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J L Haar

Publications and source records attributed to J L Haar.

At least 19 recordsLinked to original sources
PubMed1992

The effects of thymus supernatant on the thymus homing ability of aged murine bone marrow cells.

This study examined the effect of thymus supernatant on the ability of bone marrow cells from senescent mice to home to the thymus. An in vitro and an in vivo assay were employed. The in vitro assay used a blind well migration of aged bone marrow cells to thymus supernatant across a membrane with 5-microns pores. The in vitro assay measured the ability of aged bone marrow to repopulate the thymus of an irradiated host. Our results support previous reports that the bone marrow from old mice has a greatly reduced ability to migrate to thymus supernatant and to repopulate the thymus of an irradiated host. Further, we found that a brief treatment of the old bone marrow with thymus supernatant significantly improved its thymus homing ability both in vitro and in vivo.

Aging↗
PubMed1992

Conditioning of Nude bone marrow increases in vitro migration to thymus supernatant.

The thymus must be continuously seeded by cells termed prothymocytes in order to maintain normal T-cell development (Scollay et al. 1986). Using parabiotic studies, the source of prothymocytes appears to be either from the fetal liver or the adult bone marrow (Roderwald et al. 1992). The ability of the body to distinguish self from non-self and mount a functionally mature immune response is dependent upon the intrathymic education of these cells. Therefore, it is apparent that successful migration of prothymocytes into the thymus is an inescapable event in the development and maintenance of the immune system. Utilization of the athymic Nude mouse is a valuable asset in the elucidation of the mechanisms influencing the migration of bone marrow cells into the thymus. Its aberration enables investigators to examine the effect of thymic factors on cells previously devoid of thymic influence. In an attempt to understand the migration of normal prothymocytes into the thymus, we analyzed the in vitro migration of athymic bone marrow cells towards newborn thymus supernatant. Adult athymic murine bone marrow cells were incubated in either thymus supernatant or media and allowed to migrate toward one or the other. Similar control experiments were performed using CBA adult mice. Results indicate that athymic bone marrow migration towards both supernatant and media can be restored to control levels after incubation in thymus supernatant.

Animals↗
PubMed1992

Dexamethasone and hydrocortisone enhance the in vitro migration of prethymic stem cells to thymus supernatant.

The migration of prethymic stem cells from the bone marrow to thymus supernatant was examined in a blind well migration assay following treatment with glucocorticoids (GCS). To study the in vivo effects of GCS, time release pellets containing dexamethasone (DEX) were implanted subcutaneously in young adult CBA/J mice for 7, 14 and 21 days. After seven and 21 days of DEX treatment, enhanced migration of bone marrow lymphoid cells to thymus supernatant occurred. To study the in vitro effects of GCS on prethymic stem cell migration, bone marrow cells were incubated for one or six hours in media containing dexamethasone (DEX), hydrocortisone (HCS), or medium alone. After a six-hour incubation with GCS, significantly more bone marrow cells migrated toward thymus supernatant in vitro than bone marrow cells incubated in medium alone. The enhanced migration of cells to thymus supernatant seen in this assay may reflect a feedback mechanism whereby bone marrow cell migration is enhanced to restore the thymic lymphocyte reserves depleted following treatment with GCS.

Animals↗
PubMed1992

Restraint and sound stress reduce the in vitro migration of prethymic stem cells to thymus supernatant.

Murine bone marrow cells were examined in an in vitro assay to determine whether stress modulates the migration of prethymic stem cells to thymus supernatant. Adult CBA/J mice were either restraint or sound stressed for two hours daily for five days. Bone marrow cells were removed and migrated toward newborn thymus supernatant in an in vitro migration assay in blind well chambers. Bone marrow cells from animals which had been stressed for five days showed a significant decrease in the percent migration to thymus supernatant when compared to bone marrow cells from age-matched control mice. This suggests that either a smaller proportion of precursor cells are available in the bone marrow for migration to the thymus or the number of cells remains the same but these cells are less responsive to chemoattractive factors in the supernatant, thus causing them to migrate at a decreased rate.

Animals↗
PubMed1991

Bone marrow-thymus axis in senescence.

