Mouse Programmed cell death 1 ligand 1(Cd274，PD-L1), is a member of the growing B7 family of immune proteins.It involved in the costimulatory signal essential for T-cell proliferation and IFNG production in a PDCD1-independent manner. Interaction with PDCD1 inhibits T-cell proliferation by blocking cell cycle progression and cytokine production.B7-H1 has been identified as one of two ligands for programmed death1 (PD1), a member of the CD28 family of immunoreceptors. B7-H1 is constitutively expressed in several organs such as heart, skeletal muscle B7-H1 expression is upregulated in a small fraction of activated T and B cells and a much larger fraction of activated monocytes. The costimulatory function of B7-H1 is critical for enhancing maturation and differentiation of T-cells in lymphoid organs.B7-H1 expression is also induced in dendritic cells and keratinocytes after IFN gamma stimulation. Interaction of B7-H1 with PD1 results in inhibition of TCR-mediated proliferation and cytokine production. The B7-H1:PD1 pathway is involved in the negative regulation of some immune responses and may play an important role in the regulation of peripheral tolerance.