||CTLA-4 (cytotoxic T lymphocyte-associated molecule-4) is a T cell surface glycoprotein and a member of the immunoglobulin superfamily. The 223-amino acid human protein contains a leader sequence, a single extracellular V domain, a transmembrane domain, and a cytoplasmic tail encoded by 4 exons, respectively (1). It is a disulfide-linked homodimer in the extracellular domain at cysteine residue 120 (2). CD28 is structurally related to CTLA-4, with CTLA-4 sharing 27% (murine) to 31% (human) amino acid identity with CD28 (1). Both CTLA-4 and CD28 bind to B7-1 (CD80) and B7-2 (CD86) on antigen presenting cells, with CTLA-4 binding at a 20- to 50-fold greater affinity than CD28 does (3). CD28 delivers an activation signal to T cells while CTLA-4 transmits an inhibitory signal to T cells (4). CD28 is found in considerable amounts on the cell surface of the majority of resting T cells whereas CTLA-4 presents significantly lower expression, predominantly appearing after T cell activation (5).
||CD152, ALPS5, CELIAC3, GRD4, GSE, IDDM12
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