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.