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F Lefèvre

Publications and source records attributed to F Lefèvre.

At least 55 records · Page 3Linked to original sources
PubMed1994

Interferon response in pigs: molecular and biological aspects.

This paper reviews the current state of knowledge on porcine interferons (IFN). Three type I IFN subfamilies (IFN alpha, beta and omega) and one type II IFN (IFN gamma) have been identified in the porcine species. A list of the known porcine IFN genes and already produced recombinant proteins, as compiled from the literature, was included. Two major aspects of porcine IFN were discussed: (1) IFNs as host responses to infections, and (2) IFNs in pregnancy. The first part mainly focusses on the IFN production by virus-infected pigs and the nature of IFN alpha secreting leukocytes. The second part reviews recent data showing the secretion of two different IFNs by the pig embryo at the time of implantation. One striking finding was that a non-lymphoid tissue, namely the porcine trophoblast, was able to secrete high levels of IFN gamma. In addition, the expression of another, newly described, IFN gene was also shown in pig trophectoderm. This novel trophoblastic type I IFN differs from the others in size and sequence. Several hypotheses are discussed on the possible role(s) of porcine embryonic IFNs at the initial stages of gestation.

Animals↗
PubMed1994

Coronavirus transmissible gastroenteritis virus-mediated induction of IFN alpha-mRNA in porcine leukocytes requires prior synthesis of soluble proteins.

We studied the expression of interferon alpha (IFN alpha)-mRNA in porcine non-adherent peripheral blood mononuclear cells (PBMC) after induction by the coronavirus transmissible gastroenteritis virus (TGEV). We found that protein synthesis inhibition by cycloheximide (CHX) blocked IFN alpha-mRNA expression, except when PBMC were preincubated with a conditioned medium as a potential source of cytokines. These data indicate that IFN alpha-mRNA induction by TGEV requires de novo synthesis of proteins. Moreover, they suggest that IFN alpha-mRNA induction in porcine leukocytes by TGEV involves mechanisms identical to those described for the herpes simplex virus in humans. In addition, experiments performed with a TGEV mutant, dm 49-4, previously characterized for its low ability to induce IFN alpha, showed that addition of a conditioned medium could not normalize its IFN alpha-inducing ability. Therefore, the defect of the dm49-4 mutant may be at the level of the final triggering signal to PBMC.

Actins↗
PubMed1993

A novel and atypical type one interferon gene expressed by trophoblast during early pregnancy.

Low stringency screening of day 14-15 pig conceptus cDNA library using an interferon (IFN)-omega probe has led to the isolation of a novel type one (type I) IFN gene physiologically expressed by trophoblast during the period of implantation in the uterus. It encodes a 170-amino acid preprotein with two potential N-glycosylation sites and a predicted N-terminal signal peptide of 21 residues. This protein was shorter and richer in Cys residues than other type I IFNs and distantly related to all of them including IFN-tau, the trophoblast IFNs of ruminants, with amino acid identities ranging between 27 and 42%. Moreover, its antiviral activity was resistant to neutralization by antisera directed against several IFN-alpha, -beta, -omega, and -tau family members. The pig genome contained only two intronless, non-allelic loci homologous to the cDNA, one of them corresponding to the cDNA. This gene had a single transcription initiation site. Its upstream putative regulatory regions had no similarity with those of other type I IFN genes and did not display the typical clustering of short sequence motifs thought to be involved in virus inducibility but, instead, a modular structure of 30-40-base pair direct repeats. These data highlight the very atypical characteristics of this gene and its product and suggest that it represents the first member of a yet unknown family of type I IFNs present in other mammalian species according to sequence divergence analysis.

Amino Acid Sequence↗
PubMed1991

Production of two species of interferon by Large White and Meishan pig conceptuses during the peri-attachment period.

