Cytotoxic T-lymphocyte protein 4 (CLTA-4) is a transmembrane glycoprotein that is a member of the CD28/B7 family of co-stimulatory receptors and is a negative regulator of T cell activation.{55177,46977} CLTA-4 exists as a homodimer and is composed of an extracellular immunoglobulin variable (IgV) domain that interacts with the co-stimulatory molecules CD80 (Item No. 32013) or CD86 (Item No. 32010) and a cytoplasmic tail that mediates CTLA-4 trafficking and cellular localization, as well as association with the signal transduction enzymes PI3K, SHP-2, and PP2A and the clathrin adaptor proteins AP-1 and AP-2.{55177} It is constitutively expressed on the surface of regulatory T cells and is confined within intracellular vesicles in naïve T cells.{46977} CTLA-4 localizes to the cell surface upon activation of naïve T cells by antigen-presenting cells (APCs) displaying MHC-bound antigen and expressing CD80 and CD86. CTLA-4 competes with CD28 (Item No. 32014), a co-stimulatory molecule also expressed on T cells that drives T cell activation, for binding to CD80 or CD86, inhibiting T cell activation and promoting T cell anergy. Ctla4-/- mice develop a lymphoproliferative autoimmune disorder that is perinatal lethal.{55178} High tumor levels of CTLA-4 have been associated with poor prognosis in individuals with nasopharyngeal carcinoma, melanoma, or non-small cell lung cancer (NSCLC).{55177} SNPs in CTLA4 have been found in individuals with various autoimmune diseases, including systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), as well as cancer.{55179} Formulations containing anti-CTLA-4 monoclonal antibodies have been used in the treatment of advanced melanoma.{55177} Cayman's CTLA-4 Extracellular Domain (human, recombinant) protein can be used for cell-based assay applications. This protein is a disulfide-linked homodimer. The reduced monomer, comprised of CTLA-4 (amino acids 37-162) fused to His-tagged human IgG1 Fc at its C-terminus, consists of 374 amino acids, has a calculated molecular weight of 41.6 kDa, and a predicted N terminus of Ala37 after signal peptide cleavage. As a result of glycosylation, the monomer migrates at approximately 50 to 55 kDa by SDS-PAGE under reducing conditions.