Macrophage stimulating proteins (MSP), also known as hepatocyte growth factor-like proteins (HGFL) and MST1, are members of the HGF family of growth factors. MSP is secreted in the form of inactive single-stranded precursors (pro-MSP) that are ligands of the transmembrane receptor tyrosine kinase receptor (RON) (RON; Also known as MST1R). Since its discovery, MSP has been shown to play a key role in regulating inflammation in peripheral tissues in a variety of disease models. Recent evidence also suggests that MSP has a beneficial role in regulating lipid and glucose metabolism in the liver, thereby hinting at MSP as a key regulator in maintaining metabolic homeostasis while inhibiting inflammatory processes. MSP induces proliferation of macrophages and keratinocytes and activation of osteoclasts. It also inhibits LPS or IFN-induced iNOS and IL-12 expression by macrophages and prevents apoptosis of epithelial cells isolated from extracellular matrix.