Renata Brelińska

The significance of the subcompartments of the marginal zone for directing lymphocyte traffic within the splenic pulp of the rat.

SummaryThese studies were designed to gain more detailed information on the sites of lymphocyte migration into the marginal zone, on lymphocyte segregation within this area and on subsequent migration of the cells in individual compartments of the rat spleen. A lymphocyte population enriched in T-lymphocytes was obtained from rat lymph nodes and was labeled with 5-(3H)uridine in vitro. Observations on localization of labeled lymphocytes at short time intervals following their intravenous transfusion into syngeneic recipients, indicate that the sites of emigration from the blood are the internal and external layers of the marginal zone. From here, the cells migrate towards the periarteriolar lymphoid sheath and the red pulp.

Macrophages and interdigitating cells; their relationship to migrating lymphocytes in the white pulp of rat spleen.

SummaryThe pathway of lymphocyte migration through the white pulp of rat spleen and the relationship of migrating cells to the accessory cells (marginal zone macrophages and interdigitating cells, IDCs) of the white pulp compartments were analysed. Donor lymphocytes were obtained from lymph nodes, enriched for T lymphocytes and labeled in vitro with 5-(3H)uridine. They were injected intravenously into syngeneic recipients from which samples of spleen were taken at short intervals from 3 to 300 min after injection. Autoradiographs of semithin and ultrathin sections showed that, in the internal layer of the marginal zone (MZ), lymphocytes tended to accumulate within some regions in close proximity to marginal-zone macrophages before migrating into the periarteriolar lymphoid sheath (PALS). The lymphocytes enter PALS between protrusions of the accessory cells located in the peripheral area of the sheath. During migration towards the central area of PALS, a close contact between both cell types was noted. In the central area of PALS, preferential accumulation of lymphocytes around IDCs was observed. Labeled lymphocyte distribution within PALS and the rate of cell migration through the white pulp seem to depend on lymphocyte-IDC contact. A common feature of accessory cells which may affect the migration of lymphocytes in both MZ and PALS is the presence of Birbeck granules.

Pathways of lymphocyte migration within the periarterial lymphoid sheath of rat spleen

SummaryMale Wistar rats were injected intravenously with 5-(3H)uridine-labeled lymphocytes isolated from lymph nodes of syngeneic donors and enriched in T cells. After short periods of time (3 to 120 min after injection), labeled lymphocytes were localized in spleen compartments using autoradiography to identify routes of lymphocyte movement from blood into splenic parenchyma and to follow migration pathways of recirculating lymphocytes within the periarterial lymphoid sheath (PALS). Topographical analysis of labeled lymphocytes was performed in specific planes of PALS characterized by the diameter of the arterial vessel and termed PALS large, PALS medium, and PALS small (PALS L, PALS M, PALS S, respectively). Attention was also paid to accumulations of labeled lymphocytes close to the arterial vessel wall. Initially, labeled lymphocytes were localized in PALS S and PALS M near the terminal branching of arterial vessels and in the marginal zone (MZ). We conclude that lymphocytes emigrate from blood into splenic parenchyma within two white pulp compartments: in MZ, and directly within PALS through the wall of capillary vessels. The sequential accumulation of labeled cells near arterial vessels of increasing diameter suggests that the recirculating pool of lymphocytes migrates into the central part of PALS L by two routes: from MZ, and along arterial vessels from PALS S and PALS M.

Distribution of different cell types within the rat thymus in the neonatal period of life

SummaryThis study attempted to define reciprocal positions of cell types within the thymus. Random or non-random contacts between specific cell types were analyzed by means of graph theory. For analysis, thymus blocks were sectioned serially and, then, thymus cells were categorized into types, based on morphological criteria. The distribution of individual cell types within the cortex, cortico-medullary zone and medulla was presented in form of a map. In the analysis, three types of epithelial cell, characteristic of each thymus zone, macrophages, Langerhans-like cells and lymphocytes were found in non-random relations to one another. Moreover, characteristic groups of cells associated with one another were also demonstrated.

