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Biomedical subjects

M Daëron

Publications and source records attributed to M Daëron.

At least 19 recordsLinked to original sources
PubMed1992

Induction of tumor necrosis factor-alpha production by mast cells via Fc gamma R. Role of the Fc gamma RIII gamma subunit.

Murine mast cells produce cytokines in response to cross-linking of high affinity receptors for IgE (Fc epsilon RI). Murine mast cells also express the two types of low-affinity receptors for IgG, murine (m)Fc gamma RII, and mFc gamma RIII. We examined the ability of mFc gamma R to trigger a cytokine response such as TNF-alpha production by mast cells. We found that the mFc gamma RII- and mFc gamma RIII-positive mouse mastocytoma cells MMC-1 released TNF-alpha when challenged with F(ab')2 fragments of the rat anti-mFc gamma RII/III 2.4G2 mAb and mouse anti-rat IgG F(ab')2. The release of TNF-alpha was preceded by an increase in TNF-alpha transcripts. mFc gamma RII and mFc gamma RIII have 95% homologous extracellular domains but unrelated transmembrane and intracytoplasmic (IC) domains. mFc gamma RII are single chain receptors whereas mFc gamma RIII associate with a homodimeric gamma-chain that also associates with Fc epsilon RI and TCR. In order to analyze the ability of mFc gamma RII and III to trigger the synthesis of TNF-alpha, we studied RBL-2H3 cells transfected with corresponding cDNA. Rat basophilic leukemia (RBL) transfectants expressing mFc gamma RIII produced TNF-alpha in response to 2.4G2 F(ab')2, but not transfectants expressing mFc gamma RII. Non-transfected RBL cells and mFc gamma RII- or mFc gamma RIII-expressing transfectants, however, released TNF-alpha in response to a rat IgG2a mAb. The respective roles of the alpha and gamma subunits of mFc gamma RIII were examined by studying the production of TNF-alpha by RBL cells expressing deletant and chimeric mFc gamma R. The deletion of intracellular amino acids of the Fc gamma RIII alpha subunit did not prevent 2.4G2 F(ab')2 from triggering the synthesis of TNF-alpha. The substitution of the IC domain of mFc gamma RII for that of mFc gamma RIII gamma, but not that of Fc gamma RIII alpha, enabled 2.4G2 F(ab')2 to trigger the release of TNF-alpha by RBL transfectants. A cytokine response can therefore be induced in mouse and rat mast cells through Fc gamma R. This response is triggered upon cross-linking of mFc gamma RIII but not mFc gamma RII. It depends on the IC sequences of the gamma but not of the alpha subunit of mFc gamma RIII.

Animals↗
PubMed1992

Murine recombinant Fc gamma RIII, but not Fc gamma RII, trigger serotonin release in rat basophilic leukemia cells.

Murine Fc gamma RII and Fc gamma RIII have highly homologous extracellular domains, but unrelated transmembrane and intracytoplasmic (IC) domains. Murine Fc gamma RIIb1 and b2 are two isoforms of single-chain receptors which differ only by 47 aa in their IC domain. Murine Fc gamma RIII are composed of an IgG-binding alpha-chain, the intracellular portion of which is unrelated to that of Fc gamma RII, and of a homodimeric gamma-chain which also associates with Fc epsilon RI. Murine mast cells express Fc gamma RII, Fc gamma RIII, and Fc epsilon RI. They can be induced to degranulate by murine IgG immune complexes or by F(ab')2 fragments of the rat anti-murine Fc gamma RII/III mAb 2.4G2, complexed to mouse anti-rat (MAR) F(ab')2. In order to determine which murine Fc gamma R can activate mast cells, cDNA encoding murine Fc gamma RIIb1, Fc gamma RIIb2 or Fc gamma RIII alpha were stably transfected into RBL-2H3 cells. Murine Fc gamma RIII but not Fc gamma RIIb1 or Fc gamma RIIb2 induced serotonin release when aggregated by (2.4G2-MAR) F(ab')2 complexes. The respective roles of the IC domains of murine Fc gamma RIII subunits in signal transduction were investigated by stably transfecting cDNA encoding IC-deleted or chimeric murine Fc gamma R into RBL-2H3 cells. The substitution of the IC domain of murine Fc gamma RII for that of murine Fc gamma RIII gamma, but not that of murine Fc gamma RIII alpha, conferred the ability to trigger serotonin release. The deletion of IC sequences of the alpha subunit did not alter the ability of murine Fc gamma RIII to trigger serotonin release. It follows that 1) murine Fc gamma RIII, but not Fc gamma RII, can induce RBL cells to release serotonin, 2) the aggregation of the IC domain of the murine Fc gamma RIII gamma subunit is sufficient, but 3) the IC domain of the murine Fc gamma RIII alpha subunit is neither sufficient nor necessary for triggering serotonin release.

