Clonal repopulation in reticular tissues of x‐irradiated mice: Effect of dose and of limb‐shielding

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Abstract
Chromosome studies in irradiated mice have indicated that following high sublethal whole‐body exposure regeneration of the reticular tissues occurs in a clonal fashion. With increasing doses, from 100 to 700 rads, these organs appeared to be repopulated from fewer and fewer surviving stem cells. In a few instances at the highest dose, the progeny of the same cell apparently differentiated to marrow cells at one site and to lymphoid cells in others, suggestive evidence of a totipotent hematopoietic stem cell in the adult mouse.Chromosome studies in mice receiving 900 rads with one limb shielded have indicated repopulation of the thymus and other reticular tissues by undamaged cells from the shielded marrow. Such marrow‐derived cells, perhaps by restoring immunological competence or by non‐immunological contact inhibition, could account for the known effect or limb shielding in reducing the incidence of radiation‐induced thymic lymphomas.