The rates of recovery of colony-forming units (CFU) and of hematopoietic stroma following x-irradiation were compared. Hematopoietic stromal function of femurs and spleens was assessed by assaying the number of CFU in those sites 6 wk after implanting them subcutaneously into isogeneic hosts. Whereas the number of CFU returned to preirradiation levels in 6 wk, the hematopoietic stroma did not recover significantly in 9 wk. The reasons for regeneration of CFU in a defective stroma were next investigated. Two contributing factors were identified: (1) Stromal damage following 950 rads is such as to retard the rate of regeneration of CFU without significantly limiting the eventual number of CFU in the site, and (2) Radiated mice contain factor(s), possibly humoral, which accelerate the rate of regeneration of CFU.

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© 1974 by American Society of Hematology, Inc.
1974
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