One of a group of related proteins made by leukocytes (white blood cells) and other cells in the body. IL-11 is made by support cells in the bone marrow. It causes the growth of several types of blood cells. Oprelvekin (IL-11 made in the laboratory) is used as a biological response modifier to increase the number of platelets, especially in patients receiving chemotherapy for cancer. IL-11 is a type of cytokine. Also called interleukin-11.