Observations on the settling and recoverability of transplanted hemopoietic colony-forming units in the mouse spleen.

A series of experiments was designed determining the seeding and ultimate to study the effect of spleen size on retention of CFU in the spleen of a the seeding and retention of spleen recipient mouse is the size of the colony-forming units (CFU) after inspleen. It is concluded that the most jection into irradiated mice. The cellureasonable value of the fraction’ of larity of the spleens of recipient mice injected CFU that produces spleen was varied using a variety of expericolonies should be determined from mental procedures, and the resulting the number of CFU recoverable from spleen colony production was anathe fully shrunken spleen. In these lyzed with respect to CFU seeding. mice, the fraction was 9.5#{176}/o. It was found that the major factor T HE FRACTION (f) of spleen colony-forming units (CFU) injected into a lethally irradiated mouse that produces hemopoietic colonies in the spleen has usually been determined by the secondary transplantation method of Siminovitch et al.’ Several more recent reports have shown that the number of CFU that can be recovered from the spleen of an irradiated animal following an injection of hemopoietic cells depends on the interval of time between the injection and the assay.2’4 One of these3 demonstrated that the number of CFU recoverable is directly related to the number of cells in the spleen at the time of assay. The explanation suggested for this relationship was that after injection CFU enter the spleen, but as the spleen collapses due to the radiation, the CFU are expelled or destroyed. It was concluded that the calculation of the f number should be based on the number of CFU recoverable from the fully shrunken spleen, rather than on the maximum numbers recoverable, i.e., about 2 hr after injection. It had earlier been suggested5 that the initial decrease (after about 2 hr) in the number of CFU per spleen was due to an inability to extract and disperse all the CFU from the spleen. This same suggestion has been enforced more recently by Till and McCulloch,6 who have reported experiments in which colony production in W/W” mice receiving different doses of radiation (including no radiation) remained the same. In an attempt to clarify the fate of CFU entering the spleen after intravenous injection, a variety of experiments have been carried out and are reported in this paper.