GM-CSF is an acidic glycoprotein with a molecular weight of approximately 23kDa, containing internal disulfide bonds. It is primarily produced by mesenchymal cells present in the hematopoietic environment and peripheral inflammatory sites, responding to various inflammatory mediators. GM-CSF stimulates the formation of granulocytes and macrophages from bone marrow precursor cells, promoting the production of neutrophil, macrophage, and mixed granulocyte-macrophage colonies. It can also stimulate eosinophil colony formation from fetal liver progenitor cells. GM-CSF is generally undetectable in the blood of healthy individuals, but its levels may increase under certain conditions such as inflammation or cancer treatment. It stimulates functional activities in mature granulocytes and macrophages. GM-CSF plays a crucial role in maintaining lung homeostasis as a key homeostatic factor in the alveoli. At low levels, it promotes the development and long-term maintenance of alveolar macrophages. In the absence of GM-CSF, there is a defect in alveolar macrophage function, increasing the risk of pulmonary infections and leading to lung diseases. Abnormal expression of GM-CSF can also lead to symptoms such as inflammation, pain, tissue damage, and may promote the production of other pathogenic cytokines.