CD86 (B7-2) is a 60-100 kDa variably glycosylated protein in the B7 family. B7 family members are transmembrane cell surface molecules that play important roles in immune activation and the maintenance of immune tolerance. B7-2 is highly expressed on activated antigen presenting cells (APC), e.g. B cells, dendritic cells and monocytes as well as on vascular endothelial cells. B7-2 and the closely related CD80 (B7-1) exhibit overlapping but distinct functional properties. Their binding to CD28, which is constitutively expressed on T cells, enhances T cell receptor signaling and also provides TCR-independent costimulation. B7-1 and B7-2 additionally bind the CD28-related protein CTLA-4, which is up-regulated and recruited to the immunological synapse (IS) at the onset of T cell activation. CTLA-4 ligation inhibits the T cell response and supports regulatory T cell function. B7-2 is expressed earlier than B7-1 following APC activation and both proteins bind with higher affinity to CTLA-4 than to CD28. B7-2 promotes the stabilization of CD28 in the IS, while B7-1 is primarily responsible for promoting CTLA-4 recruitment and accumulation in the IS. The relative participation of B7-1 and B7-2 in T cell costimulation can also alter the Th1/Th2 bias of the immune response. Both B7-1 and B7-2 serve as cellular receptors for B species adenoviruses.