Dendritic cells also mediate a response because naive cytotoxic
T lymphocytes do not display MHC-II molecules. An activated helper T-lymphocyte attaches it's TCR to the MHC-II of the dendritic call and this also involves the CD4 co-receptor. The CD4 co-receptor is necessary because even the license to kill needs a license to kill.
The Dendritic cell now has an activated helper t-lymphocyte attached. The MHC-I of the dendritic cell can now attach to the TCR of a Cytotoxic T lymphocyte along with a CD8 co-receptor.
The activated cytotoxic T lymphocyte seeks out virus infected cells and attaches its TCR to their MHC-1 along with the CD8 co-receptor. A release of cytotoxins lyses the infected cell and it is no more a threat.
This may seem rather boring when all I mention is how the helper T lymphocyte uses the dendritic cell to activate a cytotoxic T lymphocyte, but currently this is undergoing more research and is rather interesting. There aren't any really good reasons for the use of a dendritic cell for this purpose. Like I mentioned earler, immunology isn't like James Bond having a license to kill. A license to kill requires a license to kill, and requires another license to kill.