Outside looking in: the inner workings of the cross-presentation pathway within dendritic cells.

The entry of exogenous antigen into the MHC class I-restricted cross-presentation pathway can contribute to CD8(+) T cell tolerance and immunity, in particular to peripheral self-antigens or selected viruses and bacteria showing restricted tissue tropism. Dendritic cells are the key cross-presenting cells and, as such, they are thought to carry specialized machinery dedicated to this purpose. Two recent papers describe intracellular components tailored to the dendritic cell cross-presentation pathway.