Death and destruction of activated T lymphocytes.

The massive clonal expansion that occurs during an antigen-specific immune response results in the flooding of immune organs with activated T lymphocytes. At the end of a specific response, the vast majority of these activated T cells are cleared from the immune system. The T cells receive signals through specific death receptors that are expressed as a result of activation. Death receptors transmit their apoptotic signals through the activation of caspases. Function of the death receptors is intimately linked to cell-cycle control, and many cell-cycle control proteins are caspase substrates. Among CD8+ T cells, apoptotic death occurs at a specific site, the sinusoids of the liver. The liver appears to contain a mechanism for the trapping and killing of activated T cells, rendering it an immunologically privileged site.