Enables MHC class II protein binding activity and transmembrane signaling receptor activity. Involved in negative regulation of regulatory T cell differentiation; plasmacytoid dendritic cell activation; and regulation of immune response. Acts upstream of or within cell surface receptor signaling pathway; negative regulation of interleukin-2 production; and positive regulation of natural killer cell mediated cytotoxicity. Located in external side of plasma membrane and extracellular region. Orthologous to human LAG3 (lymphocyte activating 3).
