Demonstration of Spleen Colonies on Grafted Spleens in the Radiation Chimera

We have demonstrated the post‐irradiation development of countable endogenous spleen colonies in spleens transplanted intraperitoneally 6 weeks prior to X‐irradiation of the host. We have further demonstrated countable exogenous spleen colonies on spleen grafts transplanted prior to the irradiation of the host and the injection of bone‐marrow cells. Although autografted spleens in irradiated recipients did not attain their presplenectomy mass, the number of colony forming units (CFU)/10⁵ injected cells assayed after irradiation and bone‐marrow cell injection was about the same as in sham‐splenectomized mice. Isografted spleens in sham‐splenectomized mice were much smaller than the host or autografted spleens and the number of CFU/10⁵ injected cells assayed per isograft was only 25–33 % of that observed in host mice.