This gene encodes a cell surface membrane protein of the immunoglobulin superfamily. This protein is expressed in pro-B-cells and is thought to play a role in their differentiation. In mice，expression of this gene is induced in the thymus when anti-CD3 antibodies are injected and large numbers of thymocytes undergo apoptosis. Mice deficient for this gene bred on a BALB/c background developed dilated cardiomyopathy and died from congestive heart failure. These studies suggest that this gene product may also be important in T cell function and contribute to the prevention of autoimmune diseases. CD279 is an immunoglobulin superfamily member，also known as Programmed Cell Death 1. Programmed Cell Death 1 is expressed on a subset of CD4-CD8 thymocytes，and on activated T and B cells. Programmed Cell Death 1 is thought to be involved in lymphocyte clonal selection and peripheral tolerance. The Programmed Cell Death 1 ligands，PDL1 (also known as B7H1) and PDL2 (B7DC)，are members of the B7 immunoglobulin sup