The granulocyte macrophage colony-stimulating factor (GM-CSF) is a homodimeric cytokine composed of 144 amino acid with molecular weight of 22kDa. GM-CSF functions as a white blood cell growth factor which stimulates stem cells to produce granulocytes and monocytes. It is used clinically to treat neutropenia in cancer patients undergoing chemotherapy, in AIDS patients during therapy, and in patients after bone marrow transplantation. GM-CSF is found in high levels in joints with rheumatoid arthritis and blocking GM-CSF may reduce the inflammation or damage.