Plays a critical role in induction and maintenance of immune tolerance to self (PubMed:11238124). As a ligand for the inhibitory receptor PDCD1/PD-1, modulates the activation threshold of T-cells and limits T-cell effector response (PubMed:11238124). Through a yet unknown activating receptor, may costimulate T-cell subsets that predominantly produce interleukin-10 (IL10) (PubMed:11015443, PubMed:12719480). The PDCD1-mediated inhibitory pathway is exploited by tumors to attenuate anti-tumor immunity and escape destruction by the immune system, thereby facilitating tumor survival (PubMed:12218188, PubMed:27281199). The interaction with PDCD1/PD-1 inhibits cytotoxic T lymphocytes (CTLs) effector function (PubMed:12218188). The blockage of the PDCD1-mediated pathway results in the reversal of the exhausted T-cell phenotype and the normalization of the anti-tumor response, providing a rationale for cancer immunotherapy (PubMed:12218188). Interacts with PDCD1 (PubMed:11015443). Interacts with CMTM4 and CMTM6 (By similarity). Highly expressed in the heart, thymus, skeletal muscle, and lung. Weakly expressed in the kidney, spleen, thyroid, and liver. Expressed on activated dendritic cells, B-cells and macrophages. Expressed in numerous tumor cells lines of lymphoid origin. Up-regulated by IFNG treatment in monocytes. Up-regulated on dendritic cells, B-cells and macrophages after activation by LPS and IFNG. Ubiquitinated; STUB1 likely mediates polyubiquitination of PD-L1/CD274 triggering its degradation. Belongs to the immunoglobulin superfamily. BTN/MOG family.