Dendritic cell elimination as an assay of cytotoxic T lymphocyte activity in vivo

We show in this paper that the survival of antigen-loaded dendritic cells i n vivo may be used as a sensitive readout of CTL activity. We have previous ly shown that dendritic cells labeled with the fluorescent dye CFSE and inj ected sub-cutaneously into mice migrate spontaneously to the draining lymph node where they persist for several days. In the presence of effector CTL responses, dendritic cells loaded with specific antigen rapidly disappear f rom the draining lymph node. In this paper we extend the above observations and set up a simple and sensitive method to reveal CTL activity in individ ual mice in vivo. Dendritic cells were labeled with two different fluorochr omes, loaded with antigen or left untreated, and mixed together before inje ction into mice. We show that only the dendritic cells loaded with specific antigen were cleared from the draining lymph node, while dendritic cells n ot loaded with antigen remained unaffected. Cytotoxic responses generated b y immunization with peptide-loaded dendritic cells, or by infection with in fluenza virus, could be revealed using this method. Comparison of the diffe rential survival of dendritic cells populations mixed together also allowed us to accurately evaluate the disappearance of dendritic cells, irrespecti ve of variability in the injection site and other parameters. Given the abi lity of dendritic cells to efficiently take up and present complex antigens , nucleic acids and apoptotic bodies, this method may also allow the evalua tion of cytotoxic activity against antigens that are not characterized in t erms of peptide epitopes. (C) 2000 Elsevier Science B.V. All rights reserve d.