Dendritic cells in autoimmune diseases.

Subclinical autoimmune responses can be frequently detected in healthy individuals. Sustained activation of autoreactive lymphocytes is, however, required for the development of autoimmune diseases associated with ongoing tissue destruction either in single organs or generalized with multiple manifestations. Clinical and experimental evidence suggests that prolonged presentation of self antigens by dendritic cells is crucial for the development of destructive autoimmune disease. We discuss here a simplified threshold model where the key parameters for the magnitude of the autoimmune response are the amount of previously ignored self peptides presented by dendritic cells and the duration of the antigen presentation in secondary lymphoid organs. Multiple factors influence the threshold for the conversion of an autoimmune response to overt autoimmune disease. Frequent or persistent viral infections of the target organ may favor autoimmune disease by increasing the amounts of released self antigens, generating cytokine-mediated bystander activation of self-reactive lymphocytes and/or sustaining a chronic response via neoformation of lymphoid structures in the target organ.