Kinetics of early and late spleen colony development.

The kinetics of spleen colony development were studied with special emphasis upon the self-replicative capacity of CFU-S, which are responsible for the early- or late-appearing spleen colonies, and upon CFU-S migration in the days following transplantation. It was found that, while the spleen colonies had a much lower daughter CFU-S content at eight days than at 11 or 12 days, many of the 8-day colonies remained in the spleen to become 12-day colonies which had many daughter CFU-S. In addition, it was found that large numbers of CFU-S were present in the splenic space between the colonies. Evidence was developed that these "intercolonial space" CFU-S were the founders of many of the late-appearing spleen colonies and that many or all of them were transported from the bone marrow to the spleen via the blood at varying times after the transplantation. Approximately one-half of the day-12 colony founders were found to arrive in the spleen after the third posttransplantation day.