Studies on control of granulopoiesis in man. I. Relationship of leukocyte colony-stimulating activity in vitro to neutrophil count in vivo.

We examined the relationship of leukocyte colony-stimulating activity (CSA) in vitro to neutrophil count in vivo. Using a standard two-layer system, cultures of 10(6) leukocytes were assayed for their ability to stimulate colony formation by human bone marrow colony-forming cells. The total leukocyte CSA per ml (TLCSA) of blood varied directly with the blood neutrophil count in a group of patients with a wide range in blood neutrophil count, and in two patients recovering from neutropenia in whom serial observations were made. In the latter two patients the rise in TLCSA did not antedate the rise in blood neutrophil count, suggesting that blood leukocyte colony-stimulating factor (CSF) per se probably has little biologic significance. However, release into the circulation of cells which generate CSF could be an important way of controlling the amount of CSF acting within the marrow. In one patient the CSA of dialyzed serum increased after the rise in TLCSA, while undialyzed serum contained no CSA.