Redefinition of lymphoid progenitors

Similarities between T and B lymphocytes might have led to the idea that these functionally distinct cells develop from a common lymphoid progenitor. However, investigations with a new clonal assay which allows for T-, B- and myeloid-lineage development indicate that commitment to T-cell and B-cell lineages occurs instead through myeloid/T and myeloid/B bipotential stages, respectively. These findings provide an opportunity to reconsider the ontogeny and phylogeny of T- and B-cell development.     

The ontogeny of gut-associated lymphoid tissue in Oreochromis-mossambicus

The ontogenesis of gut-associated lymphoid tissue (GALT) was investigated using histological procedures. Samples were taken at various time intervals to include larval, first-feeding and juvenile stages. Whole fish and tissue samples were embedded in either paraffin wax or metha-crylate resin and sections stained with Giemsa, periodic acid-Schiff (PAS), methyl green pyronin (MGP) and methylene blue. GALT was first observed as individual lymphocyte-like and macrophage-like cells in the lamina propria, and in later stages plasma cells and granulocytes were identified. Leucocytes began to infiltrate the epithelium just prior to first feeding and then rapidly once feeding had began. By day 50, GALT was equal to that observed in the adult gut.     

The effect of dibromodulcitol on resting and dividing lymphoid cells

The effect of dibromodulcitol (DBD) on the incorporation of labelled precursors into DNA and RNA fractions of PHA-stimulated human lymphocytes and of P388F lymphoma cells at various stages of their growth was studied. Both cell systems showed sensitivity to the drug within the concentration range of 1–10 μg/ml.When DBD was added before phytohaemagglutinin (PHA), human lymphocytes showed a DNA labelling that was more affected than RNA. In contrast, by adding DBD after PHA, RNA labelling was much more inhibited than DNA. In the latter case, the decrease in DNA labelling occurred only 24 h after drug treatment whereas RNA labelling was decreased 1 h after treatment. Levels of DBD which normally produced 30% inhibition in plating efficiency of P388F lymphoma cells affected uridine-5-T incorporation to a different extent at different stages of growth of the culture. Enhanced RNA labelling occurred in early exponential stage while at later stages of growth, RNA synthesis was depressed.     

Suppression of the allograft response by implants of mature lymphoid tissues in larval Xenopus laevis

One hundred and twenty-two larvae of Xenopus laevis, the South African clawed toad, at developmental stages 48, 50, 52 and 54, were implanted in the tail with two allografts from adult tissues. In each case, one allograft was from kidney, while the other was either from kidney, thymus, spleen, or liver. In any particular host the two implants were always from the same donor and the implants were all visually matched in size. The experimental period was a maximum of nine days, so as to minimize the large numbers of changes normally accompanying larval progress from stage to stage. We are concerned with the timing of allograft response initiation under the implant conditions of each experimental group at a particular point in development. An allograft response was defined as an infiltration and accumulation of small lymphocytes in the “test” kidney allograft. Larvae of all stages developed allograft responses within one week post-implantation when the variable implant was from kidney, but implants from spleen and thymus suppressed both the timing of initiation and the subsequent intensity of the response. Spleen was more effective in this regard than thymus and both were more effective in the earlier larval stages. Liver proved to be toxic to the larvae. The relationship between the maturation of the lymphomyeloid tissues and external morphological staging is also discussed.     

Ontogeny of primary lymphoid organs and lymphoid stem cells

Cells of the immune system go through a series of important developmental steps that begin early in embryonic life and include, first, the various waves of hemopoietic-cell production in the embryo and, second, the homing of these cells to the hemopoietic organs, which are the sites of hemopoiesis and lymphopoiesis in embryonic and adult life. The avian embryo is an important model for investigating these early steps; and this paper presents a comprehensive review of the work done on the early ontogeny of the avian immune system.     

Correlation of cell division and specific protein production during the course of lymphoid cell differentiation

Mice were immunized with horseradish peroxidase and injected with [³H] thymidine. Popliteal lymph node cells were submitted to electron microscopic immunocytochemistry and high resolution autoradiography in order to correlate antibody production and ability to undergo cell division at various stages of lymphoid cell differentiation. Antibody synthesis started in blast cells and increased steadily until the mature plasma cell stage was reached. Thymidine incorporation was highest in blastoid cells and decreased continuously afterwards. Chromatin dispersion was found to be paralleled by thymidine incorporation. This observation and data of other authors seem to indicate that chromatin dispersion is a prerequisite for replication. Almost all mature plasma cells were devoid of thymidine incorporation. This confirms that they are end cells apparently unable to divide.     

