B7-2/CD86 and the related B7-1/CD80 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 and vascular endothelial cells. It binds to CD28 on T cells to enhance T cell activation. It additionally binds CTLA-4 which inhibits the T cell response and supports regulatory T cell function. The relative participation of B7-1 and B7-2 in T cell co-stimulation can alter the Th1/Th2 bias of the immune response. Both B7-1 and B7-2 serve as cellular receptors for B species adenoviruses.