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Biomedical subjects

D Charron

Publications and source records attributed to D Charron.

At least 109 records · Page 6Linked to original sources
PubMed1998

Human leukemia-derived dendritic cells: ex-vivo development of specific antileukemic cytotoxicity.

The human myeloid leukemias are a diverse group of disorders characterized by massive clonal expansion of myeloid cells showing variable degrees of differentiation block. Leukemic dendritic cells were generated in culture from chronic myelogenous leukemia (CML). These were used to stimulate autologous T cells to develop leukemia-specific cytotoxicity. Available data suggest that the cells responsible for the cytolytic activity are at least in part CD8+ and HLA restricted in their function. Additional data suggest that some anti-CML cellular activity may be Fas mediated. T-cell receptor studies provide evidence for an oligoclonal response implying a recognition of a limited number of antigens. We have used culture techniques similar to those used for CML to study the ability of AML cells to differentiate toward dendritic cells. Four of five patients have shown acute leukemia-derived dendritic cells. This work offers an avenue for the development of novel strategies for the control of human myeloid leukemias.

Cytotoxicity Tests, Immunologic↗
PubMed1998

[Subtypes of the HLA-B27 molecule and association with spondylarthropathies].

HLA-B27 subtypes differ in their ethnic distribution and in their susceptibility to spondylarthropathies (SA). B*2705 and B*2702 are the most frequent disease-associated subtypes in Caucasians as well as B*2704 and B*2707 in Asia while B*2706 in Asia and B*2709 in Sardinia have been reported not to be associated to SA. Differences in antigenic peptide presentation could underlie such behavior. Several studies suggested that a Tyr C-terminal peptide anchor could be found preferentially in disease-associated subtypes and could be therefore one of the criteria in the search of putative arthritogenic peptide(s). We analyzed by HPLC and Edman sequencing peptides eluted from immunopurified HLA-B27 molecules expressed on B-lymphoblastoid cell lines or C1R transfectans of human origin. We focused our work on B*2707, associated with SA in the same geographical area where B*2706 is not. We found the same preference for Leu at the C-terminus in the peptides bound by both subtypes without any significant signal for Tyr. In the same experimental conditions a Tyr C-terminal anchor was found for B*2705, B*2702, B*2704, B*2703 and also for B*2701 and B*2708, 2 rare subtypes for which binding specificity was previously unknown. Comparison of the F-pocket aminoacid composition in these various subtypes showed a correlation between Asp at position 116 and Tyr at the peptide C-terminus. Asp116 is changed for Tyr in B*2706, B*2707 and His in B*2709, all subtypes allowing a Leu C-terminal anchor. Therefore a Tyr C-terminal anchor correlates with the HLA-B27 F-pocket composition rather than with susceptibility to SA.

Alleles↗
PubMed1998

Signal transduction via human leucocyte antigen class II molecules distinguishes between cord blood, normal, and malignant adult B lymphocytes.

Cord blood is increasingly used for hematopoietic stem cell transplantation since less severe graft-versus-host disease has been reported leading to the notion that cord blood is "naive." Human leucocyte antigen (HLA) class II molecules are expressed throughout B lymphocyte ontogeny (except the plasmocytes), are responsible for antigen presentation, and can also transmit signals. Cord blood B stimulate an allogeneic response, and this property is believed to indicate the presence of a class II-associated peptide. In this study we examined the capacity of cord blood B to transmit signals via HLA-DR. Activation and relocalization of protein kinase C (PKC) isoenzymes alpha and betaII was detected along with tyrosine kinase activation and proliferation. However, in contrast to resting adult B, generation of an intracellular calcium ([Ca++]i) flux and rapid aggregation were not detected. To address the question of whether or not HLA-DR signals throughout B lymphocyte ontogeny, we extended this study to include malignant adult B (B chronic lymphocytic leukemia [B-CLL], B mantle cell lymphoma, and B large cell leukemia). Tyrosine kinase activation and proliferation were observed in all these cell populations, albeit in the absence of [Ca++]i flux or an increase in PKC. HLA-DR therefore transmits signals throughout B lymphocyte ontogeny, although different signaling pathways are initiated in adult vs. fetal vs. malignant B. The lack of intracellular [Ca++]i flux in both cord blood and malignant B lymphocytes may represent a feature of HLA class II signaling at a particular stage of differentiation, although the downregulation of PKC clearly distinguishes between cord blood B and B-CLL.

Adult↗
PubMed1998

Effects of superantigenic stimulation on the cord blood alphabeta T cell repertoire.

