Impaired thymic regeneration in lethally irradiated mice given bone marrow from aged donors

Mice were given a lethal dose of whole-body gamma radiation and injected with 10(5) or 10(6) marrow cells from 10- to 143-week-old syngeneic donors. Nine days later, colony-forming units (CFU) were counted in the spleens of mice given 10(5) cells, and 21 days after irradiation, spleen and thymus weights were determined in the recipients of 10(6) cells. It was found that there were no significant changes with age in marrow CFU or in the ability of marrow cells to repopulate host spleens. In contrast, thymic regeneration was significantly impaired when the recipients received marrow cells from donors 117 weeks of age or older. These observations suggest that with aging there is a decrease in marrow T-cell progenitors and/or a decline in their proliferative capacity.