Cognate CD4+ help elicited by resting dendritic cells does not impair the induction of peripheral tolerance in CD8+ T cells.

Peripheral tolerance is required to prevent autoimmune tissue destruction by self-reactive T cells that escape negative selection in the thymus. One mechanism of peripheral tolerance in CD8(+) T cells is their activation by resting dendritic cells (DC). In contrast, DC can be "licensed" by CD4(+) T cells to induce cytotoxic function in CD8(+) T cells. The question that then arises, whether CD4(+) T cell help could impair peripheral tolerance induction in self-reactive CD8(+) T cells, has not been addressed. In this study we show that CD4(+) T cell activation by resting DC results in helper function that transiently promotes the expansion and differentiation of cognate CD8(+) T cells. However, both the CD4(+) and CD8(+) T cell populations ultimately undergo partial deletion and acquire Ag unresponsiveness, disabling their ability to destroy OVA-expressing pancreatic beta cells and cause diabetes. Thus, effective peripheral tolerance can be induced by resting DC in the presence of CD4(+) and CD8(+) T cells with specificity for the same Ag.