Association of specific tyrosine phosphorylation with stages of B-cell differentiation in human lymphoid leukemias

In vitro protein phosphorylation in various types of human fresh lymphoid leukemic cells (C-ALL, B-CLL, HCL and PCL: B-cell lineage and T-ALL, ATL and T-CLL: T-cell lineage) were studied. In cases of B-CLL and HCL, tyrosine protein kinase (TPK) activity was at least 5-fold higher than that in other cases of B- and T-cell lineages. B-cell leukemic cells at various differentiation stages had different endogenous substrates in tyrosine phosphorylation as well as distinct TPK activity. The P-tyr-containing proteins of 68K, 59K and 56K were detected commonly in all the cases of B-cell lineage. The phosphorylated protein of 32K was present only in cases of PCL. On the other hand, in T-ALL and ATL, the major substrate in tyrosine phosphorylation was 58K. These results suggest that the characterization of in vitro tyrosine phosphorylation provides a new means not only to distinguish T- and B-lymphoid leukemia, but also to differentiate stages of lymphoid development.     

Chicken fetal antigen: association with lymphoid development and differentiation

Rabbit antisera capable of detecting chicken fetal antigen (CFA) was prepared against 1-day chick red blood cells (RBCs) and made specific by exhaustive adsorption with adult chicken peripheral RBCs (PRBCs) from the same strain. Microcytotoxicity was used to study the incidence of CFA on lymphocytes obtained from several organs at different developmental stages in the chicken. Lymphocyte-associated CFA (LA-CFA) determinants and erythrocyte-specific CFA (ES-CFA) determinants were distinguished through the use of adsorption analysis. The high incidence of CFA-positive lymphocytes found in the fetal bursa and thymus was not equaled in the peripheral organs of the spleen, cecal tonsils, and gland of Harder. CFA expression on adult lymphocytes was restricted to the thymus and peripheral blood. It is suggested that these cells may represent a subpopulation of T lymphocytes. Adult spleen, cecal tonsils, and gland of Harder were virtually devoid of CFA-bearing lymphocytes. At fetal developmental stages when greater than 94% of the bursal B cells were CFA-positive, few, if any, of the highly differentiated Harderian B cells possessed CFA. It is suggested that LA-CFA expression is dependent upon B cell differentiation and/or the bursa (central) vs gland of Harder (peripheral) microenvironment. The pattern of CFA expression on bursacytes is discussed in light of the properties of age resistance and bursal-dependent target cells associated with virally induced lymphoid leukosis.     

Activity of some proteinases and glycosidases in human leukemic lymphoid cells at various stages of differentiation.

Activities of some glycosidases and proteinases in human leukemic lymphoid cells at various stages of differentiation have been compared. It was found that cells with different immunological phenotypes gave different enzymic spectra. Glycosidases and proteinases in lymphoid cell precursors had higher activity level than the enzymes in mature T- and B- cells. In cells of B- lineage, all activities were lower than in common precursor of lymphoid cells. In T-cells at the earlier stages of thymic differentiation, activities of all proteinases and most of glycosidases were higher than in common precursor cells whereas in mature T-helpers and T-suppressors the activities were markedly lower. Most of hydrolases in mature T-cells were twice more active than the enzymes in mature B-cells. The opposite-directional changes in activities of some hydrolases at the earlier stages of differentiation of lymphoid cells along B- or T- cells pathways are suggested.     

Stromal cells provide the matrix for migration of early lymphoid progenitors through the thymic cortex

During steady state lymphopoiesis in the postnatal thymus, migration of precursors outward from the deep cortex toward the capsule is required for normal differentiation. Such migration requires, at a minimum, expression of adhesive receptors on the migrating lymphoid cells, as well as a stable matrix of their ligands persisting throughout the region of migration. In this study, we address the nature of this adhesive matrix. Although some precursor stages bound efficiently to extracellular matrix ligands, a specific requirement for the cell surface ligand VCAM-1 was also found. In situ analysis revealed that early precursors are found in intimate contact with a matrix formed by stromal cells in the cortex, a proportion of which expresses VCAM-1. In vivo administration of an anti-VCAM-1 Ab resulted in decreased thymic size and altered distribution of early precursors within the cortex. These results indicate that precursors migrating outward through the cortex may use a cellular, rather than extracellular, matrix for adhesion, and suggest that the VCAM-1(+) subset of cortical stroma may play a crucial role in supporting the migration of early precursors in the steady state thymus.     

