The role of CD80 and CD86 costimulatory molecules is well established in the activation of T cells but not antigen presenting cells. Recently, many reports in literature have demonstrated categorically the influence of CD80 and CD86 in the activation of B cells and dendritic cells. Stimulation via CD80/CD86 in B cells can modulate their proliferation, IgG secretion and expression of pro-apoptotic and anti-apoptotic molecules, nuclear localization of NF-κB p50 subunit, phosphorylation of Rel A (p65) and IκB-alpha and increased oct-2 expression. In case of dendritic cells, it has been shown that signals induced via CD80 and CD86 enhance the production of IL-6 and IFN-γ which in turn, upregulates the expression of the enzyme indolamine 2, 3-dioxygenase that results in tryptophan catabolism and affects T cell proliferation. Interestingly, it has been shown that co-stimulation through CD80 can restrict the survival of lymphomas and can also induce apoptosis in neural stem cells. Consequently, it may be concluded that CD28/CD152-CD80/86 interaction delivers a bi-directional co-stimulation, thereby not only having impact on the function of T cells, but also antigen presenting cells.