This program uses microscopy and excellent computer animation to study the complex process of apoptosis. In the first T cell maturation stage, lymphocytes leave the bone marrow and enter the thymus from the lymphatic ducts. Upon entry, some of these future T cells interact, using their newly developed T cell receptors (TCRs) to bind to MHC molecules on the thymus. The T cells that do not bind to MHC molecules are then programmed to die—the process we call apoptosis. Remaining T cells continue to mature and proliferate. The process is demonstrated in the development of an embryonic finger. (30 minutes)