Biomedical subjects

M Daëron

Publications and source records attributed to M Daëron.

At least 37 records · Page 2Linked to original sources

PubMed1997

Structural bases of Fc gamma R functions.

This review describes structures which determine the biological activities triggered by Fc gamma R and account for the cell-mediated functions of IgG antibodies in physiology and pathology. The binding specificity and affinity of Fc gamma R depend primarily on IgG-binding structures, in their immunoglobulin-like extracellular domains. Binding is however also influenced by subunits that associate to multichain Fc gamma R. Effector and regulatory intracytoplasmic sequences that are unique to molecules of the Fc gamma RIIB family determine the internalization properties of these receptors. Immunoreceptor Tyrosine-based Activation Motifs (ITAMs) are intracytoplasmic effector sequences shared by Fc gamma R and other receptors involved in the recognition of antigen, which trigger cell activation and internalization. Immunoreceptor Tyrosine-based Inhibition Motifs (ITIMs) are intracytoplasmic sequences, shared by Fc gamma RIIB and a growing number of negative coreceptors which negatively regulate cell activation via ITAM-bearing receptors. Altogether, these structures enable IgG antibodies to exert a variety of finely tuned biological effects during the immune response.

Humans↗

PubMed1997

Chimeric immunoglobulin E reactive with tumor-associated antigen activates human Fc epsilon RI bearing cells.

Crosslinking of immunoglobulin E molecules that are bound to the Fc epsilon receptors expressed on mast cells or basophils triggers activation of these cells, resulting in the development of a type I hypersensitivity. Targeting this potent immune reaction towards tumors by using IgE that reacts with a tumor-associated antigen, may induce a local inflammation at the tumor site, and may therefore promote tumor regression. We have previously shown that murine IgE bound to tumor cells can activate murine mast cells to release TNF-alpha and histamine. To further investigate the therapeutic potential of IgE-mediated immunotherapy of carcinomas, we have developed human/murine chimeric versions, containing the murine variable regions and human constant regions, of both G250 and 323/A3 IgE. These chimeric IgEs are reactive respectively with the G250 renal cell carcinoma antigen and the Ep-CAM molecule, which is highly expressed by most carcinomas. Transfection of the respective chimeric heavy and light chain genes into recipient Sp2/0 myeloma cells yielded chimeric IgE-producing clones. Chimeric G250 and 323/A3 IgE reacted with tumor cells expressing the G250 antigen or Ep-CAM, respectively. To generate a cell line that expresses Fc receptors for human or chimeric IgE, the rat basophilic leukemia cell line RBL-7 was transfected with the human Fc epsilon RI alpha chain (RBL-7TZ) and subsequently tested for binding of chimeric IgE. Functional assays showed that both chimeric IgEs activated RBL-7TZ cells to release TNF-alpha when cultured with tumor cells that express the respective specific antigen. Furthermore, both chimeric IgEs were able to activate freshly isolated human basophils.

Animals↗

PubMed1996

Identification, molecular cloning, biologic properties, and tissue distribution of a novel isoform of murine low-affinity IgG receptor homologous to human Fc gamma RIIB1.

A cryptic splice donor site in the first intracytoplasmic (IC) exon of the murine Fc gamma RIIB gene generates a previously unknown Fc gamma RIIB isoform. Three membrane Fc gamma RIIB polypeptides of 37, 32, and 30 kDa were immunoprecipitated by Fc gamma RIIB-specific Abs, and three Fc gamma RIIB cDNAs of 1071, 987, and 930 bp were amplified by reverse transcriptase-PCR with Fc gamma RIIB-specific oligonucleotides from the mastocytoma cells P815. The 1071-bp cDNA contains all sequences of IC exons and encodes the 37-kDa Fc gamma RIIB1 isoform. The 930-bp cDNA lacks sequences of the first IC exon and encodes the 30-kDa Fc gamma RIIB2 isoform. The 987-bp cDNA has an 84-nucleotide deletion of the first IC exon 3' sequences. When stably transfected in the lymphoma B cells IIA1.6, or in the mast cells RBL-2H3, this cDNA encoded 32-kDa Fc gamma RIIB whose biologic properties were undistinguishable from those of Fc gamma RIIB1: they inhibited B cell activation when coaggregated to B cell receptors and capped when aggregated at 37 degrees C, but failed to mediate endocytosis or phagocytosis. Sequences responsible for capping and inhibition of internalization, previously assigned to sequences encoded by the first IC exon, can thus be mapped in the 19 N-terminal residues. These residues are highly conserved in human Fc gamma RIIB1. The 87-bp first IC exon of the human gene ends by a single splice site in the downstream intron and encodes a 19-amino acid insertion. The 32-kDa Fc gamma RIIB is the murine homologue of human Fc gamma RIIB1. We propose to name it Fc gamma RIIB1'. Fc gamma RIIB1' was expressed in myeloid and lymphoid cell lines, in normal spleen cells, and in resting or LPS-activated B cells.

