Granulocyte-macrophage colony stimulating factor (GM-CSF) was initially identified by its ability to stimulate the formation of granulocyte and macrophage colonies from hematopoietic progenitor cells in semi-solid media. In vivoand in vitro studies have now demonstrated that GM-CSF is a pleiotropic cytokine that induces myeloid precursor cells to proliferate and differentiate into neutrophils, monocyte/macrophages and eosinophils.

GM-CSF has also been shown to stimulate the proliferation and differentiation of erythroid and megakaryocyte progenitor cells. In addition, GM-CSF is a survival factor for and activates the effector functions of mature neutrophils, monocytes/macrophages and eosinophils.