|Detection of CTLA‑4 in Mouse Splenocytes by Flow Cytometry. Mouse splenocytes treated with Conconavalin A were stained with Rat Anti-Mouse CD3 APC‑conjugated Monoclonal Antibody (Catalog # FAB4841A) and either (A) Rat Anti-Mouse CTLA‑4 PE‑conjugated Monoclonal Antibody (Catalog # FAB434P) or (B) Rat IgG2A Phycoerythrin Isotype Control (Catalog # IC006P). View our protocol for Staining Membrane-associated Proteins.|
CTLA-4 (also known as CD152) and CD28, together with their ligands B7-1 and B7-2, constitute one of the dominant costimulatory pathways that regulate T and B cell responses. CTLA-4 and CD28 are structurally homologous molecules that are members of the immunoglobulin (Ig) gene superfamily. Both CTLA-4 and CD28 are composed of a single Ig V‑like extracellular domain, a transmembrane domain and an intracellular domain. CTLA-4 is expressed on the cell surface as either a disulfide-linked homodimer or a 24-26 kDa monomer. CTLA-4 was originally identified as a gene that was specifically expressed by cytotoxic T lymphocytes. However, CTLA-4 transcripts have since been found in both Th1 and Th2, and CD4+ and CD8+ T cell clones. Whereas, CD28 expression is constitutive on the surfaces of 95% of CD4+ T cells and 50% of CD8+ T cells, and is down regulated upon T cell activation, CTLA-4 expression is upregulated rapidly following T cell activation and peaks approximately 24 hours following activation. Although both CTLA-4 and CD28 can bind to the same ligands, CTLA-4 binds to B7-1 and B7-2 with 20-100-fold higher affinity than CD28. The physiological role of CTLA-4 in T cell costimulation is contextually defined. Full-length CTLA-4, when induced and activated, sends an inhibitory signal to the expressing T cell. It also promotes the development of Tc17 cells. Tregs constitutively express CTLA-4, a phenotype that is essential to their function. Over amino acids (aa) 36-161, mouse CTLA-4 shares 94% and 67% aa sequence identity with rat and human CTLA-4, respectively.