Control of granulopoiesis in man. III. Inhibition of colony formation by dense leukocytes

Cellular feeder layers, prepared from normal blood leukocytes, usually stimulate human marrow to form colonies. A significant increase in the stimulating activity of unseparated leukocyte feeder layers is brought about following the removal of dense leukocytes in a manner which avoids enrichment of any remaining cell type. Restoration of dense leukocytes to a dense leukocyte depleted leukocyte feeder layer results in the reduction of stimulating activity to that of an unseparated leukocyte feeder; however, addition of dense leukocytes to unseparated leukocyte feeder layers has no effect on the stimulatory activity, over the range of concentrations used in this study.