Effects of radiation on survival and recovery of T lymphocyte subsets in C3H/HeN mice.

The aims of this study were to determine the radiosensitivities of murine thymic and splenic CD4+ and CD8+ lymphocytes and to evaluate the regeneration of these cells in a model of radiation-induced hematopoietic and immune suppression. CD4+ and CD8+ cells were quantitated using two-color flow-cytometric analysis. Cells obtained from C3H/HeN mice 24 hours after exposure to 0.25-8.0 Gy (0.4 Gy/min) 60Co were used to determine D0 values. Thymic CD4+ cells contained a radiosensitive subpopulation with a D0 of 0.97 +/- 0.05 Gy and a radioresistant subpopulation that survived exposures up to 8.0 Gy. CD8+ cells also contained a radiosensitive subpopulation with a D0 of 1.24 +/- 0.05 Gy and a radioresistant subpopulation with a D0 of 3.93 +/- 2.01 Gy. Double-positive thymic CD4+/CD8+ cells were uniformly radiosensitive, with a D0 of 1.03 +/- 0.28 Gy. Multiple T lymphocyte subpopulations based on radiosensitivity and CD4/CD8 antigen expression were also observed in the spleen. When mice were exposed to a sublethal 6.5-Gy radiation dose and recovery of T lymphocyte subsets was monitored, the relative radioresistance of CD4+ cells resulted in a selective enrichment of these cells among the surviving thymocytes and splenic lymphocytes. This relative enrichment of CD4+ cells became even more prominent 7 days after irradiation, when atrophy of the organs was greatest. Similar, although less dramatic, effects were observed for CD8+ cells. These studies demonstrate that (1) multiple T lymphocyte subpopulations can be identified based on radiosensitivity and CD4/CD8 antigen expression; (2) both CD4+ and CD8+ cells contain radioresistant subpopulations, with the CD4+ subpopulation being more resistant than the CD8+ subpopulation; and (3) although the number of radioresistant CD4+ cells is quite small, they persist in increased proportions during the periods preceding and corresponding to postirradiation hematopoietic recovery.

The rhesus monkey: a primate model for hemopoietic stem cell studies.

Two heterogeneous cell populations (CP 1-7 and CP 8-10) were separated from rhesus monkey bone marrow using counterflow centrifugation-elutriation (CCE). These two cell populations were distinct with respect to morphological composition, expression of cell surface antigens, hemopoietic progenitor cell activity, and concentration of hemopoietic stem cells (HSC). The hemopoietic progenitor cell activity and HSC were concentrated in CP 8-10. In autologous transplantation studies, CP 8-10 reconstituted the lymphohemopoietic system of lethally irradiated monkeys in a manner similar to that of monkeys transplanted with unfractionated bone marrow cells. CP 1-7 was lymphocyte rich and depleted of progenitor cell activity. Transplantation of CP 1-7 led to eventual lymphohemopoietic reconstitution of irradiated monkeys; however, complete engraftment was delayed by as much as 14 days compared to either the transplantation of CP 8-10 or to unfractionated bone marrow. Thus, a presence of the HSC in the lymphocyte-rich progenitor-cell-depleted population can be detected in the rhesus model.

Studies of the action of leucogenenol on the myeloid and lymphoid tissues of the sublethally irradiated mouse.

Studies of the action of leucogenenol on the peripheral leukocytes, the myeloid cells found in bone marrow, and the lymphoid cells found in the spleen of sublethally irradiated mice strongly suggest that leucogenenol stimulates the maturation and/or cellular division of cells of both the myeloid and lymphoid series. Accordingly, as indicated by the increase in the number of peripheral leukocytes, as well as the increase in the number of myeloid and lymphoid cells found in the bone marrow and spleen, mice treated with leucogenenol appear to recover more rapidly than untreated controls.