Biofunctions of Three New B7 Family Members

ABSTRACT

Three new B7 family members, B7-H5 (VISTA, Gi24, or Dies1), B7-H6, and B7-H7 (HHLA2) were recently identified, but their functions remain uncertain. We expressed the human B7-H5, B7-H6, and B7-H7 extracellular domain human IgG1 Fc Chimeras in a mammalian cell line and investigated the functions of the purified recombinant B7-H5/Fc, B7-H6/Fc, and B7-H7/Fc proteins in vitro. To determine the functions of B7-H5 and B7-H7, human T cells were treated with plate-bound anti-CD3 and either B7-H5/Fc, B7-H7/Fc or control IgG1 Fc. The levels of multiple cytokines were measured in cell culture supernatants using R&D Systems Proteome Profiler™ Human Cytokine Array, followed by measuring individual cytokines using a series of cytokine-specific Quantikine^® ELISA kits. B7-H5 significantly reduced eight T cell derived cytokines including IFN-gamma, IL-2, IL-17, IL-4, IL-8, IL-13, IL-16, and TNF-alpha. Similarly B7-H7 markedly decreased five cytokines including IFN-gamma, IL-2, IL-17, IL-8, and TNF-alpha. To investigate the bioactivity of B7-H6, NK-92 cells were treated with plate-bound B7-H6/Fc or control IgG1 Fc. B7-H6/Fc induced IFN-gamma production in NK cells in a dose-dependent manner. Furthermore, B7-H6/Fc showed binding to recombinant human NKp30/Fc. Taken together, our data suggest that B7-H5 and B7-H7 are co-inhibitory molecules for T cell activation, and that B7-H6, a major NKp30 ligand, triggers NKp30-dependent NK cell activation.