This presentation offers a brief review of the bone marrow-thymus axis in senescence, a putative model for thymocyte differentiation, and recent results of our work on the status of pre-thymic stem cells in aged mice. The data presented here provide further evidence for a thymus endocrine influence on the bone marrow stem cells, specifically lymphocyte precursors. It has been postulated that the thymic hormones may act on lymphocyte precursors in the bone marrow and that the loss of thymic factors during senescence may be a contributing factor to the decreased cellular immune function. This study used Haar's in vitro model to investigate the bone marrow-thymus axis in aged mice. Erythroid-depleted bone-marrow cells from 3-month- and 24-month-old CBA (Thy 1.2) mice were placed in the upper half of a blind-well chamber with thymus supernatant in the lower half. Experimental cells were treated with thymus supernatant for 1 hr prior to migration. This study confirmed that pre-thymic stem cells in aged bone marrow are deficient in their ability to migrate to the thymus supernatant. It also revealed that treatment of the old bone marrow with thymus supernatant, made from neonatal thymus cultures, could dramatically improve the thymus migrating ability of the aged bone-marrow stem cells.

Aging↗
PubMed1989

Enhanced in vitro bone marrow cell migration and T-lymphocyte responses in aged mice given subcutaneous thymic epithelial cell grafts.

Thymic epithelial cell cultures from newborn CBA/J mice were developed and grown on collagen-coated dextran beads. These thymic epithelial cells were transplanted subcutaneously into aged syngeneic mice. After several weeks, enhanced in vitro migration of host bone marrow cells occurred to supernatants prepared from neonatal thymus cultures in thymic epithelial cell grafted mice compared to control aged mice. Percent migration equaled that of migration from control young adult mice. In addition, enhanced T-lymphocyte responses were observed in aged mice given thymic epithelial cell grafts as compared to aged controls.

Aging↗
PubMed1989

Defective in vitro migratory capacity of bone marrow cells from viable motheaten mice in response to normal thymus culture supernatants.

"Viable motheaten" mice are severely immunodeficient and develop autoantibodies early in life. The thymus appears normal for the first 3-4 weeks, after which there is depletion of cortical thymocytes and a diminution in the size of the organ until it is atrophic. The present study utilized an in vitro migration assay, in which bone marrow cells from viable motheaten mice were found to have a greatly diminished capacity to migrate in response to normal thymus supernatant when compared to normal bone marrow cells. It was also determined that thymus supernatant prepared from newborn viable motheaten mice was chemoattractive to normal bone marrow but not to viable motheaten bone marrow. The results of in vivo reconstitution of lethally irradiated viable motheaten mice with normal bone marrow cells also show that the thymus of the mutant is normal in its ability to attract and be repopulated by normal donor bone marrow. Therefore, the premature thymic involution of viable motheaten mice is related to the inability of bone marrow cells from these mice to migrate or respond to signals from the thymus.

Animals↗
PubMed1988

In vivo homing of thymus-enriched bone marrow cells.

A population of adult CBA/J mouse bone marrow (BM) cells enriched by in vitro migration to supernatant prepared from neonatal thymus was labeled with a DNA-binding fluorochrome, Hoechst dye No. 33342 (H33342). Labeled cells were injected into irradiated recipients in order to compare the in vivo localization of the migration-enriched BM (MEBM) cells to the localization of injected nonenriched BM (NEBM) cell controls. A characteristic difference in the distribution of localized cells was observed in the spleen but not in other lymphoid organs. At 2 hr after injection the MEBM cells were located in the marginal zones surrounding the periarterial lymphoid sheaths (PALS) of the splenic white pulp. At 6 hr after injection the MEBM cells were seen distributed between marginal zones and the PALS and by 16 hr they had localized almost exclusively in the white pulp. In contrast, the NEBM cells were located in the marginal zones or red pulp for the duration of the experiment. These observations show that the MEBM cells home selectively to T-cell areas of the spleen. Direct immunofluorescent monoclonal antibody staining of H33342-labeled cells obtained from the recipient spleens at 16 hr demonstrated that the MEBM cells were negative for Thy-1 antigen, indicating that acquisition of Thy-1 was not prerequisite to the observed homing. The results are compared to known localization patterns of mature lymphocytes.

