Thymic Lymphoid Cells Research Articles

Diurnal variations in thymic lymphoid cell decay. Studies of intact, adrenalectomized, and adrenaline-treated mice.

ABSTRACT Diurnal variations in thymic lymphoid cell decay have been demonstrated using nigrosin dye exclusion to indicate cell viability. A two maxima curve was obtained during the period of observation (24 hours). Adrenalectomy prevented the variations and decreased the mean decay during the experimental period as compared to intact animals. Injection of adrenaline into adrenalectomized mice resulted in a sharp increase in cell decay lasting half an hour.

Cellular immunity in vitro: elaboration of MIF by thymic and marrow lymphoid cells.

SummaryDifferent populations of guinea pig lymphoid cells demonstrate marked heterogeneity in their ability to elaborate an in vitro chemical mediator of cellular immunity, migration inhibition factor. A concentration of 2.5% lymph node cells obtained from animals demonstrating cutaneous reactivity to tuberculin protein effectively inhibited the migration of peritoneal exudate cells from normal donors. Thymic and bone marrow cells were relatively ineffective in this assay; no significant reduction in the area of migration was observed with cell concentrations as high as 20%. The presence of a second but numerically small population of immunologically active cells in both these central lymphoid organs was suggested by the inhibition of migration in assays using 25% cells from sensitized donors. Results of these in vitro assays were further confirmed by in vivo cell transfer experiments.

An autoradiographic study of the normal decay of lymphoid cells in the mouse thymus.

The cellular decay of thymus single cell suspensions was studied by combined nigrosin dye exclusion and 3H‐thymidine autoradiography. Nigrosin stained, Feulgen dyed thymic cell smears were examined at intervals after injection of 3H‐thymidine into NMRI mice aged 30–45 days. Lymphoid cells of DNA‐synthesizing as well as non‐DNA‐synthesizing populations were found to decay. The decaying cells descendig from DNA‐synthesizing cell populations took up nigrosin mainly in the premitotic phase of their generation cycle. Percentage of non‐viable DNA‐synthesizing cells (8 per cent) and the average nigrosin staining time of the DNA‐synthesizing cell population (2 hours) indicated a decay rate in this cell fraction of 4 per cent per hour. The proliferation rate of the DNA‐synthesizing cell population was found to be 10 per cent per hour. Calculations including these values gave an average DNA‐synthesizing cell cycle time of 7 hours. Throughout the experimental period of 14 days, the non‐DNA‐synthesizing cell population showed random cellular decay. However, a specific cellular decay took place 3–5 days after injection of 3H‐thymidine, indicating a life span of approximately 4 days for many small thymocytes. The total thymic grain counts were used as a measure of organ radioactivity. The first days after injection showed massive reutilization of 3H‐thymidine released by cell decay during this period. In conclusion, a combination of autoradiography and dye exclusion of unfixed thymic cell suspensions leads to useful kinetic parameters of thymic lymphoid cell decay in situ.

The effect of epithelial remnant and whole organ grafts of thymus on the recovery of thymectomized irradiated mice.

Work has been presented which suggests that thymus epithelial reticular cells are not effective in restoring the microscopic morphology of lymphoid tissues and their immunologic capacities. They function in recruiting precursors of thymus lymphocytes from the host animals to produce an organ which, after it becomes architecturally normal, can reconstitute the defective host. Intact thymus grafts in situ from 10-14 days, but not for shorter periods of time, have been shown to result in a return toward normal of these two parameters. Evidence is offered to show that few dividing cellular components in the lymphoid tissue originate from the thymus remnant grafts, and that a minor cellular component is contributed by the intact grafts. These data support the concept that the structural and functional development of the lymphatic tissue in thymectomized animals is dependent on thymus lymphoid cells and/or their products, and that the epithelial-reticular cells do not have a direct action in peripheral lymphoid reconstitution.

Thymic Lymphopoiesis and Cell Loss in Newborn Mice

Abstract Thymic lymphopoiesis in 2 day old Swiss albino mice (Hale-Stoner strain) was studied autoradiographically based on the variation of mitotic labeling indices and intensities after a single intraabdominal injection of 3H-thymidine. Best estimates for the duration of various phases of the generative cell cycle are as follows: G2 for the majority of cells: 86-94 minutes, shortest possible duration for a small fraction of cells: 35-48 minutes; mitosis: 27-44 minutes; DNA synthesis: 7 hours; generation time: 9¼ hours. G1 could not be determined directly by the methods used but probably is short. The present data do not indicate different generation times for proliferating thymic lymphoid cells of unequal size although the very largest elements must be excluded from this statement because of rare occurrence. The results obtained in this study together with data on changes of thymic weight and proliferative activity in the neonatal period indicate that during the third day after birth, a fraction corresponding to one third of all lymphoid cells present in the organ at the end of this period is lost. In view of the extremely low pyknotic index in the thymus at this age, the present data provide support in favor of an extensive emigration of lymphoid cells being the major cause of this cell loss.

