Hemopoietic regulatory factors in human hemopoietic failures

There are two distinct hemopoietic activities in human serum that do not have the properties of the known hemopoietic lymphokines. These two activities appear not to be produced by immune competent cells. "Direct" stimulatory activity acts in primary target cultures of normal marrow. There does not appear to be a feedback mechanism between bone marrow failure and "direct" activity; it appears to reflect ongoing disease. Indirect "releaser" activity stimulates peripheral blood cells to produce hemopoietic growth factors. It is invariably elevated when release of hemopoietic growth factors is poor, indicating that a feedback mechanism exists. The peripheral blood cells of young patients, particularly young girls, respond poorly to autologous "releaser" stimulation. Results of treatment with ALG in this group are poor. However, all patients with aplastic anemia appear capable of producing adequate amounts "releaser" factor.