Haemopoietic stem cell stimulation in short-term tissue culture

Abstract

Murine serum with high levels of agar colony stimulating factor (CSF) was examined for its ability to maintain myeloid stem cell and pluripotential stem cell numbers in a short term tissue culture of normal murine bone marrow. The serum was obtained from whole body irradiated (WBI) mice and had been previously shown to have high levels of CSF. The serum was mixed with normal bone marrow suspensions, whilst mixtures of normal serum and normal bone marrow suspensions served as controls. The content of pluripotential and myeloid stem cell compartments in these short term tissue cultures were assayed at regular intervals by bone marrow transplantation or the agar colony system respectively. In the presence of WBI serum myeloid stem cell numbers were maintained for periods up to 72 hr., whilst their numbers decreased rapidly in the presence of normal serum. Similarly, but to a lesser extent, pluripotential stem cell numbers were maintained in the presence of WBI serum. These data suggest that CSF appearing in vivo has a selective stimulatory effect on committed myeloid stem cell compartments in vitro . It is postulated that WBI serum may contain a single substance which influences both proliferation and differentiation of committed myeloid stem cells, and thus may be a specific regulator of granulopoiesis at this level. The slower decline of pluripotential stem cells in the presence of a maintained myeloid stem cell compartment may be due to a lower demand for pluripotential stem cells rather than direct stimulation at this level. Such findings are in accord with the notion that CSF may be involved in the humoral regulation of granulopoiesis.