Regeneration of Thymus, Spleen and Bone Marrow in X-Irradiated AKR Mice

Regeneration of thymus, spleen and bone marrow of AKR/T1 Ald mice after whole body irradiation with 605 rad (650R) with or without treatment with 107 syngeneic bone marrow cells from AKR mice was followed. In the non-transplanted irradiated animals, cell division recommences first in the thymus (on day 6) following the biphasic pattern observed by others. Cell division in spleen (day 8) and bone marrow (day 8-12) resume later. After bone marrow treatment, all these organs begin to regenerate at about day 6 and also display a biphasic pattern of cell divisions. The proportion of donor cells remains high in bone marrow and spleen, but drops temporarily in thymus, perhaps as the result of division of damaged thymus cells. The data interpreted in a semiquantitative way suggest that the assumption that the thymus is seeded from bone marrow, is not needed to explain a biphasic pattern of thymus regeneration, rather it appears likely that cells present in thymus or deposited there immediately after injection of bone marrow cells can engender a full regeneration of the thymus.