B7-1 and B7-2, together with their receptors CD28 and CTLA-4, constitute one of the dominant co-stimulatory pathways that regulate T- and B-cell responses. Although both CTLA-4 and CD28 can bind to the same ligands, CTLA-4 binds to B7-1 and B7-2 with a 20‑100 fold higher affinity than CD28 and is involved in the down‑regulation of the immune response. B7-1 is expressed on activated B cells, activated T cells, and macrophages.
