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R Greimers

Publications and source records attributed to R Greimers.

At least 55 records · Page 3Linked to original sources
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

High-yield isolation of protoplasts from microgram amounts of shoot meristematic tissues and rapid DNA content determination by flow cytometry.

This paper describes a novel approach to rapid cell-cycle analysis of shoot meristematic cells. The method involves fixation and disaggregation of meristems into protoplast suspension and flow-cytometric analysis of these protoplasts stained with fluorescent dyes. We have developed a procedure for a high-yield isolation of protoplasts allowing an accurate flow-cytometric analysis with a few micrograms of meristem tissues. We present here determinations of total DNA content of protoplasts stained with propidium iodide in the dicotyledon Sinapis alba, and the monocotyledon Lolium temulentum.

Cell Cycle↗
PubMed1990

Effect of interferon-gamma and tumor necrosis factor-alpha on lymphoepithelial interactions within thymic nurse cells.

Isolated thymic nurse cells (TNC) represent a specialized microenvironment in vivo where thymocytes interact specifically with subcapsular epithelial cells. They are thought to play a critical role in the process of T cell differentiation. We demonstrate that recombinant murine interferon-gamma and recombinant human tumor necrosis factor-alpha can act on these interactions: they stimulate TNC-derived epithelial cells to establish interactions with thymocytes in vitro and to form new lymphoepithelial complexes. This phenomenon is partially inhibited by anti-Ia monoclonal antibodies. Implications of these findings for normal intrathymic differentiation are discussed.

Animals↗
PubMed1990

Cellular events in radiation-induced lymphomagenesis.

Fractionated whole-body irradiation induces thymic lymphomas in most of treated C57Bl/Ka mice. The cellular events occurring during the latency period consist of the emergence of preleukaemic cells and of marked alterations to the T-cell lineage and the microenvironment within the thymus. The proportions of the various thymocyte subsets are modified, suggesting a blockage in the normal differentiation process. Thymic epithelial cells are functionally modified, leading to decreased interactions with immature thymocytes. Interestingly, bone marrow grafting early after irradiation, which inhibits the development of lymphomas, induces the disappearance of preleukaemic cells from the thymus, whereas thymocyte subpopulations and thymic epithelium are restored. Interferon gamma and tumor necrosis factor alpha also prevent the onset of lymphomas. Studies on the effect of bone marrow transplantation and cytokine inoculation in split-dose irradiated mice should allow characterization of the factors that modulate the progression of preleukaemic cells towards the neoplastic state.

Animals↗
PubMed1990

Abnormal thymocyte subpopulations in split dose irradiated C57BL/Ka mice before the onset of lymphomas. Effects of bone marrow grafting.

Fractionated whole-body X irradiation (4 x 1.75 Gy at weekly intervals) induces a high percentage of thymic lymphomas in C57BL/Ka mice. The present work reports the phenotypic alterations of thymocyte subpopulations during the preleukemic period: there were a decrease of CD4+ CD8+ cells and an increase of CD4- CD8- and CD4- CD8+ cells. Marrow grafting early after irradiation that prevents lymphoma development restores the thymocyte subpopulations. In many instances, transplantation of 'preleukemic thymocyte inoculate' gives rise to an active and long lasting repopulation of recipient thymuses. However in all cases, donor lymphomas can develop after inoculation of 'preleukemic thymocyte inoculate'.

Animals↗
PubMed1989

Further studies on the mechanism of radiation induced thymic lymphoma prevention by bone marrow transplantation in C57BL mice.

Whole body fractionated irradiation induces thymic lymphomas in C57BL/Ka mice after a latent period during which intrathymic lymphopoiesis is modified; thymocyte numbers are subnormal and the epithelial component of thymic nurse cells (TNCs) is altered as estimated by the number of TNCs in vivo and by its ability to interact with immature thymocytes in vitro. A graft of normal bone marrow cells immediately after the last irradiation prevents the development of lymphomas; but when such a graft is performed 1 month later, it does not inhibit the emergence of tumors. In both cases the grafted precursors home and repopulate the thymus. However, the delayed graft does not exert any effect upon the altered epithelial component of TNCs, whereas the early one restores the numbers of TNCs and the function of their epithelial component. The results thus demonstrate that lymphoid thymic repopulation by a bone marrow graft is not sufficient to prevent the development of lymphomas and that there is an intimate relationship between tumor development and alterations of nurse cells microenvironment.

Animals↗
PubMed1987

[Interaction of radiation-induced preleukemia cells and bone marrow grafts in C57BL/Ka mice].

The repopulation of thymus inoculated with radiation-induced preleukemia cells was studied in 400 R irradiated mice grafted with normal bone marrow cells. These marrow cells gave rise to an actively regenerating thymic progeny, as well as in 400 R treated mice receiving only a bone marrow graft. Moreover, the marrow graft did not prevent the progression of inoculated preleukemic cells towards lymphoma growth.

Animals↗
PubMed1987

[Relations between the capacity of thymic repeopling and the formation of lymphoma obtained by radiation-induced preleukemic cells in C57BL/Ka mice].

We have analyzed the repopulation of thymuses injected with preleukemic cells obtained at various interval after fractionated irradiation. Our results show that preleukemic cells can repopulate the thymus transiently as normal thymocytes or they can proliferate in recipients. In all cases, preleukemic cells can give rise to donor lymphomas.

Animals↗
PubMed1987

[Cytofluorimetric study of ploidy in the preleukemic thymus in C57BL/Ka mice under fractionated irradiation].