Umbilical cord blood (CB) constitutes a promising alternative to bone marrow for allogeneic transplantation and is most remarkable for the reduced severity of GVHD compared with bone marrow. We have shown that although naive the TCR beta-chain repertoire appears fully constituted at birth in terms of mean size of the complementarity-determining region 3 (CDR3) and of the usage of V and J gene segments. Its ability to respond to exogenous stimuli was tested with staphylococcal superantigens TSST-1 and SEA (toxin at 1 ng/ml for 4 days). The amount of TCR transcripts was quantified and the percentage of representation of each BV family was calculated. TSST-1 induced BV2 expansion in both adult and CB samples. SEA activation gave a more variable pattern among individuals (adults n = 6; CB n = 6). BV6, BV18, BV22 and BV24 were the most frequently expanded families. We did not observe notable differences in either the modification of the TCRBV repertoire or the kinetics of the response to SEA superantigen between adults and newborns. These data suggest that although naive, CB lymphocytes are as equally capable as adult lymphocytes of responding to superantigen stimulation.

Adult↗
PubMed1998

Characterisation of the roles of CD95 and CD95 ligand in cord blood.

The increasing use of umbilical cord blood in transplantation has led to a renewed interest in the immunological characterisation of this material. This study addresses the question of whether the CD95 molecule and its ligand are expressed and are functional in mediating cell death in cord blood mononuclear cells. These molecules have a crucial role in the homeostasis of haematopoietic cell populations in the adult and also contribute to graft-versus-host disease. CD95 is the most well studied receptor mediating a signal for cell death by apoptosis and its inducible ligand has been demonstrated to mediate cell death of multiple types of CD95 expressing cells. The object of this study was to examine whether cord blood mononuclear cells could behave either as targets for CD95-mediated cell death or as mediators of cell death due to the expression of CD95L. The results of this study lead us to suggest that cord blood mononuclear cells enjoy some immunological privilege due to the relatively low level of expression of CD95 (in comparison with adult peripheral blood lymphocytes) and the expression of the CD95 ligand.

Adult↗
PubMed1998

[HLA-B27 molecular subtypes and spondylarthropathies].

The close association between HLA-B27 and spondyloarthropathies remains unexplained. Twelve HLA-B27 subtypes designated B*2701 to B*2712 have been described in various populations. Variations in the ability of these alleles to carry susceptibility to spondyloarthropathies may exist, and may be ascribable to differences in endogenous peptide presentation. This hypothesis was evaluated by a study of peptide-binding motifs of endogenous peptides extracted from various HLA-B27 alleles. A peptide motif with a tyrosine residue at the C-terminus was not characteristic of HLA-B27 subtypes carrying susceptibility, consistent with the known lack of association of B*2707 with spondyloarthropathies. However, at the level of the individual, differences may exist between endogenous peptides presented by subtypes that do and do not confer susceptibility.

Alleles↗
PubMed1997

Measles virus nucleocapsid protein binds to FcgammaRII and inhibits human B cell antibody production.

Despite the development of an efficient specific immune response during measles virus (MV) infection, an immunosuppression occurs contributing to secondary infections. To study the role of nucleocapsid protein (NP) in MV-induced immunosuppression, we produced recombinant MV NP. Purified recombinant NP exhibited biochemical, antigenic, and tridimensional structure similar to viral NP. By flow cytometry, we showed that viral or recombinant NP bound to human and murine B lymphocytes, but not to T lymphocytes. This binding was specific, independent of MHC class II expression, and dependent of the B lymphocyte activation state. The murine IIA1. 6 B cell line, deficient in the Fc receptor for IgG (FcgammaRII) expression, did not bind NP efficiently. Transfected IIA1.6 cells expressing either murine FcgammaRIIb1 or b2, or human FcgammaRIIa, b1*, or b2 isoforms efficiently bound NP. Furthermore, this binding was inhibited up to 90% by monoclonal antibodies 2.4G2 or KB61 specific for murine and human FcgammaRII, respectively. Finally, the in vitro Ig synthesis of CD40- or Ig-activated human B lymphocytes in the presence of interleukin (IL)-2 and IL-10 was reduced by 50% in the presence of recombinant NP. These data demonstrate that MV NP binds to human and murine FcgammaRII and inhibits in vitro antibody production, and therefore suggests a role for NP in MV-induced immunosuppression.

Animals↗
PubMed1997

Inhibitor (IK) of IFN-gamma induced HLA class II antigens expression also inhibits HLA class II constitutive expression in the human Raji B cell line.

The expression of major histocompatibility complex (MHC) class II antigens is constitutive in professional antigen presenting cells (APCs) but can also be induced by interferon-gamma (IFN-gamma) on the majority of the non professional APCs (e.g. fibroblasts). We have recently characterised a new factor called IK which is an efficient inhibitor of IFN-gamma induction of MHC class II antigens expression. Here, we demonstrate a novel role for IK in MHC class II expression since over-expression of this protein by stable transfection into human B cells led to a total disappearance of constitutive MHC class II mRNA expression. The class II transactivator (CIITA) is necessary for both constitutive and IFN-gamma induced MHC class II expressions. Examination of CIITA mRNA in IK stably transfected clones revealed a marked reduction of CIITA mRNA transcription. Taken together these results demonstrate that the IK protein plays a key role in the constitutive expression of MHC class II antigens and that inhibition induced by IK is upstream of CIITA in this regulatory pathway.