Animals↗
PubMed1992

[The Fc portion of antibodies].

The binding of an antibody to antigen is only the first step of the antigen-antibody reaction. The Fab portions of the antibody determine its specificity and enable the binding of antigen, but the Fc portions is responsible for its biological activity. This biological activity depends on interactions between the Fc portion and specific receptors, Fc Receptor (FcR). FcR are expressed at the surface of many different cell types. Their aggregation by complexed antibodies triggers the activation of cells, which exert their biological activities on antigen-bearing structures. Fc-FcR interactions couple humoral and cellular immunity.

Immunoglobulin Fc Fragments↗
PubMed1992

Regulation of the expression of murine alpha- and beta-Fc gamma R genes.

Murine low-affinity receptors for the Fc portion of IgG are of two types: Fc gamma RII and Fc gamma RIII. Murine Fc gamma RII and III have 95% homologous extracellular (EC) domains and bind the same ligands, but different transmembrane (TM) and intracytoplasmic (IC) domains. They, however, have unrelated TM and IC domains. Murine Fc gamma RII are single-chain receptors, encoded by the beta-Fc gamma R gene. Murine Fc gamma RIII are composed of two subunits: the ligand-binding alpha-subunit, encoded by the alpha-Fc gamma R gene and the gamma-subunit, encoded by another gene which belongs to a family of genes encoding dimeric subunits of multichain receptors. The expression of murine Fc gamma RII and Fc gamma RIII depends on a number of mechanisms which do the following: (1) determine the tissue-specific expression of the alpha- and beta-Fc gamma R genes by selectively unmethylating DNA in specific 5' sequences in different cell types; (2) regulate the initiation of the transcription of the alpha- and beta-Fc gamma R genes via several transcription factors; (3) up- and downregulate the amount of alpha- and beta-Fc gamma R transcripts in response to cytokines; (4) decide the alternative splicing of IC exons of the beta-Fc gamma R gene and generate the different Fc gamma RII isoforms; (5) possibly regulate the translation of alpha- and beta-Fc gamma R transcripts in different cells; (6) control the assembly of the Fc gamma RIII subunits and their membrane insertion, and (7) determine the turnover of Fc gamma RII and III in the presence and absence of ligands by affecting the internalization, shedding and proteolytic cleavage of the receptors. These mechanisms altogether contribute to make a variety of cells capable of responding differently to antigen-antibody complexes, depending on environmental stimuli.

Animals↗
PubMed1992

Sequence and length heterogeneity of alpha Fc gamma R transcripts in AKR mice.

The murine low-affinity receptors for IgG, Fc gamma RIII and Fc gamma RII, are encoded by the alpha and the beta Fc gamma R genes, respectively. By contrast to the sequence and the molecular polymorphism of human Fc gamma RIII, no heterogeneity of the murine Fc gamma RIII has been reported and a single alpha Fc gamma R transcript was observed. We describe here a double heterogeneity of alpha Fc gamma R transcripts. First, by S1 mapping of alpha transcripts and by cloning of cDNA coding for Fc gamma RIII, we found a strain-related sequence heterogeneity: four amino acids in the coding region and two stretches of nucleotides in the 3' untranslated sequences differ between alpha transcripts of AKR and BALB/c mice. Second, in AKR mice, we found a cell-dependent length heterogeneity: a short 0.9 kb alpha transcript was present in peritoneal thioglycolate-elicited cells (PEC) from AKR mice. This transcript was present neither in mast cells and NK cells from AKR and BALB/c mice nor in PEC from BALB/c mice. A short cDNA, with a deletion of all the 3' untranslated sequences, has been cloned from AKR PEC, and corresponds to the short alpha transcript. All the differences found in the 3' untranslated sequences of AKR alpha transcripts are located within the fifth exon of the mouse alpha Fc gamma R gene.

Amino Acid Sequence↗
PubMed1991

Soluble Fc gamma receptors II (Fc gamma RII) are generated by cleavage of membrane Fc gamma RII.

This study describes the production of soluble Fc gamma RII by a cell line, D1B1, obtained by transfection of mouse L cells with a murine beta 1 Fc gamma RII cDNA. Upon incubation at 37 degrees C, radioiodinated D1B1 cells release a 39-kDa soluble Fc gamma RII, reacting with the rat anti-mouse Fc gamma RII monoclonal antibody 2.4G2, and binding to mouse IgG2a, IgG2b and IgG1 but not IgG3. In contrast to the transmembrane 50- to 70-kDa receptor, this soluble Fc gamma RII does not react with antibodies directed against a peptide corresponding to the 15 carboxy-terminal intracytoplasmic amino acids of beta Fc gamma RIII. N-Glycosidase F treatment generates a 18-kDa polypeptide. A 32- to 40-kDa soluble Fc gamma RII, which resolves into 18.5- and 20-kDa polypeptides after deglycosylation, was also isolated from the culture medium of unlabeled D1B1 cells. Therefore, this study indicates that soluble Fc gamma RII corresponding to the two extracellular domains of Fc gamma RII are generated by cleavage of membrane Fc gamma RII. Proteolysis occurs most probably at the vicinity of the transmembrane region of the receptor, around amino acids 165 to 180.