IgG Fc receptor-bearing cells during early lymphoid cell development in the chicken

Cells from intraembryonic mesenchyme, yolk sac, bursa of Fabricius, and thymus from chicken embryos at different stages of development were studied for the presence of IgG Fc receptors by EA-rosette formation and binding of heat-aggregated chicken IgG (agg IgG). Cells with Fc receptors were found in high frequency in the intraembryonic mesenchyme as early as on the third day of incubation, in the yolk sac on the 7th day, in the bursa on the 10th day, and in the thymus on the 16th day of embryonic development. In the bursa the number of agg IgG binding cells increased with the age of the embryo and remained high after hatching, whereas in the thymus the peak value (76%) was observed on the 16th embryonic day, and after hatching only about 10% of the cells expressed the agg IgG receptors. The results also suggest that the appearance of IgG Fc receptors precedes the expression of B-L (Ia-like) antigens and of cytoplasmic and surface immunoglobulins on early lymphoid cells of the chicken embryo.     

Reappraisal of histogenesis in the bursal lymphoid follicle of the chicken.

The development of the bursal follicle and the appearance of the follicle-associated epithelial (FAE) cell and the reticuloepithelial (REp) cell were studied. The stages of development of the bursal follicle were observed by light and electron microscopy; an anticytokeratin monoclonal antibody was also used. At the beginning of follicle development, a mesenchymal cell cluster is observed in the tunica propria; the cluster becomes wedged in a niche of the surface epithelium, and gradually it is completely surrounded by the epithelium itself, which closes under the clump of mesenchymal cells. The epithelial cells lying upon the mesenchymal clump become necrotic, and a number of mesenchymal cells bulge out, forming the FAE cells. The epithelial cells that have closed under the mesenchymal nodule become stratified and form the REp cells; they become star-shaped because the medullary-lymphoid cells grow between them. Finally, the cortex is formed, possibly as a result of the migration of medullary cells before they peripheralize. It is concluded that FAE cells are not specialized epithelial cells, as they do not react to an anticytokeratin monoclonal antibody; on the contrary, they are formed by mesenchymal stemcells that bulge into the lumen and change their character after moving into the epithelium. The REp cells appear in the follicular primordium shortly after the bursal follicle begins to develop; the pronounced reactivity of the REp cells to an anticytokeratin monoclonal antibody supports the hypothesis of their epithelial origin.     

Mitosis-arresting effects of cigarette smoke condensate on human lymphoid cell lines

Whole-smoke condensates from the University of Kentucky reference cigarettes induced partial mitotic arrest in 4 human lymphoid cell lines. Treatment of cells for 3 h with 100 and 200 μg of cigarette-smoke condensate/ml of culture medium increased the frequency of metaphases and decreased the proportion of anaphases in the treated cell populations. Cytoskeletal studies using antitubulin immunofluorescence techniques and transmission electron microscopic studies demonstrated that in early stages of mitosis the formation of aster and the separation of centrosomes in condensate-treated cells were comparable to those of untreated control cells, but the poleward migration of centrosomes was inhibited. Arrested metaphases revealed two centrosomes surrounded by aggregated chromosomes in the center of each cell but the structure of the centrioles, microtubules and the kinetochores appeared normal. The results demonstrate the presence of antimitotic compounds in the tobacco-smoke condensate.     

Organogenesis of lymphoid tissues

The development of lymphoid organs depends on the correct expression of several molecules within a defined timeframe during ontogeny. Although this is an extremely complex process, with each secondary lymphoid tissue requiring subtly different signals, a common framework for lymphoid development is beginning to emerge. Drawing on studies of lymph nodes, Peyer's patches and nasal-associated lymphoid tissue, an integrative model of lymphoid-tissue development, involving adhesion molecules, cytokines and chemokines, which emphasizes the role of interactions between CD3-CD4+CD45+ 'inducer' cells and VCAM1+ICAM1+ stromal 'organizer' cells is presented.     

Effect of hydrogen ion concentration in the medium on the state of chromatin in lymphoid cells

Effect of medium acidity (pH 7.2 divided by 6.6) on the state of lymphoid tissue cells was studied by microspectrofluorimetry, electrophoresis and IR-spectroscopy. Two stages of the cell structural-functional changes were found at H2CO3 acidification of the medium. The first one is a reversible transition of chromatin from the state of dense sphere to the margination state when chromatin is located along the membrane. The second one is an irreversible destruction of chromatin and the cell death. The margination stage is related to the formation of non-specific DNA-membrane contacts, while the chromatin destruction stage to the "proton breakdown" of the macromolecules and their supramolecular complexes. A relationship between the degree of margination reversibility and the value of the medium acidification and the time of cell incubation in it is shown. Different functional significance of chromatin marginated state is discussed.     