Amino Acid Sequence↗

PubMed1996

Building up the family of ITIM-bearing negative coreceptors.

The acronym (ITAM) for immunoreceptor tyrosine-based activation motif was first proposed in September 1994, during the 8th Meeting on Signals and Signal Processing in the Immune System held in Kecskemet, Hungary, to designate the di-tyrosine-based YxxL activation motifs that had been previously understood by Michael Reth to account for the cell-triggering properties of BCR, TCR and FcR. It was then agreed, by those who signed the collective letter John Cambier had been commissioned to submit to Immunology Today (Cambier, J.C. (1994) Immunol. Today 16, 110-110) that it was premature to propose ITIM (for immunoreceptor tyrosine-based inhibition motif) to designate the one inhibitory sequence containing a single Ys1L motif that had been identified in the intracytoplasmic domain of a low-affinity Fc receptor for IgG. Right away, ITAM became unanimously accepted and widely used in the literature. Remarkably, ITIM was soon adopted too and, in September 1996, a whole session of the 9th Signal Meeting, held in Tihany, Hungary, was devoted to ITIM. During the last 2 years, evidence accumulated that indeed accredited the ITIM concept.

Amino Acid Sequence↗

PubMed1996

Selective in vivo recruitment of the phosphatidylinositol phosphatase SHIP by phosphorylated Fc gammaRIIB during negative regulation of IgE-dependent mouse mast cell activation.

We demonstrated previously that the low-affinity IgG receptors Fc gammaRIIB, which are coexpressed with the high-affinity IgE receptors Fc epsilonRI in mouse mast cells, can inhibit IgE-induced release of inflammatory mediators and cytokines by these cells. Inhibition was found to require the coaggregation of the two receptors and to depend on the presence of a tyrosine-based inhibition motif (ITIM) in the intracytoplasmic domain of Fc gammaRIIB. We report here that the coaggregation with Fc gammaRIIB does not prevent Fc epsilonRI from triggering activation signals in BMMC and induces the tyrosine phosphorylation of Fc gammaRIIB. Phosphorylated ITIM peptides bound in vitro to three SH2 domain-containing phosphatases present in BMMC lysates: the phosphotyrosine phosphatases SHP-1 and SHP-2. and the inositolphosphate phosphatase SHIP. Using BMMC generated from the SHP-1-deficient motheaten mice, SHP-1 was found to be dispensable for inhibition of mast cell activation. When analyzed for in vivo association, SHIP coprecipitated with phosphorylated Fc gammaRIIB, whereas SHP-1 or SHP-2 did not. These observations altogether indicate that Fc epsilonRI actively participates in its own regulation and that the mechanisms by which Fc gammaRIIB inhibit cell activation might be different in mast cells and in B-cells.

Animals↗

PubMed1996

Impaired IgG-dependent anaphylaxis and Arthus reaction in Fc gamma RIII (CD16) deficient mice.

The family of receptors for IgG (Fc gamma R) plays an essential role in antibody-mediated effector functions of the immune system. However, the specific contribution of each of the Fc gamma R classes to in vivo immune reactions is still unclear. Here, we demonstrate that mice deficient for the ligand-binding alpha chain of Fc gamma RIII lack NK cell-mediated antibody-dependent cytotoxicity and phagocytosis of IgG1-coated particles by macrophages. Strikingly, these mice lack IgG-mediated mast cell degranulation, are resistant to IgG-dependent passive cutaneous anaphylaxis, and exhibit an impaired Arthus reaction. These results indicate a prominent role for Fc gamma RIII in inflammatory and anaphylactic responses, making this receptor a potential target in immunotherapy.

Animals↗

PubMed1995

Phosphatidylinositol hydrolysis and an increase in Ca2+ concentration in the signal-transduction process triggered by murine Fc gamma RIII are not required for protein kinase C translocation.

