M-CSF selectively stimulates the proliferation and differentiation of monocytes/macrophages. It acts on both progenitor cells and mature cells of the monocyte/ macrophage lineage. In addition to its hematopoietic effects, M-CSF can stimulate monocytes/macrophages to produce a variety of cytokines, including prostaglandins,
IL-3, tumor necrosis factor, and G-CSF.69 These secre-tory substances are capable of having effects on other accessory cells. M-CSF also stimulates the cytostatic and cytotoxic activities of macrophages against tumor cells. Many cell types in the body can produce M-CSF, includ-ing fibroblasts and monocytes/macrophages.