Animals↗
PubMed1988

Antimitogenic actions of lectins in cultured human fibroblasts.

It was previously reported that the lectins wheat germ agglutinin (WGA) and concanavalin A (Con A) inhibit the mitogenic actions of multiple peptide growth factors in human fibroblasts without having a significant effect on mitogen binding. The current studies were designed to further examine the mechanisms of this antimitogenic action of lectins. Addition of WGA at progressively later times after stimulation of fibroblasts with peptide mitogens revealed significant inhibition of DNA synthesis even when the lectin was added 16-20 h after growth factors. This suggests an inhibitory effect on a pathway occurring late in G1, or close to the G1/S boundary. WGA also inhibited stimulation of DNA synthesis by non-peptide agents such as colchicine and vanadate ion, indicating that the lectin inhibits a common distal step in the mitogenic response, rather than acting primarily on events occurring at the level of the growth factor-receptor interaction. WGA had a rapid (within 30 min) inhibitory effect on insulin-stimulated amino acid uptake, but Con A, which like WGA blocked mitogen-stimulated 3H-dT incorporation, had little effect on stimulation of amino acid uptake. Thus the inhibition of DNA synthesis and amino acid uptake by lectins appear to be mediated by distinct mechanisms. WGA binding to fibroblasts persisted even when the lectin was removed from the incubation medium, but unlike 125I-EGF, which was rapidly internalized at 24 degrees C, little 125I-WGA was internalized. Incubation of fibroblasts for 20 h with WGA or Con A was not toxic to cells, since reversal of lectin binding by the appropriate saccharide allowed normal subsequent stimulation of DNA synthesis by EGF and insulin. However, the observation that cells exposed to antimitogenic lectins undergo a marked decrease in cell spreading suggests that changes in cell shape may be relevant to the mechanism by which lectin-treated fibroblasts become unresponsive to mitogenic stimulation.

Aminoisobutyric Acids↗
PubMed1988

Augmentation of pre- and post-thymic T-lymphocyte responses in thymic epithelial cell grafted nude mice.

Thymic epithelial (T-E) cell cultures from newborn mice, grown on dextran beads coated with denatured collagen, were injected subcutaneously into athymic "nude" mice. After 8 weeks, enhanced in vitro migration of T-E cell grafted nude mouse bone marrow cells occurred to thymus supernatants prepared from neonatal thymus cultures. Percent migration was equal to the migration of control AKR bone marrow. In vivo T-lymphocyte responses were also significantly enhanced in T-E cell grafted nude mice as compared to controls.

Animals↗
PubMed1987

Chemoattraction enrichment of thymus-homing bone marrow cells.

It has been reported that a population of cells from mouse bone marrow migrates to supernatant made from the incubation of minced fragments of new-born mouse thymuses and that the migrated population is enriched for immature lymphoid cells. In the present study, we show that this method enriches for thymic-homing cells. Migration-enriched cells were labelled with fluorescein isothiocyanate (FITC) and were injected into the tail veins of lethally irradiated mice. Cell suspensions of the thymuses from these experimental mice had 8.1 +/- 1.8% fluorescing cells compared to control mice given equal numbers of non-migration-enriched FITC labelled cells which had 2.4 +/- 1.7% positive cells.

Animals↗
PubMed1987

The initial characterization of a thymus factor chemotactic to bone marrow cells.

