Hemopoietic Spleen Colonies in the Rat

Hemopoietic spleen colonies were obtained in Fischer-334 rats by injecting isologous bone-marrow cells into heavily irradiated recipients. Total-body irradiation doses as high as 1400 rads did not inhibit the development of endogenous colonies. These colonies, however, were very small, seldom exceeding 1 mm in diameter. In contrast, exogenous spleen colonies, observed 12 days after bone-marrow infusion, had a mean diameter of 1.3 mm and could be easily counted when colonies measuring less than 1 mm in diameter were not scored. The number of colony-forming units in rat bone marrow was between 4 and 5 per 105cells. Most of the endogenous and exogenous spleen colonies showed erythroid differentiation, but myeloid elements and a few megakaryocytes could also be observed.