CD28 is one of the most important costimulatory molecules expressed by naive and primed T cells and is essential for full T cell activation and the development and homeostasis of Treg cells. CD80 (B7-1) and CD86 (B7-2) represent the two structurally homologous ligands of CD28, which are expressed by antigen-presenting cells (APCs), including dendritic cells (DCs). Expression of each ligand is upregulated by infection, tissue injury, or the production of inflammatory cytokines or after the contact of APCs with activated T cells. CD86 seems likely to play a more critical role in providing early and sustained costimulatory signals, whereas CD80-derived signals modulate the fate of the T cell response rather than its initiation. CTLA-4 is homologous to CD28 and binds CD80-CD86 with a much higher affinity than CD28. Consequently, CD28 competes with CTLA-4 to bind CD80 and CD86, resulting in enhanced T-cell responses by up-regulating cytokine secretion and inducing cell proliferation.
Learn more: cd80/cd86