Thymus supernatants were produced by cluturing minced newborn CBA/J mouse thymuses in serum-free media for 48 h. Supernatants thus obtained were chemotactic to a subset of bone marrow cells as assessed in blind well chambers, and enriched for immature lymphoid cells in the migrating cell population. The enriched population of cells was shown to be capable of homing to the thymus of an irradiated mouse in vivo in a significantly higher percentage than nonmigrated bone marrow cells. In this report, initial characterization of the factor(s) responsible for this in vitro migration is presented. Several well studied thymic factors were compared with the thymus supernatants for their ability to induce migration of bone marrow cells in vitro. Thymulin (FTS-Zn), FTS, and TP-5 (the pentapeptide fragment of thymopoietin) were used. None of these factors demonstrated chemotactic properties in the migration assay using concentration ranges in which other in vitro activities have been observed. The chemoattractive activity of the supernatant was unaltered by ultracentrifugation. The effects of temperature on the chemotactic properties of thymus supernatant were examined, and a fifty percent decrease in observed migration occurred with thymus supernatant heated to 100 degrees C for 1 h. In addition, incubation of the supernatant for 1 h at 37 degrees C with chymotrypsin, but not with trypsin, inhibited migration, presumably by inactivation of the active factor. Using Amicon microconcentrators, the supernatant was separated into several fractions based on molecular weight. Initial data suggest that the active fraction is in the less than 10,000 mw range.

Animals↗
PubMed1987

In vitro bone marrow cell migration to supernatants prepared from thymic epithelial cell cultures.

Thymic epithelial cell cultures were established from neonatal CBA/J mice by inhibition of fibroblast overgrowth. Epithelial cells were identified by their cobblestone appearance in culture, by the presence of keratin, and by ultrastructural analysis demonstrating desmosomes. Supernatants were prepared by incubation of confluent cultures of these cells in serum-free media. Using blind well chambers, these supernatants were chemoattractive to murine bone marrow cells, enriched for immature lymphoid cells, and decreased the myeloid to lymphoid ratio in the migrating cell population. Interleukin 2 had no effect as a modulator of this chemoattraction, nor did it possess chemoattractive properties. Supernatants prepared from epidermal growth factor stimulated thymic epithelial cells possessed significantly enhanced chemoattractive properties to bone marrow cells, and was found to be a thymic epithelial cell mitogen. Supernatants from serum-free cultures of thymocytes also induced a significant migration of bone marrow cells but were found to enrich for mature myeloid cells.

Animals↗
PubMed1985

Ultrastructural analysis of acute lymphoblastic cells: peanut lectin binding correlates with degree of differentiation of the leukemic cells.

Peanut agglutinin (PNA) has been shown to bind selectively to immature cells. Bone marrow cells from some children having acute lymphocytic leukemia (ALL) bind PNA while cells from other ALL patients do not bind, the significance being that the patients whose cells bind PNA have a poorer prognosis than those not binding PNA. In the present study, PNA was conjugated to horseradish peroxidase and the two cell types were compared. Cells binding PNA are immature compared with the non-PNA-binding cells.

B-Lymphocytes↗
PubMed1983

The liver hemopoietic environment: I. Developing hepatocytes and their role in fetal hemopoiesis.

Mouse fetal liver was studied ultrastructurally to identify and characterize the developing hepatic parenchyma or prehepatocyte which may be responsible for producing the liver hemopoietic environment. It was observed that as the liver develops, there is close association of endodermal and mesenchymal cells in the region of the septum transversum. Numerous intercellular adhesions were observed between endodermal cells and mesenchymal cells. Twenty-four after endodermal and mesenchymal cells first intermingle, the liver extravascular space consisted of spherical hemopoietic cells dispersed among a heterogenous population of dark and light cells. The reticulum of prehepatocytes formed a three-dimensional cellular network which structurally supported the hemopoietic cells residing in the liver. By 12 days of gestation, prehepatocytes were a homogenous population of dark, stellate cells joined together by numerous intercellular adhesions. Broad areas of intercellular association were noted between processes and prehepatocytes and hemopoietic cells; however, no intercellular junctions between these two disparate cell populations were observed at this or any stage in development. Characteristics reflecting a cell population capable of synthesis and secretion of proteinaceous substances, namely, dilated Golgi apparati, increased numbers of polyribosomes and profiles of rough endoplasmic reticulum (RER), two types of vacuoles and/or vesicles, and intercellular microvillus-lined spaces, were observed in the prehepatocytes between 12 and 17 days gestation. By day 17 of gestation, glycogen accumulation, biliary channel development, appearance of a subendothelial microvillus surface, nuclear shape and chromatin pattern, and arrangement of cytoplasmic organelles reflected the maturation of prehepatocytes into hepatocytes, the adult liver parenchyma.

Animals↗