STUDIES OF HEMATOPOIESIS IN MURINE SPLEENS: SIGNIFICANCE OF HEMATOPOIETIC COLONIES FORMED ON THE SURFACE OF SPLEENS

ABSTRACT Conies of hematopoietic tissue are formed in spleens of lethally irradiated mice by the injection of small numbers of hematopoietic cells. Some of these colonies appear as surface colonies, others can be identified only in serial sections of the spleen. The present studies have related the number and cellular composition of total hematopoietic colonies in the murine spleen to their visual recognition on the splenic surface. These studies demonstrate that only 50% of the total colonies in a spleen are recognized as surface colonies and that of those colonies on the surface, approximately 80% contain erythroid elements. At least four factors play important roles in the recognition of hematopoietic colonies as splenic surface colonies: (1) dose of repopulating cells or hematopoietic stem cells injected into the irradiated animal; (2) location of colonies within the spleen; (3) size of colonies; and (4) cellular content of the colonies. These studies demonstrate that surface colony formation reflects primarily erythropoiesis and not total hematopoiesis.