CD116 is a 70-85kD a chain of the GM-CSF receptor. It combines with CDw131 B chain to form the high affinity GM-CSF receptor. A soluble form of CD116, which binds GM-CSF with a relatively low affinity, has been identified. In addition, an alternatively spliced form of CD116 with an altered cytoplasmic tail has been described. CD116 is expressed on various myeloid cells including monocytes, macrophages, neutrophils, eosinophils, dendritic cells and their precursors, fibroblasts, and endothelial cells. CD116 is expressed on myeloid leukemias, osteogenic sarcoma cell lines, osteoblast-like cells and breast and lung carcinoma cell lines.