The ploidy of the thymus was studied in C57B1/Ka mice irradiated with 4 weekly X-Ray doses of 1.75 Gy. The determination of nuclear DNA content was performed by flow cytometry of intact thymocytes labeled with propidium iodide in presence of a mixture of chicken and rainbow trout red blood cells as internal reference standards. The method has been tested by detecting the sex difference in DNA content of G0/G1 of normal thymic mouse cells. The mean value was 2.9% higher in female mice. The thymus of almost 60% of irradiated male mice present a slight hypoploidy of 2.6% one month after the last irradiation.

Animals↗
PubMed1987

[Migration of bone marrow cells toward the thymus in C57BL/Ka under fractionated irradiation].

Fractionated whole body X-irradiation (4 X 1.75 Gy at weekly intervals) induces a high percentage of thymic lymphomas in C57BL/Ka mice. These tumors develop after a long latency period during which the thymic lymphopoiesis is deeply altered. In the present work, we test wether those modifications are due to lack of prothymocyte homing to preleukemic thymuses. Our results show that the preleukemic state of the thymus don't prevent the homing of normal marrow precursors grafted immediately after an irradiation of 4 Gy. Thus the alterations of thymic lymphopoiesis observed after a leukemogenic irradiation are not due to a modification in the thymus receptivity to thymocyte precursors.

Animals↗
PubMed1986

Phenotype of thymic lymphomas in the mouse.

The MP2 cell line was established from a murine leukemia virus-induced thymic lymphoma. Half of the cells were consistently L3T4 positive and less than 5% of the cells were Lyt-2 positive. Single cell cloning on the basis of the presence or absence of Lyt-2 allowed the isolation of four clones with stable phenotypes: (1) Lyt-2-, L3T4-; (2) Lyt-2+, L3T4+; (3) Lyt-2-, L3T4+; (4) Lyt2+, L3T4-. These data are discussed in relation to tumour cell heterogeneity and to normal T-cell differentiation pathways.

Animals↗
PubMed1986

Cellular aspects of radiation leukemogenesis in C57 BL/Ka mice: alterations to thymic microenvironment and lymphopoiesis.

After a leukemogenic split dose course of irradiation, thymic nurse cells (TNCs) disappear. We have correlated this with the loss of an epithelial cell surface antigen (recognized by monoclonal antibody ER-TR3 and tentatively identified as Ia). In addition, epithelial cells have lost their capacity to interact with fetal thymocytes in vitro. Marrow grafting early after irradiation, that prevents the development of lymphomas, restores thymic nurse cells and thymocyte population. Such reconstitution and lymphoma prevention were not observed when marrow grafting was performed later (1 month after irradiation) during the preleukemic period.

Animals↗
PubMed1986

Production and characterization of monoclonal antibodies raised against BoLA class I antigens.

Monoclonal antibodies (MoAbs) reacting with bovine leukocyte membrane antigens have been prepared by fusion of mouse myeloma cells (SP2/0.Ag.14) and spleen cells of mice immunized with various cell types. Three of these MoAbs detected membrane components showing the typical structure of class I MHC molecules; indeed, immunoprecipitation studies revealed that these components were proteins composed of two subunits of 44,000 and 12,000 daltons apparent molecular weight. The density of these antigens in the cells of various leukocyte lineages was determined by solid phase radioimmunoassay, immunogold staining and cytofluorometry. Their expression seemed similar to that of class I molecules in other species, namely heavy on the mononuclear blood cells and weaker on the neutrophils and platelets. The eosinophils appeared more positive than the neutrophils, while the erythrocytes were negative. Cross-inhibition and sequential immunoprecipitation experiments demonstrated that these MoAbs recognised different epitopes either on a single molecule or on cross-reacting molecules. One antibody appeared to be raised against the monomorphic bovine beta-2-microglobulin, while the two other antibodies detected the heavy chain of polymorphic class I-like products. The authors propose that the BoLA class I polymorphism should be studied by determination of the fixation ratio of the monomorphic anti-beta 2M versus the polymorphic anticlass I antibodies amongst the animals.

Animals↗
PubMed1986

Effects of marrow grafting on preleukemia cells and thymic nurse cells in C57BL/Ka mice after a leukemogenic split-dose irradiation.

A split-dose regimen of whole-body irradiation (4 X 175 rad at weekly intervals) induced thymic lymphomas in C57BL/Ka mice after a latent period of 3-9 months. Meanwhile, preleukemia cells arose in the thymus and bone marrow and persisted until the onset of lymphomas. Simultaneously, thymic lymphopoiesis was impaired; thymocyte numbers were subnormal and thymic nurse cells disappeared in a progressive but irreversible fashion. The depletion of these lymphoepithelial complexes, which are normally involved in the early steps of thymic lymphopoiesis, was related to altered prothymocyte activity in bone marrow and to damaged thymic microenvironment, perhaps as a consequence of the presence of preleukemia cells. The grafting of normal bone marrow cells after irradiation prevented the development of lymphomas. However, marrow reconstitution did not inhibit the induction of preleukemia cells. They disappeared from the thymus during the second part of the latent period. At the same time, thymic lymphopoiesis was restored; thymocytes and nurse cell numbers returned to normal as a consequence of the proliferation of grafted marrow-derived cells within the thymus. The results thus demonstrated an intimate relationship between preleukemia cells and an alteration of thymic lymphopoiesis, which particularly involved the nurse cell microenvironment. Some preleukemia cells in marrow-reconstituted, irradiated mice derived from the unirradiated marrow inoculate. Thus these cells acquired neoplastic potential through a factor present in the irradiated tissues. The nature of this indirect mechanism was briefly discussed.

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