LAG3, a member of the immunoglobulin superfamily and a homolog of CD4, arose from a gene duplication event. Similar to CD4, LAG3 binds to MHC class II （MHCII）, but it also interacts with FGL-1, α-synuclein fibrils （α-syn）, galectin-3 （Gal-3）, and lymph node sinusoidal endothelial cell C-type lectin （LSECtin）. As an immune checkpoint, LAG3 inhibits the activation of its host cell, promoting a more suppressive immune response. On T cells, LAG3 reduces the production of cytokines and granzymes, as well as cell proliferation, while encouraging differentiation into T regulatory cells.