LAG3 (Lymphocyte Activating 3) is a Protein Coding gene. 2 alternatively spliced human isoforms have been reported. LAG3, also known as CD223 and Lymphocyte activation gene 3, belongs to the immunoglobulin (Ig) superfamily. The LAG3 gene contains 8 exons. It is selectively expressed in activated T and NK cells. LAG3 contains 4 extracellular Ig-like domains and has a negative regulatory function in T cells. It also acts as a new marker of T cell-induced B cell activation. As a soluble molecule, LAG3 activates antigen-presenting cells through MHC class II signaling, leading to increased antigen-specific T-cell responses in vivo. Diseases associated with LAG3 include Smoldering Myeloma and Kyphoscoliotic Heart Disease.