA from the respective cells yielded translation products, in oocytes, that were characteristic of the cells from which the mRNA was derived. We conclude that human cells contain at least two structural genes for interferon, coding for polypeptides differing in primary sequence. Fibroblasts synthesize a single species of interferon; lymphoblastoid cells synthesize two species, the fibroblast and leukocyte types.

Animals↗
PubMed1976

Superinduction of interferon with metabolic inhibitors: possible mechanisms and practical applications.

Ten years have passed since cycloheximide was first shown to enhance endotoxin-induced production of interferon in mice, in the first demonstration of what was later called the superinduction of interferon. Various inhibitors of protein and RNA symthesis, as well as combinations of these inhibitors, have been shown to act as superinducing agents of interferon production stimulated by polyriboinosinic-polyribocytidylic acid. The evidence that superinduction is due to the suppression of a mechanism of post-transcriptional regulation of interferon synthesis is rather convincing. The notion (first proposed about six years ago) that this modification is caused by a protein "repressor" remains the most plausible, albeit still unproved, hypothesis. The availability of systems that translate with fidelity interferon messenger RNA isolated from induced cells should prove most useful in the elucidation of post-transcriptional control mechanisms of interferon synthesis and of interferon superinduction. Meanwhile, superinduction has become a useful tool for the production of large quantities of interferon. In particular, this technique has been successfully applied to the production of interferon from human diploid fibroblasts. The clinical potential of this material remains to be critically examined.

Animals↗
PubMed1975

Cell-free synthesis of human interferon.

With mRNA prepared from induced human fibroblasts biologically active human interferon was synthesized de novo in a cell-free extract from mouse cells. The identity of the antiviral activity as human interferon was demonstrated by its species and antigenic specificity.

Animals↗
PubMed1975

Two antigenically distinct species of human interferon.

Rabbit antisera prepared against interferon produced in human fibroblast cell cultures stimulated with poly(1).poly(C) neutralized the activity of interferon preparations produced in various human fibroblast cultures timulated either with poly(1)poly)C) or with viruses. However, these antisera showed no detectable neutralizing activity against interferon produced in cultures of human leukocytes. On the other hand, most rabbit antisera against the human leukocyte interferon were active in neutralizing both homologous interferon and fibroblast interferons. A preparation of antiserum against leukocyte interferon, active against both leukocyte and fibroblast interferons, was shown by affinity chromatography to have two distinct antibody populations, one of which was specific for the fibroblast interferon. We conclude that the heterologous neutralizing activity of sera from rabbits immunized with leukocyte interferon is liekly to be due to the presence of two antigenic species of interferon. The major antigenic species of leukocyte interferon preparations (designated "Le") is distinct from huamn fibroblast interferon. The minor species of leukocyte interferon ("F") is either identical with, or closely related to, interferon produced in human fibroblast cultures.

Animals↗
PubMed1975

Inhibition of interferon secretion by vinblastine.

The plant alkaloids vinblastine and colchicine are known to arrest cells in mitosis by virtue of their binding to spindle protein. These drugs are also capable of binding to microtubule protein and causing these structures to disaggregate into nonfunctional subunits (1, 2). Microtubular structures are thought to be involved in the secretory process of a number of proteins including insulin (7), collagen (4), and thyroid hormone (12). In this report we present our findings on the effects of these two drugs on the synthesis and secretion of interferon in a high producing human foreskin fibroblast strain (FS-4) (11).

Cell Line↗
PubMed1974

Increased interferon production in human cells irradiated with ultraviolet light.

Polyinosinate-polycytidylate [poly(I).poly(C)]-induced interferon production in cultures of human foreskin fibroblast strains was increased by ultraviolet irradiation of cells at the time of exposure to inducer or at 2 h after induction. Incubation of cells with interferon prior to induction (priming) and ultraviolet irradiation exerted a cooperative enhancing effect on interferon production. The resulting interferon yields were generally somewhat higher than the yields from cultures subjected to sequential treatment with cycloheximide and actinomycin D.

Journal Article↗
PubMed1973

Stabilization of interferon messenger RNA activity by treatment of cells with metabolic inhibitors and lowering of the incubation temperature.

Interferon production was induced in a strain of human diploid foreskin cells with poly(I).poly(C). Cycloheximide was included in the culture medium at the time of addition of the inducer. Actinomycin D was added to the cultures 4 or 5 hr later, before the inhibition of protein synthesis was reversed at 6 hr. Thus, subsequent interferon synthesis had to be directed by messenger RNA synthesized before addition of actinomycin D. The amount of interferon produced after such treatment was about 50-fold greater than in cells induced with poly(I).poly(C) but not treated with inhibitors. Experiments using cordycepin suggested that in spite of the continued presence of the inducer the synthesis of the bulk of interferon messenger RNA was completed within the first 2 hr of exposure of cells to poly(I).poly(C) and cycloheximide. Transcription of interferon messenger RNA was apparently not affected when interferon synthesis was suppressed to various degrees by different inhibitors of protein synthesis, indicating the independence of transcription and translation. The high rate of interferon synthesis after the reversal of cycloheximide action was more sustained at 32 degrees than at 37 degrees . The rate of decrease of overall protein synthesis in cells treated with actinomycin D and then incubated either at 32 degrees or 37 degrees showed a similar dependence on incubation temperature, suggesting that the stability of messenger RNA (or of another actinomycin D-sensitive component required for protein synthesis) was greater at the lower temperature.

