Interleukin 11 (IL-11) is a protein that in humans is encoded by the IL11 gene. IL-11 is a cytokine and first isolated in 1990 from bone marrow-derived fibrocyte-like stromal cells. It was initially thought to be important for hematopoiesis, notably for megakaryocyte maturation, but subsequently shown to be redundant for platelets, and for other blood cell types, in both mice and humans. It is also known under the names adipogenesis inhibitory factor (AGIF) and was developed as a recombinant protein (rhIL-11) as the drug substance oprelvekin.