Thymic nurse cells: Their functional ultrastructure

Thymic nurse cells are defined in vitro as multicellular complexes of epithelial cells and thymocytes. Although these structures have been implicated in the intrathymic differentiation of thymocytes, little is known about the biology of this cell complex and about the occurrence of the cells in the thymus in situ. Therefore, to clarify the matter, in this review we have presented characteristics of epithelial cells capable of forming complexes with thymocytes, in light of the literature data and the experience of the authors. The structure of cells within the complexes allowed us to distinguish three types of thymic nurse cells. Three‐dimensional reconstruction of the thymus and observations employing TEM and SEM demonstrated the presence of distinct types of complexes in various topographic regions of the thymus. Where possible, the functional relevance of the morphological data was analyzed. Microsc. Res. Tech. 38:250–266, 1997.

Thymic nurse cells: differentiation of thymocytes within complexes

SummaryThymic nurse cell complexes (TNC-c) were isolated from thymuses of BDF1 mice at pre-determined intervals during the 12-week latency period that precedes the development of leukemias. T-cell leukemias were induced by a single i.v. injection of 50 mg/kg of methylnitrosourea (MNU). In order to clarify processes taking place in TNC-c, the complexes of mice after MNU injection were compared with TNC-c of age-matched control mice, with respect to their number per thymus, the distribution of TNC-c according to their size (the number of intra-TNC thymocytes reflects the type of TNC-c), the number of intra-TNC thymocytes that undergo DNA synthesis, and the phenotype of thymocytes inside TNC-c. During the latency period of leukemogenesis, the effects of MNU were shown to involve, in addition to changes in number of TNC-c, a decrease in the number of thymocytes incorporating labeled thymidine, viz., the number of dividing cells, thus affecting the size distribution of TNC-c types. Intra-TNC thymocytes of control mice were heterogeneous in their phenotype and represented cells at varying stages of their maturation cycle. MNU administration was followed by selective differentiation of thymocytes within TNC-c to Lyt 1-thymocytes in some and to Lyt 2-thymocytes in others, Lyt 1 and Lyt 2 being specific antigens expressed by thymocytes.

Thymic nurse cells: division of thymocytes within complexes

SummaryThymic nurse cell complexes (TNC-c), isolated from mouse thymuses at 1 and 2 h after i.v. injection of 6-(3H)thymidine, were analyzed in autoradiographs of semithin serial sections with regard to their size and the distribution of labeled thymocytes in individual types of complexes. The total number of thymocytes per complex reflects the type of complex. In a parallel study, localization of labeled thymocytes within individual zones of thymic cortex was examined. Thymocyte division within complexes may yield sequential complex generations differing in number per complex. However, thymocytes within complexes differ from each other in division kinetics. Half of the thymocytes that had been labeled 1 h after injection divided within 2 h. The rapidly dividing fraction of thymocytes were distributed within small complexes containing 2–8 cells and corresponded to the distribution of labeled cells in the outer thymic cortex. The proportion of labeled cells within large complexes resembled the distribution of labeled cells in the deep cortex. The data support the view that microenvironmental factors within TNC-c are responsible for both inducing thymocytes to enter the cell cycle and the negative selection (cell death) of some thymocytes.

Homing of hemopoietic precursor cells to the fetal rat thymus: intercellular contact-controlled cell migration and development of the thymic microenvironment

Colonization of rat thymic anlage by the first wave of hemopoietic precursor cells (HPc) was investigated by means of transmission electron microscopy and immunocytochemistry. HPc began migration into the thymic anlage between 13 and 13.5 gestation days (GD), terminated colonization at about GD 16, and migrated sequentially through the two compartments of the thymic anlage under the control of typical populations of stromal cells. First, HPc migrated through the external compartment of the perithymic mesenchyme, tightly interconnected with fibroblasts. The type of junctions between the cells indicated that the fibroblasts played a role in the control of HPc trafficking and in their entrance to the epithelial compartment. The second stage of colonization was initiated by the entrance of HPc to the epithelial compartment and their interaction with thymic epithelial cells (TECs). Based on morphological criteria, two populations of HPc were distinguished that colonized the anlage at various stages of its development. The predominant population with ultrastructural traits common to thymocytes “homed” into the epithelial type primordium. A small number of HPc, identified by protein S-100 expression and by Birbeck’s granules as precursors of dendritic cells, colonized lymphoepithelial anlage in which subsets of cortical and medullary TECs could be distinguished. Thymocyte migration and their reciprocal interactions with cortical TECs differed from the trafficking of dendritic cells toward the medulla. The results demonstrated the influence of maturing thymocytes on the development of cortical epithelial cells and the dynamic organization of the medullary microenvironment with direct involvement of dendritic cells.