B-Lymphocytes↗
PubMed1997

HLA class II-mediated death is induced via Fas/Fas ligand interactions in human splenic B lymphocytes.

HLA class II molecules, expressed on the surface of antigen-presenting cells, are responsible for the presentation of antigen-derived peptides to CD4+ helper T lymphocytes. Signaling via these molecules initiates the generation of second messengers leading to programed cell death (PCD) of activated B lymphocytes. The present study examined the mechanism of HLA class II-mediated apoptosis and describes the essential role of the molecule Fas and its ligand (FasL). FasL was expressed in B lymphocytes after stimulation via HLA class II or with phorbol esters. Expression of FasL protein was significantly increased in 50% of B lymphocytes after stimulation via HLA class II, and the level of FasL mRNA was also increased either by activation with phorbol esters and ionomycin or by signaling via HLA class II. Although HLA class II signaling did not change the expression of the Fas molecule, it did lead to increased sensitivity to Fas-mediated apoptosis. The crucial role of Fas/FasL interactions was confirmed by the absence of cell death via HLA class II in B cells lacking Fas expression, and by the significant inhibition of HLA class II-mediated apoptosis in the presence of either an antagonistic anti-Fas or anti-FasL antibody. These data demonstrate FasL expression on activated human B lymphocytes and support the idea that antigen presentation could contribute to the regulation of lymphocyte populations via Fas and FasL interactions.

Antibodies, Blocking↗
PubMed1997

Association of rheumatoid arthritis with an amino acid allelic variation of the T cell receptor.

OBJECTIVE: To investigate allelic variations of T cell receptor residues for a contribution to rheumatoid arthritis (RA) susceptibility. METHODS: We conducted an RA case-control study involving 1,579 northwest Europeans: 766 patients with erosive and rheumatoid factor-positive disease and 813 control subjects. Productive changes of segments TCRAV6S1, TCRAV7S1, TCRAV8S1, TCRAV10S2, and TCRBV6S1, TCRBV6S7 were investigated by single-strand conformation polymorphisms. The TCRAV8S1 association was confirmed by restriction fragment length polymorphism. RESULTS: In the systematic study (77 patients and 119 controls), an increase in 1 TCRAV8S1 genotype was found in the RA patients (P = 0.0004). This finding was replicated in 2 further populations, one from France (212 patients and 254 controls) and the other from Britain (477 patients and 440 controls), with a similar odds ratio (OR), which allowed pooling of the data and confirmation of the association (OR 1.3 [95% confidence interval 1.1-1.7], P = 0.008). CONCLUSION: These findings show evidence that TCRA is an RA susceptibility locus.

Alleles↗
PubMed1997

Selectivity of the major histocompatibility complex class II presentation pathway of cortical thymic epithelial cell lines.

Major histocompatibility complex (MHC) restriction of the immune response is established during positive selection of T cells in the thymus. This occurs mainly through interactions of T cell receptor of developing thymocytes with MHC/peptide ligands on cortical thymic epithelial cells (TEC). An ongoing controversy concerns the origin and the role of peptides involved in the positive selection of thymocytes. Evidence provided here shows that processing of MHC class II complexes in cortical TEC differs from that of medullary TEC. Removal of the invariant chain associated with MHC class II complexes was rapid and complete in medullary TEC which present peptides from both exogenous and cytosolic origin. In cortical TEC, a large fraction of class II dimers remained associated with a 10-12-kDa fragment of invariant chain (Ii). Incomplete removal of Ii correlated with the inability of cortical TEC to present peptides from exogenous origin. However, presentation of peptides from cytosolic proteins by cortical TEC remained possible. Thus, most peptides from exogenous proteins may be excluded from participating in positive selection of CD4+ T cells by a mechanism limiting Ii breakdown.

Animals↗
PubMed1997

Association of the AChRalpha-subunit gene (CHRNA), DQA1*0101, and the DR3 haplotype in myasthenia gravis. Evidence for a three-gene disease model in a subgroup of patients.

Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction having multigene control. HLA-linked loci and the HB*14 micro-satellite marker located within the CHRNA gene which encodes the muscular acetylcholine receptor (AChR) alpha-subunit, the target self-antigen, were previously associated with MG. Combined analysis of these loci revealed a significant increase of DQA1*0101 alleles in HB*14+ vs. HB*14- patients and of DQA1*0501 alleles in HB*14/DQA1*0101 patients. Importantly, the effect of DQA1*0101 was independent of allelically associated DQB1 and DRB1 genes. In contrast, the effect of DQA1*0501 could not be dissociated from that of DRB1*03 and DQB1*0201 on the extended DR3 haplotype. These results indicate that a combination of three genes, of which two are linked to HLA, contributes to disease susceptibility in a subgroup of MG patients.

Adult↗