Autoradiographic Analysis of Lymphopoiesis and Lymphocyte Migration in Mice Bearing Multiple Thymus Grafts

Abstract

Lymphopoiesis was studied in 3-month-old normal C57Bl mice and in 3-month-old C57Bl mice carrying from 12 to 48 C57Bl thymus grafts using tritiated thymidine labeling. Thymus graft lymphopoiesis was found to be identical with that of normal thymus tissue and the presence of thymus grafts was found to have no influence on host thymus lymphopoiesis. No evidence was found that the massive amounts of thymus graft tissue in the mice affected any parameter of host lymph node lymphopoiesis nor was any evidence detected for the migration of thymic lymphocytes from these massive deposits of thymus graft tissue either to host lymph nodes and blood or to other organs in the host animal. It is concluded that the majority of small lymphocytes produced in the thymus and thymus graft tissue do not migrate from these tissues but die locally at the end of their intrathymic life span of 3 to 4 days.

Identification of human and rodent thymic epithelium using tetanus toxin and monoclonal antibody A2B5.

“…Lymphocytes in various stages of maturation are found throughout the thymic cortex and medulla; however, only a minority of thymic lymphocytes mature completely and migrate to peripheral lymphoid organs (2,3). Thymic epithelial cells are in intimate contact with thymic lymphocytes and as well, produce thymic hormones such as thymopoietin and thymosin a-1 (4-6).…”

Quantifying Thymic Export: Combining Models of Naive T Cell Proliferation and TCR Excision Circle Dynamics Gives an Explicit Measure of Thymic Output

“…Previous studies of thymic function have assumed that the rate of export of cells to the periphery is proportional to the volume of the TES (5, 6), but it is not obvious that there is a direct correlation between these two variables. The TES is a site of extensive expansion and selection in which less than 5% of cells survive the development process and any minor changes in the rate of production or loss of cells may have a large impact on the rate of export (7)(8)(9). In fact, although the cellular density of thymic tissue declines with age, it does not directly parallel the changes in the TES (10).…”

Incorporation of Sulfate by the Mouse Thymus: Its Relation to Secretion by Medullary Epithelial Cells and to Thymic Lymphopoiesis

“…Fewer than 10% of cells in the inner cortex incorporated thymidine-~H, and these showed no predilection to congregate near macrophages as described by Ishidate and Metcalf (15). Within 48 hr after a single injection, the entire cortex was filled with labeled cells, many of which were small lymphocytes, as reported by K6bberling (17), whereas more than 3 days is required for this turnover in adult mice (22). Counts of labeled mitotic figures during the first 6 hr after injection, analyzed by the method of Quastler and Sherman (28), indicated a combined G2 and mitotic period of less than 2 hr, 4.5-5 hr required for DNA synthesis and--with the labeling index of 70% in the subcapsular region taken to represent a homogeneous population of proliferating cells uncontaminated by small lymphocytes--a cellular reproductive cycle lasting approximately 7 hr.…”

“…Therefore it appears unlikely that lymphocytes die within the thymus at this age in sufficient numbers to account for much of the cellular turnover--as has been proposed for thymic lymphocytes in adult mice (22). Thus emigration remains to account for most of the output of thymic lymphocytes during the 2nd wk after birth, and this fortuitous circumstance provides an opportunity to assess its magnitude.…”