DCs and peripheral T cell tolerance

Tolerance is a state in which the immune system as a whole fails to make an active response to antigen. Three mutually exclusive mechanisms appear to account for the fate of antigen-specific peripheral T cells within a tolerant animal: maintenance of naive status, deletion after responding to antigen, and long term survival after responding to antigen, a mechanism that should probably be considered part of the spectrum of memory responses. The types and functional status of the DCs that present antigen in each case remain controversial. This review will summarize the indirect evidence that underlies some of the hypotheses that account for peripheral T cell tolerance.