Leukemia Inhibitory Factor （LIF） belongs to the IL-6 superfamily of cytokines. LIF is expressed in a number of tissues and cell types. The LIF receptor is a heterodimer comprised of LIF-R （gp190） and gp130, a common signal transducer for IL-6-type cytokines. Depending on cell type and context, LIF/LIF-R can activate Erk, PI3K, and Jak1/Stat1/3 pathways. LIF has a diverse array of biological activities. Murine embryonic stem cells are dependent on LIF for pluripotency and self-renewal in vitro. Exercise- induced LIF secretion in muscle induces myoblast proliferation, suggesting that LIF may play a role in exercise-induced muscle hypertrophy. LIF also negatively regulates Th2 and Th17 cell differentiation.