http://repub.eur.nl/res/aut/10929/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/9292/ 2000-01-01T00:00:00Z T-cell development is under the tight control of thymic microenvironments. Conversely, the integrity of thymic microenvironments depends on the physical presence of developing thymocytes, a phenomenon designated as 'thymic crosstalk'. We now show, using three types of immunodeficient mice, i.e. CD3(epsilon) transgenic mice, RAG(null) mice and RAG(null)-bone-marrow-transplanted CD3(epsilon) transgenic mice, that the control point in lymphoid development where triple negative (CD3(-),CD4(-),CD8(-)) thymocytes progress from CD44(+)CD25(-) towards CD44(-)CD25(+), influences the development of epithelial cells, critically inducing the extra, third dimension in the organization of the epithelial cells in the cortex. This tertiary configuration of the thymic epithelium is a typical feature for the thymus, enabling lymphostromal interaction during T-cell development. Crosstalk signals at this control point also induce the formation of thymic nurse cells. Moreover, our data indicate that establishment of a thymic cortex is a prerequisite for the development of the thymic medulla. Thus, differentiating thymocytes regulate the morphogenesis of thymic microenvironments in a stepwise fashion. http://repub.eur.nl/res/pub/8790/ 1998-01-01T00:00:00Z In the normal mouse spleen, two distinct populations of dendritic cells (DC) are present that differ in microanatomical location. The major population of marginal DC is found in the "marginal zone bridging channels" and extends into the red pulp. The interdigitating cells (IDC) are localized in the T cell areas in the white pulp. The aim of the present study was to characterize these two splenic DC populations with regard to their phenotype, in vivo phagocytic function, and turnover. Both marginal DC and IDC are CD11c+ and CD13+, but only IDC are NLDC-145+ and CD8alpha+. Notably, both populations, when freshly isolated, express the macrophage markers F4/80, BM8, and Mac-1. To study the phagocytic capacity of these cells, we employed the macrophage "suicide" technique by injecting liposomes loaded with clodronate i.v. Marginal DC, but not IDC, were eliminated by this treatment. Phagocytosis of DiI-labeled liposomes by DC confirmed this finding. The two DC populations differed significantly with regard to their turnover rates, as studied in a transgenic mouse model of conditional depletion of DC populations with high turnover. In these mice, marginal DC were completely eliminated, but the IDC population remained virtually intact. From these data we conclude that the marginal DC population has a high turnover, in contrast to the IDC population. Taken together, the present results indicate that marginal DC and IDC represent two essentially distinct populations of DC in the mouse spleen. They differ not only in location, but also in phenotype, phagocytic ability, and turnover. http://repub.eur.nl/res/pub/8670/ 1997-01-01T00:00:00Z In the murine thymus, the stroma forms microenvironments that control different steps in T cell development. To study the architecture of such microenvironments and more particularly the nature of communicative signals in lympho-stromal interaction during T cell development, we have employed the phage antibody display technology, with the specific aim of isolating thymic stromal cell-specific single-chain antibodies from a semisynthetic phage library. A subtractive approach using intact, mildly fixed thymic fragments as target tissue and lymphocytes as absorber cells generated monoclonal phages (MoPhabs) detecting subsets of murine thymic stromal cells. In the present paper we report on the reactivity of single-chain antibodies derived from three MoPhabs, TB4-4, TB4-20, and TB4-28. While TB4-4 and TB4-20 are both epithelium specific, TB4-28 detects an epitope expressed on both epithelial- and mesenchymal-derived stromal cells. TB4-4 reacts with all cortical epithelial cells and with other endoderm-derived epithelia, but this reagent leaves the majority of medullary epithelial cells unstained. In contrast, MoPhab TB4-20 detects both cortical and medullary thymic epithelial cells, as well as other endoderm- and ectoderm-derived epithelial cells. Cross-reaction of single-chain antibodies to human thymic stromal cells shows that our semisynthetic phage antibody display library, in combination with the present subtractive approach, permits detection of evolutionary conserved epitopes expressed on subsets of thymic stromal cells. http://repub.eur.nl/res/pub/26042/ 1977-03-30T00:00:00Z Peripheral blood cells- erythrocytes, granulocytes, monocytes, thrombocytes and lymphocytes-are the end products of a differentiation process which occurs in the bone marrow and, in rodents, also in the spleen. Normal haemopoietic tissue is a cell renewal system with an accurate balance between cell production originating from pluripotent haemopoietic stem cells and continuous cell loss. The important function of haemopoietic stem cells was emphasized by Till and McCulloch (1961) in bone marrow transplantation studies in mice. They noted that intravenous injection of small numbers of bone marrow cells into lethally irradiated syngeneic recipient mice caused the appearance of haemopoietic colonies in the spleen of the recipient mice. These colonies consisted either of erythroid, gran uloid, megakaryocytic or mixed cell populations (Curry and Trentln, 1967). The technique used by Till and McCulloch is known as the "spleen colony assay" and has established two major qualities of haemopoietic stem cells: (I) they have the capacity of self replication (Trentin and Fahlberg, 1963; Curry et a!., 1967) and (2) they are pluripotent since they give rise to clones of different cell types of which the differentiated "end" cells recirculate in the blood (Till and McCulloch, 1961; Becker eta!., 1963; Till, 1976). In contrast to erythroid and myeloid colonies, lymphoid colonies were not detectable with the spleen colony assay; however, Ford et al. (1966), Micklem et a!. (1966), and Wu et a!. (1968) demonstrated with chromosome marker techniques that lymphoid cells were also derived from pluripotent haemopoietic stem cells. One of the major questions in cell biological investigations of haemopoiesis concerns the factors which determine the commitment and differentiation of pluripotent haemopoietic stem cells. At present it is generally accepted that two types of factors are involved in the regulation of haemopoiesis: (I) microenvironmental factors (see 1.2), and (2) humoral factors (see 1.4).