Ultrastructure of epithelial cells in the cortex of guinea pig thymus.

Epithelial cells in the cortex of guinea pig thymus were identified by their stellate outline, large round nucleoli, and cytoplasm which contained membrane-bounded vesicles, bands of tonofibrils and desmosomes. Cells intermediate in appearance between these and undifferentiated medullary epithelial cells were seen in the deep cortex. Close contact and membrane fusion, and occasionally cytoplasmic continuity was demonstrated between the cortical epithelial cells and thymic lymphoid cells. It is suggested that the cortical epithelial cells may develop from undifferentiated medullary epithelial cells. The close contact between the cortical epithelial cells and thymic lymphoid cells may be a means of intercellular transfer of materials between these two cell types.

Lack of cytotoxicity by human thymocytes in vitro.

The phytohaemagglutinin (PHA)‐induced cytotoxic action of human blood lymphocytes against homologous cells in tissue culture was compared with the effect of human thymus cells. For quantitation of cell damage, use was made of the release of isotope from Chang cells (human liver) labelled with 51Cr‐chromate. Two young male patients with congenital heart defects served as donors. The Chang target cells were not damaged by thymic lymphoid cells added in high excess. In contrast, a small number of blood lymphocytes from the same donors tested simultaneously damaged the target cells. The thymic cells were poorly stimulated to DNA synthesis and into blastoid transformation by incubation with PHA for 3 days. PPD induced no response in the thymus cells. The blood lymphocytes reacted normally in all tests. Most thymocytes survived 24 hr inkubation while only about 25 per cent were alive after 72 hr. 70 per cent blood lymphocytes survived 72 hr incubation.It is assumed that a majority of the human thymic lymphocytes are immunologically non‐competent cells in regard to cellular immune reactivity. These cells lack cytotoxicity as well as ability to proliferate in the presence of PHA or antigens.

Growth characteristics of mouse thymus in the neonatal period.

ALTHOUGH renewed efforts have been made towards an understanding of the function(s) of the thymus, the exact mechanisms involved remain unclear. It is not known whether the thymus serves primarily as a source of immunologically competent cells, or whether it produces a substance or substances and/or contact factors which may control proliferation and immunological maturation of peripheral lymphoid cells. Combinations of such suggestions have been made repeatedly1,2. A meaningful evaluation of the existence and magnitude of thymic cell migration during the perinatal period of life requires more information on at least the following thymic growth characteristics as a function of age before and after birth: (a) the rate of thymic growth; (b) proliferative activity of thyrnic lymphoid cells; (c) the generation time of thymic lymphoid cells; and (d) a quantitative estimate of intrathymic cell death. We report here an investigation of growth and proliferative activity of the thymus of mice ranging in age from 3 days before to 6 days after birth.

STEM CELL REPLACEMENT IN NORMAL THYMUS GRAFTS.

SummaryAfter initial death of most donor lymphocytes in AKR thymus grafts in normal (AKRXT6)F1 mice, there was a temporary period during which active proliferation of surviving donor lymphocytes occurred. This population of dividing lymphocytes in the thymus grafts was subsequently completely replaced by host-type cells. The results suggest that thymic lymphoid stem cells are continuously replaced by cells entering the thymus from the circulation.

THE PATTERN OF LYMPHOPOIESIS IN THE MOUSE THYMUS AFTER CORTISONE ADMINISTRATION OR ADRENALECTOMY.

SUMMARYThe subcutaneous administration of cortisone acetate to C3H and AKR mice was followed by thymic atrophy, decreased mitotic activity in thymic lymphoid cells and a selective destruction of thyimic small lymphocytes. During the succeeding regenerative phase, mitotic activity was higher than in control thymuses and was concentrated around the PAS‐positive reticulum cells of the cortex. Following adrenalectomy, thymic lymphocyte mitotic indices rose and the weight of the thymus increased. The increased mitotic activity was again concentrated around the cortical PAS‐positive reticulum cells.These findings are further evidence indicating that PAS‐positive reticulum cells are involved in the regulation of lymphocyte mitotic activity in the mouse thymus cortex.

Quantitative cytological studies on thymic lymphoid cells in normal, preleukaemic and leukaemic mice.

Quantitative Cytological Studies on Thymic Lymphoid Cells in Normal, Preleukaemic and Leukaemic Mice