Interleukin-11, also known as AGIF, is a pleiotropic cytokine in the IL-6 family, which also includes LIF, CNTF, Oncostatin M, Cardiotrophin-1, IL-27, and IL-31. It is secreted by osteoblasts, synoviocytes, fibroblasts, chondrocytes, intestinal myofibroblasts, and trophoblasts. It is found in the plasma mainly during inflammation, and is considered to be primarily anti-inflammatory. It stimulates hematopoiesis and thrombopoiesis, regulates macrophage differentiation, and confers mucosal protection in the intestine. It has also been found to enhance T cell polarization toward Th2, promote B cell IgG production, increase osteoclast bone absorption, protect endothelial cells from oxidative stress, and regulate epithelial proliferation and apoptosis. IL-11 signals through a receptor complex that contains IL-11 R alpha and gp130. A soluble form of IL-11 R alpha can bind IL-11 and either form a signaling complex with gp130 on the cell surface or inhibit cell surface IL-11 R alpha/gp130 signaling.