Dendritic cell activation by danger and antigen-specific T-cell signalling.

Recent transplantation, animal and in vitro studies suggest a dependence of some immune reactions on tissue damage. Although many factors involved in enhancing immune responses through tissue damage have yet to be identified, recent data suggests that one of the targets of these cellular stress factors is the bone marrow derived dendritic cell (DC). DC are potent initiators of primary immune responses and hold the key to immune reactions through their ability to sense changes in their local environment and respond appropriately to induce T-cell immunity, or possibly tolerance. In the lymph node, DC are also influenced by antigen-specific signalling from T cells, which may extend and amplify DC antigen presenting capabilities, especially for the stimulation of cytotoxic responses. It now appears that both tissue damage and antigen-specific T-cell derived signals act together on the DC to promote the appropriate immune reaction to antigen. Thus DC antigen presenting behaviour is not only dependent on the context of antigen encounter in the periphery, but also on the availability of antigen-specific T cells and their T-cell receptor specificities.