Animals↗
PubMed1990

Molecular heterogeneity of murine mast cell Fc gamma receptors.

Fc gamma R expressed by mouse mast cells were characterized as functional binding sites, as membrane proteins, and as products of the two genes known to encode murine Fc gamma RII. Peritoneal mast cells, bone marrow-derived mast cells (BMMC), and the mastocytoma cells P815 were found to bear trypsin-resistant, 2.4G2+, low-affinity receptors binding mouse monoclonal IgG1, IgG2a, and IgG2b, i.e., Fc gamma RII. BMMC and P815 Fc gamma RII appeared as heterogeneous membrane proteins that, when deglycosylated, had m.w. corresponding to those of the three known products of the alpha and beta Fc gamma R genes, and differed by their respective contents in BMMC and P815 cells. Heterogeneous Fc gamma R transcripts were also found in BMMC and in P815 RNA. P815 cells contained alpha, beta 1, and beta 2 Fc gamma R transcripts, whereas BMMC contained alpha and beta 1 Fc gamma R transcripts. These data disclose an unexpected molecular heterogeneity of murine mast cell Fc gamma R. Although they appear as a single population of receptors when viewed by external ligands, mast cell Fc gamma R comprise three Fc gamma RII subtypes, encoded by the three known transcripts of the alpha and beta Fc gamma R genes, and differing by their intracytoplasmic portion. The different distributions of Fc gamma RII transcripts and corresponding Fc gamma RII subtypes in different types of mast cells may be determinant for triggering the various biologic activities of these cells.

Animals↗
PubMed1990

Unmethylation of specific sites in the 5' region is critical for the expression of murine alpha Fc gamma R gene.

Three subtypes of murine low-affinity receptors for IgG (Fc gamma RII) have been identified. One is encoded by the alpha Fc gamma R gene, two are encoded by the beta Fc gamma R gene. In the present work, we examined whether DNA methylation might control expression of the alpha Fc gamma R gene. We found that, in DNA from a panel of Fc gamma R(+) and (-) cell lines, two MspI sites of the alpha Fc gamma R gene were selectively unmethylated only in the two cell lines containing alpha transcripts. These sites, separated by a distance of 1.2 kb, are located in the 5' region of the gene. All other MspI sites were methylated in all cell lines. Furthermore, 5-azacytidine induced the demethylation and the expression of the alpha Fc gamma R gene in the Fc gamma R(-) thymoma BW5147. Both alpha Fc gamma R gene transcripts and corresponding protein products became detectable in 5-azacytidine-treated cells. The alpha Fc gamma R gene was also demethylated and expressed in mouse spleen cells cultured with human rIL-2. We conclude that a correlation links the unmethylation and the expression of the alpha Fc gamma R gene in murine cell lines as well as in nontransformed lymphoid cells responding to a physiological stimulus.

Animals↗
PubMed1990

Identification of Fc gamma RIIa, a product of the murine alpha Fc gamma R gene.

Two genes, alpha and beta, encode murine low-affinity receptors for the Fc portion of IgG (Fc gamma RII). The amino acid sequences deduced from the nucleotidic sequences of alpha and beta cDNA are highly homologous in extracellular domains. As a consequence, the protein product of the alpha Fc gamma R gene has not yet been distinguished from that of the beta Fc gamma R gene. alpha and beta cDNA, however, show no homology in sequences coding for intracellular portions. We therefore raised antibodies against a synthetic peptide corresponding to the 26 intracytoplasmic amino acids of the expected product of the murine alpha Fc gamma R gene. F(ab')2 fragments of alpha-specific antibodies thus obtained stained specifically membrane proteins which were present in cells containing alpha transcripts but not in cells containing beta transcripts only; they bound molecules carrying the 2.4G2 epitope, characteristic of the extracellular domains of murine Fc gamma RII; they immunoprecipitated material which migrated as heterogeneous glycosylated proteins of 45-55 kDa when native and, when deglycosylated, as a single polypeptide with an apparent molecular mass of 29 kDa, which is compatible with the calculated molecular mass of the protein expected to be translated from alpha Fc gamma R transcripts. These criteria identify a product of the murine alpha Fc gamma R gene as a subtype of Fc gamma RII which can be designated Fc gamma RIIa.

