%0 Journal Article %J Mol Immunol %D 2008 %T Interaction of human PD-L1 and B7-1. %A Butte, Manish J %A Peña-Cruz, Victor %A Kim, Mi-Jung %A Freeman, Gordon J %A Sharpe, Arlene H %K Animals %K Antibodies, Monoclonal %K Antigens, CD %K Antigens, CD274 %K Antigens, CD28 %K Antigens, CD80 %K Cells, Cultured %K Humans %K Lymphocyte Activation %K Mice %K Protein Binding %K T-Lymphocytes %X Numerous studies have pointed to the role of programmed death-1 ligand 1 (PD-L1) in regulating tolerance, chronic infection, and tumor immunity. Recently, we have identified murine B7-1 as a new binding partner for murine PD-L1. Human and mouse B7-1 share only 46% identity, leading us to question whether human B7-1 and PD-L1 can participate in a similar interaction. Here we show that human B7-1 can interact with human PD-L1 with affinity greater than that of B7-1 with CD28, but less than that of B7-1 with CTLA-4 or of PD-L1 with PD-1. We characterize a series of anti-human PD-L1 monoclonal antibodies and identify antibodies that can block interactions of PD-L1 with B7-1, PD-1, or both. Since PD-L1 and CD28 on T cells may compete for B7-1 as a binding partner and CD8 T cells may express high or low levels of CD28, we examined when PD-L1 and CD28 are co-expressed on CD8 T cells. We compared the time-course and extent of PD-L1 induction on CD8 CD28high versus CD28low T cells following stimulation with anti-CD3. We show that PD-L1 is induced to a higher level on CD28high T cells than on CD28low T cells upon activation. These results suggest that PD-L1 may play an important and undervalued role on human T cells. %B Mol Immunol %V 45 %P 3567-72 %8 2008 Aug %G eng %N 13 %1 http://www.ncbi.nlm.nih.gov/pubmed/18585785?dopt=Abstract %R 10.1016/j.molimm.2008.05.014