Elevation of lymphocyte and hematopoietic stem cell numbers in mice transgenic for human granulocyte CSF

Transgenic mice expressing human granulocyte colony stimulating factor (hG-CSF) were bred to establish an experimental model for studying the biologic function of hG-CSF. The mice produced approximately 1000 pg/ml of hG-CSF in sera and expressed hG-CSF mRNA in all of the tissues examined. Granulocytosis and elevation of hematopoietic precursor number were observed in hematopoietic tissues as expected, but lymphocytosis with 5-fold increase in peripheral blood and 2-fold increase in spleen was also evident. Hematopoietic stem cells capable of reconstituting lethally irradiated recipient mice were abundant in the circulation of these transgenic mice. No disadvantageous tissue damage was observed when various organs were analyzed. As shown in this study, G-CSF has a stimulating effect on lymphopoiesis when it is expressed in a certain condition. The lymphocytosis, as well as the high level of hematopoietic stem cell mobilization into circulation, indicates a wider range of potential G-CSF activity than expected. The mice transgenic for hG-CSF described herein will contribute greatly to the understanding of the regulatory mechanism in hematopoiesis.