Murine class III receptors for IgG (mFc gamma RIII) are composed of an IgG-binding alpha chain associated with a gamma subunit dimer. These receptors have been shown to trigger the release of serotonin and tumor necrosis factor-alpha [Daëron, M., Latour, S., Hückel, C., Bonnerot, C. & Fridman, W. H. (1992) Immunobiology 185, 159-174], and are involved in endocytosis and phagocytosis [Daëron, M., Malbec, O., Bonnerot, C., Latour, S., Segal, D. M. & Fridman, W. H. (1994) J. Immunol. 152, 783-792]. Using a transfection model where the cDNA encoding mFc gamma RIII was stably transfected into the rat basophilic leukemia cell line RBL-2H3, we found that the functional efficiency of mFc gamma RIII is correlated with its ability to increase the intracellular Ca2+ concentration and to stimulate inositol phosphate metabolism. The deletion of intracellular sequences of the alpha subunit did not alter the ability of mFc gamma RIII to trigger the Ca2+ and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] response. After substitution of the intracellular domain of mFc gamma RIII for that of mFc gamma RIII gamma, but not that of mFc gamma RIII alpha, the chimeric receptor was also able to trigger Ca2+ and PtdIns(4.5)P2 responses. In contrast, all transfected receptors induced protein kinase C translocation. Furthermore, dimerization of the receptor was sufficient for the initiation of this protein kinase C translocation while a further crosslinking was necessary for the induction of the Ca2+ and PtdIns(4,5)P2 responses. Protein kinase C translocation therefore can be dissociated from Ca2+ mobilization, PtdIns(4,5)P2 turnover and mast cell secretory responses induced by murine Fc gamma RIII.

Amino Acid Sequence↗

PubMed1995

Regulation of tyrosine-containing activation motif-dependent cell signalling by Fc gamma RII.

Crosslinking of the B-cell receptor (BCR) for antigen to low-affinity receptors for IgG (Fc gamma RII) inhibits B-cell activation induced by BCR aggregation. The cell-triggering properties of the BCR depend on tyrosine-containing activation motifs (TAM), in the intracytoplasmic domain of its Ig alpha and Ig beta subunits. TAMs also account for the cell-triggering capabilities of the T-cell receptor (TCR) for antigen, in T lymphocytes, and of the high-affinity receptor for IgE (Fc epsilon RI), in mast cells. Using as a model, rat basophilic leukemia cells (RBL-2H3) stably transfected with cDNA encoding wild-type or mutated murine or human Fc gamma RIIB and chimeric molecules having the intracytoplasmic domain of the FcR gamma subunit or of TCR-CD3 zeta subunit, we found that the inhibitory properties of Fc gamma RII are neither restricted to B cells nor to BCR-dependent cell activation, but can be extended to other cells and, as a general rule, to TAM-dependent cell activation.

Animals↗

PubMed1995

The same tyrosine-based inhibition motif, in the intracytoplasmic domain of Fc gamma RIIB, regulates negatively BCR-, TCR-, and FcR-dependent cell activation.

The cell-triggering properties of BCR, TCR and FcR depend on structurally related immunoreceptor tyrosine-based activation motifs (ITAMs). Fc gamma RIIB have no ITAM and do not trigger cell activation. When coaggregated to BCR, they inhibit B cell activation. We show here that, when coaggregated to these receptors, Fc gamma RIIB inhibit Fc epsilon RI-, Fc gamma RIIA-, and TCR-dependent cell activation. Inhibition also affected cell activation by single ITAMs, in isolated FcR or TCR subunits. The same tyrosine-based inhibitory motif (ITIM), which is highly conserved in murine and human Fc gamma RIIB and that was previously shown to inhibit BCR-dependent B cell activation, was required to regulate TCR- and FcR-dependent cell activation. Our findings endow Fc gamma RIIB, and thus IgG antibodies, with general immunoregulatory properties susceptible to act on all ITAM-containing receptors.

Amino Acid Sequence↗

PubMed1995

Regulation of high-affinity IgE receptor-mediated mast cell activation by murine low-affinity IgG receptors.

