Hemopoiesis in spleen and bone marrow cultures

Long-term cultures established from spleen cells were compared to those established from bone marrow cells for their ability to maintain hemopoiesis as measured by the presence of hemopoietic progenitor cells (in vitro CFU) and multipotent stem cells (CFU-S). The frequency of both in vitro CFU and CFU-S increased dramatically during the first 2 weeks in the spleen cultures. Following this early peak of activity, the number of progenitors and stem cells declined to undetectable levels by week 6 of culture. During this short phase of hemopoiesis, large amounts of GM-CSF could be detected in the supernatant of the spleen cultures. In contrast, bone marrow cultures did not share this early peak of hemopoiesis; however, they maintained activity for much longer periods of time than did the spleen cultures. When spleen stem cells were seeded onto functional bone marrow adherent cells, spleen-derived in vitro CFU were maintained well beyond week 6 of culture. Spleen cultures established from athymic nu/nu mice showed a greatly reduced ability to support hemopoiesis while those from S1/S1d mice maintained GM-CFU as well as cultures from normal mice.