Colony-stimulating factors (CSFs), also called haematopoietic growth factors, are secreted glycoproteins which regulate bone marrow production of circulating red and white cells, and platelets. Colony-stimulating factors bind to receptor proteins on the surfaces of hemopoietic stem cells and thereby activate intracellular signaling pathways which can cause the cells to proliferate and differentiate into a specific kind of blood cell. Colony-stimulating factors include: macrophage colony-stimulating factor (M-CSF), Granulocyte macrophage colony-stimulating factor (GM-CSF) and Granulocyte colony-stimulating factor (G-CSF). The M-CSF is secreted to stimulate hemopoietic stem cells to differentiate into macrophages or other related cell types. M-CSF appears to play a major role in promoting and maintaining reservoirs of human immunodeficiency virus type 1 (HIV-1) in infected individuals. GM-CSF is secreted by macrophages, T cells, mast cells, endothelial cells and fibroblasts. GM-CSF stimulates stem cells to produce granulocytes (neutrophils, eosinophils, and basophils) and monocytes. G-CSF is a glycoprotein, growth factor or cytokine produced by a number of different tissues to stimulate the bone marrow to produce granulocytes and stem cells. G-CSF then stimulates the bone marrow to release the produced cells into the blood.