Immune suppressive molecule that inhibits antigen-specific T-cell activation by acting as a major ligand of LAG3. Responsible for LAG3 T-cell inhibitory function. Binds LAG3 independently from MHC class II (MHC-II). Secreted by, and promotes growth of, hepatocytes. Homodimer. Interacts (via the Fibrinogen C-terminal domain) with LAG3 (via Ig-like domains 1 and 2). Secreted in the blood plasma.