LIF(eukemia inhibitory factor) is a pleiotropic cytokine with roles in several different systems. LIF plays a crucial role in maintaining the pluripotency of embryonic stem (ES) cells by inhibiting their spontaneous differentiation, which is vital for stem cell research and potential therapeutic applications. This 202 amino acid secreted glycoprotein is produced by various cell types, including activated T lymphocytes, monocytes, mast cells, and neuronal cells, and is essential for promoting the survival and growth of axons in vitro. Additionally, LIF is implicated in immune tolerance at the maternal-fetal interface, suggesting its importance in reproductive biology. Beyond its role in stem cell maintenance, LIF may also influence fat and bone metabolism and is involved in the regulation of epithelial conversion during kidney development.