CSF2, also named as GM-CSF, is an important hematopoietic growth factor and immune modulator, which is produced by a variety of cell types including T cells, macrophages, endothelial cells and fibroblasts upon receiving immune stimuli. It was originally recognized as a stimulator for the proliferation of granulocytes and macrophages from bone marrow precursor cells. It has also been shown to promote the survival and activation of mature myeloid cells and therefore contributes to the maintenance of innate immune homeostasis. Recent studies suggest that GM-CSF also has proinflammatory functions and plays critical roles in the development of autoimmune and inflammatory diseases, particularly in Th17 driven diseases. GM-CSF also plays a role in embryonic development by functioning as an embryokine produced by reproductive tract.