CD152 (CTLA-4 (cytotoxic T-lymphocyte associated protein 4)) and CD28 are structurally homologous molecules that are members of the immunoglobulin (Ig) gene superfamily. Both CD152 and CD28 are composed of a single Ig V-like extracellular domain, a transmembrane domain and an intracellular domain.
CD152 and CD28 are both expressed on the cell surface as homodimers or as monomers. CD152 was originally identified as a gene that was specifically expressed by cytotoxic T lymphocytes. However, CD152 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, CD152 expression is upregulated rapidly following T cell activation and peaks approximately 24 hours following activation. Although both CD152 and CD28 can bind to the same ligands, CD152 binds to B71 and B72 with 20-100-fold higher affinity than CD28.
CTLA4 (cytotoxic T-lymphocyte associated protein 4) or insulin dependent diabetes mellitus 12 (IDDM12) is responsible for inhibiting T-cell proliferation and facilitates T cell apoptosis. This protein is expressed post-antigen presentation and thus, is involved in immune and autoimmune disorders. It is implicated in the pathogenesis of various T cell mediated autoimmune disorders.