Carbon Radioisotopes↗
PubMed1972

Production of high-titered interferon in cultures of human diploid cells.

The effect of incubation with interferon prior to the stimulation of interferon production (priming) and of sequential treatment with cycloheximide and actinomycin D (superinduction) on the interferon yield from polyinosinic-polycytidylic acid (poly I.poly C)-induced diploid human foreskin cell cultures (FS-3 strain) was studied. Suitable priming with interferon produced, on the average, about an eightfold increase over the control yield, with a greater increase noted on some occasions when the control interferon yield was very low. Under the optimal conditions carefully defined in our experiments, superinduction produced about a 100-fold increase over the average control yield, resulting in interferon yields of about 10,000 reference units from cultures containing about 10(6) cells. Combined superinduction and priming did not produce yields markedly higher than obtainable by superinduction alone. Essentially similar results were obtained in cultures of human embryonic kidney cells and in FS-3 cells stimulated with other double-stranded polynucleotide inducers. However, stimulation of cells with certain concentrations of a mixture of diethylaminoethyl-dextran and poly I.poly C altered the interferon response; the yield was considerably higher than in cells stimulated with poly I.poly C alone, but it could not be markedly increased further by superinduction.

Cell Line↗
PubMed1972

Suppression of the intracellular growth of Shigella flexneri in cell cultures by interferon preparations and polyinosinic-polycytidylic acid.

A strain of Shigella flexneri type 2a was found to multiply intracellularly in cultures of the diploid human cell strain FS-1 and in secondary rabbit kidney cells. When inoculated cultures were stained and observed under the light microscope, it appeared that the cytoplasm of infected cells became gradually filled with bacteria. Various preparations of human and rabbit interferon were found to suppress the intracellular bacterial growth in homologous cells. Polyinosinic-polycytidylic acid (poly I.poly C) had a similar inhibitory effect. Rabbit interferon preparations did not cause a significant suppression in human cells. Suppression of the bacterial growth could be demonstrated in two ways: (i) by showing that treatment with either homologous interferon or poly I.poly C reduced the proportion of infected cells determined by counting the total number of cells and the number of cells with 10 or more bacteria in several microscopic fields selected at random, or (ii) by showing that a suppression in (3)H-uridine incorporation by bacteria occurs in infected cultures treated with actinomycin D after incubation with interferon or poly I.poly C. (Uridine incorporation by the bacterium is insensitive to actinomycin D.) Treatment of cells with actinomycin D before incubation with interferon prevented the development of cellular resistance to bacterial infection. Interferon preparations did not have an inhibitory effect on the extracellular growth of S. flexneri in a broth culture. These findings show that the range of activity of the interferon system apparently extends to intracellularly growing bacteria.

Animals↗
PubMed1972

Control of interferon synthesis: effect of diethylaminoethyl-dextran on induction by polyinosinic-polycytidylic acid.

Interferon production in cultures of rabbit kidney cells (RKC) stimulated with 10 to 250 mug of polyinosinic-polycytidylic acid (poly I.poly C) per ml peaked at 3 to 4 hr after the exposure of cells to inducer and rapidly declined thereafter. On the other hand, RKC stimulated with poly I.poly C (10 or 2 mug/ml) in the presence of diethylaminoethyl (DEAE)-dextran (100 or 20 mug/ml, respectively) produced a protracted interferon response, with the release of interferon continuing for over 24 hr. The kinetics of interferon production in RKC stimulated with lower concentrations of the mixture of poly I.poly C and DEAE-dextran were similar to the response produced by poly I.poly C alone (10 to 250 mug/ml). Only the responses that terminated early were paradoxically enhanced by treatment with low doses of actinomycin D or with cycloheximide. Cells stimulated with 50 mug of poly I.poly C/ml showed hyporesponsiveness to a second interferon induction with poly I.poly C when restimulated 7 hr after primary induction. This hyporesponsiveness could be overcome by restimulating with higher concentrations of the poly I.poly C-DEAE-dextran complex. The results are compatible with the hypothesis that the early termination of interferon production and hyporesponsiveness to repeated induction with poly I.poly C are due to a cellular repressor exerting negative control on interferon synthesis, and that the increased cellular uptake of poly I.poly C in the presence of DEAE-dextran may effectively neutralize the repressor. These results also suggested that the often observed different kinetics and the varied effects of inhibitors of ribonucleic acid or protein synthesis on interferon responses in various cells and in cells stimulated with different inducers (such as with viruses as compared with polynucleotides) need not imply the existence of fundamentally different mechanisms of interferon production.

Animals↗