Antiviral activities present in uterine flushings from pregnant Large White, Large White 'hyperprolific', and prolific Meishan gilts, between Days 8 and 20 of gestation were compared. Flushings (20 ml) from all gilts between Days 14 and 20 were positive in an in-vitro interferon (IFN) assay using vesicular stomatitis virus as a challenge infection. Highest antiviral activities (of up to 400,000-1,200,000 total Units/flushing) were obtained at Day 16 of gestation, i.e. clearly after the beginning of attachment. There was no major difference between breeds although, at Day 14, flushings from Meishan gilts yielded significantly higher titres than those from the other two, suggesting a correlation with the previously described earlier trophoblast elongation in Meishan gilts. Conceptus cultures contained antiviral activity, with values very close to those obtained in vivo, but the difference between breeds was not significant. Cultures from Day 20 on contained very little antiviral activity. The antiviral activity was associated with a mixture of at least two IFNs, one of which was IFN-alpha like, and the other was serologically identified as an IFN-gamma, that is an 'immune IFN', previously found to be secreted only by T lymphocytes. This finding may have implications for our understanding of the immunology of early pregnancy.

Animals↗
PubMed1990

Interferon-gamma gene and protein are spontaneously expressed by the porcine trophectoderm early in gestation.

The nature and the source of the antiviral activity found in the reproductive tract of pregnant gilts early in gestation were analyzed. Two antigenically distinct antiviral activities were found in uterine flushings and in supernatants of conceptus-conditioned culture medium between days 12 and 20 of gestation, using Madin Darby bovine kidney cells and vesicular stomatitis virus as a challenge in the antiviral bioassay. One component was antigenically identified as interferon-gamma (IFN-gamma). Northern blot analysis of conceptus poly(A)+ RNA with a human IFN-gamma cDNA probe revealed two mRNA of 1.3 and 1.4 kb. In addition, immunoprecipitation of metabolically labeled conceptus secretory proteins with an antiserum raised against purified porcine rIFN-gamma resulted in four bands in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, with molecular mass 18.5 to 24.5 kDa. Pre-electrophoresis incubation of the immunoprecipitate with glycopeptidase F, which removes N-linked carbohydrates, yielded a single band of 16.5 kDa. Finally, staining of ultrathin sections by indirect immunofluorescence using the same antiserum to rIFN-gamma revealed that all cells of extra-embryonic trophectoderm contained intensely fluorescent granules in their apical cytoplasm. Neither endoderm nor embryonic cells stained positive. These results clearly show that IFN-gamma, known so far as a T or NK cell-derived lymphokine, is spontaneously and intensively secreted by the porcine trophectoderm, an embryonic tissue not related to the hematopoietic lineage. They also suggest that the implanting conceptus, at least in the porcine species, could play an active role in immune interactions with the mother.

Animals↗
PubMed1990

Contribution of molecular biology to the study of the porcine interferon system.

We have performed molecular studies on the pig interferon (IFN) system (i) to analyse the role played by endogenous IFN in neonatal viral enteritis such as transmissible gastroenteritis and possibly to obtain, via recombinant DNA technology, a new anti-infectious and immunomodulatory agent in this species, (ii) to characterize the structure and biological functions of the IFN-like antiviral activity produced by the porcine embryo at the time of implantation in the uterus. By probing porcine genomic libraries with human and porcine IFN-alpha probes to isolate related genes, we have shown that the porcine IFN-alpha multigene family included, like several other mammalian species, two subfamilies of related but distinct genes. Class I subfamily contains at least 11 loci, located on chromosome no. 1, among which nine have been cloned and two (potentially functional) sequenced. Class II subfamily, which is specifically expressed by the embryo of ruminants before implantation, contains at least seven loci among which six have been cloned. One of the sequenced class I loci: PoIFN-alpha 1 encodes a 189 amino acids (AA) preprotein. After removal of the sequence encoding the putative signal peptide (23 N-terminal AA) this gene was inserted into an Escherichia coli bicistronic expression vector allowing intracellular synthesis of mature porcine IFN-alpha 1 (methionyl IFN-alpha 1). Expression of the recombinant protein was optimized by insertion of a seven base pairs long random synthetic sequence in the intercistronic region, followed by cloning in E. coli and immunodetection of clones expressing high amounts of recombinant protein. The E. coli strain obtained produced high levels of a 18,000 Da protein exhibiting the same in vitro overall biological properties as leucocyte derived porcine IFN (LeuIFN). However, it had a stronger antiviral effect on porcine cells than LeuIFN. After immunoaffinity purification to a specific activity of 5-10 x 10(7) International Units (IU)/mg of protein, pharmacokinetic and pharmacological studies were realized to determine the in vivo half life of this rIFN-alpha in the pig. These experiments revealed no major toxic effects in newborn (given 5 x 10(6) IU/kg) or adult (1 X 10(6) IU/kg) pigs. A significant pyrogenic effect (+ 1.5 degrees C) was noted only in the adults.

