Immune suppressive molecule that inhibits antigen-specific T-cell activation by acting as a major ligand of LAG3 (PubMed:30580966). Responsible for LAG3 T-cell inhibitory function (PubMed:30580966). Binds LAG3 independently from MHC class II (MHC-II) (PubMed:30580966). Secreted by, and promotes growth of, hepatocytes (PubMed:11470158, PubMed:19880967).