How dying cells alert the immune system to danger

To avoid potential damage to the host, an inflammatory response is rapidly mobilized on detection of intracellular signals that are released from dying cells. Much has been learned about these 'danger' signals, but several key issues remain unresolved, as discussed by the authors. When a cell dies in vivo, the event does not go unnoticed. The host has evolved mechanisms to detect the death of cells and rapidly investigate the nature of their demise. If cell death is a result of natural causes — that is, it is part of normal physiological processes — then there is little threat to the organism. In this situation, little else is done other than to remove the corpse. However, if cells have died as the consequence of some violence or disease, then both defence and repair mechanisms are mobilized in the host. The importance of these processes to host defence and disease pathogenesis has only been appreciated relatively recently. This article reviews our current knowledge of these processes.