Jack L. Haar

A light and electron microscopic study of myelopoietic cells in the perihepatic subcapsular region of the liver in the adult aquatic newt, Notophthalmus viridescens.

SummaryThe liver of the newt, Notophthalmus viridescens, consists of several incompletely separated lobes of parenchymal tissue each of which is covered by a perihepatic subcapsular region (PSR) of myeloid tissue. This tissue contains neutrophils and eosinophils in various stages of differentiation. As neutrophils develop from myeloblasts to late neutrophilic myelocytes, two types of granules appear. The primary granules (type of granules formed first) are more electron dense and smaller than the secondary granules (type of granules formed later). The primary granules first appear at the stage designated early neutrophilic myelocyte, and the secondary granules appear at the stage of the maturing neutrophilic myelocyte. The eosinophils present are characterized by much larger granules than those observed in neutrophils. Cells in the PSR which superficially resemble small lymphocytes are primitive stem cells that give rise to neutrophils and eosinophils. The liver PSR is invested by a visceral peritoneum of simple squamous mesothelial cells some of which are ciliated.

Epithelium and Associated Lymphocytes of Developing Human Fetal Appendix

The epithelium and lamina propria of the human fetal appendix between 7.5 and 18 weeks of gestation was examined with electron microscopy. At 7.5 weeks the epithelium was composed of stratified columnar cells; scattered mesenchymal cells appeared in the lamina propria. By 13.5 weeks of gestation the epithelium was composed of simple columnar cells with a microvillous surface, goblet cells containing numerous mucinogen granules and argentaffin cells with elongated electron-dense granules. Also at 13.5 weeks of gestation some free lymphocytes were observed within the lamina propria as well as an occasional migrating lymphocyte within the epithelium between the columnar cells. At 18 weeks of gestation the simple columnar epithelial cells were tightly packed, the goblet cells were secretory and lymphocytes again appeared singly within the epithelium and lamina propria. No evidence of groups of lymphocytes or developing primary follicles within the lamina propria was observed in this study.

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.

Separation of non-proliferating from proliferating thymic lymphocytes based on light scatter analysis.

SummaryTwo populations of thymic lymphocytes from eight-week-old mice were separated based on the light scatter intensity they generated while passing through a flow cell analyser. The two populations were subsequently studied morphologically and analysed for the relative amount of DNA present in each cell. Cells having a low light scatter intensity had a high nuclear: cytoplasmic ratio, a heterochromatic nucleus, and a proliferative index (S + G2 + M) of only 23%. Cells with a high light scatter intensity had a low nuclear: cytoplasmic ratio, dispersed chromatin, frequently a uropod with budding microvilli and a proliferative index of 71%. The low light scatter cells resemble small cortical thymocytes or lymphocytes from the thoracic duct described by others. The highest light scatter cells resemble medium lymphocytes shown by others to be proliferative.

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.

Chemoattraction enrichment of Thymus-homing bone marrow cells

Abstract. 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.

Effect of Sound Stress on the Migration of Prethymic Stem Cells

The thymus has been established as an essential organ for the normal development of immune function in young mammals. Recent evidence suggests that the thymus also plays an active role in the maintenance of the immune system through life.’ To perform its role as a primary lymphoid organ, the thymus must attract extrinsic stem cells or prothymocytes. Precursor cells migrate from the bone marrow during the neonatal period throughout adulthood to carry out this function?’ A blind well assay system was developed to examine the “bone marrow-thymus axis” in vitro. It was used to demonstrate that a subset of murine bone marrow cells is capable of migrating through a Nuclepore membrane toward a supernatant derived from cultured newborn mouse thymuses. The migrated cells are enriched for a “null” cell population, that is, Thy 1 and surface immunoglobulin negative cells.4 When injected into an irradiated host, these cells are capable of repopulating the thymus in a significantly higher percentage than do nonmigration-enriched bone marrow cells. This significant in vivo thymus homing suggests that selective migration to thymus supernatant enriches for a prethymic cell population? In the present study the effect of sound stress on the bone marrow-thymus axis was examined using the in vitro migration assay. Histologic sections and weights of thymus, spleen, and adrenal glands were also examined for alterations resulting from the sound stress. Young adult female CBA/J mice were exposed to a 2-second, high intensity sound ( 110 db at 2900 Hz, variable interval of 1 minute) 2 hours daily for 5 days. Twentyfour hours later, the femurs and tibias were dissected from the animals; bone marrow cells were separated and suspended in media. In vitro migration assays were carried out using blind well chambers. Thymus supernatant from 3-day-old mice was used as the attractant in the bottom wells separated from the bone marrow cells in the top wells by Nuclepore membranes having 5-ym diameter pores. After 90 minutes of incubation, cells migrating to the bottom chambers were collected, counted, and compared to the number of migrated cells from the bone marrow of nonstressed mice. Migrations to Iscove’s media alone were carried out simultaneously to calculate the nonspecific background migration. The in vitro assay showed a significant decrease in the percentage of migration of bone marrow cells from experimental sound-stressed animals when compared with control nonstressed age-matched mice (TABLE 1). When thymus, spleen, and adrenal glands of the experimental animals were compared with those of the control animals, no significant changes in organ weights (TABLE 2) and no apparent histologic changes