Emergence of committed B lymphoid progenitors in the developing chicken embryo.

The formation of B lymphoid restricted progenitors was followed during chicken embryonic development by monitoring the appearance of the various Ig gene rearrangements (DJH, VHDJH, V lambda J lambda), as a sensitivity that allows the detection of a single rearranged cell. By quantifying the DJH committed progenitor populations, we describe their evolution in different compartments at different developmental stages. The yolk sac is the first site where DJH-positive cells are observed (at days 5-6 of development); via the general circulation, they then seed the various organs while undergoing VHDJH and V lambda J lambda rearrangements, which occur simultaneously but lag behind DJH by one to several days. These progenitor populations decline with time in most lymphoid sites and only expand in the bursa. RAG-1 expression is observed in the bursa in the absence of ongoing rearrangement activity and thus appears to be an improper marker of rearrangement in the chicken. Commitment to the B cell lineage seems to result from an intrinsic cell program, but the survival and expansion of the committed B progenitors require the specific microenvironment of the bursa.     

Modeling immune reactivity in secondary lymphoid organs

Models of the dynamical interactions important in generating immune reactivity have generally assumed that the immune system is a single well-stirred compartment. Here we explicitly take into account the compartmentalized nature of the immune system and show that qualitative conclusions, such as the stability of the immune steady state, depend on architectural details. We examine a simple model idiotypic network involving only two types of B cells and antibody molecules. We show, for model parameters used by De Boeret al. (1990,Chem. Eng. Sci. 45, 2375–2382), that the immune steady state is unstable in a one compartmental model but stable in a two compartment model that contains both a lymphoid organ, such as the spleen, and the circulatory system. This work was performed under the auspices of the U.S. Department of Energy.     

Purine nucleoside phosphorylase synthesis and turnover in human lymphoid cells

We have studied the turnover and synthesis of purine nucleoside phosphorylase by using a polyclonal rabbit antiserum to this protein. The turnover of purine nucleoside phosphorylase was studied in the B lymphoblast cell, WI-L2, by specific immunoprecipitation of [3H]leucine-labeled proteins. The half-lives for total protein and purine nucleoside phosphorylase were 14.5 and 14.1 hr, respectively. For cells cultured in the presence of inosine the half-life of purine nucleoside phosphorylase was reduced to 11.2 hr. The synthesis of purine nucleoside phosphorylase was analyzed during phytohemagglutinin-stimulated T cell transformation by pulse labeling cells with [35S]methionine. Purine nucleoside phosphorylase synthesis increased greater than 10-fold during the first 12 hr of transformation and continued to a maximum of 30-fold. The relative rate of purine nucleoside phosphorylase labeled to total proteins was 0.04% in unstimulated T cells and increased to 0.18% 12 hr after stimulation. These studies identify some preferential synthesis of purine nucleoside phosphorylase during the early stages of T cell transformation.     

Comparative analysis of the destroying effects of prednisolone and irradiation of lymphoid cells]

The hormone-induced and post-irradiation changes in the molecular weight of a single-stranded DNA (SSDNA) in alkaline nuclear lysates and the activities of DNAses and pyknotic nuclei from rat thymocytes were studied. It was shown that 1 hr after injection of prednisolone (1 mg per 100 g of body weight) the molecular weight of SSDNA in the lymphoid organs is decreased with a subsequent increase by the 6th hour. The hormone-induced degradation of DNA is not accompanied by any marked increase in the activities of DNAses or by an appearance of pykotic nuclei in the thymocytes. The irradiation of the animals at a dose of 900 R leads to an irreversible decrease of the molecular weight of SSDNA in the lymphoid organs, to a steady increase of the DNAse activity and a sharp increase of the amount of pyknotic nuclei in the thymocytes. Studies on the mechanism of post-hormonal degradation of DNA in rat thymocytes in vitro demonstrated that prednisolone exerts its effects on the early and late stages of DNA degradation.     

Histological studies on the lymphoid organs in prenatal larvae of platy,Xiphophorus maculatus L (Poeciliidae: Teleostei)

The thymus was very large and tightly packed by lymphocytes in prenatal larvae of platy, Xiphophorus maculatus L., whereas the lymphoid tissues in the spleen and trunk kidney were poorly developed at these stages. We therefore suggest that the specific cellular defence is developed much earlier than the corresponding humoral defence mechanisms in this species.