Allergic symptoms result from the release of granular and lipidic mediators and of cytokines by inflammatory cells. The whole process is initiated by the aggregation of mast cell and basophil high-affinity IgE receptors (Fc epsilon RI) by IgE and antigen. We report here that IgE-induced release of mediator and cytokine can be inhibited by cross-linking Fc epsilon RI to low-affinity IgG receptors (Fc gamma RII) which are constitutively expressed on mast cells and basophils. Using a model of stable transfectants in RBL-2H3 cells expressing endogeneous rat Fc epsilon RI and recombinant murine Fc gamma RII, we showed that inhibition requires that Fc epsilon RI be crosslinked to Fc gamma RII by the same multivalent ligand. Inhibition of cross-linked receptors left non-cross-linked Fc epsilon RI capable of triggering mediator release and was reversible upon disengagement. Both isoforms of wild-type Fc gamma RII were equally capable of inhibiting Fc epsilon RI-mediated mast cell activation provided they had an intact intracytoplasmic domain. Our results demonstrate that mast cell secretory responses triggered by high-affinity receptors for IgE may be controlled by low-affinity receptors for IgG. This regulation of Fc epsilon RI-mediated mast cell activation is of potential interest in mast cell physiology and in allergic pathology.

Animals↗

PubMed1995

Intracytoplasmic sequences involved in the biological properties of low-affinity receptors for IgG expressed by murine macrophages.

Murine macrophages express several receptors for the Fc portion of IgG antibodies (Fc gamma R). These are high-affinity Fc gamma RI, which bind monomeric IgG2a, and low-affinity Fc gamma RII and Fc gamma RIII, which bind IgG1, IgG2a and IgG2b immune complexes. Fc gamma Ri and Fc gamma RIII are multichain receptors. They are composed of an IgG-binding alpha subunit, associated with the same FcR gamma subunit that also associates with mast cell high-affinity IgE receptors (Fc epsilon RI). Fc gamma RII are single-chain receptors. They exist as two isoforms, Fc gamma RIIb1 and Fc gamma RIIb2, differing by a 47-amino acid insertion in the intracytoplasmic domain of Fc gamma RIIb1. Using a model of stable transfectants, we analyzed the biological activities triggered by Fc gamma R and, by site-directed mutagenesis, we mapped functional sequences in the intracytoplasmic domains of recombinant Fc gamma R. A single tyrosine-based activation motif (ITAM), in the intracytoplasmic domain of the FcR gamma subunit of Fc gamma RIII and Fc gamma RI, triggers cell activation, endocytosis and phagocytosis. Two distinct motifs, in the intracytoplasmic domain of Fc gamma RIIb2, trigger endocytosis and phagocytosis, respectively. The Fc gamma RIIb1-specific intracytoplasmic insertion mediates capping and down-regulates Fc gamma RII-dependent internalization. A tyrosine-based inhibitory motif (ITIM), in intracytoplasmic sequences common to Fc gamma RIIb1 and Fc gamma RIIb2, was identified as down-regulating ITAM-dependent cell activation. The variety of biological properties of Fc gamma R implies that macrophage responses triggered by IgG antibodies depend on the complex interplay between different Fc gamma R having common ligands that are coexpressed by mouse macrophages.

Amino Acid Sequence↗

PubMed1994

Aggregated IgE mimic interleukin-3-induced histamine synthesis by murine hematopoietic progenitors.

Similar to interleukin-3 (IL-3), IgE acts on murine bone marrow cells by inducing histamine production. This effect does not result from degranulation of histamine-containing cells, but from histamine synthesis, as assessed by the following findings. (1) The histamine content of freshly isolated bone marrow cells is too low to account for the increase in extracellular histamine levels. (2) Neither IL-3 nor IgE induced histamine production in the presence of the specific inhibitor of histidine decarboxylase (HDC), the histamine-forming enzyme. (3) Both the enzymatic activity and the mRNA expression of HDC were enhanced in response to IL-3 or IgE. Artificial aggregation or formation of IgE immune complexes augmented ther effect on histamine synthesis, indicating that the aggregated form is responsible for this biologic activity. Yet, it is apparently not mediated by Fc epsilon RI because their cross-linkage by dinitrophenyl bovine serum albumin after presensitization with IgE did not induce histamine production by hematopoietic progenitors. Among other aggregated isotypes tested, only IgG2a and, to a lesser extent, IgG1 had a consistent but lower effect, whereas IgM and IgA were completely inactive. The target cells of IL-3 and IgE in terms of histamine synthesis do not belong to mature bone marrow populations, especially mast cells. They copurify with hematopoietic progenitors in the low-density layers of a discontinuous Ficoll gradient where they represent around 5% of the cells, as determined by in situ hybridization. This percentage remained the same, regardless of whether the cells were stimulated by IgE or IL-3 alone or by a combination of both, suggesting a common responder cell. In accordance with this notion, histamine-producing cells could not be distinguished from each other on the basis of density, size and internal structure, or rhodamine (Rh) retention. Finally, the effect of IgE is not caused by the induction of IL-3 because anti-IL-3 antibodies did not abrogate the effect of IgE.

