Dendritic cells as targets for cytotoxic T lymphocytes.

Dendritic cells (DC) carry antigen into lymph nodes where they may cluster with CD4 and CD8+ lymphocytes and activate both subsets in the initiation of immune responses. Since DC do not leave the lymph nodes in the efferent lymph they may die within the lymph nodes. Another possibility is that they are targets for cytotoxic T cells (CTL) when expressing appropriate epitopes. This possibility was tested in vitro using human peripheral blood DC to stimulate the development of primary CTL in response to HIV-1 or one of its T-cell epitopes (e.g. env 111-126) and secondary CTL in response to type A influenza virus. Pooled CTL generated during six day cultures in 60 replicate 20 microliters hanging drops were tested in a conventional CTL assay. The HIV or HIV peptide stimulated CTL lysed HIV infected DC while the influenza-virus induced CTL killed DC targets infected with this virus. DC were not lysed significantly until they had been exposed to virus for 2-3 days and thus are not highly susceptible to lysis. However, killing of DC after 2-3 days infection with virus may be a feedback mechanism for removing antigen presenting cells after they have stimulated T cell responses. Removal of persistently infected DC by CD8+ CTL may also contribute to the reduction in DC numbers observed in blood and skin in HIV infection.