has role molecule CD80/CD86 B7.1 (CD80) and B7.2 (CD86) - the two structurally homologous ligands of CD28 - are expressed by professional antigen-presenting cells (APCs), such as dendritic cells (DCs), macrophages and activated B cells, belong to the immunoglobulin superfamily and might exist as dimers and monomers, respectively. B7.1/B7.2 ligand