Oncostatin M, also known as OSM, is a protein that in humans is encoded by the OSM gene. OSM is a pleiotropic cytokine that belongs to the interleukin 6 group of cytokines. Of these cytokines it most closely resembles leukemia inhibitory factor (LIF) in both structure and function. However, it is as yet poorly defined and is proving important in liver development, haematopoeisis, inflammation and possibly CNS development. It is also associated with bone formation and destruction. OSM signals through cell surface receptors that contain the protein gp130. The type I receptor is composed of gp130 and LIFR, the type II receptor is composed of gp130 and OSMR.