|Detection of CTLA‑4 in NS0 Mouse Cell Line Transfected with Human CTLA-4 and eGFP by Flow Cytometry. NS0 mouse myeloma cell line transfected with human CTLA-4 and eGFP was stained with either (A) Goat Anti-Human CTLA‑4 APC‑conjugated Antigen Affinity-purified Polyclonal Antibody (Catalog # FAB386A) or (B) Normal Goat IgG Allophycocyanin Control (Catalog # IC108A). View our protocol for Staining Membrane-associated Proteins.|
CTLA-4 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 and CD28 are both expressed on the cell surface as disulfide-linked homodimers or as monomers. The genes encoding these two molecules are closely linked on human chromosome 2. 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 currently being studied.