Antibodies against B7-DC with differential binding properties exert opposite effects

Programmed cell death 1 (PD-1) is an immunoregulatory receptor on T cells that binds two ligands, B7-H1 and B7-DC. Although accumulating reports suggest a critical role for the B7-H1:PD-1 pathway in peripheral tolerance, the actual involvement of B7-DC has not been well confirmed. Here, we established a new MAb against mouse B7-DC (MIH37) and compared its functional properties with a previously established anti-B7-DC MAb (TY25). Binding analyses using flow cytometry demonstrated that MIH37 showed an approximately four-fold higher binding affinity to B7-DC and stronger inhibitory effects on B7-DC:PD-1 binding. In contrast to the effects of TY25, treatment with MIH37 at both sensitization and challenge inhibited hapten-induced contact hypersensitivity reactions. Furthermore, the addition of MIH37 inhibited OVA-specific T cell responses in vitro. The inhibitory effects of MIH37 were counteracted by co-blockade with PD-1 and absent in PD-1-deficient mice, suggesting PD-1-dependent action of MIH37. Our present results suggest that greater complexities of PD-1-mediated functions are induced via ligand binding for controlling immunity and tolerance.