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CD152, also known as CTLA-4 （cytotoxic T-lymphocyte-associated protein 4）, is a protein receptor that functions as an immune checkpoint. It is a member of the immunoglobulin superfamily and is expressed on the surface of T cells. The CD152 gene consists of 4 exons and encodes a protein with a signal peptide, an Ig-like domain, a transmembrane region, and a cytoplasmic domain. CD152 plays an essential role in regulating T cell activation by binding to its ligands CD80 and CD86, which are expressed on antigen-presenting cells. This binding can inhibit the over-activation of T cells, thus maintaining immune homeostasis.