T cell activation by antigen-presenting cell (APC) requires co-stimulatory signaling.¹

• Binding of the CD28 receptor to ligands CD80 or 86 on an antigen-presenting cell (APC) provides a co-stimulatory signal requisite for T cell activation and the consequent inflammatory cascade.¹ This interaction is followed by T cell expression of cytotoxic T-lymphocyte–associated antigen-4 (CTLA-4).²
• In the normal immune response, CTLA-4 competes for CD28 binding to CD80/86. CTLA-4 has a higher binding affinity for CD80/86 and its binding blocks T cell activation by CD28.²
• In addition, CTLA-4 binding delivers a negative signal that downregulates T cell function and inhibits the excessive expansion of activated T cells.²