Animals↗

PubMed1994

Tyrosine-containing activation motif-dependent phagocytosis in mast cells.

FcR capable of triggering cell activation share with BCR and TCR a conserved intracytoplasmic tyrosine-containing activation motif (TAM). Besides cell activation, these receptors trigger other biologic responses, such as endocytosis of soluble ligands. Murine mast cells express two types of FcR that, when aggregated by antibodies and multivalent Ag, trigger the release of inflammatory mediators and cytokines. These are high affinity receptors for IgE (Fc epsilon RI) and low affinity receptors for IgG (Fc gamma RIII). They comprise each an IgE- or IgG-binding alpha-subunit and two TAM-containing subunits that associate with both receptors: a beta-subunit and a homodimeric gamma-subunit that can associate also with the other subunits of the TCR. Herein, we focused on biologic activities triggered in mast cells via the TAM of the gamma-subunits. Using rat basophilic leukemia (RBL) cells stably transfected with cDNA-encoding murine Fc gamma RIII alpha, we found that murine Fc gamma RIII trigger the phagocytosis of antibody-coated erythrocytes. Using RBL transfectants expressing Fc gamma RIII with a deletion of the intracytoplasmic domain of Fc gamma RIII alpha or chimeric receptors having the extracellular and transmembrane domains of Fc gamma RII and the intracytoplasmic domain of Fc gamma RIII alpha, we showed that intracytoplasmic sequences of Fc gamma RIII alpha are neither necessary nor sufficient for Fc gamma RIII to trigger phagocytosis. Using RBL transfectants expressing chimeric receptors having the extracellular and transmembrane domains of Fc gamma RII and the TAM-containing intracytoplasmic domain of murine Fc gamma RIII gamma, we demonstrated that intracytoplasmic sequences of Fc gamma RIII gamma are sufficient to trigger phagocytosis. Using RBL transfectants expressing the same Fc gamma RII-III gamma chimeras, in the TAM of which one, the other, or both tyrosine residues were mutated, we established that tyrosines in the TAM sequence are required for phagocytosis. Our results endow TAM gamma with previously unknown triggering capacities and Fc gamma RIII with new biologic properties.

Amino Acid Sequence↗

PubMed1994

Biological activities of murine low-affinity Fc receptors for IgG.

Murine low-affinity Fc receptors for IgG (Fc gamma RIIb 1, Fc gamma RIIb2, and Fc gamma RIII) bind the same IgG subclasses and are not distinguished by available anti-Fc gamma RII/III mAbs (2.4G2). They trigger various biological activities, among which are the internalization of soluble and particulate immune complexes, cell activation, and its regulation. To determine the biological properties of the three murine receptors, each was expressed by stable transfection of corresponding cDNAs in two model cells: the murine lymphoma B cell IIA1.6 and the rat basophilic leukemia cell RBL-2H3. Biological activities of recombinant receptors were triggered with soluble immune complexes or 2.4G2 IgG in IIA1.6 cells, which express no Fc gamma R, and with 2.4G2 Fab or F(ab')2, cross-linked with mouse anti-rat F(ab')2 in RBL, which express rat Fc gamma R. Conditions for studying cell activation and endocytosis in both cell models are described, as are conditions for studying phagocytosis in RBL cells and antigen presentation or regulation of cell activation in IIA1.6 cells. Internalization of immune complexes was triggered by Fc gamma RIIb2 and Fc gamma RIII, but not by Fc gamma RIIb1. Intracytoplasmic sequences required for phagocytosis and endocytosis could be distinguished in Fc gamma RIIb2, but not in Fc gamma RIII. Cell activation was restricted to Fc gamma RIII. Fc gamma RIII-mediated endocytosis, phagocytosis, and cell activation involved the consensus tyrosine-containing activation motif found in the intracytoplasmic domain of the gamma subunit. Regulation of cell activation was induced by both Fc gamma RII isoforms and depended on the same sequence as endocytosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Distinct intracytoplasmic sequences are required for endocytosis and phagocytosis via murine Fc gamma RII in mast cells.

