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M P Defresne

Publications and source records attributed to M P Defresne.

At least 37 records · Page 2Linked to original sources
PubMed1995

Spontaneous and induced apoptosis after whole body radiation exposure: experimental approaches. Observations in radio-induced thymic lymphomagenesis.

Radio-induced thymic lymphomagenesis is associated with alterations in the balance between thymocyte subsets and cytokinetic perturbations. The objectives of this work were to investigate whether these alterations are associated with alterations in the basic levels of thymocyte apoptosis. For this purpose, we tested DNA fragmentation by gel electrophoresis, analyzed DNA content by propidium iodide staining of ethanol fixed cells and looked for DNA strand breaks on tissue sections by in situ end labeling. We described an increase of the levels of apoptosis in cultured thymocytes during the preleukemic period, while the basic levels of apoptosis observed in situ are similar in normal and in preleukemic thymuses. We propose that after leukemogenic irradiations, there is an increase of cells wherein the cell suicide program is activated but that environmental thymic factors rescue them from apoptosis. Preleukemic cells could belong to this abnormally surviving population of cells "programmed to die," wherein additional genomic abnormalities would lead to fully neoplastic transformation.

Animals↗
PubMed1994

Human CD34+ fetal liver stem cells differentiate to T cells in a mouse thymic microenvironment.

Hematopoietic stem cells differentiate in the thymus to T cells along precisely defined intermediates. This process is thymic epithelium dependent and involves cytokines and cell-cell interactions between thymic stroma and T-cell precursors. Here we report that highly purified human CD34++ fetal liver stem cells differentiate to mature T cells, when seeded into isolated fetal thymic lobes of severe combined immunodeficient mice, and subsequently cultured in vitro. The human stem cells differentiate sequentially into CD4+CD8-CD3-, CD4+CD8+CD3-, CD4+CD8+CD3+, and finally, CD4+CD8-CD3+4 and CD4-CD8+CD3++ cells. Phenotypic analysis for additional maturation markers showed that these CD4 and CD8 single-positive thymocytes are fully maturate cells. By immunochemistry, human HLA-DR+ cells with a dendritic morphology could be detected. This novel chimeric human-mouse fetal thymus organ culture offers a tool to study human T-cell ontogeny in vitro and is a rapid and reliable test method for T-cell precursor activity of cultured or transfected human stem cells.

Animals↗
PubMed1994

The ER-TR4 monoclonal antibody recognizes murine thymic epithelial cells (type 1) and inhibits their capacity to interact with immature thymocytes: immuno-electron microscopic and functional studies.

The thymic stroma is heterogeneous with regard to cellular morphology and cellular function. In this study, we employed the monoclonal antibody ER-TR4 to characterize stromal cells at the ultrastructural level. To identify the labelled cell type, we used two techniques: immunogold labelling on ultrathin frozen sections and immunoperoxidase staining on thick "vibratome" sections. ER-TR4 reacted with thymic Type 1 epithelial cells (according to our classification). A dense labelling appears in the cytoplasm of cortical cells using the two techniques. Immunogold labelling identified small cytoplasmic vesicles whereas the cytoplasm and the cell membrane seem to be labelled with the immunoperoxidase technique. ER-TR4 also identified isolated thymic nurse cells (TNC), and was observed in vitro to inhibit the capacity of some type 1 epithelial cells to establish interactions with immature thymocytes. This finding supports the hypothesis that the factor is involved in the formation of lymphoepithelial interactions within thymic nurse cells, and thus in the relations that immature thymocytes establish with the thymic microenvironment.

Animals↗
PubMed1994

Analysis by in situ hybridization of cytokine mRNA expression in the murine developing thymus.

We have used in situ hybridization to investigate the expression of IL-1, IL-2, IL-4, IL-6 and IFN-gamma genes by thymic cells during fetal development in mice. Two waves of mRNAs were detected in thymic cells for IL-1 at days 16 and 19 of gestation, for IL-2 at days 14 and 18, and for IL-4 at days 14 and 16. Three peaks for IL-6 were observed at days 13, 17 and around birth. Finally, only one peak of cells positive for IFN-gamma was detected. Whereas cells positive for IL-1 were generally grouped and more often localized in the external area of the thymus, the other positive cells were isolated and evenly distributed in the thymus. Our results illustrated the presence of cytokine transcripts in the developing thymus following a developmentally controlled sequence and support the hypothesis that cytokines could play a role in T cell development.

Animals↗
PubMed1994

Thymus involvement in murine acquired immunodeficiency (MAIDS).

Due to self-renewal of the peripheral pool of T-cells, adult thymectomy has normally little influence on immunocompetence. However, thymus might play a more important role in the setting of viral-induced cytopathic effects on T-cells in the periphery. Therefore, thymus weight, cell numbers, and subset distribution were sequentially analysed after infection with RadLV-Rs, a viral mixture known to induce murine retrovirus induced immunodeficiency (MAIDS). Infection induced thymic atrophy (concerning organ weight as well as total cell number) which culminated seven weeks after inoculation. The atrophic process mostly reflected the depletion of double positive CD4+ CD8+ cells since their proportion sharply decreased around week 6. Single positive T-cells were less affected by the process. The proportion of B-cells progressively increased. Surprisingly, there was a strong correlation between the extent of atrophy and the frequency of B-cells in the thymus. Finally, an abnormal CD4+ T-cell subset lacking Thy-1 and previously described in the periphery also appeared in the thymus and its frequency was strongly correlated with the expansion of B-cells in this organ.

Animals↗
PubMed1993

Evidence that insulin-like growth factor 2 (IGF2) is the dominant thymic peptide of the insulin superfamily.

