Mouse Lymphocyte Activation Gene 3 (LAG3) Protein

Background

LAG3 (lymphocyte-activation gene 3), also known as CD223, is a cell surface protein that plays a critical role as an immune checkpoint inhibitor. It functions as a negative regulator of T cell activity and is predominantly expressed on activated T cells, regulatory T cells (Tregs), and natural killer (NK) cells. LAG-3 belongs to the immunoglobulin (Ig) superfamily and is structurally similar to CD4, although it performs an inhibitory rather than activating function. Its primary ligand is the major histocompatibility complex (MHC) class II, and it binds with much higher affinity than CD4, providing it with strong immunoregulatory capabilities. As an immune checkpoint receptor, LAG-3 is critical for maintaining immune homeostasis and preventing autoimmune reactions by moderating immune responses. Its expression is upregulated during chronic infections and in cancer, often contributing to T cell exhaustion, a state in which T cells progressively lose function due to prolonged antigen exposure. This makes LAG-3 a therapeutic target in immuno-oncology and chronic infection therapies. The blockade of LAG-3 has shown potential in restoring T cell function, thereby enhancing anti-tumor and anti-pathogen immune responses.