Adherent cell dependent colony-stimulating activity in human serum: A granulopoietic regulator?

Bacterial infections and trauma which increase production of granulocytes and monocytes by the bone marrow, may do so through factors in serum capable of stimulating growth of granulocyte-macrophage cells in vitro. Human serum possesses two types of colony stimulating activity (CSA), one which stimulates granulopoietic progenitor cells directly, and another which results from the interaction of serum and bone marrow adherent cells (monocyte-macrophages) or peripheral blood leucocytes: adherent cell dependent CSA. These activities are due to different factors which may be separated by gel filtration. Sera of 7 patients undergoing hystectomy who developed post-operative infection showed post-operative elevation of the adherent cell dependent activity in all cases but no change in direct acting CSA. These results suggest that the direct acting CSA in human serum does not represent the principal humoral 'message' to the bone marrow from sites of trauma and infection in the tissues and that granulopoiesis may be controlled indirectly by the action of a different humoral factor which increases production of CSA by marrow monocyte-macrophages. Preliminary experiments suggest that lymphocytes stimulated by bacterial products be one source of this factor.