The central T-cell tolerance of neuroendocrine functions has been proposed to be primarily induced by the thymic repertoire of neuroendocrine self antigens. The present study aimed at characterizing the human thymic insulin-related autoantigen able to represent the pancreatic B-cell function in face of the developing T-cells. Immunofluorescence studies were performed on human and rat thymic sections, as well as on the rat IT-45R1 thymic epithelial cell line using several antibodies to epitopes of the insulin peptide superfamily. These studies identify beyond any doubt that insulin-like growth factor 2 (IGF2) is the dominant thymic peptide of the insulin family. The sequence of an insulin-derived autoantigen is proposed. This autoantigen is a nonamer and has a hydrophobic residue leucine (L) at position 9. In the human species, this autoantigen would primarily be tolerogenic for the pancreatic B-cell endocrine function during fetal development.

Amino Acid Sequence↗
PubMed1993

Mixed phenotype murine leukemias.

Cell lines were derived from eight individual leukemias induced by X-rays in NFS mice. First typed as null cells (surface immunoglobulin negative, Thy-1 negative), they turned out to have a mixed phenotype with myeloid cytochemical markers, pre-B surface antigens and molecular markers of pro-B lymphocytes. They represent murine models for mixed phenotype (pro-pre-B-myeloid) leukemias.

Animals↗
PubMed1992

Analysis by in situ hybridization of cells expressing mRNA for tumor-necrosis factor in the developing thymus of mice.

We have used in situ hybridization to investigate the expression of TNF-alpha genes by thymic cells during fetal development in mice. In 14-day-old fetal thymuses, very scarce cells produce TNF-alpha mRNA. A second phase of cytokine gene expression starts on day 16. The density of positive cells progressively increases up to day 20. Thymuses at 15 days of gestation and after birth do not express detectable cytokine mRNA. In an attempt to identify the nature of the TNF-alpha mRNA-producing cells, acid phosphatase activity, which is characteristic of the macrophage lineage, was studied in the same thymuses. Acid phosphatase-positive cells only appear on day 15. Their frequency increases up to birth. However, no correlation can be established between acid phosphatase--and TNF alpha mRNA--positive cells. The results indicate that a small subset of thymic cells is responsible for TNF-alpha mRNA production during ontogeny: These cells are not yet identified. The possible role of TNF-alpha in thymic ontogeny is discussed.

Acid Phosphatase↗
PubMed1992

Identification of nuclear triiodothyronine receptors in the thymic epithelium.

Thymic epithelial cell physiology is known to be under neuroendocrine control. In particular, thyroid hormones modulate thymic hormone secretion by thymic epithelial cells in vivo and in vitro, thus suggesting the existence of specific receptors for those hormones in this component of the thymic microenvironment. Yet, thyroid hormone-binding sites have previously been detected only in crude thymus fractions and lymphocytes. We, thus, decided to search for T3 receptors in the thymic epithelium, by using an antinuclear T3 receptor monoclonal antibody. In situ immunohistochemical analysis of thymic frozen sections showed nuclear labeling of both lymphoid and nonlymphoid cells in the cortex and medulla. Moreover, in vitro studies using thymic epithelial cell lines and the so-called thymic nurse cells revealed a positive reaction in the chromatin, with nucleoli remaining negative. Immunoblot data clearly showed a single protein band of 57K reactive with the antinuclear T3 receptor antibody in murine thymus extracts as well as in the thymic epithelial cell lines. Lastly, in vitro treatment of these cells with T3 resulted in a transient, yet profound, down-modulation of the receptor. In conclusion, our findings provide molecular evidence that the action of thyroid hormones on thymic epithelium occurs via the typical 57K nuclear T3 receptors.

Animals↗
PubMed1991

Induction of thymocyte proliferation by supernatants from a mouse thymic epithelial cell line.

The thymic stroma plays a critical role in the generation of T lymphocytes by direct cell-to-cell contacts as well as by secreting growth factors or hormones. The thymic epithelial cells, responsible for thymic hormone secretion, include morphologically and antigenically distinct subpopulations that may exert different roles in thymocyte maturation. The recent development of thymic epithelial cell lines provided an interesting model for studying thymic epithelial influences on T cell differentiation. Treating mouse thymocytes by supernatants from one of TEC line (IT-76M1), we observed an induction of thymocyte proliferation and an increase in the percentages of CD4-/CD8- thymocytes. This proliferation was largely inhibited when thymocytes were incubated with IT-76M1 supernatants together with an anti-thymulin monoclonal antibody, but could be enhanced by pretreating growing epithelial cells by triiodothyronine. We suggest that among the target cells for thymulin within the thymus, some putative precursors of early phenotype might be included.

Animals↗
PubMed1991

Colocalization of immunoreactive oxytocin, vasopressin and interleukin-1 in human thymic epithelial neuroendocrine cells.

Monoclonal antibodies to oxytocin (OT) and vasopressin (VP) revealed some positively staining stromal cells in the subcapsular cortex and in the medulla of the human thymus. We further demonstrated that these cells are a subset of epithelial endocrine cells and also contain immunoreactive interleukin-1 together with the neuropeptides. In addition, the thymic cells stained by monoclonal antibodies directed to the cyclic part of oxytocin or vasopressin also contained some immunoreactive neurophysins. These data support the concept of intrathymic synthesis of neurohypophyseal-like peptides fitting the hypothalamic model. However, we observed that, contrary to the situation in the brain, OT- and VP-like peptides colocalized in the same thymic cells. Furthermore, one monoclonal antibody, specific for the tail part of oxytocin, did not label thymic cells. Therefore, thymic neuropeptide(s) could be related to, but distinct from, authentic OT and VP. These observations suggest some molecular differences between hypothalamic and thymic oxytocin biosynthetic pathways which need to be further investigated.

Antibodies, Monoclonal↗