CD279, also known as programmed death 1 (PD-1), is expressed on activated splenic T cells, B cells, and thymocytes. Its expression can also be induced on activated myeloid cells. PD-1 participates in lymphocyte clonal selection and peripheral tolerance by binding to its ligands B7-H1 (PD-L1) and B7-DC (PD-L2). The interaction between PD-1 and PD-L1 has been reported to be crucial for positive selection and plays a role in shaping the T-cell repertoire. Negative co-stimulation via PD-L1 is essential for the long-term survival of intratesticular islet allografts.