Animals↗
PubMed1989

Trypanosoma musculi co-express several receptors binding rodent IgM, IgE, and IgG subclasses.

The present work demonstrates the expression of receptors for the Fc portion of rodent Ig by the murine parasite Trypanosoma musculi. By using a rosette assay adapted to the parasite morphology and by flow cytometry analysis, three distinct receptors were identified. A receptor binding rabbit or rat polyclonal IgG and mouse monoclonal IgG1, IgG2a, and IgG2b was found on parasites purified from the blood and the peritoneal cavity of infected mice and on parasites maintained in culture conditions. This IgG receptor was degraded by pepsin. A separate receptor, binding only mouse monoclonal IgG3 was observed on cultured parasites. A receptor binding rabbit, rat, and mouse IgM was found on cultured and peritoneal parasites, but not on blood parasites. This receptor did not bind IgG or IgA but it bound mouse and rat IgE as well as IgM. It was degraded by trypsin. IgG and IgM/IgE receptors were co-expressed on single parasites. They were not of host origin but synthesized by trypanosomes as shown by reexpression in vitro after proteolytic degradation. Their expression was variable with the development of trypanosomes both in vitro and in vivo.

Animals↗
PubMed1989

Identification of the Fc gamma RII-related component of murine IgG-BF.

Suppressor murine IgG-BF produced by the T cell hybrid (T2D4) expressing low affinity Fc gamma R (Fc gamma RII) contain four biologically active polypeptides of pI 5.2, 6.3, 7.7 and 8.3, respectively. They were fractionated by affinity chromatography on immunoadsorbents coupled with F(ab')2 fragments of the monoclonal anti-Fc gamma RII antibody 2.4G2 and by hydrophobic interaction chromatography. Both methods led to the identification of biologically active IgG-BF which react with 2.4G2 and of IgG-BF which do not react with 2.4G2. Molecules bearing the epitope recognized by 2.4G2 had an apparent pI of 5.3 while the pI of those which did not express this epitope were 6.3, 7.8 and 8.5, respectively. Therefore, one IgG-BF polypeptide of pI 5.3 is probably related to Fc gamma RII.

Animals↗
PubMed1988

Methylation in the 5' region of the murine beta Fc gamma R gene regulates the expression of Fc gamma receptor II.

In order to identify possible mechanisms regulating the expression of Fc gamma RII, we have examined the methylation status of the beta Fc gamma R gene in a panel of Fc gamma RII (+) and (-) cells belonging to several different lineages. We used beta 1 cDNA probes, derived from beta Fc gamma R gene transcripts which encode murine Fc gamma RII molecules. We found that all CCGG sequences detected with these probes were methylated in the genomic DNA of the Fc gamma RII-(-) cells. By contrast, two CCGG sites were found to be selectively unmethylated in the DNA of all Fc gamma RII(+) cells tested. These sites could be assigned to the region of the 5' end of the beta Fc gamma R gene. Besides, the treatment of Fc gamma RII(-) thymoma cells BW5147 with 5-azacytidine induced a hypomethylation of the beta Fc gamma R gene concomitantly with the transcription of that gene as seen by Northern blotting and the expression of functional Fc gamma RII. Conversely, the DNA-methylating agent ethyl methanesulfonate completely reversed the phenotype of the 5-azacytidine-treated cells to that of the Fc gamma RII(-) BW5147 parent cells. In ethyl methanesulfonate-treated cells, the beta Fc gamma R gene was remethylated and the corresponding transcript was no more detectable. We conclude that the methylation of a specific 5' segment of the beta Fc gamma R gene regulates the expression of Fc gamma RII in murine T cells, B cells, mast cells, and macrophages, possibly by controlling the gene transcription.

Animals↗
PubMed1987

[Regulation and dysregulations of immunoglobulin E synthesis].

Compared to other isotypes of immunoglobulins, IgE antibodies are present in exceedingly low concentrations in normal serum, because their synthesis is maintained under the strict control of several intricate regulatory mechanisms. These normally unapparent mechanisms become accessible to investigations in a number of pathological dysregulations. One may distinguish three orders of controls. An elementary isotypic circuit, constructed on the interactions between IgE Fc portions and IgE-binding molecules, directly regulates IgE synthesis by IgE-secreting B cells. IgE-binding molecules are themselves controlled by several lymphokine cascades, depending on external and genetic factors. The functioning of the IgE isotypic circuit is coordinated with other circuits, corresponding to other immunoglobulin isotypes, by means of an isotypic network, connected to other homeostatic systems of the organism. The dissection of these regulatory mechanisms and an understanding of their interactions are potentially useful for new therapeutic approaches.

Humans↗