Relative Effect of Thymocytes from Irradiated Donors on Hemopoiesis in P → F 1 Chimeras 1

Summary

Thymocytes exposed in vivo to 200 R of X-rays 72 hr prior to transplantation enhanced marrow growth almost twice that seen in mice similarly treated with non-irradiated thymocytes. Growth of marrow was evaluated by the spleen colony-forming technique. These results confirm and extend previous data from this laboratory for which a cell-to-cell interaction has been postulated as a basis for augmentation of bone marrow growth by thymocytes. The present data show a minimal effective ratio (thymocyte: marrow cell) of 8:1 for irradiated thymocytes compared to a value of 16:1 for unirradiated thymocytes.

On the basis of our results and the known differential radiosensitivity of thymocytes, we suggest that the less radiosensitive blastic lymphoid cells of the thymus are responsible for augmentation of poor growth of parental bone marrow transplanted into lethally X-irradiated F₁ mice.