Animals↗
PubMed1990

Production, purification and biological properties of an Escherichia coli-derived recombinant porcine alpha interferon.

Recombinant plasmids for intracellular synthesis of mature porcine interferon alpha 1 (IFN-alpha 1) in Escherichia coli were constructed. High amounts of antiviral activity were obtained [up to 4 x 10(5) international units (IU) per ml of bacterial culture]. Recombinant porcine IFN-alpha 1 (rIFN-alpha 1) was purified to homogeneity by monoclonal antibody immunoaffinity and was found to have the expected Mr (17.5K) and N-terminal sequence (except for the apparent lack of an N-terminal methionine). Its specific antiviral activity was 5 x 10(7) to 10 x 10(7) IU/mg MDBK cells. In vitro biological properties of this purified rIFN-alpha 1 were compared to those of virus-induced porcine leukocyte interferon: the two interferons shared similar antigenic determinants and had the same ability to induce a cytocidal effect on primary cultures of pig kidney epithelial cells. However, rIFN-alpha 1 was at least six times more active in inducing an antiviral state on homologous porcine cells. These properties are discussed in the light of a possible in vivo use of the purified recombinant molecule.

Animals↗
PubMed1989

[The interferon system: structure, biology, applications].

This article presents an overview of (i) the structural features of the 3 types of mammalian interferon proteins (alpha, beta, and gamma) and of the gene families encoding them, (ii) the main biological effects and molecular events mediated in vitro and in vivo by these molecules and (iii) their present use in human and veterinary medicine. Recent results are detailed concerning the involvement of some interferon subspecies in physiological processes such as regulation of growth and differentiation of some cell lineages, interaction with other cytokines and possible hormonal effects of interferons.

Animals↗
PubMed1978

Effects of prazosin and phentolamine on cardiac presynaptic alpha-adrenoceptors in the cat, dog and rat.

In cats, dogs and rats, clonidine (20.0 microgram/Kg, i.v.) reduced the sustained tachycardia evoked by a continuous electrical stimulation of cardiac sympathetic nerve fibres. This effect of clonidine resulting from stimulation of cardiac presynaptic alpha-adrenoceptors could be completely antagonized by phentolamine and prazosin in the dog and the cat, whereas in the rat, prazosin, unlike phentolamine, failed to effectively inhibit the clonidine induced reduction in heart rate. The calculated doses of phentolamine and prazosin needed to produce a 50% antagonism were of similar magnitude in the dog, but in the cat prazosin was about three times less potent than phentolamine. As opposed to clonidine, LD 3098, a potent vascular postsynaptic alpha-adrenoceptor stimulating imidazoline, and phenylephrine (20.0 microgram/Kg, i.v.) did not significantly alter the sympathetic tachycardia in the pithed rat and the spinal dog. These results indicate that compounds stimulating postsynaptic alpha-adrenoceptors may be inactive as agonists of cardiac presynaptic alpha-adrenoceptors within the same animal species. Furthermore, a compound showing selective activity as an antagonist of vascular alpha-adrenoceptors in one species may not necessarily exert the same selective effects in other animals as demonstrated here for prazosin.

Animals↗
PubMed1977

Vascular beta-adrenoceptor stimulating properties of phenylephrine.

In pithed rats pretreated with propranolol changes occurred in the slopes of dose--pressor response curves to i.v. phenylephrine and noradrenaline but not to LD 3098, a pure alpha-adrenoceptor stimulant. In dogs, cats, and spontaneously hypertensive rats pretreated with an alpha-adrenoceptor blocker, i.v. phenylephrine induced vasodilatory responses which were antagonised by propranolol. These results indicate that phenylephrine, in addition to its known beta1-agonistic properties, stimulates the vascular beta2-adrenoceptors.

Adrenergic beta-Agonists↗