ABSTRACT
Growth kinetics of the donor-type thymus cell population after transplantation of bone marrow into irradiated syngeneic recipient mice is biphasic. During the first rapid phase of regeneration, lasting until day 19 after transplantation, the rate of development of the donor cells is independent of the number of bone marrow cells inoculated. The second slow phase is observed only when low numbers of bone marrow cells (2.5 x 10(4)) are transplanted. The decrease in the rate of development is attributed to an efflux of donor cells from the thymus because, at the same time, the first immunologically competent cells are found in spleen. After bone marrow transplantation the regeneration of thymocyte progenitor cells in the marrow is delayed when compared to regeneration of CFUs. Therefore, regenerating marrow has a greatly reduced capacity to restore the thymus cell population. One week after transplantation of 3 x 10(6) cells, 1% of normal capacity of bone marrow is found. It is concluded that the regenerating thymus cells population after bone marrow transplantation is composed of the direct progeny of precursor cells in the inoculum.
Subject(s)
Bone Marrow Cells , T-Lymphocytes/cytology , Thymus Gland/cytology , Animals , Bone Marrow Transplantation , Cell Division , Cell Survival/radiation effects , Hematopoietic Stem Cells/cytology , Mice , Radiation Chimera , Regeneration , Spleen/cytology , T-Lymphocytes/radiation effectsABSTRACT
Three mouse thymocyte subpopulations with differing sensitivity to dexamethasone were characterized by size and density. Distribution patterns were determined for thymocytes during normal development and during regeneration after treatment with dexamethasone. From these, the subpopulation proportions were calculated and cell population kinetics were evaluated. Medium-sized low density cells (type III) were least sensitive to dexamethasone and showed a relatively slow regeneration rate. The small cells of intermediate density, "early cortical" cells (type II), exhibited the most rapid regeneration rate, while the growth rate of the small cells of high density (type I) was intermediate. Cells of intermediate and high density were relatively sensitive to dexamethasone. The ratio of the phytohemagglutinin to concanavalin A (Con A) response increased after dexamethasone treatment with the increase in the proportion of type III cells. Con A responses were attributed to type II and type III cells. A tentative multipathway model for intra-thymic T cell development is presented. Large cells, not confined to a certain trajectory in the density gradient, may represent a pool of proliferating cells of the other three types.
Subject(s)
Dexamethasone/pharmacology , Models, Biological , Regeneration , T-Lymphocytes/cytology , Thymus Gland/physiology , Animals , Cell Count , Cell Separation , Concanavalin A/pharmacology , Lymphocyte Activation , Male , Mice , Mice, Inbred C57BL , Mice, Inbred CBA , Phytohemagglutinins/pharmacologyABSTRACT
Thymosin and THF were prepared from total normal calf thymus (TT), from calf thymus depleted of thymocytes by whole-body irradiation (TE), and from calf thymus lymphocytes (TL). The activities of these products were compared in four different in vitro assays that monitored for various T-cell functions. The results suggest that the preparations obtained from thymus epithelium are more active in inducing T helper cell function in nude/nude mouse spleen cells than substances isolated from thymus lymphocytes. The latter seem to act on a more advanced step in the T cell line differentiation.
