Ultrastructural analysis of erythroid colonies in diffusion chambers in irradiated rats. Effect of cytosine arabinoside administration on donor rats.

Ultrastructural observations of erythroid colonies in diffusion chambers implanted in lethally irradiated rats are reported. The donor cells were obtained from rats treated with cytosine arabinoside (250 mg/kg body weight) 6 h prior to seeding. The marrow of donor rats contained a high proportion of stem cells committed to the erythroid line. 9 days after implantation, vast numbers of erythroid colonies developed in the diffusion chambers. The erythroid cells were observed arranged around a central macrophage resembling erythroid islands in bone marrow. Erythroid colonies most probably differentiated from committed stem cells in the inoculum. It is postulated that development of erythroid colonies in diffusion chambers is conditioned by, among other factors, the presence of a special type of macrophages. These macrophages have the same function as those of central reticular cells (CRC) in bone marrow erythroid islands.