LAG3 (Lymphocyte Activating 3) is a Protein Coding gene. Two 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 activaTwion. 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.