In the present work, we studied the phagocytic and endocytic properties of murine Fc gamma RII in mast cells. Mouse mast cells express high-affinity receptors for monomeric IgE and three low-affinity receptors for complexed IgG: Fc gamma RIIb1, Fc gamma RIIb2, and Fc gamma RIII. In previous studies we showed that, when aggregated by multivalent ligands, murine Fc gamma RIII, but not Fc gamma RII, triggers the release of inflammatory mediators and cytokines by mast cells. Upon Fc gamma R aggregation, mast cells not only release intracellular materials, they also internalize particulate and soluble immune complexes. We compared the ability of the two Fc gamma RII isoforms to trigger phagocytosis and endocytosis in RBL-2H3 cells stably transfected with cDNAs encoding wild-type, deleted, and tyrosine mutant Fc gamma RIIb1 or Fc gamma RIIb2. We found that Fc gamma RIIb2, but not Fc gamma RIIb1, triggered both phagocytosis and endocytosis. We identified distinct intracytoplasmic sequences necessary for Fc gamma RIIb2-mediated endocytosis and phagocytosis respectively, and we observed that two tyrosine residues, located in each of these sequences, are critical for endocytosis and/or phagocytosis. Our data indicate that the two internalization pathways diverge as early as signal transduction.

Amino Acid Sequence↗

PubMed1993

Trypanosoma cruzi infection in mice enhances the membrane expression of low-affinity Fc receptors for IgG and the release of their soluble forms.

The membrane expression of low-affinity Fc receptors for IgG (Fc gamma RII/III) on cells and the number of Fc gamma RII/III(+) cells were studied by flow cytometry, using the 2.4G2 MoAb, in mice infected by Trypanosoma cruzi. Cells from spleen, mesenteric lymph nodes and peritoneum were collected on days 10, 20, 30 and 40 post infection (p.i.). The in vivo serum level of soluble Fc gamma RII/III, as well as its in vitro release by cells from infected mice were studied. Parasitaemia and IgG1, IgG2a and IgG2b T. cruzi-specific antibody titres were also recorded. Both the expression of Fc gamma R on cell membrane and the absolute number of Fc gamma R(+) cells increased in spleen and in mesenteric lymph nodes, but not in peritoneum. The modifications in spleen occurred in the early and late parasitaemic phase of infection, i.e., before and after detection of T. cruzi-specific antibodies (from day 10 to 40 p.i.). In mesenteric lymph nodes, the variations were observed only in the early acute infection, when antibodies were not yet detectable at significant levels (on days 10 and 20 p.i.). Higher levels of soluble Fc gamma R were detected in sera and in culture supernatants of spleen and lymph node cells from day 20 to 40 p.i. These results show that T. cruzi infection in mice upregulates the expression and the release of Fc gamma RII/III, in the acute phase of infection, before as well as after the rise of antibody response.

Animals↗

PubMed1993

An Fc gamma RII-, Fc gamma RIII-specific monoclonal antibody (2.4G2) decreases acute Trypanosoma cruzi infection in mice.

In order to study the role of Fc gamma Rs in Trypanosoma cruzi infection in mice, the 2.4G2 monoclonal antibody (MAb), specific to the extracellular domains of Fc gamma RII and Fc gamma RIII, was injected intraperitoneally into mice. Flow cytometry studies of uninfected mice showed that 2.4G2 MAb bound to peritoneal and lymph node cells, respectively, on days 2 and 6 after injection. Repeating 2.4G2 injections every 3 to 4 days decreased the availability of Fc gamma Rs on peritoneal, lymph node, and spleen cells. Injections of 2.4G2 MAb into T. cruzi-infected mice, at days -1, 3, 7, 11, 16, 20, and 24 relative to infection, reduced mortality in comparison with that in infected animals injected with an unrelated MAb (50 versus 93.3% mortality; P < 0.01). Parasitemia in 2.4G2-treated mice was significantly (three times) lower than in control animals on days 21 and 24 postinfection (P < 0.05), before parasite-specific antibodies were detectable at significant levels. Immunoglobulin and T. cruzi-specific antibody levels were similar in all groups of mice. These results indicate that repeated injections of 2.4G2 MAb administered to acutely infected mice reduce the in vivo infection level, suggesting that Fc gamma Rs play a role in the early host invasion by T. cruzi parasites.

Acute Disease↗

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↗